Lecture Notes XI

Internal Combustion Engines – MAK 493E

MIXTURE PREPERATION in CI ENGINES

Prof.Dr. Cem Soruşbay

Istanbul Technical University

Internal Combustion Engines – MAK 493E

Mixture Preperation

Introduction

Atomization of fuel, sprays

Fuel systems - in-line systems, distributor systems

Common-rail systems, unit pump and unit injector systems

Fuel Atomization

In Diesel engines, fuel-air mixture is prepared as a result of fuel injection into the cylinder at the end of compression stroke (usually before TDC) during a limited time (crank angle) interval.

The purpouse of fuel injection is to provide good mixing of air and fuel in the limited time available, by increasing the surface area of the liquid fuel as a result of atomization

Dividing unit fuel volume into droplets of 100 x 10-6 [m] diameter would increase the total surface area by 10,000 times.

Liquid Atomization

Liquid atomization is effected by internal and external forces.

controlled by Reynolds number defining the balance between inertia effects and viscous effects

Re = u D /

Atomization at Low Speeds

Rayleigh regime : internal effects are dominant

surface tension, fuel density, liquid column diameter

Any disturbance produces break-up of liquid column

Weber : indicated the importance of viscous effects

Heavy fuel, (left) 5000 cS

Diesel fuel (right) 6 cS

Atomization at High Speeds

Atomization at High Speeds

Secondary Atomization

Weber number

DuW h

e

2

Spray Structure

In difusion flames, combustion is controlled by the mixing rate of the fuel and air.

The local conditions in the combustion chamber such as the air-fuel ratio, temperature, pressure control the ignition of the fuel and the combustion process. Heat and mass transfer in the combustion chamber and the fluid flow (air flow) also effects this process.

Spray structure,

core

breakup length

spray tip penetration

Fuel Sprays

Fuel Sprays

Fuel Sprays

Temperature Contours

Temperature distribution inside the cylinder

Diesel Combustion Phases

Droplet Size Distribution

Droplet Size Distribution

Sauter Mean Diameter

p = 2 and q = 3 : Sauter Mean Diameter

indicates the total Area-to-Volume ratio applicable for the whole spray

o

m

o

m

o

m

o

m

D

D

p

D

D

q

D

D

p

D

D

q

pq

qp

dDdD

dVD

dDdD

dVD

dDdD

dnD

dDdD

dnD

D3

3

ii

ii

nD

nDD

2

3

32

Droplet Size Measurements

Droplet Size Measurements

Droplet Size Measurements

Diesel Engines

Fuel system

Injection Pump – in line system

Injection Pump

Injection Pump

Injection Pump – fuel metering

Injector

Injector

Nozzles

Nozzles

Delivery Valve

Direct Injection Diesel Engine

Indirect Injection Diesel Engine

Distributor-Type Injection Pump

1. Injection Timing Adjustement 2. Roller 3. Cam Plate 4. Axial Piston 5. Control Sleeve 6. High-Pressure Chamber 7. Fuel Outflow to Nozzle 8. Leak-Off x. Effective Stroke

Yıldız pompa

Distribütör tipi pompa

Distributor-Type Injection Pump

Diesel Fuel Systems

In-line pumps Common Rail Unit-injector/pump

Common-Rail System (Truck engine)

CR-System Production Location Bursa

Nozzles

Nozzle Holder Assemblies

Pump Elements

Common Rail Injector

Products

Common Rail System for Passanger Cars

Common-Rail System for Heavy Duty Engines

Common-Rail (Truck Rail Basic Design)

RDS

rail pressure sensor

DBV

pressure limiter

valve

Common-Rail System

Tank Prefilter

Other sensors

High

pressure

pump

CP3

Rail

Gear

pump Filter

Rail pressure

sensor

Accelerator

pedal

Engine

speed

(crank)

Engine

speed

(cam)

Other actuators

Control unit

Pressure

limiter valve

High pressure

Low pressure

Injector

Flow limiter

Metering

unit ZME

Fuel System Control

Flow Limiter

Two-step Pressure Limiting Valve

Rail Pressure Sensor Features

Common Rail Fuel Injector (Heavy Duty)

Magnet Group:

- Magnet core

from solid

Armature Group:

- Single piece Armature

Valve Group:

- Reduced control volume

- Improved piston

geometry

Injector body:

- Optimized high pressure bore geometry

- Improved backflow hydraulics

Nozzle:

- Miniature sac hole or

sac hole respectively

- Nozzle guided pushrod

- Single needle guidance

- Flat shoulder

Common Rail Fuel Injector CR-InjectorPrinciple of function

RBOS/EPK1-Ren

0

20

40

60

80

100

120

140

160MPa

0.0 0.5 1.0 1.5 2.0 2.5 3.0

ms

current solenoid

lift of armature

pressure in control chamber

lift of nozzle needle

injection rate

on signal

rail pressure

Common Rail Fuel Injector – First Generation

CRIN 1 – 1st Generation

CR Injector – Principle of Function

CR Injector Map

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

10^3

backflow counterpressure: 0 bar and 0.5

bar

low ripple:

spherical valve piston

tip

backflow pressure sensitivity:

armature geometrie optimized,

reduced volume in armature

group and enlarged backflow

bore

ca43/44n7

1600 bar

1000 bar

600 bar

250 bar

linear characteristics at high injection

rates: reduced volume in armature group

-10-505

1015202530354045505560

200 250 300 350 400 450 500 550 600

CR System Roadmap (P Cars and Light DutyTrucks)

98 99 2000 01 02 03 04 05 06 07 08 09

CR 1. Gen. MV 1350 bar

CR 2. Gen. MV 1600 bar

CR 2. Gen. Piezo 1600 bar

CR 3. Gen. Piezo 1800

bar

CR 4. Gen.

Piezo

• 2000 bar

• Pressure amplifier

• New control functions

• EDC17C / 42V

• Fuel metered

high pressure pump with

increased performance

• EDC16C+

• Improved top-head /

Compact injector

• Multiple injection (4 - 5)

• Fuel metered

high pressure pump

• EDC 16C/16C-P

CR Fuel Injector – Comparison

2. Generation

magnet core control chamber

geometry

DGV

intermediate

pin

armature high pressure

bore design

1. Generation

CR Fuel Injector – 2. Generation (for Trucks)

Injector body

CR Fuel Injector – 2. Generation (for Trucks)

Solenoid

CR Fuel Injector – 2. Generation (for Trucks)

Valve Group

High Pressure Pump

High Pressure Pump

CR Systems Status

1. Generation, 1350 bar systems

Euro III achieved with different applications

Low combustion noise with pilot-injection

Production of different applications (3 to 8 cylinders)

2. Generation, 1600 bar

Euro IV achieved with different applications

Combustion noise further reduced with 2 pilot-injections

HD Diesel Engine – EURO IV

Advanced combustion characteristics combustion chamber, swirl, number of nozzle holes

Advanced air management system

high excess-air ratio, λ 1.8 (steady state and transient)

Advanced supercharging system

“super” VGT or electronic powered charger

Close loop EGR system with VGT and linear EGR valve

efficient charge air cooling and EGR cooling

Application with retarded SOI for low EGR Rate

High injection pressure 1600 bar

Oxidation Catalyst for soluble fraction

Sulphur free fuel

Conclusion:

steady state test ESC possible

transient test ETC only possible with all mentioned measures

CR System – Comparison of Injection Strategies

PI MI Pol

Pilot injection Main injection Post Injection

Injector

Crank angle 0° 180°

Needle

lift

Cylin

der

pre

ssure

DI Engine – warm up after cold start at -20O C

0 15

250

750

100

0

125

0

1500

500

0

30

60

20 25 30 35 35 40 45 50 s

35 30 25 45 40 50

%

Op

acity

Speed

Time

rpm without pilot injecton with pilot injecton

Influence of Pilot Injection on Noise and Emissions

0.0 0.5 1.0 1.5 2.0 3.0 2.5 3.5

Pilot injection quantity mm3/stroke

1.9 TDI with CR, speed = 1500 rpm, pme = 5 bar, rail pressure = 800 bar

g/kWh

4.0

3.0

2.0

1.0

0.0

g/kWh

0.8

0.6

0.4

0.2

0.0

Soot

Nois

e

dB (A)

88

86

84

82

80

Soot

Noise

NOX

NO

X

HD Diesel Engine – Post Injection

0

NOx 0

g/kW h

4 6 7 9

0.1

0.2

0.3

0.5

BS

N

210

NOx

g/kW h 230

bsfc

without post injection with post injection

215

220

225

5 8

0.4

0 4 6 7 9 5 8

Variation of start of injection with appended post injection (rail pressure = 900 bar) Fuel quantity of post injection approx. 12 mg/str

SOI = +2

retarded advanced start of main injection

1400 rpm, 75% Load

Common Rail System – Passenger Car

Late post inj. for HC production

(increase of exhaust temp.)

Main injection

Coupled post injection

(soot reduction)

„Split main“ for stable

rich operation (storage cat.)

Pilot injection for

noise reduction

Type Approval Data of HD Engines ( > 85 kW )

0 0 1 2 3 4 5 6 NOx 7

0.05

0.10

0.15

0.20

g/kWh

Euro II (10/95)

Euro III (10/00) So

ot

Euro IV Euro V

State of the art

Low swirl combustion elevated injection pressure injection rate shaping partly EGR

+ cooled EGR part.-trap

NOX-cat. part.-trap

Exhaust Gas Aftertreatment for P Cars

Assessment of aftertreatment for Diesel-PC, EURO IV and up Priority I (PM Reduction):

Particulate trap technology is politically necessary and technically suggestive; short-term market release

Priority II (NOx Reduction):

With market release of low-sulphur fuel NOx trap has high potential; further development necessary; medium-term market release NOx reduction with urea/water remains an individual solution

Diesel Emission Reduction Technologies – P Cars

Lean NOx

Trap

Reductant HC

Added

Reductant

Urea

Oxidation Catalyst

Diesel

Particulate Filter + Selective

Catalytic

Reduction

Less

PM

Lower

NOx

Less

PM

Lower

NOx

Exhaus

t

PM

Exhaust NOx

Exhaus

t

PM

Exhaust NOx

Influence of Pilot Injection on Noise and Emissions

Diesel Emission Reduction Technologies - EGR

High Pressure Amplifier Piston CR System APCRS – Schematic View

700 bar fuel pressure

Fuel tank Injector

High pressure pump

Leakage

Leakage Amplifier piston

Common Rail

High Pressure Amplifier Piston CR System APCRS – Schematic View

700 bar fuel pressure

Fuel tank

Pilot Injection

Injector

Amplifier piston

Common Rail

High pressure pump

Leakage

Leakage

High Pressure Amplifier Piston CR System APCRS – Schematic View

Fuel tank

Pilot Injection

700 bar fuel pressure

Fuel tank Injector Leakage

Leakage Amplifier piston

High pressure pump

Common Rail

High Pressure Amplifier Piston CR System APCRS – Schematic View

Main Injection

700 bar fuel pressure

Fuel tank Injector Leakage

Leakage Amplifier piston

High pressure pump

Common Rail

High Pressure Amplifier Piston CR System APCRS – Schematic View

Fuel tank

Main Injection

700 bar fuel pressure

Fuel tank Injector

Amplifier piston

High pressure pump

Leakage

Leakage

Common Rail

High Pressure Amplifier Piston CR System APCRS – Schematic View

Fuel tank

Main Injection

700 bar fuel pressure

Fuel tank Injector

Amplifier piston

High pressure pump

Leakage

Leakage

Common Rail

High Pressure Amplifier Piston CR System APCRS – Schematic View

700 bar fuel pressure

Fuel tank Injector

Amplifier piston

High pressure pump

Leakage

Leakage

Common Rail

HD-Engine with CRS, Pilot Injection n = 1200 rpm, full load

Possible Black Smoke Reduction with Post-Injection

Unit Injector and Unit Pump for Commercial Vehicles

Unit Pump for Commercial Vehicles

Unit Injector for Passenger Cars

Unit Injector for Passenger Cars

Unit Injector System for Passenger Cars

Unit Injector System – Generations G1 and G2

Time

PNozzle

Generation N1 : 1600 bar

Generation N2 : 1800 bar

Unit Injector for Commercial Vehicles

Applications of Diesel Fuel-Injection Equipment