Performance and Emission Characteristic of a Turbocharged Spark-ignition Hydrogen-Enriched...

7/27/2019 Performance and Emission Characteristic of a Turbocharged Spark-ignition Hydrogen-Enriched Compressed Natrual Gas Under Wide Open Throttle Operatin

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Performance and emission characteristics of a turbocharged

spark-ignition hydrogen-enriched compressed natural gas

engine under wide open throttle operating conditions

Fanhua Ma*, Mingyue Wang, Long Jiang, Jiao Deng, Renzhe Chen, Nashay Naeve,Shuli Zhao

State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, PR China

a r t i c l e i n f o

Article history:

Received 16 July 2010

Received in revised form

13 August 2010

Accepted 13 August 2010

Available online 17 September 2010

Keywords:

Wide open throttle

Combustion

Emission

a b s t r a c t

This paper investigates the effect of various hydrogen ratios in HCNG (hydrogen-enriched

compressed natural gas) fuels on performance and emission characteristics at wide open

throttle operating conditions using a turbocharged spark-ignition natural gas engine. The

experimental data was taken at hydrogen fractions of 0%, 30% and 55% by volume and was

conducted under different excess air ratio (l) at MBT operating conditions. It is found that

under various l, the addition of hydrogen can significantly reduce CO, CH4 emissions and

the NOx emission remain at an acceptable level when ignition timing is optimized. Using

the same excess air ratio, as more hydrogen is added the power, exhaust temperatures and

max cylinder pressure decrease slowly until the mixtures lower heating value remains

unchanged with the hydrogen enrichment, then they rise gradually. In addition, the early

flame development period and the flame propagation duration are both shorter, and the

indicated thermal efficiency and maximum heat release rate both increase with more

hydrogen addition.

2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

1. Introduction

Recently, environmental protection and energy conservation

have been increasingly concerned worldwide, more and more

attention in the auto industry has been shifted to the use of

alternative fuels. Among all these potential fuels, hydrogen isconsidered to be the most desirable alternative fuel used in

vehicle engines [1]. Hydrogen has many advantages, such as it

can be obtained from electrolysis of water and the electricity

used can be generated by solar energy, which means

hydrogen is a kind of real renewable energy, or an ideal energy

carrier [2].

However, there are many potential problems in hydrogens

production, storage and distribution if hydrogen is used as

energy. At present, hydrogen is limited used as additive to

other fuels, and HCNG (hydrogen-enriched compressed

natural gas) has been regarded as the most potential energy to

take the place of engine oil in a short time [3]. HCNG, also

called Hythane (themixtures of H2 and CNG), is the alternative

gas fuel which blends the H2 and CNG (compressed naturalgas) at a given ratio. The research and development of HCNG

engine can be treated as the transitional technological means

to the wide use of hydrogen energy. In addition, HCNG vehi-

cles commercialization can be beneficial to the hydrogen

energys infrastructure.

Some thermal and chemical properties of hydrogen and

methane, which is the main component of natural gas, are

compared in Table 1 [4]. As can be seen, hydrogen has a wider

* Corresponding author. Tel./fax: 86 10 62785946.E-mail address: [email protected] (F. Ma).

A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e

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 5 ( 2 0 1 0 ) 1 2 5 0 2 e1 2 5 0 9

0360-3199/$ e see front matter 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

doi:10.1016/j.ijhydene.2010.08.053
mailto:[email protected]://www.sciencedirect.com/http://www.elsevier.com/locate/hehttp://dx.doi.org/10.1016/j.ijhydene.2010.08.053http://dx.doi.org/10.1016/j.ijhydene.2010.08.053http://dx.doi.org/10.1016/j.ijhydene.2010.08.053http://dx.doi.org/10.1016/j.ijhydene.2010.08.053http://dx.doi.org/10.1016/j.ijhydene.2010.08.053http://dx.doi.org/10.1016/j.ijhydene.2010.08.053http://www.elsevier.com/locate/hehttp://www.sciencedirect.com/mailto:[email protected]


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flammable mixture range, lower ignition energy and much

faster burning speed, all of which are helpful to improveengines lean burn capability; and CNG reserves are abundant

and result in relatively low emissions compared with tradi-

tional gasoline and diesel in combustion engines. HCNG fuel

possesses advantages of both H2 and CNG. We can attribute

HCNG engine remarkable combustion speed to the hydrogen

contribution. Addition of hydrogen increases burning velocity

of HCNG [5]. Therefore, it is a potential alternative fuel to

vehicle engines.

An engines performance during WOT (wide open throttle)

conditions directly indicates the engines maximum power

performance includingthe vehiclesmaximumspeed, maximum

acceleration andgrade abilityetc [6].Hence,thereisalwaysmuch

attention paid to the engines WOT parameters.This paper specifically deals with the engines performance

and emission characteristics in a turbocharged spark-ignition

(SI) natural gas engine at WOT operating conditions under

various operating conditions including different spark timing,

excess air ratio (l), with different fuel: CNG, 30% HCNG, 55%

HCNG, percentages of hydrogen are measured on a per

volume scale.

2. Previous work

Over the past several years, there has been extensive researchrelated to hydrogen-enriched fuels, of which some focuses on

the influence of the hydrogen addition on the engines overall

performance. This research includes the engines power,

efficiency, and combustion, emission performance under

various engine speeds, excess air ratios, ignition timings andMAP(Manifold Absolute Pressure) including medium load, low

load and even idle conditions.

Ma et al. carried out a series of experiments to research the

port-injection HCNG engines combustion and emission

characteristics under various ignition timings. They found

that the combustion duration and ignition delay are both

reduced linearly with the addition of hydrogen, and the NOx,

CO and THC (total hydro-carbon emissions) emissions all

descend with the increase of spark advance angle, and ascend

as the MAP increases [7].

Wang et al. investigated the combustion behavior of

a direct injection engine operating on various fractions of

NGe

hydrogen blends [8]. The results showed that the brakeeffective thermal efficiency increased with the increase of

hydrogen fraction at low and medium engine loads. The rapid

combustion duration decreased, the heat release rate and

exhaust NOx increased with the increase of hydrogen fraction

in the blends. Their study suggested that the optimum

hydrogen volumetric fraction in NGehydrogen blends is

around 20% to get compromise in both engine performance

and emissions.

Collier et al. pointed out that the engine application which

could achieve the greatest advantage from HCNG was heavy-

duty engine [9]. They achieved a major reduction in NOxemission in a Daewoo heavy-duty engine fuelled with HCNG

containing 30% hydrogen at all power levels while kept COand THC in the same range of a conventional CNG engine.

Table 1 e Comparison of hydrogen and methane [4].

Fuel characteristics Hydrogen(H2)

Methane(CH4)

Equivalence ratio ignition lower

limit in NTP air

0.1 0.53

Mass lower heating value(kJ/kg) 119,930 50,000

Density of gas NTP(kg/m3

) 0.083764 0.65119Volumetric lower heating value at

NTP (kJ/m3)

10,046 32,573

Stoichiometric air-to-fuel ratio 34.20 17.19

Volumetric fraction of fuel in air,

l 1

0.290 0.095

Volumetric lower heating value in

air l 1

2913 3088

Burning speed in NTP air(cm/s) 265e325 37e45

Flame temperature in air(K) 2318 2148

NTP denotes normal temperature (293.15K) and pressure (1 atm).

Table 2 e Engine specifications.

Item Value

Engine make DONGFENG MOTOR CO., LTD,

China

Engine type in-line 6 cylinders,

spark ignition

Aspiration method Turbocharged intercooledCompression ratio 10

Bore (mm) 105

Stroke (mm) 120

Displacement Volume(L) 6.234

Rated power/speed 154 kW/2800 rpm

Maximum torque/speed 620 Nm/1600 rpm

Full-load minimum fuel

consumption rate

198 g/kW h

Table 3 e Measurement instruments specifications.

Instruments Range Sensitivity Linearity

Cylinder pressure sensor (Kistler6117B) 0e20 Mpa 16.8 pC/bar 0.6% FSO

Charge Amplifier (Kistler5011B) 10e9.99 105 (10V FS) 0,01e9.99 104 pC/M.U.;

0,01e9.99 104 mV/M.U.

0.05% FS

Crank angle generator (Kistler2613B) 1w2.0 104 r/min 0.1e6 e

Mass air flow meter (ToCeil20N100114LI) 0w1000 Nm3/h 1% 0.24%

Alicat Mass CNG flow meter 0.5(S)CCM_1500(S)LPM 0.4% e

Alicat Mass hydrogen flow meter 0.5(S)CCM_1500(S)LPM

0.4%e

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 5 ( 2 0 1 0 ) 1 2 5 0 2 e1 2 5 0 9 12503
http://dx.doi.org/10.1016/j.ijhydene.2010.08.053http://dx.doi.org/10.1016/j.ijhydene.2010.08.053http://dx.doi.org/10.1016/j.ijhydene.2010.08.053http://dx.doi.org/10.1016/j.ijhydene.2010.08.053


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Through the experiments aimed at optimizing the intake

system for HCNG application, they found that the homoge-

neousness of fueleair mixture was very important to NOxemission.

Bauer and Forest reported a test conducted on a single

cylinder cooperative fuel research engine operating on

mixtures of hydrogen in methane of 0%, 20%, 40% and

60% by volume. [4] Each fuel was tested at the speeds of

700 and 900 rpm, full and part loads, and equivalence

ratios from stoichiometric to the partial burn limit. The

experiment results showed that hydrogen enrichment

reduced the value of spark advance for best torque anddecreased power due to a reduction in volumetric lower

heating value. Furthermore, their experiment got an

unusual result which is rarely found in others research-

esdengines thermal efficiency drops as hydrogen frac-

tion increases.

Marie Bysveen studied the engines emission and

performance with different mixtures including: pure CNG,

and 29% H2 by volume in CNG. For each mixture, four engine

speeds were investigated and the engines performance was

tested under full-load conditions. The lean limit for the pure

CNG tested in the engine is approximately l 1.8 and the

lean limit for the HCNG is even leaner. The efficiency for

HCNG is greater than that of CNG for the same l, and thedifference in break thermal efficiency between HCNG and

CNG for the same l increases with increasing excess air

ratio [10].

However, very few studies involved various operating

conditions including different spark timing, excess air

ratio (l) with CNG to high hydrogen ratio HCNG fuel under

WOT operating conditions in a turbocharged spark-igni-

tion natural gas engine. Considering that the WOT

performance is very important to actual road conditions,

the purpose of this research is to study the engines

combu sti on a nd e mi ss io n p erf or man ce at W OT

conditions.

3. Experimental apparatus and test method

The experiments were carried out on a six-cylinder, single

point injection, SI NG engine (see Table 2 for

specifications).

Fig. 1 e Schematic of the fuel supply system.

Table 4 e Test engine specifications.

Item Value

Engine Speed 1200 rpm

Hydrogen fraction by volume 0%, 30%, 55%

Intake manifold absolute pressure Wide Open Throttle

Spark timing

Excess air ratio

MBT

1.0 to lean burn limit

0.0 0.2 0.4 0.6 0.8 1.0

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.23

Jk/eulavgnitaehrewoLerutniM

m(

3)

1-

Enriched hydrogen ration /vol%

=1

=1.2

=1.4

=1.5

=1.6

=1.8

=2.0

=2.2

10

Fig. 2 e Mixture lower heating value at various hydrogen

enrichments.



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4.2. In-cylinder pressure data and combustion

parameters

Fig. 5 shows in-cylinder pressure curve under various l with

different fuel: pure CNG, 30%HCNG, 55%HCNG. From Fig. 6(a)

we can see, as the mixture is leaner, the max in-cylinder

pressure is smaller. Fig. 6(bed) shows further the position of

the max in-cylinder pressure is later before the l 1.5. On the

other hand, when l> 1.5,the max in-cylinder pressure is more

near the TDC.

Fig. 6 illustrate heat release rate under various l withdifferent fuels. We can safely make a conclusion from the

figure: as l raise, the max heat release rate decreases gradu-

ally. While under the same l, hydrogen-enriched improves the

max heat release rate since more hydrogen-enriched can

expand the lean burn limit and improve the combustion

performance.

In this paper, we define the early flame development period

as the crank angles (CA) from ignition to 10% cumulative heat

release, and flame propagation duration as crank angles (CA)

from 10% to 90% cumulative heat release. Fig. 7(a) implies the

early flame development period relation with l. As the mixture

becomes leaner, the early flame development period is longer,

which means lean mixture goes against with the flame cores

formation and rapid development [16]. Besides, hydrogen

enrichment shortens the early flame development period since

the combustion speed is faster and in-cylinder temperature

increases, which is good for the flame propagation.

Fig. 7(b) shows the relation between the flame propagation

duration and l. Its variation tendency is similar to the early

flame development period. The increment of l leads the

flame development period longer. In addition, hydrogen

enrichment shortens the flame development period. Quad-

ers research implies that the engines flame development

period is almost the same on the lean burn limit conditionswith different fuels [17]. From this, at the same l, the fuel of

shortest flame development period is best at lean burn.

Hydrogen enrichment can expand the mixture fuels lean

burn limit and enable the engine work at bigger l, which is

good for improving the engine efficiency and emission

performance.

Fig.8 shows the variation of COVimep versus excess air ratio

with three different fuels. It is found that a high hydrogen

ratio can significantly extend the lean burn limit. Quaders

research has shown that no matter what type of fuel used, the

combustion duration remains nearly the same when the

engine reaches its lean limit. This is to say although

combustion duration will be prolonged as the engine is

a

b

c

d

Fig. 5 e (a) Max cylinder pressure versus excess air ratio. (b) In-cylinder pressure for CNG. (c) In-cylinder pressure for 30%

hydrogen volumetric ratio. (d) In-cylinder pressure for 55% hydrogen volumetric ratio.



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decreases at first and then increase as l increases. This

appearance is suitable for fuel of any hydrogen enrichment.

The decrease of CO emission is due to the increase of oxygen

content in the mixture which is beneficial for the reduction of

CO. The increase of CO is also because of the unstable

combustion which includes some incomplete oxidation that

produces CO. It is also obvious that the minimum value of CO

emission occurs at a larger l as more hydrogen is enriched.This is because hydrogen enrichment expands the lean burn

limit.

5. Conclusion

The study presented is an experimental study aimed at

investigating the effect of various hydrogen ratios of HCNG

fuel on performance and emission characteristics under WOT

operating conditions using a turbocharged spark ignited

natural gas engine. The experimental data was taken for

hydrogen fractions of 0%, 30% and 55% by volume and wasconducted under various operating conditions including

different spark timings and excess air ratios (l).

The following main conclusions were drawn from this

study:

1. Using the same fuel mixture, as l increases the engines

torque, power, MAP and exhaust temperature gradually

decrease. While using the same excess air ratio, as more

hydrogen is added, the mixtures lower heating value

decreases, resulting in a decrease in power output and

a reduction in exhaust temperature, the turbo become less

efficient, the MAP appears to similarly decrease. Further-

more, due to hydrogens rapid combustion velocity theangle of maximum power becomes more advanced.

2. The maximum in-cylinder pressure decreases as l

increases. When hydrogen is added without holding the

mixtures lower heating value constant, the position of max

in-cylinder pressure occurs later as l is increased; however

when the mixtures lower heating value is held constant,

the position moves closer to TDC.

3. Using various fuel mixtures, the maximum heat release

rate reduces as l increases. Hydrogen enrichment can also

enhance the maximum heat release rate.

4. Using the same fuel mixture, as l increases both the early

flame development period and flame propagation duration

are extended. While holding l constant, increased

a

b

Fig. 7 e (a) Spark to 10% MFB burn duration versus excess

air ratio. (b) 10%e90% MFB burn duration versus excess air

ratio.

Fig. 8e

COVimep versus excess air ratio.

Fig. 9 e Indicated thermal efficiency versus excess air ratio.



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