STUDY AND APPLICATION OF PREDICTIVE DI-PULSE

MODEL FOR DIESEL COMBUSTION IN GT-POWER

GT-SUITE Conference Italiana, Torino 15/6/2015

A. Gallone, S. Pizza, A. Capra, M. Rimondi - General Motors Powertrain Europe

D. Bellomare - Powertech Engineering

GM CONFIDENTIAL

AG

EN

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1. DI-PULSE MODEL OVERVIEW

2. MODEL CALIBRATION DATA

3. RESULTS

4. SUMMARY AND NEXT STEPS

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Page 7

Page 12

Page 15

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1. DI-PULSE MODEL

What is it?DI-Pulse is a predictive combustion model designed to handle modern injection

strategies: the model predicts the combustion rate and associated physical quantities

for direct-injection diesel engines with single and multi-pulse injection events.

Why?To increase predictive capabilities of the GT-Power model, in order to be more independent from testing data.

DI-Pulse +other features

GT-Power

Testing

GT-Power

Testing

In-cylinder pressure data

are needed to calibrate

combustion in GT-Power

No emission prediction

Possibility to perform

virtual pre-calibration

NOx & Soot emission

prediction

4

DI-Pulse calibration

4 coefficients

100 in-cylinderpressure data from

testing

Combustion profileanalysis

100 Burn rates

Physical quantities andengine parameters of 100engine operating points

~ 20 in-cylinderpressure data from

testing+

~ 20 injection profiles

N injectionprofilesPhysical quantities, engine

parameters and emissionsof N engine operating points

NOx & Sootmodels

calibration

vs.Fast run time: only 5-10% longer

of non-predictive combustion

(for typical engine models)

+

1. BENEFITS OF DI-PULSE MODEL

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DI-Pulse calibrationThe 4 calibration parameters are:

Entrainment Rate Multiplier

Ignition Delay Multiplier

Premixed Combustion Rate Multiplier

Diffusion Combustion Multiplier

A DoE run was carried out varying the 4 parameters.

DI-Pulse emissions modelsNOx model: based on the extended Zeldovich mechanism (the calibration of 2 parameters

is required by a DoE).

SOOT model: 3 different models (all require the calibration of 2 parameters):

Hiroyasu model

Modified Hiroyasu model

Nagle and Strickland-Constable model

1. CALIBRATION OF DI-PULSE MODEL

Different size/family: SDE, MDE and LDE;

Different turbocharger system: FGT and VGT;

Different EGR type (temperature and quantity): LP and HP;

Different swirl motion: inlet port geometry and swirl flap;

Different peak firing pressure (PFP) level.

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ENGINE SIZE turbo EGR TYPE swirl flap PFP LEVEL

1 SMALL VGT LP + HP N MEDIUM

2 MEDIUM FGT HP N LOW

3 MEDIUM VGT HP Y HIGH

4 LARGE VGT HP Y MEDIUM-HIGH

1. ENGINES CONSIDERED IN THE STUDY

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INJECTOR:

hole geometry: diameter (0.116-0.139 mm) and

number (7-8)

discharge coefficient (Cd=1 considered constant)

injection rate profiles

CYLINDER:

initial conditions to calculate the trapped mass that means air

(volumetric efficiency) + fuel + residual gases (residual%)

and boundary conditions for heat transfer (Twall)

measured pressure cycles, to compare with predicted ones

flow characteristics (it seems they not affect the results)

CRANKSHAFT: usual data to link piston position and

then combustion chamber volume to crank angle.

DI-Pulse calibration is carried out on a single cylinder model (same as a CPO model): since this

kind of model doesn’t have valves, initial in-cylinder conditions at IVC have to be imposed.

2. SINGLE CYLINDER TO CALIBRATE DI-PULSE

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For each engine point the fuel injection rate profile is

required: in this work the measured profiles were chosen.

The raw data coming from EVI measurements are processed

in order to obtain ‘clean’ and more physical injection profiles.

Injection rate differences between Zeuch and EVI methods:

SOI -> EVI signal delayed by 50-70 s (0.7 CA at 2000 RPM);

SHAPE -> distorsion;

EOI -> EVI shows not plausible tails and echos.

2) Signal shifted (60 micros) and compensated (optional)1) Signal filtering: noises, tail and echo removed

2. INJECTION RATE PROFILES PROCESSING

signal currentEVIZeuch

EVIfiltered

EVIfiltered + shifted + compensated

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2. CALIBRATION POINTS CHOICE

EGR ZONE

The trend in calibration point choice is to reduce the

total number of calibration points, preferring the EGR

area, that plays a key role in the current emissions

cycles.

Furthermore, from a sensitivity study,

the EGR points affect greatly the

calibration results, much more than

full load or other points.

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DI-PULSE PARAMETER min max

ENTRAINMENT RATE MULTIPLIER 0.95 2.8

IGNITION DELAY MULTIPLIER 0.3 1.7

PREMIXED COMBUSTION RATE MULTIPLIER 0.05 2.5

DIFFUSION COMBUSTION RATE MULTIPLIER 0.4 1.4

SETTING: a “latin hypercube“ DoE run was

carried out varying the DI-Pulse parameters in

the advised ranges.

A total number of 2000 points is suggested, that

means a run time about 3 hours for 18 engine

working points (depending from HW and licences

capabilities).

POST PROCESSING (parameter to optimize):

BURN RATE RMS: an “improved“ BR RMS value is available in the standard RLT results;

IMEP error: not used for optimization, only for check.

_ =( )

2. DOE SETTING AND POST PROCESSING

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NOx MODEL SETTINGCalibration carried out on EGR points only and based on two main parameters:

NOx multiplier: multiplier to the predicted net rate of NOx formation

N2 oxidation activation energy multiplier: multiplier to the activation energy of the

N2 oxidation rate

Calibration effectuated by a DoE run, in order to minimize the error between simulated and

measured NOx concentrations

SOOT MODEL SETTINGCalibration carried out on EGR Points only and based on two main parameters:

Soot Formation Multiplier

Soot Burnup Multiplier

Calibration effectuated by a DoE run, in order to minimize the error between simulated and

measured SOOT concentrations

2. CALIBRATION OF EMISSION MODELS

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3. BURN RATES AND CYLINDER PRESSURES

injection rate

measured signals

calculated signals

Full load calibrationFull load prediction

High load prediction

Low load prediction(also calibration affected by same approximation)

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1000

rpm

3000

rpm

1250

rpm

1500

rpm

1750

rpm

2000

rpm

2250

rpm

2500

rpm

2750

rpm

3. NOx EMISSIONS

LESS ACCURATE

IN GENERAL for the analyzed engines a

goodness prediction chart can be used to

highlight the different zones where the cylinder

pressure cycles are in agreement or not with the

measured ones.

The predictive capabilities for NOx emissions are

affected by the quality of the DI-Pulse predicted

cylinder pressure and temperature: in the points

where the pressure and temperature are well

predicted, also the NOx model seems to work

properly.

measured

calculated (calibration + prediction)

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#4 - EGR 11.8%EGR SWEEP AT PART LOAD

3. ASSESSMENT OF PREDICTIVE CAPABILITY

Prail SWEEP AT PART LOAD

#1 - Prail 68 MPa

#5 - prail 38 MPa

calibrationcalibration

predictionprediction

NOx: physical trend(a bit sensitive to Prail)

SOOT: physical trend,values improvable

SOOT: physical trend(a bit sensitive to Prail)

NOx: physical trend andvalues as previuos page

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Low computational and model calibration efforts are required;

The cylinder pressure prediction is satisfying mainly at medium-high engine loads;

The cylinder pressure prediction at low engine load points is less accurate, in particular in

the EGR zone with multiple pilot injections;

The DI-Pulse model is sensitive to different engine operating conditions;

Acceptable predictive capabilities for NOx and SOOT have been obtained, influenced by the

quality of the predicted cylinder pressure and temperature (mainly for NOx).

4. SUMMARY

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IMPROVEMENTS IN COMBUSTION PREDICTION:

additional efforts are still needed to improve predictive capabilities for multiple pilot injections

and reach satisfactory sensitivity to the swirl.

DEEP ASSESSMENT FOR NOx AND SOOT MODELS:

additional attempt to have an acceptable prediction with engine virtual calibration intent: in

the GT-Power V7.5 version some additional options and improvements are available for NOx

emissions prediction.

4. PERSPECTIVES AND NEXT STEPS

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INVESTIGATION ABOUT INJECTOR MODEL:

study in deep the effect of the calculated fuel

injection pressure: with a constant Cd approach,

the calculated value is representative of the

pressure within the sac and it is not constant,

whereas using a Cd variable with tip lift, the

calculated pressure could be more constant and

similar to the rail value (to check if there is an

effect on predicted combustion).

4. PERSPECTIVES AND NEXT STEPS

fully detailed injector model (GT)

simple geometric andfluid properties +

empirical behaviour

hemi-empirical/statistic injector model

injection pressure in the sac (calculated)

use of an injector model to

become independent from test

bench data, moving from

measured injection rate

profiles to simulated ones.

injection rate

profileselectrical signal

THANKS FOR YOUR ATTENTION

ANY QUESTIONS?

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