an investigation of engine performance parameters and artificial intelligent emission prediction of...

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An investigation of engine performance parameters andartificial intelligent emission prediction of hydrogenpowered car

Tien Ho�, Vishy Karri, Daniel Lim, Danny Barret

School of Engineering, University of Tasmania, GPO Box 252-65, Hobart, Tasmania 7001, Australia

a r t i c l e i n f o

Article history:

Received 10 March 2008

Received in revised form

16 April 2008

Accepted 16 April 2008

Available online 9 June 2008

Keywords:

Hydrogen powered car

Prediction emission

Emission characteristics

Hydrogen internal combustion

engine

Artificial neural networks

Hydrogen engine operating

conditions

nt matter & 2008 Internane.2008.04.037

thor. Tel.: +61 3 6226 7869.: [email protected] (T. H

a b s t r a c t

With the depletion of fossil fuel resources and the potential consequences of climate

change due to fossil fuel use, much effort has been put into the search for alternative fuels

for transportation. Although there are several potential alternative fuels, which have low

impact on the environment, none of these fuels have the ability to be used as the sole ‘‘fuel

of the future’’. One fuel which is likely to become a part of the over all solution to the

transportation fuel dilemma is hydrogen. In this paper, The Toyota Corolla four cylinder,

1.8 l engine running on petrol is systematically converted to run on hydrogen. Several

ancillary instruments for measuring various engine operating parameters and emissions

are fitted to appraise the performance of the hydrogen car. The effect of hydrogen as a fuel

compares with gasoline on engine operating parameters and effect of engine operating

parameters on emission characteristics is discussed. Based on the experimental setup, a

suite of neural network models were tested to accurately predict the effect of major engine

operating conditions on the hydrogen car emissions. Predictions were found to be 74% to

the experimental values. This work provided better understanding of the effect of engine

process parameters on emissions.

& 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights

reserved.

1. Introduction

A four cylinders manual Toyota Corolla was successfully

converted to use hydrogen as a fuel in its internal combustion

engine. Certain characteristics of hydrogen make it unique for

application as an automotive fuel. The wide flammability

limits of hydrogen allow for a larger range of air to fuel

mixtures to be used at different engine operating conditions.

This means that very lean mixtures may be used for lower

emissions while enriched mixtures could be used when

additional power is required. In addition, the fast burn

characteristics of hydrogen also enables it to be able to

tional Association for Hyo), [email protected].

operate well at higher engine speed while its gaseous form

and ease of combustion can help when performing engine

cold starts. However, there is an overall decrease in power

output when using lean mixtures [1]. Hydrogen also has a

very high flame propagation rate even with lean mixtures

providing a very sharp rise in pressure immediately after

spark ignition [2]. The combination of the ability to run at very

lean mixtures and fast flame propagation allow hydrogen

engines to run very efficiently. In general, hydrogen has the

following dedicated advantages over gasoline [3]: reduce

engine oil dilation, reduce engine wear, reduce the emissions

as well as increase the fuel economy. The use of hydrogen as a

drogen Energy. Published by Elsevier Ltd. All rights reserved.au (V. Karri).

dx.doi.org/10.1016/j.ijhydene.2008.04.037

mailto:[email protected]

mailto:[email protected]

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Nomenclature

UTAS University of Tasmania, Australia

HART Hydrogen & Allied renewable Technology re-

search program

AS Australian standard

ECU engine control unit

BMEP brake mean effective pressure

BSFC brake specific fuel consumption

WOT wide open throttle

LCV lower calorific value

ppm part per million

RMSE root mean square error

NFPA National Fire Protection Agency

I N T E R N AT I O N A L J O U R N A L O F H Y D R O G E N E N E R G Y 3 3 ( 2 0 0 8 ) 3 8 3 7 – 3 8 4 63838

fuel generally serves to reduce the emissions from an internal

combustion engine (Table 1).

There are several constraints to be taken into consideration

for the tuning of an internal combustion engine, which is to

be converted to run on hydrogen fuel. These include the

following design philosophies governing the conversion

process of the car: power output requirements; minimization

of fuel consumption; elimination of knock, pre-ignition, self-

ignition and backfire; minimization of emissions; smooth

operation of the engine; good drivability; easy to upgrade in

the future.

Table 1 – Specifications of the conversion vehicle [18]

Manufacturer ToyotaModel Corrolla

Series Ascent

Body type Hatchback

Year of manufacture 2002

Type Inline, four cylinders, DOHC, VVTi

Total displacement 1794 cm3

Compression ratio 10.0:1

Fuel type Unlead petrol RON 91 or Higher

Maximum power output 100 kw@6000 RPM

Maximum torque 171 Nm@4200 RPM

Length 4385 mm

Width 1695 mm

Height 1475 mm

Wheelbase 2600 mm

Driven wheels Front wheel drive

Transmission Five speed manual

Fig. 1 – Prioritization of various

2. Brief description of hydrogen conversioncar and neural network model

The design and construction of the hydrogen conversion

based on the following seven basic systems of the conversion:

hydrogen storage system; hydrogen re-fuelling system; hy-

drogen piping system; pressure regulation system; fuel

delivery system; fuel and engine management system; safety

system as in Fig. 1.

The hydrogen storage system includes two E-size cylinders,

with a total hydrogen capacity of 0.5 kg. These cylinders were

made to comply with the requirements of AS 2875 [4], which

very closely replicates the requirements of AS 4838 [5], as

required by AS 2739 [6]. The two cylinders were found to be

able to be fitted across the vehicle, provided that the foremost

cylinder was mounted higher than the rearmost cylinder.

The hydrogen re-fuelling system has the cylinder adaptor

hoses were fitted with lock-off valve, as well as non-return

valves. In addition to these valves were the bleed valves,

which were fitted to the hoses. These were in order to bleed

off any residual hydrogen pressure from between the hydro-

gen cylinder valves and the non-return valves.

The hydrogen piping system have the vast majority of the

hydrogen piping system was produced using solid tube. The

tube, which was selected, was of one half-inch external

diameter, and it was made from annealed stainless steel. The

rated pressure of this tubing was 350 bars, with a burst

pressure of over 1400 bars, as required by both NFPA 52 and

AS 2739 [6,7]. The pressure regulation system include

CIGWeld dual stage high flow industrial hydrogen gas

regulator, rated to 200 bars inlet pressure.

stages of the conversion [18].

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I N T E R N A T I O N A L J O U R N A L O F H Y D R O G E N E N E R G Y 3 3 ( 2 0 0 8 ) 3 8 3 7 – 3 8 4 6 3839

The fuel delivery system injects the hydrogen into the air

entering the engine’s piston cylinders. It was decided that the

design of the new stainless steel manifold should resemble

that of the plastic manifold as closely as possible, in order to

minimize any changes of the engine’s gasoline tuning away

from that of the standard engine as seen in Table 2. In

addition, the quantum gaseous fuel injector, which is low

impedance injector, was used as hydrogen injection. It can be

seen that there is very minor changes to the original factory

design.

The fuel and engine management system controls the fuel

delivery system, in order to have it deliver the required mass

of hydrogen to the engine’s cylinders, at the precise timing,

which is required. It also controls various other aspects of the

engines operation, such as the ignition timing, and the

engines variable valve timing system. It also gives output

signals, which are used for the safety system. The Motec

M400 engine control unit (ECU) for engine management was

used while being fuelled by hydrogen and stock Toyota ECU

for engine management while being fuelled by gasoline.

Table 2 – Design of new inlet manifold [19]

Manifold calculations OEM manifold

Part Symbol Value

Inlet runner length L1 0.48

Inlet runner volume Vr 0.000733

Including bellmouth volume Vb 0.000012

Average inlet runner area A1 0.001526

Final inlet runner area Amin 0.0013

Air duct length L2 0.4

Air duct area A2 0.00283

Total plenum volume V2 0.0028

Primary plenum volume V2(2) 0.0017

Secondary plenum volume V2(3) 0.0011

Compression ratio Rc 10

Cylinder volume Vs 0.00045

Speed of sound c 343

Pi Pi 3.141593

Computed value ‘‘a’’ a 0.44945

Computed value ‘‘b’’ (Total) b 10.18182

Computed value ‘‘b’’ (Primary) b(2) 6.18182

Computed value ‘‘b’’ (Secondary) b(3) 4.00000

Mean cylinder volume V1 0.000275

Runner dia

Runner area

Runner circ 0.1327

Frequency (total plenum) f1 11798

Frequency (total plenum) f2 4915

Helmholtz f (total plenum) fh 3491

Frequency (primary plen) f1(2) 12346

Frequency (primary plenum) f2(2) 6028

Helmholtz f (primary plenum) fh(2) 4480

Frequency (secondary plenum) f1(3) 13237

Frequency (secondary plenum) f2(3) 6990

Helmholtz f (secondary plenum) fh(3) 5569

Notes: Runner length includes bellmouths within plenum and the length

For new manifold, 11 mm plate flange with area Amin all the way throu

Average inlet runner area includes bellmouth volume.

The safety system design includes leak detection system,

fuel shut-off switch and solenoid valve, flashback arrestor,

pressure relief valves and filtration. The leak detection

system includes a hydrogen sensor, which is placed directly

above the hydrogen storage tanks, mounted directly below

the vehicle’s radio antenna. The sensor’s circuitry is set to

alert the driver at a hydrogen concentration of one tenth of

the lower explosive limit.

Fuel shut-off is a high-pressure solenoid valve. This valve is

a ‘‘normally closed’’ valve, which ensures that whenever

power is lost to the solenoid, the valve will close. The

Flashback Arrestor is a high flow ‘‘Demax 5’’ unit produced

by IBEDA. In the event of a flashback travelling back into the

hydrogen fuel system, past the fuel injectors, the flashback

arrestor will quench the flame, limiting the hydrogen, which

is subjected to the flashback to that which is within the fuel

rail. The hydrogen pressure relief system was designed in

three stages. The first stage is built into the hydrogen tanks’

valves. This pressure relief stage is in the form of a burst disc,

set to 245 bars. The second stage is placed within the engine

New manifold Change

Units Symbol Value Units %

m L1 0.48 m 0.00

m3 Vr 0.000760 m3

m3 Vb 0.000015 m3

m2 A1 0.001584 m2 3.79

m2 Amin 0.0013 m2

m L2 0.4 m 0.00

m2 A2 0.00283 m2 0.00

m3 V2 0.0028 m3 0.00

m3 V2(2) 0.0017 m3

m3 V2(3) 0.0011 m3

N/A Rc 10 N/A

m3 Vs 0.00045 m3

m/s c 343 m/s

N/A Pi 3.141593 N/A

N/A a 0.46647 N/A

N/A b 10.18182 N/A

N/A b(2) 6.18114 N/A

N/A b(3) 4.00068 N/A

m3 V1 0.000275 m3

0.045 m

0.00159 m2

m 0.1414 m

RPM f1 12013 RPM 1.83

RPM f2 4918 RPM 0.05

RPM fh 3556 RPM 1.88

RPM f1(2) 12562 RPM 1.75

RPM f2(2) 6036 RPM 0.13

RPM fh(2) 4564 RPM 1.88

RPM f1(3) 13446 RPM 1.58

RPM f2(3) 7009 RPM 0.28

RPM fh(3) 5673 RPM 1.87

within the head’s inlet port.

gh plus 20 mm transition from A1 to Amin.

ARTICLE IN PRESS

Table 3 – Engine parameters and appropriate source ofmeasurement sensor [18]

Parameter Designation Sensor/source

1. Engine RPM RPM Stock ECU

2. Throttle position TP Stock ECU

3. Mass air flow Amass MAF sensor via stock

ECU

4. Manifold air

pressure

MAP MAP sensor via stock

ECU

5. Fuel actual pulse

width

FAPW Motec ECU lookup

table

6. Ignition advance ladv Motec ECU lookup

table

7. Exhaust gas

temperature

EGT1 EGT sensor via Motec

ECU

8. Lambda La1 Lambda sensor via

PLM

9. Intake air

temperature

AT Stock ECU

10. Engine

temperature

ET Stock ECU

11. Output power PWR Dynamometer


compartment, in the high-pressure section of the hydrogen

piping system. It is placed upstream of the solenoid valve, and

it is set to a pressure, which is lower than that of the tanks’

valves burst discs. This comprises of two pressure relief

components. The first (set to the lowest pressure) is a

proportional relief valve. The second is a burst disc, set to

slightly lower than the rated pressure of the pressure

regulator. The third stage is pressure relief stage situated

within the low-pressure fuel supply line. This has the effect of

limiting the pressure, which is applied to the flashback

arrestor, and the fuel injectors in the event of a pressure

regulator malfunction.

A portable five-gas exhaust emission analyser, manufac-

tured by OTC-SPX, was used to measure the exhaust gas

emissions include: oxygen (O2), oxides of nitrogen (NOx),

carbon dioxide (CO2), carbon monoxide (CO) and hydrocar-

bons (HC). The exhaust gas emission analyser was set up in

order to send data directly to on-board personal computer for

data logging. The exhaust sampling tube was directed

through a condenser and a water separator. This was for the

purpose of removing as much water from the exhaust gas as

possible. The removal of the water from the exhaust gas was

required to ensure the longevity of the exhaust gas emission

analyser. The addition of these pieces of equipment had the

effect of increasing the time delay between the emission of

the exhaust gases and the sensing of them. Because of this

time delay, it was necessary to match data between the

engines operational parameters with the relevant exhaust gas

emissions. This was done by matching relatively steady-state

operating conditions with relatively steady-state exhaust gas

Fig. 2 – Data mat

emissions. This process took into account the time which was

required for the exhaust gas analyser to draw a full volume of

exhaust gas into the piping, cooling and water separation

system. The delay was approximately two minutes. The

exhaust gas emissions were measured without the use of an

ching [18,19].

ARTICLE IN PRESS

Fig. 3 – Map of engine parameters to emission output.


exhaust catalyst. The purpose of this was to compare the

emissions in an untreated state to gain a truly scientific

comparison of the emissions (Fig. 2).

The developed prediction neural network models were

accurate predict hydrogen car emission parameters including

CO, CO2, HC, NOx as a function of various engine parameters

such as: engine speed, throttle position, mass airflow,

manifold air pressure, fuel pulse width, engine power,

ignition advanced, engine temperature, air temperature, air

fuel ratio, exhaust gas temperature as shown in Table 3. The

neural network as predicting model was chosen for this

research because of the following reasons [10–16]: the ability

to model non-linear process, adaptive learning, self-organiza-

tion, real time operation, and ease of insertion into existing

technology. As a result, neural networks have proven

themselves in practice for accurate performance prediction.

Initially, the back-propagation neural networks model with 11

algorithm such as: Levenberg–Marquardt, gradient descent,

gradient descent with momentum, gradient descent

with adaptive learning rate, gradient descent with momen-

tum and adaptive learning rate, resilient back propagation,

scaled conjugate gradient, conjugate gradient with Fletch-

er–Reeves updates, conjugate gradient with Polak–Ribiere

updates, conjugate gradient with Powell–Beale restarts, one

step secant were used to analyze and predict various

parameters. Through extensive experimentation covering a

comprehensive range of prediction performances, Leven-

berg–Marquardt was proven itself is the most accuracy

algorithm when performing the project prediction tasks [17]

(Fig. 3).

3. Results and discussion

The experimental methodology which has been used within

this research project provided a basis for the measurement of

various essential engine operating parameters, such as the

engine’s rotational speed, power output, levels of the various

exhaust gas emissions, fuel flow rate, and fuel mixture

formation. The engine testing procedures outlined were in

compliance with the requirements of the relevant Interna-

tional Standard, ISO 15550:2002 [9]. This ensured that the

results, which were obtained, were suitable for subsequent

scientific analysis. The discussion on the results obtained has

been presented as below:

1.
Effect of hydrogen as a fuel compared with gasoline on
engine parameters.

2.
Effect of hydrogen as a fuel compared with gasoline on
emission characteristics.

3.
Artificial neural networks as an intelligent approach to
predict emissions performance.

3.1. Effect of hydrogen as a fuel compare with gasoline onengine parameters

3.1.1. Engine powerTypically, for the same engine operation conditions, the

engine output while fuelled by hydrogen was found to be

around half of that of the engine while fuelled by gasoline.

However, at 5000 RPM and WOT, the power output for

hydrogen operation was as high as 63% of that of gasoline

operation. This is due to the increased fuel delivery of the

hydrogen engine’s calibration around these conditions. This

increased fuel delivery (resulting in a lower Lambda value)

was specifically programmed in order to increase the max-

imum power output of the engine. Fig. 4(a) is the graph of the

brake power of the modified engine for both hydrogen and

gasoline. It can be seen that the curves are similar to each

other in shape. This is due to the general induction

characteristics of the engine, which are similar for operation

with both fuels. There are two main reasons for the loss of

power. The first reason is that the injection of hydrogen into

the inlet manifold displaces air. At stoichiometric air to fuel

ratio, hydrogen displaces approximately one third of the air

within the inlet manifold, while vaporized gasoline only

displaces around 1% of the air within the inlet manifold. The

proportion of the air which is displaced by hydrogen

decreases as the fuel and air mixture is weakened. This

reduction of the quantity of fuel directly reduces the energy

input into the engine. This, in turn, directly decreases the

power output from such an engine. This is the second major

reason. However, it is expected that any such decrease will be

minimal. The maximum power output of the hydrogen-

fuelled engine was found to be 50.7 kW (at 5000–6000 RPM).

This is 60.5% of the maximum gasoline-fuelled power

output.

3.1.2. Engine torqueThe brake power of an engine is directly proportional to the

torque and engine speed. For this reason, it is not surprising

to find that the engine’s torque output shows the same

proportional characteristics as were present for its power

output. The gasoline-fuelled engine has a peak torque of

168.3 N m at an engine speed of 4000 RPM, with a secondary

peak of 155 N m at 2000 RPM. This is compared to hydrogen

operation, having 100.1 and 93.7 N m at the same engine

speeds, respectively, as shown in Fig. 4(b).

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40

50

60

70

80

90

100

BM

EP

(MP

a)

1000 2000 3000 4000 5000 6000 700010

20

30

40

50

60

70

80

90

Engine Speed (RPM)

Bra

ke P

ower

(Kw

)

HydrogenGasoline

HydrogenGasoline

HydrogenGasoline

HydrogenGasoline

HydrogenGasoline

HydrogenGasoline

20

22

24

26

28

30

32

34

36

Bra

ke T

herm

al E

ffici

ency

(%)

1000 1500 2000 2500 3000 3500 4000 450030

30.5

31

31.5

32

32.5

33

33.5

34

34.5

35

Engine Speed (RPM)

Bra

ke T

herm

al E

ffici

ency

(%)

10

15

20

25

30

35

40

45B

SFC

(g/k

wh)

1000 2000 3000 4000 5000 6000 700080

90

100

110

120

130

140

150

160

170

Engine Speed (RPM)

1000 2000 3000 4000 5000 6000 7000Engine Speed (RPM)

1000 2000 3000 4000 5000 6000 7000Engine Speed (RPM)

1000 2000 3000 4000 5000 6000 7000Engine Speed (RPM)

Bra

ke T

orqu

e (N

.m)

Fig. 4 – (a) Effect of hydrogen as a fuel compare with gasoline on brake power at various engine speed at WOT; (b) effect of

hydrogen as a fuel compare with gasoline on brake torque at various engine speed at WOT; (c) effect of hydrogen as a fuel

compare with gasoline on break mean effective pressure at various engine speed at WOT; (d) effect of hydrogen as a fuel

compare with gasoline on brake specific fuel consumption at various engine speed at WOT; (e) effect of hydrogen as a fuel

compare with gasoline on brake thermal efficiency at various engine speed at WOT; and (f) effect of hydrogen as a fuel

compare with gasoline on break mean effective pressure at various engine speed at 75% throttle opening.


ARTICLE IN PRESS


3.1.3. Break mean effective pressureThe brake mean effective pressure (BMEP) of an engine

is equivalent to the engine’s torque, divided by its dis-

placement. For this reason, the BMEP curve for a given

engine is simply a scaled version of the torque curve.

Maximum BMEP for the gasoline-fuelled engine was found

to be 93.8 MPa at 4000 RPM, while it was 55.8 MPa at the

same engine speed for the hydrogen-fuelled engine as shown

in Fig. 4c.

00.20.40.60.8

11.21.41.61.8

2

0NOx (ppm)

Lam

bda

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0Brake Power (Kw)

NO

x (pp

m)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

CO

(%)

40001000 2000 3000 5000

10 20 30 40 50 60

0Brake Power (Kw)

10 20 30 40 50 60

HydrogenGasolinePoly. (Gasoline)Poly. (Hydrogen)



Fig. 5 – Effect of hydrogen as a fuel compare with gasoline on em

position; (b) throttle position versus NOx; (c) brake power versus

and (f) brake power versus HC.

3.1.4. Brake specific fuel consumptionAt WOT, the BSFC for the gasoline-fuelled engine ranges

between 40.9 and 42.5 g/kW h (average 41.6 g/kW h), while for

the hydrogen-fuelled engine it ranges between 14.4 and

15.2 g/kW h (average 15.0 g/kW h) as shown in Fig. 4(d). This

gives a ratio of gasoline BSFC to hydrogen BSFC of 2.77. This

was fully expected, as hydrogen’s lower calorific value (LCV) is

119.9 MJ/kg, compared to 44.5 MJ/kg for gasoline (a ratio of

hydrogen LCV to gasoline LCV being 2.69).

0

500

1000

1500

2000

2500

3000

3500

4000

0Throttle position

NO

x (pp

m)

0

2

4

6

8

10

12

14

16

Brake Power (Kw)

CO

2 (%

)

0

20

40

60

80

100

120

140

160

HC

(ppm

)

0 10 20 30 40 50 60

Brake Power (Kw)0 10 20 30 40 50 60

802010 30 40 50 60 70




ission characteristics; (a) Lambda versus NOx at 25% throttle

NOx; (d) brake power versus CO2; (e) brake power versus CO;

ARTICLE IN PRESS

Table 4 – Experimental data patterns for hydrogenemission prediction.

RPM Number of data

25% Load 50% Load 75% Load

1500 145 145 145

2000 145 145 145

3000 145 145 145

4000 Not enough power 145 Faulty results

Table 5 – Back-propagation neural networks architecture

Type of networks Three layer feed-forwardbackpropagation

Hidden layer 8 Neurons

Output layer 1 Neuron

Transfer function ‘tansig’, ‘purelin’

Training algorithm Levenberg–Marquardt

Weight/bias learning function ‘learngdm’

Performance function ‘mse’

Number of epochs between

showing the progress

100

Maximum number epochs to

train

3000

Performance goal 0.00001

Learning rate 0.1

Learning rate increase

multiplier

1.05

Learning rate decrease

multiplier

0.75

Momentum constant 0.9

Table 6 – Summarize emission prediction results forhydrogen-powered car

Averages NOx CO2 CO HC

Error (value) 1.4956 0.0003 0 �0.06

STD (value) 9.3467 0.0037 0.0002 0.409

Error (%) 0.3797 0.1866 �0.4163 �0.255

RMSE (value) 9.3467 0.0037 0.0002 0.429

RMSE (%) 1.6581 2.2868 3.5185 1.5772


3.1.5. Engine efficiencyIt is quite clearly seen that operation on hydrogen is generally

more efficient than operation on gasoline at most engine speeds

while operating at WOT as shown in Fig. 4(e). Much of this can

be attributed to the fact that the engine is fuelled by a rich air to

gasoline mixture at WOT. This is for the express purpose of

increasing the power output at WOT. While the air to gasoline

ratio is made to be rich at WOT, the air to hydrogen ratio is still

lean at WOT. The net result is that the efficiency of the gasoline-

fuelled engine suffers more due to enrichment than does the

hydrogen-fuelled engine under the same conditions.

In contrast, the efficiency of the hydrogen fuelled engine at

nearly all other tested operating points was lower than that of the

gasoline fuelled engine, due to two main reasons as shown in

Fig. 4(f) (75% throttle opening). Firstly, the power output of the

gasoline fuelled engine while not at WOT is significantly higher

than that of the hydrogen fuelled engine. Secondly, the tuning of

the gasoline engine was the culmination of potentially thousands

of hours of experimental work by the manufacturer of the engine.

3.2. Effect of hydrogen as a fuel compare with gasoline onemission characteristics

3.2.1. Emission of oxides of nitrogenThe emission of NOx increases markedly as the lambda value

decreases toward unity, and has a minimum at a lambda

value of around 1.87 as shown in Fig. 5(a). In addition, at no

point in time did the emission of NOx from the hydrogen-

fuelled engine exceed that from the gasoline fuelled engine as

shown in Figs. 5(a)–(c). The results can be seen most markedly

at operating conditions with small (25%) throttle position.

This can be attributed to the fact that the hydrogen fuelled

engine was always operated at a lean air to fuel ratio, which

has been shown to result in low emissions of NOx gases.

3.2.2. Emission of carbon dioxideThe reduction in the emission of carbon dioxide is a major

advantage of hydrogen-fuelled engines over gasoline-fuelled

engines. The hydrogen-fuelled engine does not emit absolutely

zero carbon dioxide. However, the emission of carbon dioxide is

virtually negligible, being between 0.05% and 0.29%, compared

with between 14.44% and 14.58% from the gasoline-fuelled

engine as shown in Fig. 5(d). The emission of carbon dioxide

from the hydrogen fuelled engine can be attributed to two

factors. Firstly, any carbon dioxide within the air before it enters

the engine will remain as carbon dioxide. This is expected to be

a minor contributor to the general emission of carbon dioxide.

Secondly, during each cycle of the engine some lubricating oil

makes its way into the combustion chamber, past the piston

rings, through the crankcase ventilation system, and through

the valve guides. Because of this, it is impossible to eliminate

carbon dioxide emissions from hydrogen fuelled internal

combustion engines. However, the concentration of the carbon

dioxide emitted is negligible in comparison to that of gasoline

fuelled internal combustion engines. The carbon dioxide emis-

sion level of this engine was higher than it was expected to be.

3.2.3. Emission of carbon monoxideThe emission of carbon monoxide from hydrogen fuelled

internal combustion engines is negligible in comparison with

that from gasoline fuelled internal combustion engines. The

emission of carbon monoxide from the hydrogen engine was

extremely low, at 0.005–0.020%, compared to 0.326–0.767% for

the gasoline engine as shown in Fig. 5(e).

3.2.4. Emission of hydrocarbonThe hydrocarbon emission level from the hydrogen engine

was notably lower than that of the gasoline fuelled engine as

shown in Fig. 5(f). In the case of a gasoline-fuelled engine,

most of the hydrocarbon emissions come from un-burnt fuel

passing through the exhaust system. In contrast, in a

ARTICLE IN PRESS


hydrogen-fuelled engine, all hydrocarbons must come from

the combustion of the lubricating oil. The emission of

hydrocarbon from the hydrogen engine was lower than those

of gasoline engine, at 20–37 ppm, compared to 50–152 ppm for

the gasoline engine.

0

200

400

600

800

1000

1200

1400

1600

1800

2000

NO

x va

lue

ActualPredicted

ActualPredicted

ActualPredicted

ActualPredicted

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.004

0.006

0.008

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0.012

0.014

0.016

0.018

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0.022

CO

(%)

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15

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35

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55

HC

(ppm

)

0 10 20 30 40 50Number of Testing data




Fig. 6 – Comparison of actual emission and predictio

3.3. Neural networks for hydrogen powered car emissionprediction

The neural networks created were included 11 previous

mentioned inputs and four emissions output parameters

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Freq

uenc

y

0

5

10

15

20

25

30

35

40

45

50

Freq

uenc

y

0

5

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Freq

uenc

y

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-15 -10 -5 0 5 10Error (actual - predicted values)




n performance results for hydrogen powered car.

ARTICLE IN PRESS


(as shown in Fig. 3), which is cover a comprehensive range of

data variation through many different testing engine condi-

tions. The data set used for training and testing the neural

networks for prediction of hydrogen emissions consists of

1450 data patterns as shown in Table 4.

The back-propagation neural networks are part of the

MATLAB neural networks toolbox, which is used to appraise

the predictive models [17]. In each of the studied prediction

hydrogen powered car emission parameters, the large num-

ber of data (1400 data) was used for a training set and 50 data

were used for a testing set. The best back-propagation neural

networks architecture was set with suitable parameters as

shown in Table 5.

In order to provide a measure of accuracy of the predictions

as well as provide a means of comparison between each of

the different neural networks, several parameters are used.

These are defined as: average error (value), standard deviation

(value), average error (%), root mean square error (value), root

mean square error (%).

3.3.1. Emission of NOx

It can be seen that very good prediction results were obtained

for CO2 emission prediction with the %ARMS error was 1.6581

and average deviation was 9.3467 as shown in the histogram.

3.3.2. Emission of CO2

The prediction result was obtained for prediction of CO

emission with %ARMS error was 2.2868% and deviation was

0.0037.

3.3.3. Emission of COThe prediction result was obtained for prediction of CO with

%ARMS error was 3.5185% and deviation was 0.0002.

3.3.4. Emission of HCThe prediction result was obtained for prediction of HC with

%ARMS error was 1.5772% and deviation was 0.409. Table 4

summarises the study performance of each of the emission

prediction parameters (Table 6, Fig. 6).

4. Conclusion

From the measured parameters, various engine characteris-

tics were calculated, and compared for operation using

gasoline and hydrogen as fuels, brake power and torque of

the car’s engine when running on hydrogen was generally

about 50–60% of that of gasoline as well as brake specific fuel

consumption was in line with expectations from the respec-

tive lower calorific values of the two fuels. In addition,

thermal efficiency was similar for the two fuels, hydrogen

being more efficient at lower power output, and gasoline

being more efficient at higher power output. Beside that, the

emission of NOx was significantly lower for hydrogen opera-

tion than for gasoline operation and its lowest values were

achieved with lambda value around 1.87. Similarly, the

emission of carbon dioxide and carbon monoxide and

hydrocarbon from the hydrogen engine was extremely low

compared the gasoline engine. Finally, the excellent results of

prediction emissions of hydrogen-powered car were achieved

in almost cases with average percentage root mean square

error less than 74%.

Acknowledgments

The authors are deeply grateful to all of the Hydrogen & Allied

Renewable Technology research members as well as Intelli-

gent Hydrogen Car project for sharing ideas and concept

along the way.

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