Marquette University | Milwaukee School of Engineering | Purdue University | University of California, Merced | University of Illinois, Urbana-Champaign | University of Minnesota | Vanderbilt University Free Piston Engine Based Off-Road Vehicles Chen Zhang, Keyan Liu, Feng Wang Prof. Zongxuan Sun University of Minnesota Industry/University Engagement Summit June 6 – 8, 2016
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Free Piston Engine Based Off-Road Vehicles · Cylinder (OPOC) Design • Direct Injection • Uniflow Scavenging Variable compression ratio • Advanced combustion strategy • Multi-fuel
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Marquette University | Milwaukee School of Engineering | Purdue University | University of California, Merced | University of Illinois, Urbana-Champaign | University of Minnesota |
Vanderbilt University
Free Piston Engine Based Off-Road Vehicles
Chen Zhang, Keyan Liu, Feng Wang
Prof. Zongxuan Sun
University of Minnesota
Industry/University Engagement Summit
June 6 – 8, 2016
2
Outline
• Project Overview
• Control of FPE
• Trajectory based combustion control
• FPE based independent pressure and flow control
Basic concept
Demonstration through simulations
• Summary and future work
3
Project Overview Major
Objectives/Deliverables
Industry support
• What are your research goals?
Investigate the design, control and testing
of the FPE based off-road vehicles to
improve their fuel efficiency and reduce
emissions
• How does this project fit into the CCEFP’s
overall research strategy?
Increasing energy efficiency of fluid power
Improving and applying the energy storage
capabilities of fluid power
Reducing environmental impact of fluid
power
• What is the original contribution of this
project?
Controlling hydraulic FPE in real-time to
generate the required pressure and flow
rate Independently.
designing appropriate hydraulic actuation
system for both linear and rotary motion to
reduce or remove throttling losses.
How can industry help / contribute?
Providing operating duty cycle for off-
highway vehicles.
Providing industrial guidance on modeling,
experimental system design and
applicability of this technology
• What are the expected major objectives
and/or deliverables?
Control of the FPE to provide required
pressure and flow rate independently.
Design of efficient hydraulic actuation
systems for modular and digital fluid power
sources.
Evaluation of the FPE based off-road vehicles
and comparison with conventional vehicles.
4
Control of FPE: the FPE at UMN
• Opposed Piston Opposed
Cylinder (OPOC) Design
• Direct Injection
• Uniflow Scavenging
Variable compression ratio
• Advanced combustion strategy
• Multi-fuel operation
Reduced frictional losses
Fast response time
Higher power density
Internally balanced
Modularity
Exhaust Ports
Intake Ports
IntakePorts
ExhaustPorts
Check Valves
Servo Valve
On-off Valve
On-off Valve
LP
HP
Outer Piston Pair
Inner Piston Pair
Hydraulic Chambers
5
• System Modeling– Combustion model
– Hydraulic model
– Gas dynamics
– Piston dynamics
• Hardware improvement– Sensor identification
– Sensor calibration
– Pre-charge system
– DAQ and control system
– Moog valve and Lee valves
– Ignition control
– High pressure DFI system
– Supercharger system
• Implementation of Advanced Control– Virtual Crankshaft design
– Engine motoring tests
– Engine combustion tests
The developed robust repetitive controller acts as a
virtual crankshaft that would force the piston to follow
the reference signal through the hydraulic actuator.
• Engine start
• Misfire recover
• Real time frequency and compression ratio control
Control of FPE: Virtual Crankshaft
Experiment set-up in UMN test cell
6
Control of FPE using virtual crankshaft:
Motoring Test
Gas pressure, hydraulic chamber pressure and piston
tracking performance (from top to bottom)
Virtual crankshaft is able to actively
regulate the piston motion of the
FPE to track any prescribed
trajectory reference. [1]
Feedforward controller is also
developed to further improve the
performance of the virtual
crankshaft mechanism. [2]
[1] Li, K., Sadighi, A. and Sun, Z. (2014). Active motion control of a
hydraulic free piston engine. IEEE/ASME Transactions on Mechatronics,
volume (19), pp. 1148-1159.
[2] Li, K, Zhang, C. and Sun, Z., "Precise piston trajectory control for a
free piston engine." Control Engineering Practice, 34 (2015): 30-38.
7
(Top to bottom): Piston motion, combustion chamber
pressure, hydraulic chamber pressure and control signal
Continuous combustion
operation is achieved
Each fuel injection causes a
strong combustion occurrence
Virtual crankshaft is able to
maintain continuous engine
operation even with cycle-to-
cycle combustion variation
Frictional loss (FMEP):
50Kpa (conventional ICE
with the same size: 140Kpa)
Control of FPE using virtual crankshaft:
Continuous Combustion test
8
Control of FPE: Virtual Crankshaft
Virtual
crankshaft
mechanism
Trajectory based
combustion control
• Improved thermal efficiency [3]
• Reduced emissions [4]
• Optimal trajectory based on load requirement and fuel property [5]
Independent pressure and
flow rate control
• Producing the required flow rate at different pressure in real time
• Fast response time to load variation
[3] Zhang, C., Li, K. and Sun, Z., “Modeling of Piston Trajectory-based HCCI Combustion Enabled by a Free Piston Engine”, Applied Energy, vol. 139, pp. 313-326, 2015.
[4] Zhang, C. and Sun, Z., “Using Variable Piston Trajectory to Reduce Engine-out Emissions”, Applied Energy, vol.170, pp. 403-414, 2016.
[5] Zhang, C and Sun, Z., “Optimization of Trajectory-based HCCI Combustion”, DSCC 2016.
• Optimal trajectory based on load requirement and fuel property [5]
Independent pressure and
flow rate control
• Producing the required flow rate at different pressure in real time
• Fast response time to load variation
[3] Zhang, C., Li, K. and Sun, Z., “Modeling of Piston Trajectory-based HCCI Combustion Enabled by a Free Piston Engine”, Applied Energy, vol. 139, pp. 313-326, 2015.
[4] Zhang, C. and Sun, Z., “Using Variable Piston Trajectory to Reduce Engine-out Emissions”, Applied Energy, vol.170, pp. 403-414, 2016.
[5] Zhang, C and Sun, Z., “Optimization of Trajectory-based HCCI Combustion”, DSCC 2016.
13
Independent Pressure and Flow control
Virtual
Crankshaft
Hydraulic FPE
IPFC
Output flow rate
at load pressure
Piston Position
Servo
valve
signal
Reference
Measured
load pressure
Required flow rate
Fuel injection Amount
• The key component is the Independent Pressure and Flowrate Controller (IPFC),
which is able to synthesis a unique trajectory reference for the hydraulic FPE,
and derive the corresponding fuel injection amount, according to required flow
rate and measured load pressure.
• The synthesized trajectory reference is then sent to the virtual crankshaft, which
ensures accurate piston motion tracking by adjusting the opening of the servo
valve through different servo valve signal.
• The variable opening of the servo valve can also affect the output flow rate at
different load pressure produced by the FPE
Basic Concept
+Error
-
14
Positive
Chamber 1&3
Load
To Load
Net flow
Chamber 2
From Tank
To Tank
From Load
Negative
Independent Pressure and Flow control
1
3
2
Basic Concept
15
Independent Pressure and Flow control
Switching Point+
-
+
-
16
Trajectory Generation
Independent Pressure and Flow control
Net Hydraulic Force
Left Gas Force Right Gas Force
• The piston pair is subject to the
hydraulic force and the gas
forces.
•The hydraulic force is the net
force in all hydraulic chambers,
while the gas force is subject to
ideal gas law.
•By switching the servo valve
between the top position and
bottom position, the hydraulic
force direction is changed.
•The piston motion is subject to
the Newton second law 𝑥 = −𝐹𝑔_𝑙 − 𝐹𝑔_𝑟 ± 𝐹ℎ𝑦
𝑚
𝐹𝑔_𝑙 𝐹𝑔_𝑟
𝐹ℎ𝑦
𝐹𝑔_𝑙: Ideal gas law,
Instantaneous combustion model
𝐹𝑔_𝑟: Ideal gas law
𝐹ℎ𝑦 = (𝑃𝑙𝑜𝑎𝑑 − 𝑃𝑡𝑎𝑛𝑘) × 𝐴𝑝𝑖𝑠𝑡𝑜𝑛, Constant
17
Different piston trajectory leads to various flow rate at a specific load pressure.
Independent Pressure and Flow control
18
Desired
actuator speed
Actuator
pressure
Valve opening cmd
Hydraulic
actuator
+
+ PIDFree Piston
Engine Actuator
speed
Flow
Fraction of
displacementValve
Hydraulic plant
Hydraulic pressure source
Fluid
capacitor
_
Delta
pressure +
+
Source
pressure
PID
_
Combining FPE with the actuator
Independent Pressure and Flow control
Control scheme of hydraulic controls for the FPE and actuator
Virtual
Crankshaft
Hydraulic FPE
IPFCPiston Position
Servo
valve
signal
Reference
Fuel injection Amount
+Error
-
Output flow rate
at load pressureMeasured
load pressure
Required flow rate
19
Independent Pressure and Flow control
Case study: wheel loader working hydraulic circuit