optical techniques in gasoline engine performance and ... · as liquid fuel enters the combustion...

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Optical Techniques in Gasoline Engine

Performance and Emissions Development

TC GDI engines: analysis and development techniques to solve

pre-ignition and soot formation issues

Ernst Winklhofer

AVL List GmbH, Graz Austria

June 2014

Gaydon, UK

contact: [email protected]

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TC GDI engines – some topics

As liquid fuel enters the combustion chamber of an SI engine

1. it must evaporate and mix with air to support formation

of a premixed flame

2. it must keep away from cold surfaces to avoid • fuel film formation

• oil dilution

• deposit formation

otherwise:

see movies on soot formation

m1, m2: premixed + diffusion

m3, m4: premixed

and examples for pre-ignition

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66*1011

3

PN 6*1011 /km allows PN 66*1011 /test

Euro 6c in 2017:

PN < 66*1011 in the 20 minute

NEDC test

TC GDI engines – PN particle number emissions

what is our target ?

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TC GDI engines – PN particle number emissions

The PN Euro 6c limit –

eliminate the root causes: find measures to avoid soot formation

Spray and flame movies show that

avoiding diffusion flames is key to

soot free combustion.

How can we use this in practical

engine development ?

Achieving the Euro 6c target:

5

Spray and flame movies show that

avoiding diffusion flames is key to

soot free combustion.

How can we use this in practical

engine development ? Step 1

select correct hardware for

• airflow

• fuel injection

• piston surface

correct hardware – what is it?

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Step 1


• airflow….port development for

volumetric efficiency and tumble

• fuel injection: injector

• piston surface: piston bowl

Injector – piston combinations


workflow on the optical engine:

we take an injector – piston combination

and use spray / flame movies to guide our

selection of injection parameters for soot free

combustion.

Result: tradeoff trends on stability and

emissions for given hardware combination

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injection variations:

pressure, timing,

multiple, etc.

catalyst heating

soot – stability

tradeoff

Step 1


• airflow….port development for

volumetric efficiency and tumble

• fuel injection: injector

• piston surface: piston bowl


our criterion for „correct“:

- lowest engine out soot at

- lowest IMEP fluctuations

here: data show tradeoff in

cat heating point


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injection variations:

pressure, timing,

multiple, etc.

TC GDI: the correct package of development

techniques enables „soot free“ combustion.

What is in this package ?

Selecting correct hardware under

guidance of the optical engine tests

We use optical engine tests for visual

evaluation of flame – injection relations

catalyst heating

soot – stability

tradeoff

Step 1


• airflow

• fuel injection

• piston surface

…in reference operating points

at the optical engine

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Results

step 1: injector + piston + a set of

parameters to start combustion

developmnet in multicylinder engine

Step 1

select correct hardware at optical engine

Step 2

multicylinder engine development to meet all

combustion requirements including PN and PI

– pre-ignition quality

Step 3

Vehicle calibration for the NEDC test

„correct package of development techniques“

[1] Fuchs H. et al.: “Methods and criteria for fuel injector integration in boosted

gasoline direct injection engines”. IMECHE, 13-14 May 2009, London

[2] Fuchs H. et al: “MIXTURE QUALITY EVALUATION FOR TRANSIENT MODE

GASOLINE ENGINE CALIBRATION”, ICEF2010-35098, ASME 2010

[3] Fraidl, G., Winklhofer E.: “Entwicklungsmethodik für Euro 6 GDI Motoren”, 10.

Internationales Symposium für Verbrennungsdiagnostik, Baden Baden Mai 2012

[4] Dobes Th. et al.: “Optical Combustion Analysis with Spark Plug Sensors for

Particulate-optimized EU6 Calibration”, Haus der Technik, Berlin Dez. 12, 2012

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diagnostics in step 2 and 3:

fiber optic spark plugs for flame radiation

evaluation show PN sources in stationary

and transient tests

Step 1

select correct hardware at optical engine

Step 2

multicylinder engine development to meet all

combustion requirements including PN and PI

– pre-ignition quality

Step 3

Vehicle calibration for the NEDC test

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Spark plug sensor

type Application / purpose result

Cylinder

comparison,

synchronous

measurement

Best / worst cylinder

Find soot sources in

transient test

Injection calibration

for transient test

l

Refined local

analysis, aging, long

term stability

Quality and risk

assessment

single channel

„7+1“

80#

12

1

2

3

….access and exploit local information in

normal engine operation

0

200

400

600

800

1000

0 400 800 1200

Time - seconds

accu

mu

late

d fla

me

ra

dia

tio

n -

re

l. u

nit

3

2 1

on piston at start

on intake side at high load

cycle resolved data for

1. do not spray onto the cold piston

2. do not spray onto the intake valves

Here: a 20 minute NEDC

test script

13 Confidential

With such guidance we apply

modifications to injector and

injection parameters

tailpipe PN

measurement

Before / After

modifications

0

200

400

600

800

1000

0 400 800 1200

Time - seconds

accu

mu

late

d fla

me

ra

dia

tio

n -

re

l. u

nit

3

2 1

on piston at start

on intake side at high load

Smaller transient peaks

Less high load sooting

Smaller start hills

limit

target range

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Euro 6 PN limits

PN Summary

Select correct hardware

use flame analysis to guide

combustion development

use in-vehicle flame sensors to

calibrate emissions tests

The result: achieve development

targets well below EU6c limit

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Pre Ignition

16 Internal

Current Limits of

Turbocharged Gasoline Engines

Limitations:

-60 -30 0 30 60 90 120

Kurbelwinkel [Grad]

PC

YL [bar]

0

20

40

60

80

100

120

Knock Pre-Ignition

Irregular combustion: development and calibration of highly boosted SI engines

17 Internal

Engine Speed [rpm]

BM

EP

1000 2000 3000 4000 5000 6000

Avoid PI events: PI classes

LSPI – low speed pre-ignition: high temperature

acts over time to initiate combustion. It sets a

natural limit to high load – low speed operation

Load

Speed

deposits

parameter

18 Internal

Engine Speed [rpm]

BM

EP

1000 2000 3000 4000 5000 6000

Avoid PI events alltogether: PI classes

Thermal pre-ignition: heat transfer from surfaces

to mixture initiates ignition. Engine load is most

dominant.

Load

Speed

deposits

parameter

19 Internal

Engine Speed [rpm]

BM

EP

1000 2000 3000 4000 5000 6000

Avoid PI events alltogether: PI classes

Sporadic pre-ignition: residual deposits initiate

ignition. Deposits formation history is most

dominant.

Load

Speed

deposits

parameter

20 Internal

On engine test bed first task is to avoid PI events at all

The combustion analysis task:

understand dominant parameter to define suitable improvement

21 Internal

PI analysis on engine test bed

PI event analysis:

Flame data identify ignition

centers

Event statistics together with test

variants analysis provide

guidance for combustion system

improvement

the spark plug flame sensor to find PI ignition spots

22 Internal

Ex

In

Ex

In

gro

up

1

gro

up

2

gro

up

3

group 4

-20 deg CA 20

-20 deg CA 20

PI events are detected with a fiberoptic

multichannel spark plug sensor

gro

up

2

gro

up

1

gro

up

4

gro

up

3

Spark Cyl pressure

8 mm 8 mm

Flame moves

across spark

plug in 4 deg

CA ( = 8 mm)

Flame moves

from ignition point

to spark plug in 4

deg CA ( 8

mm)

PI location:

1. in topmost sensor group:

near cylinder head

2. in direction of center intake

3. ~ 8 mm from spark plug

border

1 2

3

PI location is derived from

flame data and sensor

channel configuration

23 Internal


Ex

In

Ex

In

Test of variants shows:

Combustion chamber

temperature is foremost PI

parameter

The first choice in a GDI engine:

use late injection for charge

cooling

from single event data

to PI distribution

statistics

24 Internal


Ex

In

Ex

In


to PI distribution

statistics

Ex

In

Ex

In


use late injection for charge cooling

retard injection

25 Internal


Ex

In

Ex

In


to PI distribution

statistics

Ex

In

Ex

In


use late injection for charge cooling

retard injection

BUT:

Spray on piston impingement

puts a limit to what late injection

can achieve

26 Internal

PI tuning: find the balance between temperature and deposits effects

the degrees of freedom: A: cooling B: wallfilm C: injector

27 Internal

PI tuning: find the balance between temperature and deposits effects

the degrees of freedom: A: cooling B: wallfilm C: injector

28 Internal

FS

N,

D-F

lam

e o

n p

isto

n

0

10

20

30

40

PI

Eve

nts

/ h

r

Smoke Number

Diffusion flame on piston

PI Events

Engine operation variant

High load soot is pointer towards PI issues

the wallfilm issue: engine out soot and diffusion flame

signatures are pointers for PI risk.

The actions: find the balance between charge cooling benefits

and fuel deposit formation

we use guidance available from flame measurement

29 Internal

Mixture formation quality is best evident in fiber

optic flame measurement data

early injection late injection

Diffusion flame signatures show spray impact on valves (A) and on piston (B).

Target:

late injection for effective charge cooling

just short of spray – piston deposit formation

A

A

B

30 Internal

test bed result

injection parameters (fuel pressure, SOI1, DOI1, SOI2, DOI2)

in balance between late injection charge cooling at still acceptable mixture

quality

is there any benefit in the vehicle tests ?

31 Internal

see vehicle test improvement in reference

Martin Ogris, Ernst Winklhofer: “Irregular combustion: development and calibration of highly boosted SI engines”, 4th International Conference on Knocking in Gasoline Engines, Berlin, 2013-12-09

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thank you

optical techniques in gasoline engine performance and ... · as liquid fuel enters the combustion...

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