Spark Ignition Engine Combustion - İTÜweb.itu.edu.tr/~sorusbay/SI/LN01.pdf · Spark Ignition Engine Combustion MAK 652E ... Pulkrabek, W.W., Engineering Fundamentals of the Internal

1

Istanbul Technical University - Automotive Laboratories

Spark Ignition Engine Combustion

MAK 652E

Introduction to Combustion Process in Engines

Prof.Dr. Cem Soruşbay

Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories

Contents

Course information

Combustion process in engines

Classification of engines

Conventional engines

Advance concepts in engine combustion

2


Information

Prof.Dr. Cem Soruşbayİ.T.Ü. Makina Fakültesi Otomotiv LaboratuvarıAyazağa Yerleşkesi, Maslak – 34469 İstanbul

Tel. 212 – 285 3466 [email protected]

http://web.itu.edu.tr /sorusbay/SI/SI.htm


Course Plan

Introduction to engine combustion process

Premixed combustion in engines

Stratified charge engines, lean combustion, cyclic variations

Combustion modelling in engines, thermodynamic models

Multidimensional modelling of SI engines

Chemical kinetics of HC combustion

Autoignition in engines, knock modelling

Exhaust emissions, kinetics of pollutant formation

3


Assessment Criteria

Midterm examinations 2 x 15 = 30 %

16th March, 2017

27th April, 2017

Project 20 % to be submitted by 11th May, 2017

Final examination 50 %


References

Soruşbay, C., Lecture Notes, İ.T.Ü., 2010 (Power Point presentation)

Soruşbay, C. et al., İçten Yanmalı Motorlar, Birsen Yayınevi, İstanbul, 1995.

Pulkrabek, W.W., Engineering Fundamentals of the Internal Combustion Engine, Prentice Hall, New Jersey, 1997.

Mattavi, J.N. And Amann, C.A. (Eds.), Combustion Modelling in Reciprocating Engines, Plenum Press, New York, 1980

Ramos, J.I., Internal Combustion Engine Modelling, Hemisphere Publishing Corp. New York, 1989.

Turns, S.R., An Introduction to Combustion - Concepts and Applications, Mc Graw - Hill, New York, 1996.

4


References

Merker, G.P. et al., Simulating Combustion, Springer Verlag, Berlin, 2006.

Heywood, J.B., Internal Combustion Engine Fundamentals, McGraw Hill Book Company, New York, 1988.

Weaving, J.H., Internal Combustion Engineering : Science and Technology, Elsevier Applied Science, London, 1990.

Stone, R., Introduction to Internal Combustion Engines, Macmillan, London, 1994.

Arcoumanis, C and Kamimoto, T., Flow and Combustion in Reciprocating Engines, Springer Verlag, Berlin, 2009.

Other references given in the list (see web page of the course)


Combustion Process in Engines

Internal Combustion Engines (IC-engines) produce mechanical power from the chemical energy contained in the fuel, as a result of the combustion process occuring inside the engine

IC engine converts chemical energy of the fuel into mechanical energy, usually made available on a rotating output shaft.

Chemical energy of the fuel is first converted to thermal energy by means of combustion or oxidation with air inside the engine, raising the T and p of the gases within the combustion chamber.

The high-pressure gas then expands and by mechanical mechanisms rotates the crankshaft, which is the output of the engine.

Crankshaft is connected to a transmission/power-train to transmit the rotating mechanical energy to drive a vehicle.

5


Combustion Process in Engines

Most of the internal combustion engines are

reciprocating engines with a piston that reciprocate

back and forth in the cylinder.

Combustion process takes place in the cylinder.

There are also rotary engines

In external combustion engines,

the combustion process takes place outside

the mechanical engine system


Energy Conversion

(Merker et.al, 2006)

6


Energy Conversion


Classification of Engines

Method of ignition

Spark Ignition (SI) engines,

ignition is by the application of external energy (to spark plug) mixture is uniform (conventional engines), mixture is non-uniform (stratified-charge engines)

Compression Ignition (CI) engines,

ignition by compression in conventional engine (Diesel engine), pilot injection of fuel in gas engines (eg, natural gas and diesel fuel –> dual fuel engines)

7


GDI Engines


History of Engines

Huygens (1673) developed piston mechanismHautefeuille (1676) first concept of internal combustion enginePapin (1695) first to use steam in piston mechaanism

“Modern” engines using same principles of operation as present engines – previously no compression cycle

Lenoir (1860) driving the piston by the expansion of burning products - first practical engine, 0.5 hp, mech efficiency up to 5%

Rochas (1862) four-stroke concept was proposedOtto – Langen (1867) produced various engines, 11% efficiency

Otto (1876) Four-stroke engine prototype built, 8 hpClark (1878) Two-stroke engine was developedDiesel (1892) Single cylinder, compression ignition engine

8


History of Engines


Otto Cycle

Otto cycle (heat addition at constant-volume)2

3 p

p

9


Diesel Cycle

cut-off ratio

(load ratio)

Diesel cycle (heat addition at constant-pressure)

2

3

V

V


Comparison of Ideal Cyles

Otto cycle

Diesel cycle

Dual cycle

1

11

kOttoth

)1(

1

11

1

k

k

kDieselth

)1( 1

1

11

1

k

k

kDualth

10


Comparison of Ideal Cycles

For > 1 and k > 1

term is greater than 1

therefore t-otto > t-dies for a constant value of compression ratio

Also t-otto > t-dual > t-diesel

efficiency of Dual cycle lies between Otto and Diesel cycles according to the value of

)1(

1

k

k


Comparison of Engines

In real engines,

SI engines have a compression ratio between 10:1 to 12:1

this value is limited due to engine knock

CI engines have compression ratio higher than 14:1 to provide temperature and pressure required for self ignition of the fuel

compression ratio of 16:1 to 18:1 is sufficient for efficiency, but used for improving ignition quality

high compression ratio increases thermal and mechanical stresses

11


Comparison of Engines


SI Engines

a) Full load b) Part load

SI engine losses at full load (WOT) and part load

(Merker et.al, 2006)

12


SI Engines

a) Full loadb) Part load


SI Engines

Engine map with lines of constant fuel consumption

13


Losses in Real Engine


Losses in Real Engine

14


Conventional Diesel Engines

Phases of combustion process in a Diesel engine,Ignition delay periodPremixed combustion phaseMixing-controlled combustion phaseLate combustion phase


Conventional Diesel Engine

Conventional Diesel engine combustion

Temporal trajectories of equivalence ratio () and temperature

for injection timing of 25, 15 and 5 oCA BTDC

Eq

uiv

ale

nce

ra

tio

Temperature

15


Conventional Diesel Engine

Vibe parameter

(Mehdiyev, 2008)

m = 1.95“M” engine

m = 1.2“MR” process

m = 0.65CR injection


NOx – PM Trade-off

00 1 2 3 4 5 6 NOx7

0.05

0.10

0.15

0.20

g/kWh

Euro II (10/95)

Euro III (10/00)Soot

Euro IVEuro V

State ofthe art

Low swirl combustionelevated injection pressureinjection rate shapingpartly EGR

+ cooled EGRpart.-trap

NOX-cat.part.-trap

16


NOx – PM Trade-off Curve

NOx vs. Soot Trade-Off

0,20

0,40

0,60

0,80

1,00

1,20

1,40

100 150 200 250 300 350 400 450

NOx [g/h]

So

ot

[g/h

]

map=200 kPA AA9

map=200 kPA AA3

map=180 kPA AA9

map=180 kPA AA3

map=160 kPA AA9

map=160 kPA AA3


NOx – PM Trade-off

PIMIPol

Pilot injectionMain injectionPost Injection

17


NOx – PM Trade-off Curve

(Sorusbay et al., Int J Vehicle Design, 2007)


Split Injection Strategies

MAIN INJECTION

PRE INJECTION +MAIN INJECTION

PRE INJECTION +SPLIT MAIN INJECTION

18


Operating Regions in Relation to NOx and PM

Emissions of NOx and PM


Operating Regions in Relation to NOx and PM

Emissions of NOx and PM at various load conditions

(Akihama, SAE 2001-01-0655)

19

Limitations for SI Engines

(Source : Morey, 2011)

Compression and

Combustion

Friction Loss

Heat Loss

Incomplete oxidation

Slow burning

Knock limit

Efficiency limited by CR

Gas Exchange Process

Heat Loss

Pumping Losses

Waste heat out Exhaust

Inefficient valve timing

at varying speeds

Limitations for CI Engines

Major limitations with Diesel engines today

Controlling NOx and PM emissions

Reducing fuel consumption, CO2 emissions

Real-World exhaust emissions

PEMS

20

Real-World Exhaust Emissions

(Source : International Council on Clean

Transportation, 2015)

Advanced Combustion Concepts

Compression Ignition (CI) engines have higherefficiency at part load operation, longer lifetime andrelatively lower emissions of CO2, CO and unburned HC

Spark Ignition (SI) engines have higher powerdensity and lower combustion noise.

In the history of engine design and development, there have been many attempts to combine theadvantages of both CI and SI engines.

21

Gasoline Direct Injection Engines

Conventional Spark Ignition Engines

pre-mixed combustion

homogeneous and stoichiometric

mixture prepared in the manifold

GDI Engines

in-cylinder mixture formation

stratified charge with a globally

lean mixture

Spray guided GDI Engine

Gasoline Direct Injection Engines

(Source : Freeland et al., FISITA, 2013)

NEDC test Residency Points

shift up for

downsized GDI engine

o 2.4 liter , V6 engine

• 1.2 liter , I3 engine

22

Advanced Combustion Concepts

(Source : Ulas, PhD Thesis, TU Eindhoven, 2013)

Low Temperature Combustion

(Source : Wagner, SAE Paper No.2003-01-0262)

Heavy EGR application

23

HCCI Engines

Homogeneous Charge Compression Ignition engines : lean and homogeneous mixture is compressed until p and T are high enough for autoignition to ocur

HCCI ignition is governed by chemical kinetics andhistories of cylinder pressure and temperature (inlet air temperature, compression ratio, residual gas ratio andEGR, wall temperature). Combustion starts simultaneouslyall over the cylinder

Reaction rate is much lower than knock in SI engines due toa higher dilution of the fuel with air or residual gases (EGR)

HCCI Engines

High thermal efficiency due to high compression ratio, rapid heat release rate

Low specific fuel consumption with lean mixture

Low NOx emissions

Difficulties in controlling ignition and combustion over a wide range of engine operating conditions

24


Diesel and HCCI Engines

Comparison between conventional Diesel engine and HCCI engine

Longer induction time for HCCI and lower cylinder temperatures


HCCI Engines

Homogeneous Change Compression Ignition engines have features from both SI and CI engines;

Lean and homogeneous mixture is compressed until p and T are high enough for autoignition to occur

Combustion starts simultaneously all over the cylinder

Reaction rate is much lower than knock in SI engines due to a higher dilution of the fuel with air or residual gases (EGR)

25


HCCI Engines

Autoignition process is controlled by time history of p and T during intake and compression stroke

autoignition is mainly governed by the H (hydrogen), OH (hydroxyl), H2O2 (hydrogen peroxide) and HO2 (hydroperoxyl) radicals

H2O2 and HO2 concentrations increase progressively during compression as p and T increases

These two radicals also govern low temperature reactions (LTR), or cool flame

At temperatures between 1050 and 1100 K, H2O2 decomposes and forms OH that quickly reacts with fuel molecules to produce heat and water -> autoignition starts -> high temperature reactions (HTR)take placeconcentration of H and OH radicals inc rapidly, while H2O2 concentration drops

(Manente, V., PhD Thesis, Lund University, 2007)


HCCI Engines

Change of mole fractions

OH (hydroxyl),

H2O2 (hydrogen peroxide) , HO2 (hydroperoxyl) radicals

26


HCCI Engines

Autoignition temperature is controlled by the fuel used

it is between 1050 – 1100 K for fuels with no LTR

such as natural gas, iso-octane, gasoline with high aromatics

fuels with LTR, it is between 920 – 950 K

gasoline with high paraffin content, fuels containing n-heptane


Advantages vs Disadvantages

HCCI combustion has fast burning rateclose to ideal Otto Cycle (higher thermal efficiency than Diesel cycle)

lower fuel consumption (low CO2 emissions) compared to SI and CI engines of a given output power and CR

lower pumping losses compared to SI engines at part load (no throttle), but CI engines have higher part load efficiency

HCCI engines operate lean (with T below 1900 K) and due to fast combustion residence time of nitrogen at T higher than 2000 K is very short

Fast burning results in high pressure rise ratenoise emissions, structural damagesdifficult to control combustion phasing, ignition relies on spontaneous autoignition

Low temperature combustion inc HC emissions from the engine

27


HCCI Engines

Soot formation region is with equivalence ratio above 2 and temperature between 1700 – 2500 K

Thermal NOx formation region is with equivalence ration below 2 and combustion temperature above 2000 K


Controlling HCCI Engines

HCCI ignition is governed by chemical kinetics of mixture and histories of p and T in combustion chamber

Controlling combustion and ignition;

In-cylinder temperature

inlet air temperature

compression ratio

residual gas ratio and EGR

wall temperature, cooling water temperature, wall deposits

Air-fuel chemistry

dual fuel injection system (fuels with different ignition tendancies)

Mixture composition

fuel stratification in direct injection

28



solid lines : HCCI

dotted lines : Diesel

(Aceves et al.

SAE 2001-01-2077)

Performance map for Volkswagen TDI 4-cyclinder engineHCCI engine is more efficient at low torque at any speedHigher efficiency is due to faster combustion

(approaching to ideal Otto cycle)



Performance map for Volkswagen TDI 4-cyclinder engine

HCCI engine has,

72% of max torque obtained by Diesel

88% of the power obtained by Diesel

while producing practically no PM and less than 100 ppm NOx

under all operating conditions

Needs no delay to reduce NOx

Simulation results by Aceves et al., (SAE 2001-01-2077)

29


Gasoline and HCCI Engines

Saab SVC, VCR, HCCI, =10:1 - 30:1

General Motors L850, HCCI, =18:1 - SI, =18:1, ( =9.5:1 std)

Scania D12 Heavy duty diesel engine, HCCI, =18:1

Fuel: US regular Gasoline

(Johansson, Lund University, 2009)

SI engine


HCCI Engines

Wiebe (Vibe) function

Double - Wiebe function

(Yasar et al., Appl Thermal Engineering, 2008)

30


HCCI Engines


HCCI Engines

31


HCCI Engines

PCCI Engines

Premixed charge compression ignition engines : mixture of the fuel with air is provided prior to theinitiation of combustion due to early injection of the fuelinto the cylinder at low pressure and temperatureconditions for autoignition to take place.

Combustion is controlled by chemical kinetics. Incylinder temperature levels are controlled by applyingheavy exhaust gas recirculation (EGR) rates to dominateignition process, which also controls NOx and PM emissions.

32

PCCI Engines

Misfire especially at low load conditions is a potential problem

Rapid pressure rise at high loads and uncontrolledignition timing are other issues which can cause lowthermal efficieny and engine damage

Dual Fuel Combustion

Premixed Natural Gas induced into the cylinder duringthe intake stroke and ignited by pilot injection of Diesel Fuel

Lean operation is possible providing reduction in emissions and improvement in fuel consumption

City Bus fleet in Istanbul(1992)

33

RCCI Engines

Reactivity Controlled Compression Ignition engine : mixtureis formed with early injection of the fuel into the cylinder

Low octane fuel injected earlier can

be blended with high octane fuel with

post injection

Fuel blend ratio and injection timing

are the parameters for control

(Source : Reitz, 2011)

RCCI Engines

Varying the mixture ratio of fuel blends with differentreactivity levels can provide considerably high thermalefficiencies.

Relatively low injection pressures, in comparison to fuelinjection systems used in modern diesel engines, provideenergy saving.

Low temperature combustion reduce NOx emissionswhile the level of uniformaty of the mixture reduce PM emissions.

34


Advanced Combustion Systems

Injection timing and ignition


Advanced Combustion Systems

HCCI homogeneous charge compression ignition

UNIBUS uniform bulky combustion system

PCCI premixed change compression ignition

PREDIC premixed lean diesel combustion

MK modulated kinetics

LTRC low temperature rich combustion

PCI premixed charge ignition

35

Modulated Kinetics

Basic MK concept,

low temperature, premixed combustion system aimed at simultaneously reducing NOx and PM emissions (in a Diesel engine)

Low T can be obtained by heavy EGR reducing O2 concentration

-> but reduced O2 concentration increases PM in diffusion combustion

Fuel and air is mixed before combustion,

fuel injection time is retarded so that ignition delay is prolonged

(Kimura et al., SAE 1999-01-3681)


Modulated Kinetics

(Kimura et al., SAE 2001-01-0200)

36


Documents

Spark Ignition Engine Combustion - İTÜweb.itu.edu.tr/~sorusbay/SI/LN01.pdf · Spark Ignition Engine Combustion MAK 652E ... Pulkrabek, W.W., Engineering Fundamentals of the Internal