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Simulation Models for Spark Ignition Engine: A Comparative Performance Study

Ashish Chaudhari, Upendra Garg, Vinayak Kulkarni, Niranjan Sahoo

Indian Institute of Technology GuwahatiGuwahati, Assam, INDIA-781039

IV th International Conference on Advances in Energy Research, IIT BOMBAY 2013

April 10, 2023 ICAER-2013 Slide 2 of 32

PRESENTATION OUTLINE PRESENTATION OUTLINE

Introduction

Background

Objectives

Model Development

Results and Discussion

Validation of Simulink Model

Validation of CFD Model

Conclusions

April 10, 2023 Slide 3 of 32

INTRODUCTIONINTRODUCTION

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- The Internal combustion engines have been present since a century and their performance, fuel economy has been greatly improved from the past and will continue to increase.

- There has been a lot of research going on worldwide experimentally to bring new fuel injection and combustion technologies for gasoline and diesel engines such as HCCI (Homogeneous Charge Compression Ignition), GDI (Gasoline Direct injection) etc. which are more efficient and produce lesser emissions [1].

- All the technologies introduced, cannot be tested experimentally as it is costly affair and time consuming.

- The mathematical model based simulation using different environments like Simulink, CFD etc makes the analysis easy, less time consuming and economical, for the different technologies.

- The results of these simulations can be implemented for the new technology in the engine.

Sr No Name of author Work reported Fuel used Outcome

01 Ismail and Mehta(2011)

Estimation of irreversibility using quasi –three dimensional combustion model

Hydrogen fuel More than 90% fuel undergoes combustion and 20-30% availability found destroyed.

02 Rakopoulos et al.(2005)

Computationally development of combustion model for observing the effect of irreversibility

Hydrogen and hydrocarbon fuel

Availability destroyed found to be14.99 to 15.02%..

03 Hongqing and Huijie (2010)

Second law analysis with two zone combustion model

Surrogate fuels

Found availability destroyed around 18.9%.

04 Al-Baghdadi (2006)

the effect of different fuels alone or their mixtures on the performance parameters and toxic emissions using a 2-zone simulation model.

Gasoline, ethanol, hydrogen

Ethanol add with 30% gasoline improves output power, reduces NOx. it increases heat release rate and also sfc.

05 Wu et al., (2009)

developed the modified heat transfer model for predicting the heat transfer rate value

Gasoline accurate and improved over the other models developed by researchers.


BACKGROUNDBACKGROUND


OBJECTIVESOBJECTIVES

- To develop a computer model for simulating a 4-stroke SI engine running on any hydrocarbon fuel.

- Model should take into account realistic heat release during combustion and heat loss from walls.

- Model should predict the cylinder pressure and temperature for one thermodynamic cycle.

- It should predict performance related variables such as Indicated W.D. , IMEP, efficiency, power and torque for a given engine at any operating condition.


MODEL DEVELOPMENTMODEL DEVELOPMENT

- A Single-zone, zero dimensional thermodynamic model is chosen for computer simulation for a four stroke SI engine.

- The model is divided into parts (subsystems) with different processes (compression, combustion, expansion, exhaust and intake) during 720º crank angle (CA) of one-thermodynamic cycle in the following sequence:

- intake valve closing (IVC), - spark timing,- end of combustion (EOC), - exhaust valve opening (EVO), - exhaust process (from EVO to EVC/IVO) and - intake process (from IVO to IVC)

- During the combustion process, the mixture can be assumed to be unburned and in expansion process (end of combustion to EVO), the cylinder consists of burned gases.

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- Spatial homogeneity of pressure for the whole cylinder, and spatial homogeneity of temperature for each zone are considered.

- From IVC to EOC, the specific heats are calculated considering only fresh gases to be present in the mixture and from EOC to EVC the properties are calculated considering only burned gases.

- The gaseous mixture follows ideal gas law.

- It is assumed that exhaust valve closes at the instant the intake valve opens.

- Heat transfer is considered to happen only during the closed cycle operation i.e. IVC to EVO.

- The Simulink model has following computation methodologies for determination of various parameters;

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Volume: - Using the geometry parameters of the engines, the cylinder volume at any crank

angle by following relation;

2

221 1 cos sin4

c

BV V a l a

Heat release during combustion: - The combustion investigation in engines has been carried out by analyzing cylinder

pressure data in single-zone thermodynamic model using Weibe function for calculating heat release during combustion [6].

- A functional form often used to represent the mass fraction burned versus crank angle curve [4].

1

01 expm

bX a

chQ- If is the heat released from combustion, it is computed from the following

relation;0

max 0

0,

,

ivc eoc

ch

beoc

anddQ

dxd Q for

d

(1)

(2)

(3)



bdx

d- Here, is the fuel mass burn rate which can be calculated from Weibe function

(Eq. 2). So the equation of mass burn fraction takes the following form; 1

0 01exp

m m

bmdx

ad

a

a

0.35 0.8a

m

-Where, is combustion completeness factor and tells about the efficiency of combustion; -It depends upon the intensity of charge motion and engine design and falls in the range of

- is the combustion duration- is the form factor that affects the shape of mass burned profile. - These parameters determine the shape of Weibe function and hence its accuracy to predict the actual heat release during combustion.

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(4)


Combustion duration:- Total mass burned and the heat release are independent of the combustion duration ( ). - It is also very important factor because if same heat is released in small combustion

duration, the rate of heat release will be more and pressure peak would be higher as compared to the large combustion duration. [7].

0 1 2 3 4 0 1

2 2

2

1 2

1 1 1 1

2

03 4 0

1 1 01

, , ,

3.2989 3.3612 1.0800 0.1222 0.9717 5.0510 10

4.3111 5.6393 2.3040 1.0685 0.2902 0.2545

;

;

r N f r f N f f

r r N Nf r f N

r r N N

f f

2

0

01

Cylinder temperature: - The first law of thermodynamics applied to a closed volume of combustion chamber in

the following manner. ch ht

ch s ht

Q dQdT dVQ dU Q W mCv P

d d d d

1 ch htdQ dQdT dV

Pd mCv T d d d

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(5)

(6)

(7)


Convective heat transfer rate: - Using the Annand‘s correlation [2, 6] for convective heat transfer coefficient is obtained.

_

_ 2; 0.7 and mean piston speed

60

b

pcp

h B S Ba

k

aNb S

7 0.73.3 10 9 5

1 0.027 1 0.027 4;air T

k Cv

Here

Pressure rise: - Ideal gas law for closed cycle operation is used to obtain the pressure rise in the

combustion chamber. The ideal gas equation can be differentiated with respect to crank angle.

00

1m RT dP dT dVP m R P

V d V d d

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(8)

(9)

(10)


Gas exchange process: - In this process, the system is considered to be open system, from which gas can leave or

enter the system.. It is correlated with the valve opening area and pressure variation with crank angle [8].

1 1

3 3

2

int1

180 180sin sin

720

1 1

;

;

evo ivoex exo in ino

evc evo ivc ivo

exhaust ake

m

A A A A

RTdp dm dV dp dm p dV

d m d V d d V d V dp

inoA exoAHere, and are maximum opening in intake and exhaust valves. Both the equations require mass flow rate which are to be found from the equations of fluid mechanics.

T PFIndicated torque and mean effective pressure: - Indicated torque as a function of crank angle [9] is obtained from the piston force by neglecting inertia of various components and friction.

2 2

sin 2sin

2 sin;

pP atm p T F an

F p p A

Piston Force ; ;

ln

a

2

4p

BA

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(11)

(12)


720

. .ivc

ivc

dVw d J p d

d

Indicated work done:

Indicated Power:

. .

120

w dP watt N

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(13)

(14)


-Based on the above formulation for the zero-dimensional and single zone thermodynamic model simulation, the Simulink model is being introduced for a four-stroke SI engine.

-This model has been built in solvers for ordinary differential equation, when the model is formulated in appropriate logical manner. The flow chart of Simulink model is shown in Fig. 1.

- First, this Simulink model is validated with the experimental conditions for the engine as given in the reference [8].

-Side by side, a CFD model has been developed for the combustion chamber of a test engine to predict its performance (Fig. 2-a).

-It is a four-strokes, air cooled, 1.8HP (HONDA make) engine with rated speed of 3600 rpm (Table 1). -In this model, one should be able to perform transient simulation with dynamic/moving mesh(Fig.2-b). -For a fixed compression ratio, it uses a module “in-cylinder” using the commercial package Fluent 6.3.

-The premixed combustion model is used for simulating engine combustion for different speeds. The performance results obtained from both the computational models are then compared.

PROCEDURE OF SIMULATIONPROCEDURE OF SIMULATION

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Simulink Model

Simulink Model

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Fig.1 Flowchart for Simulink modeling


- A 2-dimensional CFD model with Axisymmetric swirl was made for the new SI engine installed in Workshop.

- The aim was to carry out the unsteady simulation of the engine for closed cycle period (IVC to EVO) and to obtain pressure, temperature, and mass burn fraction curve with crank angle.

- The CFD model should be more accurate because its solves conservation equations for mass, momentum and energy and also predicts combustion.

Fig.2 (a) 2-D geometry of half combustion chamber at clearance volume

Fig.2 (b) Structured mesh of cylinder at TDC (360 degree CA)

CFD MODELCFD MODEL

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• Mesh is moved to crank angle corresponding to IVC i.e. 30 deg aBDC (570 deg.) as simulation would be setup from that crank angle.

Mesh Motion

Fig. 7 Clearance volume geometry

CFD MODELCFD MODEL


Setting up the physics• Three user defined functions (UDFs) are used in this problem

1. Initialize.c : To initialize the flow field.2. Laminar flame velocity.c: Function to calculate laminar flame speed at

different times.3. work.c : to compute averaged values of pressure, temperature and mass

burn fraction.

• Energy equation and turbulence are set on.

• Premixed combustion model is used. Spark location and its timing is specified.

• Setting Boundary conditions and finally selecting solvers.

CFD MODELCFD MODEL


ENGINE SPECIFICATIONSENGINE SPECIFICATIONS

Sl. no Specification Simulink validation with experimental results [8]

Simulink with CFD validation

1 Bore ( ) , mm 79.4 52

2 Stroke ( ) , mm 111.2 46

3 Connecting rod ( ), mm 233.4 81

4 Compression ratio ( ) 7.4 4.8

5 Speed ( ), rpm 4000 at 5 HP 3600 at 1.8HP

6 Spark timing ( º) -25 -20

7 Intake manifold pressure ( ), atm 1 1

8 Relative Fuel-air ratio ( ) 1 1

9 Fuel C8H18 (Gasoline) C8H18 (Gasoline)

B

2al

rN

oP

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Table 1 Specifications of engine


RESULTS AND DISCUSSIONRESULTS AND DISCUSSION

Validation of Simulink model

- Using the heat release rate obtained from experimental data [8], the combustion duration for those operating conditions of experimental engine, the reference values were found after tuning combustion model.

- At crank angles 25o before top dead centre (bTDC), the heat release rate becomes zero and can be approximately taken as end of combustion so that the combustion duration remains as 45o. The following reference parameters obtained.

1 1 1 01 1

0 09.2, 4000 , 1.1, 20 45 .r N rpm and

- With this as input to the main Simulink model for simulating the cycle for any operating condition.

- The parametric studies were done and results were compared with experimental data


Po=0.91 barPo=0.81 bar

Po=0.71 bar Po=0.61 bar

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(a) (b)

(c ) (d)


Fig. 3 (a),(b),(c ) and (d) Variation of peak pressure with crank angle at different intake pressure


Effect of intake pressure on performance with change in speed

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Fig. 5 Combustion heat release rate and pressure variation with speed

Fig. 4 Thermal Efficiency and Power variation with speed


Validation of CFD model- HRR Analysis using Gasoline Experimental Data

1 1 1 01 1

0 04.8, 3600 , 1, 20 140 .r N rpm and Reference values for tuning combustion model are


Fig. 6 (a) and (b) pressure variation with crank angle using SIMULINK


• Progress Variable (its value is 0 in unburned regions and 1 in burnt regions).

Fig. 7 Clearance volume at end of suction stroke



• Progress variable at end of combustion for different rpm. We can find combustion duration using contour plots as well.


Fig. 8 Combustion process at N=1000,2000.3000 rpm.


-The CFD model is prepared using FLUENT was verified for its results at the condition of rated power 1.8 HP at 3600 rpm. - Simulink model which emulates the combustion could then be compared with results of CFD model.

Fig. 9 (a) and (b) pressure and mass burn fraction variation with crank angle at N=1000 rpm.

(a) (b)







- Brake power

Fig .12 Brake Power variation with speed



- In this paper, an attempt has been made to address all the thermodynamic processes occurring in engine through appropriate and suitable relations.

- A single-zone zero-dimensional Simulink model presents good interface to user.

- Side by side, the CFD analysis is also performed using commercial package (Fluent).

- In the present study, the Simulink model is validated from the experimental data and found to be well agreement with the reported results.

- The Simulink analysis is performed to predict the maximum pressure after combustion.

- The deviation of mean pressure is about 6% higher as compared to experiment. However, it reduces to 1% with reduction in intake charge pressure from 0.91 bar to 0.61 bar.

- During experiment, when the speed increases from 1000 to 4000 rpm, the heat release rate rises from 3800 kJ to 4800 kJ, where as simulation shows constant heat release rate of 2000 kJ for all speeds.

CONCLUSIONSCONCLUSIONS


-After successful validation of Simulink model, the numerical analysis was carried out at rated rpm of engine (1.8 HP @ 3600 rpm) using CFD and subsequently both the results are compared.

-Here, the pressure curve shows slight variation. At low speed 1000 rpm, the maximum pressure recorded by CFD model showed relatively large deviation (≥ 8%). But with increase in speed (at 3000 rpm), the variations reduces and deviation remains below 3%.

-Mass burn fraction shows almost same trend of combustion duration. The experimental brake power shows close match with Simulink and CFD results.

CONCLUSIONSCONCLUSIONS


[1] Ganesan, V. (2007) Internal Combustion Engines. Tata McGraw Hill, Third Edition.[2] Wu, Y.Y., Chen B.C. and Hsieh, F.C. (2006) ‘Heat transfer model for small-scale air-cooled

spark-ignition four-stroke engines’. International Journal of Heat and Mass Transfer, Vol. 49, pp.3895–3905

[3] Rakopoulos C.D. and Kyritsis D.C. (2005) ‘Hydrogen enrichment effects on the second law analysis of natural and landfill gas combustion in engine cylinders’. International Journal of Hydrogen Energy, Vol. 31, pp. 1384 – 1393

[4] Rakopoulos C.D., Michos C.N. and Giakoumis E.G. (2008) ‘Availability analysis of a syngas fueled spark ignition engine using a multi-zone combustion model’. Energy, Vol. 33, pp.1378– 1398

[5] Ismail, S. and Mehta, P.S. (2011) ‘Second Law Analysis of hydrogen-air combustion in a spark ignition engine’ International Journal of Hydrogen Energy, Vol. 36, pp.931 – 946

[6] Heywood, J.B. (1988) Internal Combustion Engine fundamentals. Tata McGraw Hill,[7] Bayraktar, H. and Durgun, O. (2004) ‘Development of an empirical correlation for combustion

durations in spark ignition engines’. Energy Conversion and Management, Vol. 45, pp. 1419–1431.

[8] Ganesan, V. (1996) Computer Simulation of Spark-Ignited Engine Process. Universities press (India) Limited.

[9] Rattan, S. S. (2009) Theory of Machines. Third Edition, Tata McGraw Hill

REFERNCESREFERNCES
