Project Proposal & Feasibility Study - Calvin · PDF filePROJECT PROPOSAL & FEASIBILITY STUDY ... business aspects of this project and upon completion of this report, ... Example...

NATURAFILL © 2013, TEAM 13, CALVIN COLLEGE Last Updated: 12/9/2013

PROJECT PROPOSAL &

FEASIBILITY STUDY NaturaFill: Fuel for Thought

Team 13 Karl Bratt Jonathan Haines Andrew Hall Brandon Koster

Project Proposal & Feasibility Study NATURAFILL Last Updated: 12/9/2013

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© 2013, Karl Bratt, Jonathan Haines, Andrew Hall, Brandon Koster, and Calvin College


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Dedication

For Our Friend and Former Teammate

Eric DeGroot

1992-2013

However great our labors, this project will be forever incomplete.


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Executive Summary

This report outlines the introduction and preliminary development of a home refueling appliance to

successfully fuel a natural gas vehicle (NGV) with compressed natural gas (CNG). As a result of new

shale gas discoveries and new natural gas drilling technology, the supply of natural gas in the United

States has increased. This increase in supply has lowered the price of natural gas, making it a cheaper

fuel alternative compared to gasoline. Team 13, NaturaFill, has explored the many engineering and

business aspects of this project and upon completion of this report, NaturaFill has decided that the

designing and prototyping of this home refueling appliance is feasible and will cost approximately

$3,000.


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Table of Contents 1 Project Overview ............................................................................................................................... 1

1.1 Calvin College Senior Design ......................................................................................................... 1

1.2 Problem Statement ....................................................................................................................... 1

1.3 Industry Overview ......................................................................................................................... 1

1.3.1 Compressed Natural Gas....................................................................................................... 1

1.3.2 Benefits of CNG ..................................................................................................................... 1

1.3.3 Growth Rate Expectations .................................................................................................... 3

1.3.4 Barriers to Entry .................................................................................................................... 3

1.4 Project Proposal ............................................................................................................................ 4

1.4.1 Objective ............................................................................................................................... 4

1.4.2 Target Customers .................................................................................................................. 4

1.4.3 Existing Competitors ............................................................................................................. 4

1.4.4 Competitive Strategy ............................................................................................................ 6

1.5 Team Organization: ....................................................................................................................... 6

1.5.1 Team Members ..................................................................................................................... 6

1.5.2 Team Member Strengths ...................................................................................................... 7

1.5.3 Team Leadership and Management ..................................................................................... 7

1.6 Design Norms ................................................................................................................................ 9

1.6.1 Stewardship: ......................................................................................................................... 9

1.6.2 Trust ...................................................................................................................................... 9

2 Requirements .................................................................................................................................. 10

2.1 Safety .......................................................................................................................................... 10

2.2 Price ............................................................................................................................................ 10

2.3 Refueling Rate ............................................................................................................................. 10

2.4 Heat Loss ..................................................................................................................................... 10

2.5 Serviceability ............................................................................................................................... 10

2.6 Reliability ..................................................................................................................................... 10

2.7 Noise ........................................................................................................................................... 10

2.8 Environmental ............................................................................................................................. 10

2.9 Size .............................................................................................................................................. 11

2.10 Weather Proofing ........................................................................................................................ 11


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2.11 User Interface ............................................................................................................................. 11

2.11.1 Inputs .................................................................................................................................. 11

2.11.2 Outputs ............................................................................................................................... 11

3 Deliverables ..................................................................................................................................... 12

3.1 Project Proposal and Feasibility Study ........................................................................................ 12

3.2 Final Design Report ..................................................................................................................... 12

3.3 Working Prototype ...................................................................................................................... 12

3.4 Installation, Operation, and Service Manual .............................................................................. 12

3.5 Team Website ............................................................................................................................. 12

4 Design Considerations..................................................................................................................... 13

4.1 Compression Technology ............................................................................................................ 13

4.1.1 Alternatives ......................................................................................................................... 13

4.1.2 Decision ............................................................................................................................... 14

4.2 Hydraulic Power Units ................................................................................................................. 15

4.2.1 Alternatives ......................................................................................................................... 15

4.2.2 Decision ............................................................................................................................... 16

4.3 Natural Gas Compression Cylinder ............................................................................................. 16

4.3.1 Alternatives ......................................................................................................................... 16

4.3.2 Decision ............................................................................................................................... 17

4.4 Piston Material ............................................................................................................................ 17

4.4.1 Alternatives ......................................................................................................................... 17

4.4.2 Decision ............................................................................................................................... 17

4.5 Sealing Technology ..................................................................................................................... 17

4.5.1 Alternatives ......................................................................................................................... 17

4.5.2 Decision ............................................................................................................................... 18

4.6 Piston Ring Layout ....................................................................................................................... 18

4.6.1 Alternatives ......................................................................................................................... 18

4.6.2 Decision ............................................................................................................................... 19

4.7 Tubing ......................................................................................................................................... 20

4.7.1 Alternatives ......................................................................................................................... 20

4.7.2 Decision ............................................................................................................................... 21

4.8 Heat Removal .............................................................................................................................. 21


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4.8.1 Alternatives ......................................................................................................................... 21

4.8.2 Decision ............................................................................................................................... 23

4.8.3 Method................................................................................................................................ 23

4.9 Pressure Sensors ......................................................................................................................... 23

4.9.1 Alternatives ......................................................................................................................... 23

4.9.2 Decision ............................................................................................................................... 24

4.10 Development Board .................................................................................................................... 24

4.10.1 Alternatives ......................................................................................................................... 24

4.10.2 Decision ............................................................................................................................... 26

4.11 User Interface ............................................................................................................................. 26

4.11.1 Alternatives ......................................................................................................................... 26

4.11.2 Decision ............................................................................................................................... 28

5 Testing & Calculations ..................................................................................................................... 29

5.1 Preliminary Design Methods ....................................................................................................... 29

5.1.1 Autodesk CFD Simulator ..................................................................................................... 29

5.1.2 Engineering Equation Solver ............................................................................................... 30

5.2 Initial Testing ............................................................................................................................... 31

6 Preliminary Design Decisions .......................................................................................................... 32

6.1 Hydraulic System ......................................................................................................................... 32

6.1.1 Overview ............................................................................................................................. 32

6.1.2 Reservoir ............................................................................................................................. 32

6.1.3 Pump ................................................................................................................................... 33

6.1.4 Solenoid Valve ..................................................................................................................... 33

6.1.5 Cylinders .............................................................................................................................. 33

6.2 Natural Gas System ..................................................................................................................... 34

6.2.1 Overview ............................................................................................................................. 34

6.2.2 Residential Natural Gas Supply ........................................................................................... 34

6.2.3 Tubing.................................................................................................................................. 35

6.2.4 Check Valves ....................................................................................................................... 35

6.2.5 Relief Valve .......................................................................................................................... 35

6.2.6 Shut-off Valve ...................................................................................................................... 35

6.2.7 Manifolds ............................................................................................................................ 36

6.2.8 Pressure Gauges and Transducers ...................................................................................... 36


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6.2.9 Thermocouples ................................................................................................................... 37

6.2.10 Heat Sinks ............................................................................................................................ 38

6.2.11 Refueling Nozzle .................................................................................................................. 38

6.3 Sealing System ............................................................................................................................ 39

6.3.1 PTFE Coated Cylinder Walls ................................................................................................ 39

6.3.2 PTFE Seal Rings .................................................................................................................... 39

6.3.3 PTFE Rider Rings .................................................................................................................. 39

6.4 Control System ............................................................................................................................ 40

7 Financial Estimates .......................................................................................................................... 42

7.1 Cost of Development .................................................................................................................. 42

7.2 Cost of Production ...................................................................................................................... 42

8 Conclusion ....................................................................................................................................... 44

9 Acknowledgements ......................................................................................................................... 45

9.1 Professor Ned Nielsen ................................................................................................................. 45

9.2 Professor Steve VanderLeest ...................................................................................................... 45

9.3 Professor Matthew Heun ............................................................................................................ 45

9.4 Mr. Jimmy Moerdyk .................................................................................................................... 45

9.5 Mr. Lee Otto ................................................................................................................................ 45

9.6 Mr. Ross Persifull ........................................................................................................................ 45

9.7 Mr. Phil Jasperse ......................................................................................................................... 45

10 Appendices ...................................................................................................................................... 46

10.1 Appendix A. EES Code ................................................................................................................. 46


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Table of Figures

Figure 1. Price Equivalent per Barrel of Oil and Natural Gas .................................................................... 2

Figure 2. Oil Price as a Multiple of Natural Gas Price ............................................................................... 2

Figure 3. Number of Natural Gas Vehicles by Region (1991-2001) .......................................................... 3

Figure 4. BRC FuelMaker Phill® ................................................................................................................. 5

Figure 5. CNG Pump II® ............................................................................................................................. 5

Figure 6. Ross Persifill’s CNG Home Refueling Unit .................................................................................. 8

Figure 7. Hydraulic Cylinder Compression System ................................................................................. 13

Figure 8. Wobble Plate Compression System ......................................................................................... 14

Figure 9. Off-The-Shelf Hydraulic Power Unit Example .......................................................................... 15

Figure 10. Custom Built Hydraulic Power Unit Example ......................................................................... 16

Figure 11. Diagram of Layout 1 ............................................................................................................... 19

Figure 12. Picture of Layout 2 ................................................................................................................. 19

Figure 13. Schedule 80 Steel Pipe ........................................................................................................... 20

Figure 14. Stainless Steel Tubing ............................................................................................................. 20

Figure 15. Stainless Steel Tubing Fittings ................................................................................................ 21

Figure 16. Two Examples of Finned Tubing ............................................................................................ 22

Figure 17. Example of Tubing Loops ....................................................................................................... 23

Figure 18. Pressure Transmitter Example ............................................................................................... 24

Figure 19. Pressure Gage Example .......................................................................................................... 24

Figure 20. Touchscreen Raspberry Pi display .......................................................................................... 26

Figure 21. LCD & Keypad display ............................................................................................................. 27

Figure 22. Mobile User Interface ............................................................................................................ 27

Figure 23. Pressure Results from Simulation .......................................................................................... 29

Figure 24. Plane of Simulation Pressure Results ..................................................................................... 30

Figure 25. Hydraulic System Schematic .................................................................................................. 32

Figure 26. 4-Way, 3-Position Solenoid Valve (Exhaust Center) .............................................................. 33

Figure 27. Natural Gas System Schematic .............................................................................................. 34

Figure 28. High Pressure Natural Gas Check Valves ............................................................................... 35

Figure 29. Adjustable High Pressure Natural Gas Relief Valves .............................................................. 35


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Figure 30. Example of CNG Ball Valve ..................................................................................................... 36

Figure 31. Example of Manifold and Connections at End of CNG Compression Chamber ..................... 36

Figure 32. Pressure Transmitter Example ............................................................................................... 37

Figure 33. Pressure Gage Example .......................................................................................................... 37

Figure 34. High Pressure Pipe-Plug Thermocouple Example .................................................................. 38

Figure 35. Example of Tubing Loops ....................................................................................................... 38

Figure 36. General Purpose CNG Refueling Nozzle for Time-Fill ............................................................ 39

Figure 37. Picture of Ring Layout ............................................................................................................ 40

Figure 38. Control System Schematic ..................................................................................................... 41

Figure 39. Raspberry Pi Size Comparison ................................................................................................ 41


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Table of Tables

Table 1. NGV Reductions in Exhaust Emissions ........................................................................................ 1

Table 2. Compression Technology Decision Matrix ................................................................................ 15

Table 3. Steel Tubing Sizing Chart ........................................................................................................... 21

Table 4. Comparison of Development Boards ........................................................................................ 25

Table 5. Work and Heat Removal Calculation Results ............................................................................ 31

Table 6. Operational Budget ................................................................................................................... 42

Table 7. Cost of Production ..................................................................................................................... 43

NATURAFILL © 2013, TEAM 13, CALVIN COLLEGE Last Updated: 12/9/2013

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1 Project Overview

1.1 Calvin College Senior Design Calvin College is a Christian liberal arts college located in Grand Rapids, Michigan. Calvin’s engineering

program is ABET accredited and has a reputation for producing well-rounded engineers by integrating

this liberal arts curriculum with engineering. Senior design is the capstone of the engineering program

in which students conceive, develop, and implement a project of their interest over the course of the

year, combining material learned both inside and outside the classroom.

1.2 Problem Statement There is scarcity in the residential applications for compressed natural gas (CNG) in the United States

transportation landscape. Currently, only 605 public CNG refueling stations exist, compared to the

168,000 gasoline stations.1 In response, a few small companies, such as BRC Fuelmaker, have

developed home refueling units that run on electricity and connect to existing natural gas lines.2

Unfortunately, these models begin at $5,000 before installation.3 Therefore, the purpose of the project

is to design, build, and test a natural gas home refueling appliance that is lower cost and more reliable

than the appliances currently on the market.

1.3 Industry Overview

1.3.1 Compressed Natural Gas Natural gas is a colorless, odorless, non-corrosive, and extremely flammable mixture of hydrocarbon

gases. Natural gas, a fossil fuel, originates from the chemically breakdown of organic matter over time

to produce methane, CH4.4 When compressed to 3600psi, natural gas is termed, “CNG,” or compressed

natural gas.

1.3.2 Benefits of CNG CNG can easily be used as an alternative for gasoline in a dedicated vehicle engine or in conjunction

with gasoline in a “bi-fuel” application. In fact, the octane rating for CNG is higher than that of gasoline,

producing greater power, acceleration, and cruise speed for vehicles running on CNG. Though the

safety concerns are different, CNG’s narrow flammability range makes it inherently safer than gasoline.

In addition, emission comparisons of CNG and gasoline-fueled vehicles have revealed substantial

reductions in greenhouse gases (see Table 1. NGV Reductions in Exhaust Emissions).5

Table 1. NGV Reductions in Exhaust Emissions

NGV Potential Reductions in Exhaust Emissions (%) Carbon

Monoxide (CO) Non-Methane Hydrocarbons

(NMHC) Nitrogen Oxides (NOx)

Carbon Dioxides

(CO2) 90% 75% 60% 25%

1 http://www.afdc.energy.gov/fuels/natural_gas_locations.html 2 http://www.cngnow.com/vehicles/refueling/Pages/refueling-at-home.aspx 3 Jimmy Moerdyk, Moerdyk Energy Inc. (MEI), 9/27/13, 9:00AM 4 http://www.naturalgas.org/overview/background.asp 5 http://eerc.ra.utk.edu/etcfc/docs/EPAFactSheet-cng.pdf

http://www.afdc.energy.gov/fuels/natural_gas_locations.html


http://www.cngnow.com/vehicles/refueling/Pages/refueling-at-home.aspx

http://www.naturalgas.org/overview/background.asp

http://eerc.ra.utk.edu/etcfc/docs/EPAFactSheet-cng.pdf


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CNG not only provides a cleaner-burning fuel alternative to gasoline, it is also an economically feasible.

As a result of new shale gas discoveries and new drilling technology the supply of natural gas in the

United States has increased substantially. This increase in supply has forced the price of natural gas

down 70% over the last five years.6 The current pipeline natural gas of about $3.80 per million BTU7

has an energy equivalent price of $0.42 per gasoline gallon equivalent (GGE)8. Over the past twenty

years, this price drop has been reflected in a large price separation between gasoline and natural gas

(see Figure 1. Price Equivalent per Barrel of Oil and Natural Gas).

Figure 1. Price Equivalent per Barrel of Oil and Natural Gas9

In fact, the price of oil is over eight times higher than that of natural gas, as shown in Figure. 2. Oil Price

as a Multiple of Natural Gas Price.

Figure 2. Oil Price as a Multiple of Natural Gas Price10

6 http://www.infomine.com/investment/metal-prices/natural-gas/5-year/ 7 http://www.oil-price.net/ 8 http://www.energyalmanac.ca.gov/transportation/gge.html 9 http://pictorial-guide-to-energy.blogspot.com/2012/03/gaseous-emissions.html 10 http://www.infomine.com/investment/metal-prices/natural-gas/5-year/

http://www.infomine.com/investment/metal-prices/natural-gas/5-year/

http://www.oil-price.net/

http://www.energyalmanac.ca.gov/transportation/gge.html

http://pictorial-guide-to-energy.blogspot.com/2012/03/gaseous-emissions.html

http://www.infomine.com/investment/metal-prices/natural-gas/5-year/


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1.3.3 Growth Rate Expectations The economic and environmental incentives associated with CNG have already encouraged transit,

garbage, and transportation fleets to convert from diesel and gasoline fuel to CNG.11 Unfortunately,

this has been primarily restricted to vehicles such as taxicabs, transit and school buses, garbage trucks,

and public works vehicles. Because these vehicles are typically maintained and fueled and a central

location, it is has been economical for them to convert to natural gas. In total, the number of CNG

powered vehicles on the road is growing at a staggering rate of 30 percent a year.12 Currently, there

are 135,000 natural gas vehicles in the United States and 15.2 million worldwide13 (see Figure 3. Number

of Natural Gas Vehicles by Region).14

Figure 3. Number of Natural Gas Vehicles by Region (1991-2001)

In the coming years, it is also forecasted that the number of factory built bi-fuel vehicles will also be on

the rise. “Bi-fuel” indicates that a vehicle can run on both gasoline and natural gas fuel sources.

Presently, larger vehicles such as the 2013 Chevrolet Silverado and GMC Sierra 2500 HD are factory-

offered with bi-fuel capability. Ross Pursifull, a research specialist at Ford Motor Company, spoke with

the team15 and confirmed rumors that the 2015 Chevrolet Impala will also be built bi-fuel ready.16

Chevrolet’s decision results from increased market pressure for CNG vehicles in residential applications.

Increased demand for residential natural gas vehicles (NGVs) will correspondingly increase demand for

CNG fueling stations.

1.3.4 Barriers to Entry The biggest hurdle to widespread consumer adoption of natural gas vehicles is availability to fueling

stations. There are over 270 publically accessible gasoline fuel stations for every one station supplying

11 http://www.cngnow.com/vehicles/fleets/Pages/government.aspx 12 http://www.ngvamerica.org/media_ctr/fact_ngv.html 13 http://www.ngvc.org/about_ngv/index.html 14 http://www.iangv.org/current-ngv-stats/ 15 Pursifull, Ross; Ford Motor Company; 11/9/13, 10:00AM 16 http://blog.caranddriver.com/antelope-in-the-gas-2015-chevrolet-impala-to-gain-bi-fuel-gasolinecng-capable-v-6-model/

http://www.cngnow.com/vehicles/fleets/Pages/government.aspx

http://www.ngvamerica.org/media_ctr/fact_ngv.html

http://www.iangv.org/current-ngv-stats/

http://blog.caranddriver.com/antelope-in-the-gas-2015-chevrolet-impala-to-gain-bi-fuel-gasolinecng-capable-v-6-model/


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CNG.17 The capability to fuel a CNG vehicle at home side-steps waiting for an adequate nationwide

network of fueling stations. Unfortunately, cost has been the major deterrent away from existing CNG

home refueling units.

1.4 Project Proposal

1.4.1 Objective The objective of NaturaFill is to design, build, and test a natural gas home refueling appliance with a

production cost of less than $2,000 and refueling rate of 0.35 gasoline gallons equivalent (GGE) per

hour. The system must be capable of compressing natural gas to the standard pressure of 3,600 psi in

a safe and controlled environment.

1.4.2 Target Customers This increased use of CNG in transportation vehicles has made it seemingly more affordable and feasible

in residential applications. In total, 56 percent of American households are currently using natural gas

for residential heating.18 As a result, NaturaFill’s natural gas home refueling appliance aims to target

customers with existing natural gas lines and fossil fuel dependent vehicles. A potential secondary

market for CNG vehicles and the system would include customers desiring reduced emission large

vehicle options, such as trucks or sports utility vehicles (SUVs). The majority of electric or hybrid

powered vehicles on the market today are small with little hauling capacity. In the realm of trucks and

SVUs, natural gas vehicles are a suitable option for improved environmental impact.

1.4.3 Existing Competitors

BRC FuelMaker

FuelMaker is currently the largest producer of CNG home refueling units. Their most popular unit, the

Phill®, costs $5,000 before installation. The Phill® refuels at an average rate between 1.2-1.5 GGEs per

hour (see Figure 4. BRC Fuel Maker Phill®).

17 http://www.afdc.energy.gov/fuels/natural_gas_locations.html 18 http://www.naturalgas.org/overview/uses_residential.asp



http://www.naturalgas.org/overview/uses_residential.asp


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Figure 4. BRC FuelMaker Phill®

CNGPump

CNGPump, maker of the CNG Pump®, uses hydraulic compression for conversion of natural gas into

CNG. Their cheapest model is the CNG Pump II®, which refuels at a rate of 2 GGEs per hour.

Unfortunately, their upfront cost is $7,000 before installation, an inhibitor for most customers.19

Figure 5. CNG Pump II®

19 http://www.cngpump.com/shoppingcart/products/CNGPUMP%252d2gge-%28Time-Fill%29-Hydraulic-Fueling-Station-for-cars%7B47%7Dtrucks-%282gge-per-hour%29.html

http://www.cngpump.com/shoppingcart/products/CNGPUMP%252d2gge-%28Time-Fill%29-Hydraulic-Fueling-Station-for-cars%7B47%7Dtrucks-%282gge-per-hour%29.html

http://www.cngpump.com/shoppingcart/products/CNGPUMP%252d2gge-%28Time-Fill%29-Hydraulic-Fueling-Station-for-cars%7B47%7Dtrucks-%282gge-per-hour%29.html


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General Electric

The biggest potential competitor is General Electric (GE). They have announced a partnership with

Chesapeake Energy to develop a natural gas home refueling unit with an upfront cost of $500.20 If

proposition becomes a reality, it would undercut NaturalFill’s suggested retail price and therefore,

undermine its value proposition. From conversations with Ross Persifill, Research Specialist at the Ford

Motor Company, and other industry insiders, the general consensus suggests high unlikeliness of GE’s

proposition becoming a reality. For this reason, the team forecasts the elapse of a substantial amount

of time before GE enters this market.

1.4.4 Competitive Strategy Existing in-home refueling units are currently in the price range or $5000-$7000+ and fill at a rate of

around 2 GGEs. Today, most systems are currently made in Europe and the United States, however, it

is rumored that a less expensive Asian variety will soon be hitting the market will be released soon.

NaturaFill plans to compete by ensuring quality and safety and competing at a lower price point by

reducing the compression rate of approximately 0.35 GGEs. In actuality, this compression rate would

be comparable to charging a 100% electric vehicle overnight for average daily usage. The team’s

strategy to compete on price and differentiation will make residential use of natural gas vehicles more

feasible in the American transportation landscape.

1.5 Team Organization:

1.5.1 Team Members

Karl Bratt

Bratt is a Mechanical concentration engineering student also in pursuit of a business

minor. Originally from Racine, Wisconsin, Bratt has diverse interests in business

finance, operations, and supply chain. Bratt has had two summer internships

working for General Electric as a manufacturing engineer and continuous

improvement specialist. He is passionate about the potential business opportunities

involved with the NaturaFill project. In his free time, he enjoys playing piano, golf,

and tennis, and is an avid runner in his free time. Last year, he ran the Chicago

Jonathan Haines

Haines is a Mechanical concentration engineering student also in pursuit of a

mathematics minor. Originally from East Brunswick, New Jersey, Haines has

experience with manufacturing and has interests in the auto industry. His

experience with thermodynamics and hands on experience with manufacturing

along with his knowledge of Autodesk CFD simulator will be valuable in the design

and implementation of this design. In his free time, Jon enjoys playing guitar and

cooking.

20 http://oilprice.com/Finance/investing-and-trading-reports/Chesapeake-GE-Get-in-on-Home-Refueling-Game.html

http://oilprice.com/Finance/investing-and-trading-reports/Chesapeake-GE-Get-in-on-Home-Refueling-Game.html

http://oilprice.com/Finance/investing-and-trading-reports/Chesapeake-GE-Get-in-on-Home-Refueling-Game.html


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Andrew Hall

Hall is an Electrical and Computer concentration engineering student. Originally

from McCordsville, Indiana. Hall has obtained a comprehensive array of electrical

engineering experiences and technical skills. He has gained proficient experience

and skills in communications, marketing, research, electrical fabrication, and

component design testing. In his free time, Hall enjoys playing bass guitar in two

of the many local churches Grand Rapids offers. He also enjoys restoring and

refurbishing vintage era electronics as well as playing an occasional round of golf.

Brandon Koster

Koster is a Mechanical concentration engineering student and also pursuing a

business minor. Originally from Visalia, California, Koster has been a natural gas

transportation enthusiast for years. The future of the natural gas transportation

has been personal research interest of his, both from a business and engineering

perspective. Also, growing up as the son of a contractor, Koster gained valuable

fabricating, mechanical design, and project execution skills at a young age. In his

free time he enjoys rock climbing, cheering on the Los Angeles Dodgers, working on

his car, listening to Texas Country music, and taking road trips.

1.5.2 Team Member Strengths

Karl Bratt

Bratt's background in lean manufacturing and ergonomics will be valuable in the design and

manufacture of NaturaFill. In addition, his experience in forecasting and cost analysis will be helpful in

evaluating and marketing the value proposition of the product.

Jonathan Haines

Haines’s experience with thermodynamics and manufacturing, along with his knowledge of Autodesk

CFD simulator, will be valuable in the design and implementation of this design.

Andrew Hall

Hall’s experience in analog and digital electronic system applications will bring a highly distinguishable

attribute to the control and safety systems of NaturaFill.

Brandon Koster

Koster’s industry knowledge will serve to connect the team to companies and individuals in the industry

that will provide valuable guidance and support throughout the project.

1.5.3 Team Leadership and Management

Project Manager

Bratt will act as the Project Manager for NaturaFill. Bratt is primarily responsible for the organizational

components of the project. This includes, but is not limited to, the planning and scheduling of team

meetings, review and on-time delivery of project deliverables, and work breakdown of tasks among the

team member using Microsoft Project.

Webmaster

Hall will act as the team Webmaster. With a concentration in electrical engineering, Hall enjoys HTML

code and has experience in website development. Hall is primarily responsible for maintaining the

team’s website, email address, and Twitter page.


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Budget Manager

Koster will act as the Budget Manager for NaturaFill. Koster is primarily responsible for managing the

team’s operational budget. This includes, but is not limited to, turning in all reimbursement forms,

requesting parts purchases, and communicating with team sponsors.

Senior Design Faculty Advisor

Ned Nielsen is a Mechanical Engineering professor at Calvin College. In addition, Nielsen is the faculty

advisor for mechanically concentrated Senior Design projects. He is responsibility for providing

constructive feedback on the project throughout the course of the year. Nielsen’s extensive

engineering background will be helpful for finalizing the team’s CNG refueling unit design.

Electrical Faculty Consultant

Steve VanderLeest is an Electrical Engineering professor at Calvin College and the faculty advisor for

electrically concentrated Senior Design projects. His electrical engineering background will support Hall

in the design and optimization of NaturaFill’s pressure monitoring systems and safety controls.

Mechanical Faculty Consultant

Matthew Heun is a Mechanical Engineering professor at Calvin College. Heun has agreed to meet with

NaturaFill to address the transfer of heat released by the compression system. Heun has also given the

team advice with the use of Autodesk CFD for compression and temperature modeling.

CNG Industry Consultant

Lee Otto is the Founder and CEO of CNGPump, Inc. in Appleton, WI. Otto offered the team advice on

seal technology, heat dissipation, and control systems. Unfortunately, he was could not provide any

further technical information without compromising confidential intellectual property.

Automotive Industry Consultant

Ross Persifull is a Research Specialist at Ford Motor Company in Dearborn, MI. Persifull, a CNG

enthusiast, agreed to meet with NaturaFill and discuss the CNG industry from an automotive industry

standpoint. In addition, he demonstrated the use of a home refueling unit to fuel his own NGVs (see

Figure 6. Ross Persifull CNG Home Refueling Unit.

Figure 6. Ross Persifill’s CNG Home Refueling Unit


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Industry Mentor

Jimmy Moerdyk is the Vice President of Operations at Moerdyk Energy, Inc. in Grand Rapids, MI.21

Moerdyk has provided support and suggestions to the team based on his experience in the installation

of CNG vehicle conversions and home refueling units. Moerdyk has been enthusiastic of NaturaFill’s

$2,000 production price target.

1.6 Design Norms

1.6.1 Stewardship: As the concentration of CO2 in the atmosphere approaches the 400 ppm mark, the political, social, and

economic pressures for alternative energies has risen drastically22. Compressed natural gas, which

burns cleaner than coal or oil, is a solution to this environmental and economic challenge.

Environmental Sustainability

It has been proven that natural gas vehicles produce less emissions than traditional gasoline powered

vehicles (see Table 1. NGV Reductions in Exhaust Emissions). As worries rise on the negative effects of

greenhouse gases on the environment, the team believes that the transition from gasoline fueled

transportation to natural gas exemplifies upright stewardship over the environment.

Economic and Political Sustainability

Natural gas is widely available in the United States. In fact, 98% of the natural gas consumed in the

United States is produced in either the US or Canada.23 In addition, the price of natural gas has declined

tremendously in the past five year, especially in comparison to oil (see Figure 1. Price Equivalent per

Barrel of Oil and Natural Gas). The economic feasibility of this project promotes the team’s role as

stewards over limited financial resources.

1.6.2 Trust The team’s mission is to provide a fully-functional natural gas home refueling unit that is safe and made

easy-to-use. Safety is the team’s most important design requirement. Since a prototype malfunction

could be highly dangerous, the team will conduct all preliminary testing of the devise with a non-

combustible gaseous materials. In addition, by integrating easy-to-use controls into the device’s user

interface, the team hopes to create a level of trust with the end user. All in all, these considerations

align with our role as engineers to have integrity with the design of safe and high-quality products.

21 http://www.moerdykenergy.com/Home.php 22 http://www.gasnaturally.eu/uploads/Modules/Publications/the-role-of-natural-gas-in-a-sustainable-energy-market-final.pdf 23 http://anga.us/why-natural-gas/clean#.UmCKfPmsgyo

http://www.moerdykenergy.com/Home.php

http://www.gasnaturally.eu/uploads/Modules/Publications/the-role-of-natural-gas-in-a-sustainable-energy-market-final.pdf

http://www.gasnaturally.eu/uploads/Modules/Publications/the-role-of-natural-gas-in-a-sustainable-energy-market-final.pdf

http://anga.us/why-natural-gas/clean


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2 Requirements

2.1 Safety Due to high pressures and the flammable nature of natural gas, the most important design requirement

for the home refueling appliance is safety. The system must come equipped with gas leak detector

sensors, pressure controls, and a monitoring system to ensure that in the case of a gas leak, an

unexpected jump in pressure, or any other malfunction that the machine will be turned off in a safe

manor.

2.2 Price Since the majority of commercially available CNG home refueling units cost more than $5000, the teams

aims to design a unit that could be sold at a the $3000 price range.

2.3 Refueling Rate Nearly all of the units on the market operate with a faster fueling rate ranging from 1.2-2+ GGEs. These

are considered fast filling units since you would be able to reach near full capacity in the matter of a

few hours. The team aims to build a slow filling unit. A slow filling unit can be compared to plugging in

an electric car overnight. With a fuel rate of 0.35 GGEs and having it fill over night for an average of 8

hours a night would be able to replace nearly 20 gallons of gasoline. Therefore, the team as chosen to

design the unit to have a fueling rate of 0.35 GGEs.

2.4 Heat Loss During compression, the temperature of the natural gas increases due to work being done on the gas

and the conservation of energy. When compressing to 3600 psi without any sort of cooling the

temperature of the gas reaches a temperature of over 350 °C. This is clearly too hot to be putting into

a vehicle. Because of this, the team will design the system to make sure that the gas is around room

temperature before it goes into the vehicle.

2.5 Serviceability Many CNG enthusiasts are hands on people. Because of this, the team will design the unit to be easily

serviced by those who are knowledgeable in the industry.

2.6 Reliability Because this unit is being designed with the thought of being people’s primary source of fuel for

transportation, the unit must be reliable. This will be accomplished by stress testing the unit to insure

that it runs continuously for long periods of time.

2.7 Noise Since this unit is being designed to be used in people’s garages overnight, it only makes sense for the

unit to operate nearly silent. To achieve this, the team plans to design the unit to operate at a noise

level of under 50 dB from a distance of 10 ft. away.

2.8 Environmental Since the team values stewardship as a core value, the team plans to design the unit to be

environmentally friendly by having it run efficiently and making sure that the unit is free of leaks. Also

in the case of a leak, the unit would be designed to shut off.


11

2.9 Size Units like the one being designed are typically stored in garages. Because of this the team will design

the total size of the unit to fit reasonably in an averaged sized garage.

2.10 Weather Proofing Since not all users of this refueling unit will necessarily be putting it in their garage, the exterior casing

must be designed to be weather proof.

2.11 User Interface The user interface brings together the entire refueling unit into one easy to use screen and keypad

push button system. Designing a simple user interface is key, but will also diminish any chance for the

user to become confused on how to operate the unit.

2.11.1 Inputs Cutting down on user interaction for the sake of simplicity, there will be a simple on/off button and a

button to begin fueling. This simple user input design in turn places the leftover burden of the complex

decisions of the system to then be decided by the Raspberry Pi.

2.11.2 Outputs Following the few inputs necessary to power on and begin fueling, the user will receive a few phrases

of confirmation to ensure that the unit is fully operating. There also will be a few LED lights indicating

that the system is on, fueling, and or malfunctioning, which would throw an error message to the

display screen.


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3 Deliverables

3.1 Project Proposal and Feasibility Study NaturaFill shall submit a complete project proposal and feasibility study detailing a background on the

project, a proposed solution, and the feasibility of this solution. This report will be submitted no later

than December 9, 2013 at 3:30pm E.S.T.

3.2 Final Design Report NaturaFill shall submit a final report at the completion of the project to explain the project background,

research and data analysis, design alternatives and decisions, prototype design and testing, and final

design conclusions. This final design report will be submitted no later than May 14, 2014 at 3:30pm

E.S.T.

3.3 Working Prototype The team will demonstrate a working prototype of the refueling unit at the Engineering Department

Senior Design Night on May 10, 2014. The team hopes to demonstrate, on-stage, the refueling of an

actual natural gas vehicle.

3.4 Installation, Operation, and Service Manual In conjunction with the working prototype, NaturaFill shall deliver an installation, operation, and service

manual by May 10, 2014 at 7:00pm E.S.T. This manual shall outline all necessary instructions for

installation, operation, and corrective and preventive maintenance.

3.5 Team Website The team shall maintain a website as a means of updating the college, sponsors, and the public on the

project status. These updates shall be executed by Andrew Hall and will occur at milestones throughout

the project lifespan. All final updates to the website, including published final versions of the PPFS and

Final Design Report, must be made by May 12, 2014 at 3:30pm E.S.T.


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4 Design Considerations

4.1 Compression Technology

4.1.1 Alternatives

Hydraulic Cylinder Compression

A hydraulic cylinder compression system would use multiple double rod hydraulic cylinders to compress

the gas at a low cycle rate, compared to most other technologies. This is a technology that is slowly

being introduced as an alternative to the motor driven reciprocating compressor. Many companies and

individuals in the industry believe that it has the potential to become the industry standard technology

for compressing natural gas in the future because of the higher reliability it offers and the fact that a

unit can be assembled using off-the-shelf hydraulic components. Currently, this technology is more

developed in China than in the United States. See Figure 7. Hydraulic Cylinder Compression System, for

a diagram of this compression method.

Figure 7. Hydraulic Cylinder Compression System24

Pneumatic Cylinder Compression

A pneumatic cylinder compression system would use multiple double rod pneumatic cylinders to

compress the gas at a low cycle rate compared to most other technologies. It technology is almost

identical to hydraulic cylinder compression, the only difference being the use of pneumatic cylinders

instead of hydraulic cylinders. According to the team’s extensive research, this has technique not yet

been used to compress natural gas.

24 http://www.hydropac.com/GRAPHICS/hydrogen3b.jpg

http://www.hydropac.com/GRAPHICS/hydrogen3b.jpg


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Wobble Plate Compression

Figure 8. Wobble Plate Compression System25

A wobble plate compressor is the type of compressor typically used in air conditioning units in cars.

This design option was suggested by Lee Otto since very little work has been done to use this type of

compressor for CNG. See Figure 8. Wobble Plate Compression System, for a diagram of this

compression alternative. The team did extensive research on the potential of using wobble plate

technology to compress natural gas. After this research the team came to the conclusion that using

this technology for a senior design project was not feasible. The complexity of the linkages and the

potential for unbalance issues due to the different sizes of each compression stage was determined to

be too much for the team to execute in a nine-month timeframe.

Motor Driven Reciprocating Compression

A motor driven reciprocating compressor is the industry standard for compressing natural gas. This

option was ruled out early in the process since so much work has already been done with these types

of compressors. This compression technology as also has had many reliability issues due to its high cycle

rate.

4.1.2 Decision To make this decision, a decision matrix was created be weighting a list of desired outcomes and rating

each design alternative on a scale of one to ten. The totals were then totaled up and the design

alternative with the highest score was chosen since it accomplishes the tasks that the team as

designated as important. See the decision matrix in Table 2 for the criteria and weights used to judge

alternatives and make a decision.

25 http://www.jaguar-swansea.co.uk/aircon/systems.htm

http://www.jaguar-swansea.co.uk/aircon/systems.htm


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Table 2. Compression Technology Decision Matrix

Criteria Score Weight Motor Driven Reciprocating Compressor

Wobble Plate

Compressor

Hydraulic Cylinder Driven Reciprocating

Compressor

Pneumatic Cylinder Driven Reciprocating

Compressor

Cost to Manufacture 10 14% 8 6 7 9

Reliability 9 13% 5 6 9 7

Safety 9 13% 8 8 8 8

Ease of Use 7 10% 8 8 8 8

Serviceability 7 10% 4 3 10 10

Efficiency 6 9% 8 8 8 3

Prototype Cost 5 7% 5 8 8 10

Innovation 5 7% 1 10 8 10

Marketability 5 7% 5 5 7 6

Ability to Prototype 4 6% 5 3 8 10

Noise Pollution 3 4% 3 6 10 6

5.9 6.5 8.2 8.0

It can be seen from this matrix that the design alternative with the highest score is hydraulic

compression. Because of this, the team has decided to pursue using hydraulic compression for the unit.

4.2 Hydraulic Power Units The team discussed their needs for a hydraulic power unit with Ryan Anderson, a hydraulic power unit

technician with Bond Fluidaire, during a visit. The team discuss many of their requirements with Anderson

and they discussed ballpark pricing for their budget. The low-noise and very high run time (often >12

hours) makes the team’s hydraulic power unit specifications different than most units used in the industry.

4.2.1 Alternatives

Custom Built

These units are relatively inexpensive and easy to find. They also come in sizes that fit well with the

team’s requirements. A concern is the fact that these units are not typically designed to run for

extremely long periods of time reliably. See Figure 9 for an example of this type of power unit.

Figure 9. Off-The-Shelf Hydraulic Power Unit Example26

26 http://www.northerntool.com/images/product/2000x2000/107/1077_2000x2000.jpg

http://www.northerntool.com/images/product/2000x2000/107/1077_2000x2000.jpg


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Off-The-Shelf

These units are designed with the specific application of the unit in mind. They are constructed out of

a reservoir, hydraulic pump, electric motor, manifold, valves, and piping and put together by local

custom hydraulics companies like Bond Fluidaire. This alternative would give the team the flexibility to

select the individual components for the unit in such a way that the final unit meets all of their needs.

This would also give the team more control over the footprint of the power unit and their final product

because the reservoir could be custom made to fit in available space and the components could be

mounted in a manner that maximizes available space. The team could also save labor be possibly

building the hydraulic power unit themselves out of purchased components. See Figure 10 for an

example of this type of power unit.

Figure 10. Custom Built Hydraulic Power Unit Example27

4.2.2 Decision The team decided to use a custom-built unit. They came to this decision because they were concerned

about the off-the-shelf units not being able to deliver on the noise and run time requirements. They

would also like to give themselves the option of building the unit themselves to save cost.

4.3 Natural Gas Compression Cylinder

4.3.1 Alternatives

Thick-walled Steel Pipe

Thick-walled Steel pipe is reliable, easy to purchase, and relatively inexpensive. However, it only comes

in a limited variety of diameters. Furthermore, some machining work might need to be done to get the

inside wall to the specified exact diameter and tolerance.

27 http://www.gshydraulics.com/images/products/large/HydraulicPowerUnit01_CustomCompact.jpg

http://www.gshydraulics.com/images/products/large/HydraulicPowerUnit01_CustomCompact.jpg


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Machined Steel Rod

While this method is more labor intensive, it allows the team to maintain control of wall thickness, inner

diameter, and tolerances.

Machined Steel Block

Another alternative is to machine a pair of compression blocks. This method would require a lot of time

to machine. Another concern is that if there is an error made on one of the last steps of machining the

part would need to be scrapped and restarted which would consume a lot of time.

Reinforcement Rods

When constructing compression cylinders that are not in a block, reinforcement rods are typically used

to carry the pressure load and to hold the manifold and the cylinders together.

4.3.2 Decision The team has decided to pursue the method of thick walled steel pipe to create compression cylinders.

Doing so will allow the team to design the cylinder size to any specified diameter with minimal machine

work. This choice also reduces risk in manufacturing, in the unfortunate case there is a mistake made,

the time required to make a new cylinder would be small. Reinforcement rods will also be used to attach

the manifold to the cylinder.

4.4 Piston Material

4.4.1 Alternatives

Steel

Steel pistons could be constructed out of steel rod stock. Steel is relatively inexpensive for its strength.

Steel is the heaviest material that was considered, there were concerns about the heavier steel pistons

leading to unnecessary unbalance issues. Steel also does not conduct heat as fast as aluminum.

Aluminum

Aluminum pistons are most common in both compressors and internal combustion engines. This is a

result of their light weight and high thermal conductivity.

PTFE

There were thoughts of possibly making the pistons out of PTFE (Teflon). This would eliminate the need

for seal rings because the entire piston would be made out of an extremely low-friction material.

Disadvantages of using PTFE include the very high cost of the raw material and fact that using PTFE as

a piston material is unproven.

4.4.2 Decision The team decided to use aluminum pistons. The decision came in light of aluminum’s low weight and

high heat transfer coefficient. The team also wanted to work with a material that is commonly used in

this application and steel and PTFE did not meet that requirement.

4.5 Sealing Technology

4.5.1 Alternatives

Oil Seals

Using oil seals is the conventional method for sealing air and natural gas compressors. Oil provides

excellent wear protection and blow-back elimination. Disadvantages to using oil seals include the

added complexity involved with preventing leaks and having to check oil levels on a regular basis. Also,


18

natural gas compressor with oil seals have to have additional filters to ensure that oil does not get into

the natural gas going into the vehicle.

PTFE Coatings and Rings

Oil-less compressor technology uses low-friction cylinder wall coatings, such as PTFE (Teflon), and seal

rings made out of low friction polymers, such as PTFE or PEEK, to protect against wear and excessive

heat generation while still maintaining at tight seal. A disadvantage of this alternative is the high cost

of low-friction coatings and polymers.

Bronze Sleeves and Seals

In discussions with mentor Lee Otto, using a bronze sleeve inside the cylinder wall along with bronze

bushings as seals was discussed. This alternative would be simple and inexpensive. A disadvantage of

this alternative is the relatively high coefficient of friction of bronze compared to oil seals and PTFE.

4.5.2 Decision The team decided to use PTFE cylinder wall coatings and PTFE rings. This decision was based on the

team’s requirement for a very low friction seal, as well as the need to avoid contaminating the natural

gas with oil. Many natural gas compressors are now using this technology for the above reasons.

4.6 Piston Ring Layout

4.6.1 Alternatives

Ring Layout 1: Two Outside Rider Rings and Two Inside Seal Rings

This was the ring layout that the team came across most often in their research. It stabilizes the piston

with the rider rings on the outside. Gas can pass through grooves in the rider rings because the function

of the rider ring is only to stabilize the piston and not to seal out gas. A diagram of Layout 1 can be seen

below in Figure 11.


19

Figure 11. Diagram of Layout 128

Ring Layout Two Outside Seal Rings and Two Inside Rider Rings

The team also came across this ring layout in their research, but it was far less common than Layout 1.

Gas is sealed using the two outside seal rings and the piston is stabilized using the two inside rider rings.

An example of Layout 2 can be seen below in Figure 12.

Figure 12. Picture of Layout 2

4.6.2 Decision The team has decided to pursue Layout 1: two outside rider rings and two inside seal rings. This design

is far more common in the industry and the team hypothesizes that the gas being allowed to pass

through the rider rings freely will lead to better stabilization for the piston. If the sealing from this

layout proves insufficient the team will modify it by adding additional seal rings.

28 http://www.ihi.co.jp/compressor/en/products/process-gas/gas-recipro/images/fea_photo_01.jpg

http://www.ihi.co.jp/compressor/en/products/process-gas/gas-recipro/images/fea_photo_01.jpg


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4.7 Tubing

4.7.1 Alternatives

Thick-walled steel pipe

Thick-walled steel pipe was proposed as an alternative for the piping system. Steel pipe is readily

available and offers good sealing using NPT threads with Teflon tape. Disadvantages to this alternative

include not being able to bend it and possible corrosion of the steel because it is not a naturally

corrosion resistant alloy. A picture Schedule 80 thick-walled steel pipe is shown below in Figure 13.

Figure 13. Schedule 80 Steel Pipe29

Stainless Steel Tubing

Stainless steel tubing was also considered as an alternative for the piping system. Stainless steel tubing

is the most common method of piping compressed natural gas. An example of stainless steel tubing is

shown below in Figure 14. To change direction, the stainless steel tubing can be bent or compression

fitting can be used. Examples of these compression fittings is shown below in Figure 15. Disadvantages

include the fact that it must be ordered from a specialty supplier and adapters and fittings are more

expensive than for standard steel pipe. A chart showing stainless steel tubing sizes and wall thicknesses

and their corresponding pressure rating can be seen below in Table 3.

Figure 14. Stainless Steel Tubing30

29 http://www.amazon.com/Anvil-Fitting-Schedule-Seamless-Nipple/dp/B006N2VXCI 30 http://www.swagelok.com

http://www.amazon.com/Anvil-Fitting-Schedule-Seamless-Nipple/dp/B006N2VXCI

http://www.swagelok.com/


21

Figure 15. Stainless Steel Tubing Fittings31

Table 3. Steel Tubing Sizing Chart32

4.7.2 Decision The team decided to use stainless steel tubing for the piping system of their compressor unit. The team

is doing this to conform to industry standards for compressed natural gas piping and for the design

flexibility that will come with being able to bend the tubing. Being able to bend the tubing is also very

critical to the team’s heat sink design.

4.8 Heat Removal

4.8.1 Alternatives

Stepped Heat Removal

This approach to heat removal would remove heat in between compressions stages. The benefits of

this form of heat removal is that the highest temperature reached is lower, resulting in overall less

power used since natural gas takes less work to compress at lower temperatures. The down side to this

method is that takes up slightly more space since additional tubing and fans are required.

31 http://www.swagelok.com 32 http://www.swagelok.com/downloads/webcatalogs/EN/MS-01-107.PDF

http://www.swagelok.com/

http://www.swagelok.com/downloads/webcatalogs/EN/MS-01-107.PDF


22

Bulk Heat Removal

The bulk method of heat removal would let the natural gas compress to 3600 psi before cooling. The

benefit of this method is that all the heat transfer is done at once which saves on space used. The

downsides are that waiting until the end of the cycle to cool allows the temperature of the natural gas

to reach temperatures around 350 °C which is a safety and material cost concern. Secondly this method

is less efficient since natural gas required more work to compress natural gas at higher temperatures.

Finned Tubing

Finned tubing is a very common way to dissipate heat from a working fluid in many different

thermodynamic systems. The fins provide increased surface area for heat transfer to the air to occur

and therefore increase heat transfer rates. A disadvantage to this alternative is the fact that most

finned tubing is designed for low pressure applications and fins cannot simply be added to the team’s

high pressure tubing because separation between the tube and the fins will occur with thermal

expansion and contraction due to temperature changes. Custom finned tubes designed for high

pressure applications, where the fins and the tubes have been bonded together in a heat welding

process, are available. However, these custom, high pressure finned tube are very expensive.

Figure 16. Two Examples of Finned Tubing33

Tubing Loops

Tubing loops are also a very common way to dissipate heat from a working fluid. Adding loops to the

tubing allows for increased surface area for heat transfer to take place. There will be a higher volume

of gas in the heat sink using this method due to the increased tube length. This will allow the gas to

have more time to cool while it passes between the stages. Disadvantages to this alternative include

the additional cost of buying extra tubing and the additional labor cost involved in bending the tubing

to create the heat sinks.

Fans

Fans are a very effective way to dissipate heat from a working fluid into the surrounding air.

Disadvantages to using fans include increased noise pollution and the added potential maintenance

that come along with additional moving parts.

33 http://www.lpspa.it/UserFiles/1/Image/aleteados/hiresolution/CRW_6068hr.jpg

http://www.lpspa.it/UserFiles/1/Image/aleteados/hiresolution/CRW_6068hr.jpg


23

Figure 17. Example of Tubing Loops34

4.8.2 Decision Since the increase of size is relatively small and size is not a major concern for the design, and due to

the safety and cost concerns with bulk heat removal, the team has decided to use a stepped heat

removal method to cool the natural gas.

4.8.3 Method The method to be used for the stepped heat removal is forced convection by fans and coiled tubing.

This method of heat removal is proven and is used widely in industry. Adding fins to increase surface

area to improve heat transfer was considered but for a single tube application adding a finned surface

would not be cost effective.

4.9 Pressure Sensors

4.9.1 Alternatives

Pressure Transmitter

Pressure transmitters measure pressure using a strain gauge and output a low-voltage signal that

corresponds to a certain pressure. An example of a pressure transmitter can be seen below in Figure

18. This low-voltage signal must be converted to a digital signal using a DC to AC converter chip to be

of any use to a computer-based control system. These sensors would be used in conjunction with

thermocouples to determine the thermodynamic state of the compressed natural gas. This is critical

to creating accurate heat transfer and fluid flow models. The team needs a minimum of one pressure

transmitter, to be used on the final stage to determine when the final stage pressure has reached 3600

psi, meaning the natural gas vehicle tank is full. The disadvantage of using pressure transmitters their

relatively high cost compared to simple pressure gages.

34 http://www.lmcompressor.com/images/Web%20Page%20CNG_3021%20_.jpg

http://www.lmcompressor.com/images/Web%20Page%20CNG_3021%20_.jpg


24

Figure 18. Pressure Transmitter Example

Pressure Gages

Pressure gages are a very inexpensive way to measure the pressure throughout the various stages of

the team’s natural gas compressor. An example of a pressure gage can be seen below in Figure 19.

They are also very robust and reliable compared to pressure transmitters. The major disadvantage of

using pressure gages is the fact that data can only be recorded at the speed it can be recorded manually

by a human being. Also, using pressure gages would limit the number of real-time computer modeling

that could be done for the system because pressure data would not be constantly being feed into the

computer.

Figure 19. Pressure Gage Example

4.9.2 Decision The team has decided to use a pressure transmitter for the final compression stage and used pressure

gages for the other stages. This one pressure transmitter is necessary to tell the computer when the

natural gas vehicle tank is full. The team will do much of their testing and thermodynamic computer

modeling using a one cylinder model with a pressure transmitter, however using pressure transmitters

at every stage on the prototype was deemed to be too costly.

4.10 Development Board

4.10.1 Alternatives A table showing a variety of potential development boards is shown below in Table 4.


25

Table 4. Comparison of Development Boards35

Development Board

Raspberry Pi BeagleBone Black CubieBoard

Price $25-$30 $45-$55 $50-$60

CPU 700 MHz Low Power ARM1176JZ-F

AM335x 1GHz ARM Cortex-A8

Arm Cortex A8 1GHz

GPIO 8 GPIO pin I²C SPI UART

Two 46 pin configurable bus

Two 48 pin configurable bus

Power Consumption

5V, 1A 5V, 700mA 5V, 2A

Memory 512MB SDRAM (Model B)

2GB embedded MMC

NAND (max 64GB) SATA II, SD Card 3.0

Dimensions 8.6x5.4x1.7(cm) 10×6 (cm) 90x40x13(mm)

Application Learning

Embedded apps

Robotics

Basic Learning

Embedded apps

Robotics

Advanced Learning

Embedded apps

Video

Robotics Ease of Use Easy Easy (but closed I/O and peripherals

are not so easy to manage

The Raspberry Pi not only bridges the overall mechanical and electrical processes, it also provides

extremely necessary safety precautions as well as the ability to offer a robust user interface. The only

downside to the limited input/outputs onboard the Raspberry Pi. Likewise, the onboard I/O is limited

in connection pins, as well zero tolerance to anything above 0 or 3.3V. Consequently, the onboard

GPIO pins are connected directly to the connection pins of the processor, in turn causing potential for

the entire board to fry. With no surge protector or general protection, developers began deriving

additional designs to be added. The Slice of PI/O is just one option in the efforts to protecting the

RasPi’s unprotected general-purpose input output pins. The Slice of PI/O ad-on is a small addition to

the Raspberry Pi providing a buffer, conversion levels, analog I/O and protection devices, in order to

avoid the risk of damaging it. There are many breakout boards that have been developed and can be

easily plugged into the Raspberry Pi GPIO pins.

35 http://www.open-electronics.org/a-comprehensive-comparison-of-linux-development-boards/

http://www.open-electronics.org/a-comprehensive-comparison-of-linux-development-boards/


26

4.10.2 Decision The team has decided to use the Raspberry Pi development board because of its compact size, ease of

use, and its vast online community presence available to us for referencing as the team begins to

prototype. The BeagleBone Black and the CubieBoard both provide a few aspects that the Raspberry Pi

does not. However these development boards are more expensive, more expensive development

boards could be helpful, the team believes the Raspberry Pi is a good development board to start off

with without having to put forth a considerable amount of funds.

4.11 User Interface

4.11.1 Alternatives

Touchscreen

The touch screen user interface opens the realm of possibilities, but it can still be simplified for ease of

use purposes. A detailed representation of the touchscreen can be seen in Figure 20. Having a full

interactive screen allow the Raspberry Pi to provide the user with a more detailed response or

diagnostics error if necessary. The touchscreen user interface is interchangeable depending on the

user’s desire for a complex and or simple interface interaction.

Figure 20. Touchscreen Raspberry Pi display36

LCD & Keypad

The 16x2 LCD display and keypad is simple and easy to use all in one, which is depicted in Figure 21.

This option cuts out any possible confusion between user and unit interaction. Given LCD’s small

compact characteristics, it will be limited to what information it can output to the display. Though the

display is limited, the team has also looked into providing real time system operations analysis that the

Raspberry Pi could upload to via Wi-Fi.

36 http://learn.adafruit.com/adafruit-pitft-28-inch-resistive-touchscreen-display-raspberry-pi

http://learn.adafruit.com/adafruit-pitft-28-inch-resistive-touchscreen-display-raspberry-pi


27

Figure 21. LCD & Keypad display37

Remote Access

Incorporating the world of smartphones to the refueling unit would be quite exciting, but as a team this

option is not necessarily what the team is looking for as an interface for other non-team member users.

Incorporating an interface via a smartphone, illustrated in Figure 22, would most likely be an option

strictly for the team to utilize as it provides a convenient means for us to test and analyze the

functionality of the Raspberry Pi.

Figure 22. Mobile User Interface38

By integrating these specialized safety precautions, the refueling unit will not only be self-governing

during operations, but it will autonomously provide the ability for users to remotely survey the current

37 http://www.adafruit.com/products/1115#Description 38 http://blog.davidsingleton.org/introducing-piui/

http://www.adafruit.com/products/1115#Description

http://blog.davidsingleton.org/introducing-piui/


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environmental readings of their unit. As the team plans to allocate the necessary time to provide not

only a reliable product, but also a reliable safety system.

4.11.2 Decision The team has decided to go with the 16x2 LCD display & keypad user interface option given its overall

ease of use and simple connectivity to the Raspberry Pi. This decision was also made in light of concerns

about environmental conditions and how those might negatively affect reliable touchscreen operation.


29

5 Testing & Calculations

5.1 Preliminary Design Methods In order to determine the size requirements for the natural gas compression cylinders along with the

tubing connecting the cylinders, the team has decided to use a combination of Engineering Equation

Solver (EES) and Autodesk CFD simulator. EES will be used to perform the calculations required, it was

chosen for its ease of use, integration of thermodynamic properties, and potential for optimization.

Autodesk CFD simulator was chosen for its ability to simulate fluid flow, compression, and heat transfer

simultaneously.

5.1.1 Autodesk CFD Simulator

Overview

Due to the complexity of this project and the difficulty and expense in implementing design changes

after production begins, the team will use Autodesk CFD to test initial designs. A variety of design

changes such as length of the cylinders, diameters of the cylinders, and wall thickness of the cylinders

will be altered and simulated in order to optimize our design.

Goals

The end goal of using Autodesk CFD is to have a full working model of the system that simulates and

shows the changes in pressure and temperature as the natural gas goes through it.

Status

Currently a simple model of compression has been successfully simulated. The purpose of creating this

model was to gain understanding of how to simulate compression in CFD simulator.

Results

Figure 23 shows the trend of the data obtained from the simulation modified to account for calibration

error.

Figure 23. Pressure Results from Simulation


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Figure 24 shows a plane from the simulation pressure results showing the higher pressure after

compression.

Figure 24. Plane of Simulation Pressure Results

Next Steps

The next steps for CFD are to first of all simulate the cooling of the natural gas between compression

chambers. The second step is then to put the two parts together to create a full working model of the

system.

Obstacles

Some obstacles that still need to be resolved with Autodesk CFD Simulator are a few calibration issues,

this will be resolved once a new model with information from EES is implemented.

5.1.2 Engineering Equation Solver

Overview

In conjunction with simulating the compressor, calculations are being done in EES in order to ensure

that the results obtained from the simulation are accurate as well as create the frame work for the

initial design.

Status

A basic model has been created in EES in order to calculate a preliminary piston size, work required

from the hydraulic compressors, and heat removal needed in order to compress most effectively.

Results

Table 5 shows the results for work required from the pistons and preliminary heat removal

requirements assuming that the temperature will be brought down to about room temperature in

between compression stages. Full results and calculations can be found in Appendix A.


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Table 5. Work and Heat Removal Calculation Results

Next Steps

The next step to research methods of heat removal in order to obtain a coefficient of heat transfer so

that the amount of tubing needed to reach the temperature required along with pressure drop

associated with the tubing can be found. Also, once a model of compression is simulated in CFD, the

results can be used in an iterative manner to obtain the optimal compression ratios, compression areas,

and stroke lengths of each of the four compression cylinders.

5.2 Initial Testing In order to increase understanding of seal technology and test basic forms of compression the team

plans to borrow a hydraulic pump from the physical plant. The pump would be used along with a

hydraulic cylinder to compress and monitor a gas with similar properties but without the safety concern

associated with natural gas. From this testing the team hopes to gain information about what type of

seal should be used, experience with manufacturing and assembling a compression cylinder, and

experience working with a hydraulic pump from this testing.

Compression Stage Work Required [W] Heat Removal Required [W]

1 135.6 0

2 127.7 153

3 135.6 110.3

4 140.8 123.5


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6 Preliminary Design Decisions

6.1 Hydraulic System

6.1.1 Overview A hydraulic system will be used to convert electrical energy into mechanical work that will drive the

pistons a therefore compress the gas. An overview schematic of the proposed hydraulic system is

shown below in Figure 25.

Figure 25. Hydraulic System Schematic

6.1.2 Reservoir After discussing their needs with a hydraulic power unit technician, the team determined that they

would be best suited with a two gallon hydraulic reservoir. This reservoir is a common size and will

have all the storage capacity required to meet the team’s needs. This reservoir will be part of a custom

built hydraulic power unit.


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6.1.3 Pump After discussion with the technician mentioned above, the team also determined the type of hydraulic

pump that will be best serve the team’s needs. A submersible hydraulic pump will be used. This pump

is very standard in industry and provides better cooling and noise reduction compared to an external

pump. This pump will be part of a custom built hydraulic power unit. Sizing the pump will take place

in the spring after initial tests using a hydraulic pump lent to the team by Calvin Physical Plant.

6.1.4 Solenoid Valve After researching different valve options, the team determined that they will be using one solenoid-

operated hydraulic control valve. The chosen valve is a 4-way, 3-position, exhaust center, double

solenoid valve. A schematic of this type of solenoid operated valve is shown below it Figure 26. When

either of the two solenoids are charged, the valve will be pulled to the left or right to let fluid into one

side of the cylinders, or vice-versa when the other solenoid is charged. When neither solenoid is

charged the valve will center and exhaust fluid to the reservoir.

Figure 26. 4-Way, 3-Position Solenoid Valve (Exhaust Center)

6.1.5 Cylinders The team will be using two double-rod hydraulic cylinders to power their four-stage compressor. Exact

sizing for these cylinders will be determined after initial tests using a used, inexpensive, small single

rod, double acting cylinder.


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6.2 Natural Gas System

6.2.1 Overview The natural gas system will move the gas from a residential natural gas line, through each of the four

compression cylinders, and ultimately into the tank of a natural gas vehicle. It also is designed to

prevent backflow at every possible point and monitor the thermodynamic state of the natural gas

using thermocouples, pressure gages, and a pressure transmitter. A schematic of the natural gas

system is shown below in Figure 27.

Figure 27. Natural Gas System Schematic

6.2.2 Residential Natural Gas Supply The team’s unit will be optimized to operate on a residential natural gas system with a pressure of 2

psi. This is the industry standard for larger homes, while 0.3 psi is standard for average homes. Natural

gas utility companies will usually install a 2 psi meter/regulator on a house if the customer has a special

reason to have one. Since the team’s system is an “intensifier” type of compressor, the initial pressure

into the first stage of the compressor is very important. To protect older appliances not design to used

2 psi natural gas, the team will recommend that customers who have to upgrade to a 2 psi

meter/regulator add an additional step down regulator to their residential natural gas system so that

their other appliances can continue to operate on 0.3 psi.


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6.2.3 Tubing The team will be using stainless steel tubing to pipe the natural gas between compressor stages. The

team has selected ¼ in. OD tubing, with a wall thickness of 0.049 in. According to Table 3, this will give

the team the capability to handle 3600 psi with a safety factor of 2.

6.2.4 Check Valves As displayed in in Figure 28, the team’s design uses check valves at every point where backflow could

possibly occur.

Figure 28. High Pressure Natural Gas Check Valves39

6.2.5 Relief Valve The system utilizes an adjustable pressure relief valve after the final stage. Gas is always free to flow

in the forward direction, therefore if over-pressurization occurred anywhere in the system it will be

relieved through this relief valve. An examples of adjustable relief values made for high pressure

natural gas applications are shown below in Figure 29.

Figure 29. Adjustable High Pressure Natural Gas Relief Valves40

6.2.6 Shut-off Valve A manual shut-off valve will be utilized between the residential natural gas system and the first stage

of the compressor. The will allow the compressor to be shut of manually during servicing. An example

of a ball valve made for compressed natural gas applications is shown below in Figure 30.

39 http://www.hylokusa.com/products/valves/check-relief-valves.aspx 40 http://www.hylokusa.com/products/valves/check-relief-valves.aspx

http://www.hylokusa.com/products/valves/check-relief-valves.aspx

http://www.hylokusa.com/products/valves/check-relief-valves.aspx


36

Figure 30. Example of CNG Ball Valve41

6.2.7 Manifolds Manifolds will be used to distribute the compressed natural gas at the end of each compression

chamber. The piping system will be attached to the manifolds using NPT treaded adapters and Teflon

tape to seal the connection. These manifolds will be constructed out of steel. An example of a

manifold used to distribute gas at the end of a hydraulic natural gas compression system is shown

below in Figure 31.

Figure 31. Example of Manifold and Connections at End of CNG Compression Chamber42

6.2.8 Pressure Gauges and Transducers The team knew that they would have to monitor pressure and temperature inside each stage to test

and optimize their design. Temperature and pressure will be known so that the thermodynamic state

can be determined. This will allow the team to perform accurate heat transfer and fluid flow analyses

on the system.

Pressure transducers are very costly, however the team needed at least one to monitor the pressure

after the final stage. An example of a pressure transmitter is shown below in Figure 32. This is

necessary in order to tell the control system when the vehicle tank is full (pressure has reached 3600

psi). Regular pressure gages will be used to monitor the pressure of all other stages, these an example

of one of these gages is shown below in Figure 33.

41 http://www.hylokusa.com/compressed-natural-gas/cng-parts.aspx 42 http://www.gonaturalcng.com/wp-content/uploads/2012/11/cng_compressors.png

http://www.hylokusa.com/compressed-natural-gas/cng-parts.aspx

http://www.gonaturalcng.com/wp-content/uploads/2012/11/cng_compressors.png


37

Figure 32. Pressure Transmitter Example

Figure 33. Pressure Gage Example

6.2.9 Thermocouples As stated above, the team needs to monitor the pressure and temperature of the gas at each stage for

accurate heat transfer and fluid flow modeling. Monitoring the temperature at every stage is more

important than monitoring the pressure at each stage because it is impossible for over-pressurization

to occur during the first three stages because gas is always free to flow in the forward direction. Over-

heating, however, can theoretically occur at any stage in the system. Therefore, thermocouples will

monitor the temperature inside the natural gas compression chamber at each stage. The team has

researched possible thermocouple models that are designed to operate in a high pressure environment.

An example of a thermocouple made to operate in a high pressure environment is shown below in

Figure 34. The team will test each possible thermocouple model at high pressures to ensure that they

will operate reliably.


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Figure 34. High Pressure Pipe-Plug Thermocouple Example43

6.2.10 Heat Sinks The compressor design will utilize tubing loop heat sinks and a fan to being the compressed gas back to

room temperature following each compression stage. An example of utilizing tubing links as a heat sink

in conjunction with a fan is shown below in Figure 35. This will improve the overall isentropic efficiency

of the system and result in safer operation that is less prone to overheating.

Figure 35. Example of Tubing Loops44

6.2.11 Refueling Nozzle Fuel will be dispensed using a purchased compressed natural gas fueling nozzle. There is an accepted

industry standard for these nozzles. Any nozzle purchased will fuel any compressed natural gas vehicle.

More complex and expensive nozzles are available, but because they are design for fast-fill units.

Because the team’s compressor is a time-fill unit, the simplest nozzles will be sufficient. An example of

a general purpose compressed natural gas refueling nozzle is shown below in Figure 36.

43 http://www.novatech-usa.com/Products/Specialty-Thermocouple-Probes/WD-08516-74 44 http://www.lmcompressor.com/images/Web%20Page%20CNG_3021%20_.jpg

http://www.novatech-usa.com/Products/Specialty-Thermocouple-Probes/WD-08516-74

http://www.lmcompressor.com/images/Web%20Page%20CNG_3021%20_.jpg


39

Figure 36. General Purpose CNG Refueling Nozzle for Time-Fill45

6.3 Sealing System

6.3.1 PTFE Coated Cylinder Walls PTFE (Teflon) coated cylinder walls will provide an excellent low-friction surface for the piston rings to

move along. This coating will protect against provide an excellent low-friction seal and protection

against excessive wear on both the cylinder wall surface and the rings. This coating is most common in

oil-less compressor designs.

6.3.2 PTFE Seal Rings Two PTFE (Teflon) seal will be used to seal the gas inside the compression chamber. These rings provide

an excellent low fiction seal. These rings will be located to the inside of the two rider rings, as displayed

below in Figure 37.

6.3.3 PTFE Rider Rings Two PTFE (Teflon) rings will be used to stabilize the piston as it moves up and down the cylinder walls.

These rings will be located to the outside of the two seal rings, as displayed below in Figure 37.

45 http://www.opwglobal.com/Product.aspx?pid=138

http://www.opwglobal.com/Product.aspx?pid=138


40

Figure 37. Picture of Ring Layout46

6.4 Control System A Raspberry Pi will control the brains of our refueling unit. It will provide a unique crossover between

the mechanical and electrical operations to the CNG unit. The Raspberry Pi, depicted in Figure 39, is a

small, compact, yet powerful micro-processing development board. The basic idea of the Raspberry Pi

is its capability of becoming an embedded Linux computer, but at the fraction of the price. There are

two models of Raspberry Pi boards, but the team has chosen the model B board due to its overall

specifications upgrade from the first generation (model A) board.

A schematic of the proposed control system is shown below in Figure 38.

46 http://www.ihi.co.jp/compressor/en/products/process-gas/gas-recipro/images/fea_photo_01.jpg

http://www.ihi.co.jp/compressor/en/products/process-gas/gas-recipro/images/fea_photo_01.jpg


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Figure 38. Control System Schematic

Figure 39. Raspberry Pi Size Comparison47

47 http://www.pyrosoft.co.uk/blog/wp-content/uploads//2012/01/DSC_1046.jpg

http://www.pyrosoft.co.uk/blog/wp-content/uploads/2012/01/DSC_1046.jpg


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7 Financial Estimates

7.1 Cost of Development The estimated budget for the development of one, full-functional home refueling unit is listed in Table

6. Cost of Development. Initial research into the component costs for the preliminary Bill of Materials

resulted in a total operational budget of $2,950. All values listed on Table 6 are all subject to change

based on the purchase price for each component.

Table 6. Operational Budget

7.2 Cost of Production The estimated budget for the production of 1,000, full-functional home refueling unit is listed in Table

7. Cost of Production. Using component costs listed in the operational budget (see Table 6. Cost of

Development), a preliminary production budget was calculated by assuming industry standards in

economics of scale. The team analyzed whether to sell NaturaFill preassembled or as a kit. Selling the

product unassembled and as a kit would reduce production costs, but have less desirable implications

to the end consumer. On the flip side, selling the unit assembled would increase the cost of production

and have greater ease of accessibility for the end user. The team concluded to sell the product

preassembled in order to align with the design norm of “trust.” This resulted in a total production

budget of $1,995, still in range of the $2,000 desired budget. All values listed on Table 7 are all subject

to change based on the purchase price for each component.

Vendor Part Cost

Bond Fluidaire Hydraulic Power Unit $ 600.00

Best Metal Products Hydraulic cylinders (2) $ 350.00

DECC Company Teflon coating of compression cylinders $ 300.00

Parker Hydraulic solenoid valve $ 300.00

Alro Steel Steel pipe for compression cylinders $ 200.00

Aavolyn Rings $ 200.00

Mouser Electronic components $ 200.00

Parker Check valves $ 200.00

Kendall Electric Electronics enclosure $ 100.00

Parker CNG filling hose nozzle $ 100.00

McMaster Carr Compression Tube Adaptors $ 100.00

N/A Materials for enclosure contraction $ 100.00

N/A Miscellaneous $ 200.00

Total $ 2,950.00


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Table 7. Cost of Production

Vendor Part One Unit

Cost Economies of Scale Savings

Production Cost

Bond Fluidaire Hydraulic Power Unit $ 600.00 55% $ 270.00

Best Metal Products Hydraulic cylinders (2) $ 350.00 50% $ 175.00

DECC Company Teflon coating of compression cylinders $ 300.00 50% $ 150.00

Parker Hydraulic solenoid valve $ 300.00 25% $ 225.00

Alro Steel Steel pipe for compression cylinders $ 200.00 30% $ 140.00

Aavolyn Rings $ 200.00 30% $ 140.00

Mouser Electronic components $ 200.00 30% $ 140.00

Parker Check valves $ 200.00 25% $ 150.00

Kendall Electric Electronics enclosure $ 100.00 30% $ 70.00

Parker CNG filling hose nozzle $ 100.00 40% $ 60.00

McMaster Carr Compression Tube Adaptors $ 100.00 25% $ 75.00

N/A Materials for enclosure contraction $ 100.00 40% $ 60.00

N/A Miscellaneous $ 200.00 30% $ 140.00

N/A Direct Labor $ 100.00 0% $ 100.00

N/A Manufacturing Overhead $ 100.00 0% $ 100.00

Total $ 1,995.00


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8 Conclusion The preliminary calculation and design research confirms that the NaturaFill project is feasible. The

preliminary design includes a hydraulic system to move the compression pistons, a natural gas system

to pipe the gas between stages and prevent backflow, and a control system to operate the hydraulic

system and monitor the safety system components. Moving forward, major obstacles include

adequate heat dissipation, ensuring safe prototype operation, and properly sealing the hydraulic

cylinders to allow for compression up to 3600psi. The team’s upcoming plans for next semester begin

with the purchase of materials and components to begin assembling a prototype of the NaturaFill CNG

home refueling unit.


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9 Acknowledgements

9.1 Professor Ned Nielsen Professor Ned Nielsen is the faculty advisor for NaturaFill. The team is grateful to Professor Nielsen for

his insights and constructive criticism throughout the preliminary design process.

9.2 Professor Steve VanderLeest Professor Steve VanderLeest is an adjunct advisor for NaturaFill. The team is grateful to Professor

Nielsen for his presentation feedback and advice on the project’s electronic control systems.

9.3 Professor Matthew Heun Professor Matthew Heun is a Mechanical Engineering professor with a wide range of knowledge in

thermodynamics. The team is grateful to Professor Heun for providing feedback on the AutoCAD CFD

simulation and supporting the team’s efforts to model heat generation by the compression system.

9.4 Mr. Jimmy Moerdyk Mr. Jimmy Moerdyk is the VP of Operations of Moerdyk Energy, Inc. The team is grateful to Mr.

Moerdyk for his mentorship and industry insights.

9.5 Mr. Lee Otto Mr. Lee Otto is the CEO and founder of CNGPump, Inc. The team is grateful to Mr. Lee for his advice to

the team regarding hydraulic cylinder seal technology and safety controls.

9.6 Mr. Ross Persifull Mr. Ross Persifull Otto is a Research Specialist at the Ford Motor Company. The team is grateful to Mr.

Lee for his industry insight on the future of CNG and willingness to demonstrate the use of his CNG

home refueling unit.

9.7 Mr. Phil Jasperse Mr. Phil Jaspers is the Calvin College metal and wood shop supervisor. The team is grateful to Mr.

Jaspers for his training in metal cutting and fabrication. The team is also grateful to Mr. Jaspers for his

advice on the fabrication of components.


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10 Appendices

10.1 Appendix A. EES Code


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