utilization of predictive combustion and emission models ... · project: analysis of different...

Utilization of Predictive

Combustion and Emission Models

for Optimization of Engine Performance

Johannes Konrad, MSc.

2nd Workshop: Dual-Fuel Combustion Simulation


April 26 2018 | Rostock | Johannes Konrad | Slide 2

Outline

Motivation

Description of the Predictive Modelling Approach

1-dim Engine Model

Dual Fuel Combustion Model

NO- and Knock-Models

Adjustment of Models According to Test Bench Data

Optimization of Engine Performance due to Cylinder Cut-Out

Engine Operation with Cylinder Cut-Out

Optimization Workflow

Optimized Engine Performance

Conclusions



Focus of thermodynamic engine development

for maritime application is on:

v

v

Efficient and economic development depends on the application and

conjunction of test bench measurements and 0-dim / 1-dim / 3-dim models

Predictive 1-dim engine models:

• Provide detailed insight into fluid mechanic and thermodynamics

• Allow analyzing various development approaches due to increased calc. speed

• Display dependencies, consequently, can be utilized to solve optimization tasks

Motivation

1-dim Numerical ModelsPhoto: MAN Diesel & Turbo

• Responds

• Emissions

• Power

• Efficiency



State of the art

Medium speed dual fuel engines do not have

throttling devices to reduce air flow losses

Very lean air fuel mixture, incomplete

combustion, and increased methane emissions in low load

Project:

Analysis of different electronic cylinder cut-out sequences and optimization

of engine performance

Therefore, application of 1-dim engine model that is able to predict dual fuel

combustion, NO emissions and knock onset

Motivation

Electronic Cylinder Cut-OutPhoto: MAN Diesel & Turbo



Outline

Motivation


1-dim Engine Model








Conclusions



Description of the Modelling ApproachDevelopment 1-dim Engine Model

Electronic cylinder cut-out applied

by deactivation of gas injection

Relative air/fuel ratio of fired

cylinders is applied for control

GT-Power model of a 4-stroke dual

fuel engine with 7 cylinders in-line

Gas injection upstream of the

cylinders and direct pilot injection

Oxygen partial pressure measured

upstream of the turbine; applied to

control the gas mass flow

Prescribed torque is applied

Charge air pressure and rotational

speed are controlled by bypass at

constant relative air/fuel ratio



Description of the Modelling ApproachDual Fuel Combustion and Emissions

Increased fraction of diesel pilot fuel

in low load to achieve stable ignition

and combustion

Increased fraction of diesel

combustion leads to increased peak

temperatures and NO-emissions

Cylinder cut-out:

• Remaining fired cylinders are charged

with increased load

• Reduced fraction of diesel combustion

• Red. peak temp. and NO-emissions



Description of the Modelling ApproachDual Fuel Combustion Model

Developed during the preceding project Hercules-C at the LEC, Graz

and updated during Hercules-2 at LEC and IFA, TU-Wien

Diesel ignition delay according to Arrhenius approach

Diesel spray represented by homogeneous

package model (Hiroyasu and Stiesch)

Initial spray penetration length:

• Depends on initial package velocity, time and position

• Ignites area of the homogeneous natural gas air mixture

• Defines initial conditions of premix combustion and flame front

Source: Stiesch



Description of the Modelling ApproachDual Fuel Combustion Model

Premixed combustion of homogeneous background mixture according to

entrainment model (Tabaczynski)

Flame front (Salbrechter) expansion velocimetry depends on:

• Density difference of the burned

and unburned zone

• Turbulent flame speed, TKE, Da (Noske)

Laminar flame speed of homogenous background mixture

according to reaction kinetic calculations

Correction factors are applied to consider the influence of e.g. the methane

number and residual gas fraction (Krenn, Oppl)

Source: Salbrechter



Description of the Modelling ApproachNO and Knock Models

NO emission are simulated according to the approach of Pattas and Häfner:

• Temperature and concentration originate from Dual-Fuel combustion model

• NO formation based on elementary and atomic nitrogen (Zeldovich, Muzio)

• Hydroxyl-mechanism (Heywood) and Dinitrogen-mechanisms (Lavoie)

Knock model is based on an Arrhenius approach:

• Depends on density of the unburned zone

• Determines the concentration of a knock-relevant-species

• If the species concentration exceeds a definable threshold, the combustion is

classified knocking

Adjustment of dual fuel combustion-, knock and NO-models to test bench

measurements and raw emissions by a numerical optimization workflow



Description of the Modelling ApproachResults of Optimization Process

Reproduction with good accuracy of

combustion rates, NO emissions and

knock onset



Description of the Modelling ApproachResults of Optimization Process

Predictive engine model that represents the relevant

engine operation map with a good precision

Good correlation of high and low

pressure indication

Good fit of turbocharger efficiency

Good fit of air / fuel mass flow,

IMEP, and BMEP



Outline

Motivation


1-dim Engine Model








Conclusions



Engine Operation with Cylinder Cut-OutLoad Depending Results on Efficiency, Methane-Slip, and NO-Emissions

Static cut-out of 1 to 3 cylinder

leads to:

• Increased efficiency

• Increased fraction of burned fuel

• Reduced NO emission

Effects rise with the number of

cut-out cylinders

Number of cut-out cylinders

depends on:

• Applied load

• Relative air/fuel ratio (rAFR)

• Turbocharger and bypass

Knocking not relevant



Engine Operation with Cylinder Cut-OutResults on Efficiency

Increase of efficiency mostly due to raised fraction

of burned fuel

Effects rise with the number of cut-out cylinders

Applied load is distributed to the remaining fired

cylinders:

• Increased air mass flow to

cylinders and elevated charge air

pressure

• Increased turbocharger efficiency

• Reduced PMEP due to increased

scavenging gradient



Engine Operation with Cylinder Cut-OutResults on NO Emissions

At low load, amount of diesel

pilot is higher to ensure stable

combustion

High temperatures of diesel

combustion lead to increased

NO emissions (Zeldovich)

Combustion is shifted from partial diesel combustion

towards premixed combustion

As a result: reduced peak temp. and NO emissions

Keep NO emissions constant and increase

efficiency by richer relative air fuel ratio



Optimization of Engine PerformanceOptimization Process

GT-Power Model coupled to

developed Optimus workflow

Engine operation with defined

load

Optimization of efficiency by

var. of:

• Relative air/fuel ratio

• Number of cut-out cylinders

Optimization under

consideration of:

• NO emission constraint

• Knock onset

Efficiency increases with richer

combustion and raised number of

cut-out cylinders

Number of cut-out cylinders dep. on

load and NO emission benchmarks



Optimization of Engine PerformanceLoad Depending Optimization

Cut-out of 1 to 3 cylinders and var.

of rAFR leads to incr. efficiency

NO emissions meet the

benchmarks

Efficiency improvement:

• Increases in low load operation

• Mostly depends on elevated

fraction of burned fuel

Low load operation without cyl.

cut-out leads to lean rAFR, thus

fraction of burned fuel and

efficiency are reduced



Optimization of Engine PerformanceResults

Optimization of low load operation:

• Increased number of cut-out

cylinders

• More distinct shift from diesel to

premix combustion

• Stronger shift of rAFR to

stoichiometric

• Elevated fraction of burned fuel

Generally increased turbocharger

efficiency, thus PMEP is reduced

NO emissions benchmarks are

met



Outline

Motivation


1-dim Engine Model








Conclusions



Conclusions

1-dim DF-combustion, NO- and Knock-models

are applied; an optimization workflow is set up

Due to the static cylinder cut-out, the simulation

model predicts an increased brake efficiency

mostly based on:

• Increased fraction of burned fuel

• Reduced pumping work

The simulation model predicts reduced NO emissions

because of the shift from diesel to premixed combustion

Engine efficiency increases due to optimized rAFR and cut-out cylinders

Skip firing will be applied in the near future to prevent cylinder cool down

Photo: MAN Diesel & Turbo

Herzlichen Dank für Ihre Aufmerksamkeit!

Johannes Konrad

[email protected]

Institute for Powertrains and Automotive Technology

Vienna University of Technology

Getreidemarkt 9

1060 Vienna, Austria

Thank you for your attention!

This project has received funding from the European Union’s Horizon 2020 research

and innovation programme under grant agreement No 634135

utilization of predictive combustion and emission models ... · project: analysis of different...

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