# Modelling and it is a time taken process.

Modelling of SI and HCCI Engines on AVL

BOOST and their Comparisons and Improvements

Abstract: The main aim of this Paper is

to develop different types of Engines on Internal combustion software AVL BOOST

and Compare their results and discussing about the Improvements. The different

types of Engines are Spark Ignition(SI) and Homogeneous charge compression

ignition(HCCI). Here we are developing a single cylinder engine of SI and HCCI

working at 1500 rpm. By using the information from a literature paper we have

to calculate the given data for the BOOST software. After this we have to run

multiple simulations by adjusting different parameters to get optimal values. This

paper proves that the AVL BOOST software is good at modelling the engines,

although there is lack of experimental data, so we have to do few assumptions

while inputting data to the BOOST software. Because of this full validation of

the software’s accuracy could not be proven. The improvements were done in

terms of IMEP , NOx , Pmax

compared with the experimental results.

1.Introduction

As there are

different varieties of vehicles are coming into the market, the importance of

internal combustion engines is not decreased and as there are lot of

legislations are coming in automobile field which restricts the emissions. So,

keeping this in mind we are trying to work on reducing the emissions and making

improvements of an internal combustion engine using a software called AVL BOOST

in terms of IMep, Pmax, which leads to the increase in its efficiency with less

pollutants.

In this paper, we are doing simulation of different

engines using AVL BOOST software, as developing a prototype is costly and it is

a time taken process. By doing this simulation we can get almost exact results

as an experimental simulation process. After that we can do improvements to the

model to get better IMep and NOx.

1.1.Aims and Objectives

The aim

of this paper is modelling and simulation of different types of engines in AVL

BOOST software namely Spark Ignition(SI) and Homogeneous Charge Compression

Ignition(HCCI).

The

objectives of this paper are calibrating a particular engine model on a

particular case to get close values of Imep, Pmax, and NOx emissions. After

calibrating we have to validate it with remaining cases sourcing from the

literature review to check with experimental results of those cases. The same

procedure will be followed for both the engine models and then their results

will be compared.

Then the

improvements to be made by adjusting different parameters to make the engine

efficient is discussed.

2. Technical Reviews

2.1. AVL BOOST

AVL BOOSTTM is

an internal combustion software used to model different types of engines and

simulate them with all real simulation parameters like pressure, temperature,

volume, air-fuel ratio and some internal cylinder parameters like in cylinder

temperatures and calibration factors and some emission factors is well at a

comparatively low cost than a real life simulation with almost close results.

2.2. SPARK IGNITION(SI) ENGINE

A spark

ignition engine uses gasoline as fuel which is pumped into the cylinder with

the help of an injector at stoichiometric air-fuel ratio of 14.7:1. It works on

four strokes namely intake, compression, combustion and exhaust strokes. Here

the air fuel mixture is burned with the help of a spark plug after the air-fuel

mixture was injected into the cylinder during the intake stroke.

2.3. HCCI ENGINE

A

Homogeneous Charge Compression Ignition(HCCI) shares the properties of both

Spark Ignition and Compression Ignition engines. Here the air-fuel ratio is

different from stoichiometric air-fuel ratio and is based on lambda(?) which is multiplied by the stoichiometric air-fuel

ratio to give the actual value. This

engine also works on four strokes like the Spark Ignition Engine, but the

air-fuel mixture auto ignites under compression without the aid of a Spark

plug. But the efficiency of this engine is higher than the SI and CI engines.

3. BOOST setup of SI and HCCI Models

Figure 1- Model

of SI/HCCI Engine

Figure 1 shows the layout of both the SI and HCCI models with all the

elements like Engine, Cylinder, Connecting Pipes, Plena, Throttle, Injector and

the Junctions. The inlet and exhausts were modelled as system boundaries in

BOOST1.

The only difference between SI and HCCI layouts is the diameter of a pipe

after the throttle and throttle angles. In HCCI the throttle remains fully open

whereas in SI It will be changed according to the simulation. Both the models

were set to run for 30 cycles to allow for the convergence of the results in

the simulation1. The fuel is directly injected into

the cylinder of the HCCI model and same Injector is used for SI model also1.

3.1.

Calculations and Analysis

This step involves the Calculations of input parameters to the AVL BOOST

software using the values in the Literature Review. At first we have to

calculate the Volume of the cylinder, clearance volume and Swept volume from

the given Bore diameter, Length of the Stroke and Length of the Connecting Rod.

Then we have to calculate the cylinder volume at any crank angle using

‘C.V.Ferguson’s’ method2. After this we have to find

Logarithmic values of Cylinder volume at any crank angle and Logarithmic values

of pressure from the experimental results. Then we have to draw a graphs

between Log (P) vs Log (V) for all SI and HCCI cases.

Figure 2- Log p vs Log v graph SI

Figure 3- Log p vs Log v graph HCCI

Figures 2 and 3 shows the Log p vs Log v graphs of SI and

HCCI models for particular cases. From the HCCI graph we can observe that there

is Recompression involved in it which gives some extra pressure for the next

cycle so that the Compression of the air-fuel ratio happens rapidly and the

fuel ignites quickly. This Re-Compression occur due to neither inlet nor

exhaust valve opens at 00 TDC unlike SI engines which has positive

overlap that allows pressure to escape via the exhaust.3

3.1.1.

Rate of Heat Release(ROHR)

In the graphs there are some linear equations mentioned on

particular lines(Compression and Combustion lines) which gives us the

polytropic indices (k) which is useful to calculate Rate of Heat Release. This

is obtained from the equation

Log(P) +

K*Log(V) = Constant

After calculating this, we have to calculate the Rate of Heat

Release(ROHR) by using ‘H.R.STONE’s method’4.

ROHR =

Figure 4 Rate of Heat Release of SI case 4

Figure 4 shows the calculated Rate of Heat Release of case 4 of

Spark Ignition model and its comparison with the given experimental heat

release data. Here we can observe that there is not much difference between the

calculated and experimental data.

Figure 5 – Rate of Heat Release of HCCI case 1

Figure

5 shows the Rate of Heat Release data of case 1 of HCCI model. Here we can find

some small differences between

the calculated and experimental data. That is because of some assumptions

during the recompression which gives different pressure values. We can find

the same difference in the remaining

cases of HCCI model.

Figure 6- ROHR HCCI vs SI

Figure 6 shows us the comparison of heat release data of SI and HCCI

models. Here we can find a extreme difference in heat release between the two

models. That is because of the Recompression in HCCI which burns the fuel at a

rapid rate with more amount of heat release, whereas the SI model burns the

fuel slowly with less heat release.

3.1.2.

Mass Fraction Burnt(MFB)

After calculating Rate of Heat Release, we have to calculate Mass

Fraction Burnt(MFB). To calculate Mass Fraction Burnt we are using ‘H.R.

Stone’s method’4.

= – (+)k

?Pc*

= ?Pc(Vi/Vc)

The above equations gives us the pressure values we need to calculate

Mass Fraction Burnt. ?Pc is the pressure rise

due to combustion and ?Pc* is the

pressure rise due to combustion referred to datum volume4.

Assume that the combustion occurs after N increments which is defined by

pressure rise due to combustion becoming zero4. Then ?Pc* is directly

proportional to the mass fraction burnt4 then,

Mfb = /

Figure 7- MFB Case 1 HCCI

Figure

7 shows the comparison of calculated, Experimental and AVL BOOST Mass Fraction

Burned of HCCI model in case 1. If you can observe, the calculated Mass

Fraction Burnt and AVL BOOST are almost same.

Figure 8- MFB (SI VS HCCI)

Figure 8 shows the comparison between Mass Fraction Burned of

SI and HCCI models. Here, we can observe that the fuel is burnt rapidly in HCCI

than SI model which means the time of combustion is very less.

Figure 9- Rate of Pressure rise(RPR) SI vs HCCI

Figure 9 shows the Rate of Pressure Rise due to combustion against the

crank angle degree.

3.2.

Calibration and Validation of SI and HCCI Models

3.2.1.

Valve Timings

The valve lift and valve timings for all cases can be found from the

literature review.

Figure 10- Valve Lift of SI

The figure 10 shows the Valve timings of the SI model. Here if we can

observe that the intake lift came after the exhaust lift, that is because the

AVL BOOST starts the simulation with the combustion stroke which means it

starts at 3600 and there is a valve overlap of 200, which

means both the valves were opened for that 200 time. As per the

Literature review the valve lift is same for all the SI cases.

Figure 11- Valve Lift HCCI

The above figure shows the Valve Timings and Valve Lift of HCCI cases.

For HCCI the Valve Lift is different for different cases.

3.2.2.

Calibration and validation of SI Model

The calibration of SI model is

done on the values of IMep, Pmax and Peak Pressure Crank Angle. During

calibration we get close value of IMep, Pmax, Pmax CAD. But while validation

gave close values of IMep when compared with other values. This is because we

can change Throttle angle for all cases untill we get close values.

3.2.3.

Calibration and Validation of HCCI Model

The calibration of HCCI model is

done to get close values of IMep, Pmax and Pmax CAD. We got close values during calibration compared with

validation, as we get more differences during validation of other cases. That

is because of the lack of Heat Release Data.

4.

Results and Improvements

4.1.

Results

Table 1- Results and comparison of Given data vs AVL

BOOST data

Case Number

Data

Source

IMEP

(bar)

Pmax

(bar)

Pmax CAD

(deg)

NOx

(g/kwh)

H

C

C

I

Case 1

Given

1.81

29.82

371

0.023

BOOST

1.81

29.51

371.29

0.022

% Error

0

-1.04

+0.07

-4.35

Case 2

Given

2.80

38.3

369.5

0.148

BOOST

2.39

35.86

369.09

0.072

% Error

-14.64

-6.37

-0.11

-51.35

Case 3

Given

3.48

40.2

372

0.354

BOOST

3.06

37.13

371.96

0.072

% Error

-9.19

-7.63

0.01

-79.66

S

I

Case 4

Given

10.04

47.2

382

5.19

BOOST

10.01

45.25

381.45

3.02

% Error

-0.29

-4.13

-0.14

-41.81

Case 5

Given

1.73

14.9

372.5

3.919

BOOST

1.73

14.55

371.85

1.8

% Error

0

-2.34

-0.174

-54.06

Case 6

Given

2.58

21.1

371.5

6.774

BOOST

2.57

20.33

370.83

2.58

% Error

-0.38

-3.64

-0.18

-61.85

Case 7

Given

3.25

27.6

369.5

9.034

BOOST

3.23

26.73

368.8

3.66

% Error

-0.6

-3.01

-0.19

-59.22

Table 1 shows the results of all cases of SI and HCCI on AVL BOOST

simulation and their comparison with the given data from the literature review.

For HCCI case 1 is used for

calibration and the validation is done on the remaining cases. In case of SI case

4 is used for calibration and remaining cases are validated. Other than the

IMep, Pmax and Pmax CAD, the calibration

is also done for the NOx emissions for both SI and HCCI. The error in IMep

during the validation of HCCI model is more I.e., because of the difference in

heat release data from the experimental values whereas the error in validation

of SI cases is very less.

4.2.

Improvements

4.2.1.

SI Improvements

For SI model case 4 has been taken to improve. The Improvements are done

for better IMep and Pmax values and less NOx emissions. By changing the speed

of the engine from 1500rpm to 2000rpm and 2500rpm the NOx emissions will be

reduced and the Pressure values will be increased.

Speed of the Engine

1500rpm

2000rpm

2500rpm

IMep(bar)

10.01

10.73

11.13

PMax (bar)

45.25

47.76

48.71

NOx(g/kwh)

3.02

2.87

2.49

Table 2- Improvements of SI model (case 4 )

Table 2 shows the improvements of IMep, PMax and NOx emissions with

respect to the speed of the engine. By increasing speed from 1500rpm to 2000rpm

the NOx values decreased by 5 percent and at 2500rpm it is 17.54 percent.

4.2.2.

HCCI Improvements

In HCCI model case 1 is taken to improve. Like SI model, the same

improvement is carried out in HCCI also but at different speeds.

Speed of the Engine

1500rpm

1800rpm

2000rpm

IMep(bar)

1.81

1.98

1.96

PMax(bar)

29.51

30.67

30.48

NOx(g/Kwh)

0.022

0.016

0.012