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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
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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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