COMBUSTION SYSTEM DESIGN AND DEVELOPMENT PROCESS … SYSTEM DE… · A. Vassallo, Combustion System Design and Development Process for Modern Automotive Diesel Engines27 0 5 10 15

COMBUSTION SYSTEM DESIGN ANDDEVELOPMENT PROCESS FOR MODERN

AUTOMOTIVE DIESEL ENGINES

A. VassalloTechnical Specialist, Diesel Combustion Systems

General Motors

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Introduction

Combustion System Design & Development Process

o Overview

o Process of Engineering

o Tools

Example:

o Optical techniques applied to combustion and sprays

Summary

OUTLINE

2A. Vassallo, Combustion System Design and Development Process for Modern Automotive Diesel Engines

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The requirements posed on the combustion system of modernautomotive diesel engines have become very tightening, due to anaggressive combination of pollutant emissions, fuel economy, NVHand fun-to-drive targets. Coupled to ever-faster product developmentcycles, this requires an effective process for the design anddevelopment of new combustion systems.

Introduction


Source: GM, Dieselnet, Bosch (2015 Vienna Motoren Symposium)

Performance: + 150%Efficiency: + 30%Emissions: - 95%Combustion Noise: - 10dB(A)In the last 25 years… this has been achieved!!

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Since most of the architectural and design choices occur early in theengine development, it is nowadays practically necessary to rely onaccurate analytical tools capable to predict the performance of eachcomponent and of the overall system itself, prior than the actualhardware is available for testing.An efficient, robust and straightforward methodology that encompassesall the different development phases is equally critical to achieve theabove-mentioned targets.

Introduction


Source: Toyota (2015 Vienna Motoren Symposium)

Typical product cycle (time interval between twomajor engine redesigns) is currently about 5years (and getting shorter!), compared to 10years in the ‘80s and up to 20 years back in the‘50s (learning cycles are getting faster, withbenefits for technology introduction pace).

In the example by Toyota, a modernanalysis-driven combustion systemdevelopment process is illustrated for theirrecently-released 2.8L diesel engine.

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Such a process is fundamentally one of “alternative selection” or“sorting” of various concepts; utilizes relatively simple and quick toolsfor initial screening of ideas, while more complex, resource intensivetools are employed to refine designs that show strong potential; andincludes continuous feedback loops to develop alternative, “hybrid”designs and refine the fidelity of analytical predictions.

Introduction


“alternative selection” or “sorting” ofvarious concepts

relatively simple and quick tools for initialscreening of ideas

more complex, resource intensive toolsare employed to refine designs that showstrong potential

continuous feedback loops to developalternative, “hybrid” designs and refine thefidelity of analytical predictions Source: GM

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The present keynote describes the Combustion System Design andDevelopment Process devised and deployed by General Motors forthe new Euro 6 Diesel engines that have been recently released tothe market. The analytical tools definition, their interaction, and theirvalidation based on prototype hardware testing will be discussed.Then, state-of-the-art experimental techniques will be briefly reviewedfor better understanding of in-cylinder unsteady combustion process.

An overview about the most innovative areas under investigation andwhat the next steps could be in this continuous improvement processwill close the presentation.

Introduction


Diesel 2.0 LDiesel 1.6 LDiesel 1.3 L

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Introduction


o Overview


o Tools

Example:


Summary

OUTLINE


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GM global diesel engine line-up


A global, state-of-the-art diesel engine offer

More than 1 million diesels produced per year, sold in more than120 countries worldwide

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What do GM competitors?


Source: IAV, Toyota (2015 Vienna Motoren Symposium)

Similar elements as in the GM process, orbuilding bricks, can be recognized in theseschematics by IAV and Toyota.

Computational and experimental tools /techniques interaction (with the relatedloops) are well visible, linking 1D- / 3D-CFD and testing.

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GM Diesel Combustion System PoE(Process of Engineering)


Each “station” represents an importantmilestone in the set-up of combustion systemoverall architecture and of its inner features.«Quality valves» are used to monitorprogress with respect to program targets.

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Core elements of the Diesel Combustion System


Combustion chamber: Intake/Exhaust Ports specifications(volumetric efficiency, swirl ratio), and piston (bowl profile)

Fuel system: injector technology and pressure rating, nozzlespecifications, injection pattern capability

Air/EGR system: Turbocharger, CAC and EGR circuitspecifications (rate, temperature and imbalance)

Emissionization: matching combustion strategy with after-treatment system, Trade-offs between Engine-out andTailpipe emissions (involving CO2 & combustion noiseoptimization, system costs, deterioration factors, Ad-blueconsumption,…)

Calibration: Dyno and Vehicle integration, Control functionsdevelopment, OBD requirements

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Sorting-out the best combustion system…


“Typical” number of iterations for newcombustion systems (“majors”):

Architectures ~ 10

Alternatives screening ~ 100

1D/3D CFD Detailed Analysis ~ 25

Single-Cylinder Engine Builds ~ 5

Multi-cylinder Engine Builds ~ 2

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Setting program requirements

A. Vassallo, Combustion System Design and Development Process for Modern Automotive Diesel Engines

Setting program requirements is probably the mostcritical step decisions taken at this stage willdefine the final product about 5 years later

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Architectural screenings, best practices and 1D-CFD


S. Arrigoni, G. Avolio, L. Loudjertli, A. Renella and A. VassalloDevelopment of a 1D-CFD integrated methodology for charging and EGR circuits modeling in modern diesel engines3rd Conference: Engine Process Simulation and Turbocharging, Berlin, May 16-17th, 2011

Various EGR/charging circuit configurations (including High Pressure and LowPressure EGR) are compared and studied at 1D level in terms of capability toreach global EGR targets and in terms of their impact on fuel economy, as someof them require certain levels of throttling.

This activity helps identifying the most promising ones to bring forward to thenext optimization levels, where finer analysis involving 3D-CFD are employed.

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1D / 3D-CFD simulation loops


In this way, computationally-expensive 3D simulations canbe used to refine the predictions of highly-complexgeometries, and can provide in turn better circuitcharacteristics for a new 1D simulation loop, in a rapidlyconverging process.

The external boundary conditions calculated with 1D-code(pressure, temperature, flow rates) have been used as 3DCFD input, in order to check if they were compatible withthe geometries feasible for the EGR circuit and to carefullycalibrate the pressure drops in each portion of the CFD 1Dmodel.

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3D-CFD complete combustion system modelling


Complex 3D-CFD models of thecomplete combustion process –intake, compression, injection,combustion, expansion,blowdown – are generatedusing combination ofcommercially available software(Star-CD, Kiva, Converge,…)and user-defined routines, inparticular for spray, mixtureformation and combustion.

An example is provided into thefollowing animation.

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Genetic algorithm for bowl profile optimization


D. Wickman, R. Diwakar, S. Chang, “Low Emission Diesel Piston”,US Patent Number: 7389764, Issue Date: June 24, 2008

Using models as the one presented in the previous slide, theoverall combustion system can be simulated, and severalintake system / nozzle / piston profiles combinations can bescreened, in a powerful optimization scheme.

After several iterations (in the order of 80-100), a fewoptimized bowl profiles are generated, and can betransitioned to the SCE assessment.

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Transitioning to Single-cylinder & Multi-cylinder engines


Source: GM R&D

Single-cylinder engines are extensively used to validatesimulation tools and accurately assess fundamentaltrade-offs.The one depicted in this array of diagrams involvesengine-out NOx emissions and indicated net efficiency,for different combustion noise levels.

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Introduction


o Overview


o Tools

Example:


Summary

OUTLINE


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Optical techniques applied to combustion and sprays


CI combustion

1200rpm~ 4.5 bar BMEP

Low P Fuel Inj. (SI)High P Fuel Inj. (CI)

Cyl. PressureRoHR

SOC – Start of Comb.SOI – Start of Inj.

http://www.sandia.gov/ecn/tutorials.php

SI combustion Vs.

Source: Sandia National Laboratories

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A.E Catania, E. Spessa, G. Cipolla, A. VassalloCombustion Analysis in PCCI Diesel Engines by Endoscopic and Pressure-Based TechniquesProceedings of The Combustion Institute, Combustion Symposium, Turin, 2008

How diesel combustion looks like ina modern CR engine? Opticalimaging helps understanding…

An example taken from Turin 2008Combustion Symposium is shown.GM 2.0L diesel has been fitted within-cylinder endoscope (see pictureabove).Optical images are coupled to AVLIndicating and VisioFlame systems.

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Such a combination provides a powerfulunderstanding of the in-cylinder conditions, inparticular gas temperature and soot concentration(upper left picture).

Various injector combinations can be tested(upper right picture), showing benefit of smalldiameter holes on soot production for example.

Optical diagnostics data are also used forsimulation tool calibration (bottom left picture).

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-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14Crank angle [degree]

Ave

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CEC

GTL50%

RME50%

SME50%

Pilot Main

Combustion chamber wall

In this study published at SAE ICE 2009, optical diagnostics ofin-cylinder spray and combustion has been used to understandthe effect of various biodiesel blends on spray, mixture formationand combustion characteristics of then GM Euro4 1.9L diesel.

Images taken from bottom of the pistons are shown in clearcolors (top left), and then analyzed with two-temperaturethermometry to get temperature and soot distribution (bottomleft).

Spray penetration is also calculated from the pictures (right).

C. Beatrice, S. Di Iorio, C. Guido, E. Mancaruso, B. M. Vaglieco, A. VassalloThe Influence of Alternative Diesel Fuels on the Combustion and Emissionsof a Euro4 Automotive Diesel EngineSAE Paper 2009-24-0088

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Introduction


o Overview


o Tools

Examples:

o 2-stage charging architecture optimization

Summary

OUTLINE


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An integrated methodology for modern diesel combustionsystem development has been presented

Its main objective is the rationalization of the design process, bythe usage of analytical tool to screen several architectures,optimize the most promising ones and eventually reduceexperimental effort

Such methods are needed to capture the optimal designs due tothe diminishing returns of modern systems, which require wideinvestigations initially to identify the optimum region, and thenfine tools to target the best solution with high accuracy

Finally, a few innovative examples related to in-cylinder opticaltechniques for combustion process understanding andoptimization have been reviewed

Summary


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Thank you for the attention!


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COMBUSTION SYSTEM DESIGN AND DEVELOPMENT PROCESS … SYSTEM DE… · A. Vassallo, Combustion System Design and Development Process for Modern Automotive Diesel Engines27 0 5 10 15