Fuel 318 (2022) 123675
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Fuel
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Full Length Article
Comparison of combustion, emission and abnormal combustion of
hydrogen-fueled Wankel rotary engine and reciprocating piston engine
Hao Meng , Changwei Ji *, Gu Xin , Jinxin Yang , Ke Chang , Shuofeng Wang
College of Energy and Power Engineering, Beijing Lab of New Energy Vehicles and Key Lab of Regional Air Pollution Control, Beijing University of Technology, Beijing
100124, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Hydrogen
Wankel rotary engine
Reciprocating piston engine
Combustion and emissions
Abnormal combustion
Hydrogen-fueled Wankel rotary engine (HWRE) as an excellent power device deserves more in-depth study. The
goal of this work is to provide a more comprehensive understanding of the pros and cons of HWRE and what
should be done when developing a hydrogen-specific WRE by comparing HWRE with hydrogen-fueled recip­
rocating piston engine (HRPE), as well as some gasoline-fueled conditions, in terms of combustion, emissions and
abnormal combustion. The results show that HWRE can achieve higher power per displacement compared to the
RPE fueled by whether gasoline or hydrogen, as well as slightly low brake thermal efficiency and extremely poor
NO emission. At 2500 r/min, the maximum power per displacement of HWRE is 1.66 and 1.23 times that of
hydrogen and gasoline RPE, respectively, however, accompanying absolute reductions of 4.96% and 3.06% in
maximum brake thermal efficiency. In addition, the characteristics and mechanisms of abnormal combustion in
HWREs are different compared to HRPEs. In particular, in HWRE, the backfire can be eliminated by the
improvement of the spark plug hole, while the knock problem is more prominent. Overall, HWREs have the
potential to win a place in the future of zero-carbon engines, however, some works, such as improving thermal
efficiency, reducing thermal load and preventing knock, need to be done for the development of hydrogenspecific WRE.
1. Introduction
1.1. Research background
Since the twenty-first century, the rapid development of the econ­
omy has not only benefited mankind but also brought about problems
such as energy shortage and environmental pollution [1]. The trans­
portation sector has significant responsibility for fossil fuel consumption
as well as pollutant emissions. In particular, Carbon Dioxide (CO2),
currently the pollutant of most concern, contributes to global warming
and thus threatens human existence [2]. And research has been reported
that more than 25% of total CO2 emissions come from the transportation
sector, especially from vehicles [3]. Hence, there is a strong need to find
reasonable solutions to reduce CO2 emissions from vehicles, as well as
develop renewable energy.
Due to its atomic composition without carbon, hydrogen has
received increasing attention in recent years [4]. Table 1 comparatively
shows some physicochemical properties at 300 K and 1 atm of hydrogen,
methane and iso-octane [5]. It can be found that in addition to being a
carbon-free fuel [6], hydrogen also has other excellent physicochemical
properties, such as high diffusivity for a homogeneous mixture, low
ignition energy for energy savings, short quenching distance for high
combustion efficiency, etc [7]. Besides, different from unrenewable
methane and gasoline, hydrogen is renewable energy with various
production methods, for instance, water gas method, electrolysis of
water or saturated saltwater, decomposition of ammonia, etc [8].
Hydrogen can therefore be seen as excellent energy in line with the
theme of sustainable development. The application of hydrogen on ve­
hicles can be divided into hydrogen–oxygen fuel cells and hydrogenfueled internal combustion engines (HICEs) [9]. Compared with fuel
cells, HICEs have lower cost and more robust infrastructures, which
obtained increasing attention recently [10].
1.2. Hydrogen-fueled reciprocating piston engine
The four-stroke reciprocating piston engine (RPE) is the mainstream
ICE nowadays and is widely used in passenger vehicles, commercial
vehicles and ships [11]. Compared with gasoline-fueled RPEs (GPREs),
hydrogen-fueled RPEs (HRPEs) have been shown to have higher thermal
* Corresponding author.
E-mail address: chwji@bjut.edu.cn (C. Ji).
https://doi.org/10.1016/j.fuel.2022.123675
Received 20 December 2021; Received in revised form 8 February 2022; Accepted 20 February 2022
Available online 24 February 2022
0016-2361/© 2022 Elsevier Ltd. All rights reserved.
H. Meng et al.
Fuel 318 (2022) 123675
HWRE
MAP
MBT
NO
PI
PPD
RPE
WOT
WRE
◦
CA
λ
Nomenclature
ATDC
BTE
CA50
CO2
DI
FFT
GRPE
GWRE
HICE
HRPE
After top dead center
Brake thermal efficiency
Combustion center
Carbon dioxide
Direct injection
Fast Fourier transform
Gasoline-fueled reciprocating piston engine
Gasoline-fueled Wankel rotary engine
Hydrogen-fueled internal combustion engine
Hydrogen-fueled reciprocating piston engine
backfire, is prone to lead to uncontrolled HRPEs operation and therefore
threaten the safety of drivers and passengers [18].
Table 1
Thermodynamic properties of hydrogen, methane and iso-octane [5].
Property
Hydrogen
Methane
Iso-octane
Density (kg/m3)
Mass diffusivity in air (cm2/s)
Minimum ignition energy (mJ)
@stoich
Minimum quenching distance
(mm) @stoich
Flammability limits in air (vol
%)
Flammability limits (λ)
Adibatic flame temperature in
air (K) @stoich
Minimum auto-ignition
temperature (K) @stoich
Lower calorific heating value
(MJ/kg)
Laminar burning velocity (cm/
s) @stoich ~ 360 K
Boiling Point (◦ C)
Saturated vapor pressure (kPa)
0.08
0.061
0.02
0.65
0.16
0.28
692
~0.07
0.28
0.064
2.03
3.5
4–75
5–45
1.1–6
0.14–10
2318
0.6–2
2226
0.26–1.51
2276
858
813
690
120
50
44.3
290
48
45
− 253
13.33
(− 257.9 ◦ C)
\
130+
− 161.5
53.32
(− 168.8 ◦ C)
− 188
107
99.2
5.1
(20 ◦ C)
4.5
100
Flash point
Octane number
Hydrogen-fueled Wankel rotary engine
Manifold absolute pressure
Maximum brake torque
Nitric oxide
Port injection
Power per displacement
Reciprocating piston engine
Wide-open throttle
Wankel rotary engine
Crank angle
Excess air ratio
1.3. Hydrogen-fueled Wankel rotary engine
Wankel rotary engine (WRE) is one of the ICEs, which is mainly used
in sports cars [19], drones [20] and small military equipment [21]. The
detailed introduction of WRE can be found in previous work [22,23].
Compared with RPEs, WREs seem to have better suitability with
hydrogen for the following reasons: (1) Short quenching distance of
hydrogen [24] contributes to improving the high combustion efficiency
even if the quenching effect in WRE is severe due to its high surface-tovolume ratio of combustion chamber [25]. (2) Fast burning velocity of
hydrogen [26] facilitates the flame reach to the rear side of the com­
bustion chamber against the long flame propagation path and reverse
unidirectional flow [27]. (3) High diffusivity of hydrogen is conducive
to forming homogeneous charge even if WRE operates at high-speed
conditions, in which high BTE in WREs can usually be obtained [28].
(4) Wide flammability limits of hydrogen [29] facilitate the formation of
flame kernel even if the spark position of the spark plug is located in the
cylinder body, in which weak flow and thus high local residual gas ratio
are [30]. Besides, wide flammability limits of hydrogen mean the spark
plug aperture can be reduced, which is conducive to retarding the
cylinder-to-cylinder leakage. (5) High power characteristics of WREs
[31] can eliminate the problem of power lack caused by hydrogen to
some extent. (6) Intake stroke of WREs occurs at low-temperature zone
due to the unique structure of WREs, which greatly decreases the risk of
backfire. (7) Compact structure of WREs makes it possible to use a larger
hydrogen tank in a given volume of powertrain, which is conducive to
improving sail mileage. Stutzenberger et al. [32] found that HWRE can
achieve similar power density to GRPE and hydrogen has a good suit­
ability for GWRE. Morimoto et al. [33] demonstrated that HWRE is less
prone to backfire and therefore can operated more stably.
However, the elongated combustion chamber of WREs leads to a
longer duration of flame propagation, which may increase the possi­
bility of knock caused by the auto-ignition of end gas in a hydrogenfueled WRE (HWRE). And the flame accelerated by a unidirectional
flow can make the combustion of hydrogen more unstable. In addition,
the BTE of WREs is usually lower than that of RPEs.
efficiency [12]. Welch et al. [13] reported that the brake thermal effi­
ciency (BTE) of a hydrogen-specific RPE can exceed 45% and is higher
10%-20% than that of gasoline-fueled RPEs. Verhelst [5] and Das [10]
have provided detailed reviews in their work and only two disadvan­
tages of HRPEs are discussed here: power shortage and abnormal
combustion.
In a port injection (PI) HRPE, since hydrogen does not contain carbon
elements [14], hydrogen will occupy a larger volume of the intake
volume, about 30%, at the stoichiometric combustion, which greatly
limits the amount of fuel entering the combustion chamber. Besides, the
low volume-specific heat value of hydrogen further reduces the amount
of energy that can be flowed into the cylinder, thus hindering the real­
ization of high power [15]. Although direct injection (DI) can effectively
increase the amount of hydrogen and research also has proved that DI
HRPEs can achieve 1.17 times the theoretical power of the same spec
GRPEs, there are no commercially available hydrogen DI nozzles, the
development of which is mainly limited by lubrication [13]. Besides, the
shortened sail mileage caused by adopting DI is not conducive to the
application of HRPEs in powertrains. Supercharge is also an effective
way to improve the power of HRPEs [16], but it also leads to complex
structures.
Abnormal combustion in HRPEs is mainly divided into three types:
backfire, pre-ignition and knock, in brief, which are caused by ignition
by in-cylinder hot source in intake stroke, compression stroke and power
stroke, respectively [17]. Abnormal combustion in HRPEs, especially
2. Research content
In general, adopting hydrogen as the fuel is a trend in the develop­
ment of ICEs. HWREs and HRPEs have their pros and cons, so both
deserve more in-depth study. However, HWRE is a potential power
system with high power, related studies of which are very scarce. Hence,
based on this consideration, the goal of this work is to provide a more
comprehensive understanding of the pros and cons of HWRE and what to
do when developing a hydrogen-specific WRE by comparing HWRE with
HRPE, as well as some gasoline-fueled conditions, in terms of
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Fuel 318 (2022) 123675
WRE is operated at 2500 r/min, the NO emission corresponding to the
maximum brake power of HWRE is about 4.37 times that of GWRE. In
summary, compared with gasoline, adopting hydrogen on WRE will lead
to power deficiencies, but can greatly improve thermal efficiency.
Fig. 2 shows the power per displacement (PPD), BTE and NO emis­
sion of HWRE and HRPE. It can be seen from the left one in Fig. 2 that
HWRE has higher PPD than HRPE and the difference is gradually
increased with the increase of engine speed. At 2500 r/min, the HWRE
can achieve a maximum PPD of 22.51 kW/L, which is approximately
1.66 times the maximum PPD of 13.56 kW/L of HRPE. As depicted in the
middle one, HRPE can achieve higher BTE than HWRE at the same en­
gine speed and the difference is gradually reduced with the increase of
engine speed. At 2500 r/min, the 33.14% of maximum BTE of HRPE is
higher 4.96% in absolute value than 28.81% of the maximum BTE of
HWRE, while at 1000r/min, the difference between maximum BTE is
9.54%. The reasons are as follows: (1) High surface-to-volume ratio
caused by elongated combustion chamber of WRE is prone to produce
higher cooling lossES. Besides, the short quenching distance of hydrogen
further exacerbates this problem. (2) Due to the structural difference of
the two engines, the MBT CA50 of WRE is later about 30◦ CA than that of
RPE, which indicates that WRE inherently has a lower constant-volume
combustion degree and is, therefore, less efficient. (3) The high surfaceto-volume ratio of the WRE also makes it necessary to have more seals,
which increases friction losses. It is worth noting that the maximum BTE
at different engine speeds of HWRE are around 1.8 λ, while that of HRPE
usually appear at higher λ. It should be noted that the y-axis of the right
one in Fig. 2 represents the natural logarithm of NO emission per
displacement. As shown in the right one, as the λ is reduced, the NO
emission of HWRE exceeds that of HRPE, and HWRE achieves about 3
times NO emission than HRPE in stoichiometric ratio combustion. The
reasons are as follows: The high surface-to-volume ratio of WRE makes
its high cooling loss. The four strokes of WRE have their independent
space position [36], resulting in a very uneven heat load, which means
that the cylinder body corresponding to the power stroke has a higher
temperature. When HWER operates at lean condition, the combustion
temperature is low and the heat dissipation of WRE itself can meet the
hydrogen combustion. The high heat transfer caused by the high surfaceto-volume ratio of WRE further reduces the combustion temperature
thus generating low NO emissions. When HWRE operates at the stoi­
chiometric ratio, the extreme combustion temperature [37] of hydrogen
inundates the cooling system originally designed for gasoline combus­
tion. The high temperature of the cylinder body helps to keep the high
in-cylinder temperature, thus generating high NO emissions. Hence,
based on the above analysis, when the GWRE is transformed into the
HWRE, the cooling system needs to be redesigned to meet the high de­
mand for heat transfer. Overall, while HWREs can achieve satisfyingly
high power, their low BTE and high NO emissions relative to HRPEs
need further improvement.
Fig. 3 is the MBT ignition timing of HWRE and HRPE at varying λ at
2500 r/min. It can be concluded that compared with HRPE, the MBT
ignition timing of HWRE occurs at a more delayed crank angle at the
same λ, and the difference exceeds 10◦ CA. It can be explained by the
following reasons: The CA50 corresponding to the MBT is usually
located between 8 and 10◦ CA ATDC [11]. In the previous study [38], the
CA50 corresponding to the MBT is usually located between 35 and
40◦ CA ATDC, which is due to the special structure of WRE. In WRE, the
optimal work timing of in-cylinder pressure is 135◦ CA ATDC [34] and
considering that a low in-cylinder pressure at a much-delayed ignition
timing is not conducive to working, the timing of CA50 corresponding to
MBT is as described above. Hence the MBT ignition timing of HWREs is
later than that of HRPEs even if the different turbulence caused by the
difference between WRE and RPE also has a different effect on incylinder flame velocity.
Fig. 4 shows the PPD and BTE of GWRE and GRPE at different engine
speeds. As with hydrogen as fuel, WRE has higher PPD and lower BTE
than RPE when gasoline is used as fuel. It can be found from the right
combustion, emissions and abnormal combustion.
3. Experimental apparatus and methodology
The tested WRE in this work is the Mazda 13B, which has a
compression ratio of 10 and a displacement of 1.3 L, produced in 2002,
while the tested RPE in this work is HYUNDAI G4FD, which has a
compression ratio of 9.5 and a displacement of 1.6 L, produced in 2015.
The specifications of the two engines have been shown in Table 2.
Because of the leakage problem of WREs, it can be regarded that the
compression ratio of the two engines is approximately equal. The
experimental apparatus with uncertainty analysis of WRE [34] and RPE
[35] can be found in our previous work.
In Section 3.1: The load of HWREs and HRPEs is controlled by
qualitative control, i.e. the engine load is regulated by adjusting the
excess air ratio (λ) at wide-open throttle (WOT) condition, while the
load of gasoline-fueled WRE (GWREs) and GRPEs are controlled by
quantitative control, i.e. the engine load is regulated by adjusting the
throttle percentage at the stoichiometric ratio. The whole hydrogenrelevant test is performed at maximum brake torque (MBT) ignition
timing. And the gasoline-relevant test is performed based on the original
engine.
In Section 3.2: Due to the lack of abnormal combustion data for
HRPEs, some comparative work is based on the conclusions of other
scholars.
4. Results and discussions
4.1. Combustion and emissions
Fig. 1 shows the comparison of brake power, BTE and nitric oxide
(NO) emission between HWRE and GWRE. In particular, limited by the
hydrogen supplying system, the test engine speeds of HWRE are only
from 1000 to 2500 r/min, while that of GWRE are from 1500 to 4500 r/
min. It can be found from the top two in Fig. 1 that the brake power of
HWRE and GWRE gradually increases with the decrease of λ and the
increase of manifold absolute pressure (MAP), respectively. At 2500 r/
min, the maximum brake power of HWRE is 29.30 kW, about 82% of
35.39 kW, which is the maximum brake power of GWRE. From the
middle two in Fig. 1, it can be seen that the highest BTE of GWRE is
located around 2500 r/min and middle load, which is 23.95%. For the
HWRE, the highest BTE also appears around the middle load. The BTE of
HWRE gradually increases with increasing engine speed within the
tested range, and there is a possibility of further increasing the BTE
outside the tested range. When similar engine speed and brake torque
are achieved, HWRE usually achieves higher BTE than GWRE. The
highest BTE at 2500 r/min of HWRE is 28.85%, which is higher about
20% than that of GWRE, an absolute value of 4.9%. In particular, the
bottom two in Fig. 1 illustrate the contour plot of the natural logarithm
of NO emission. As shown in the bottom two in Fig. 1, HWRE has an
extremely high NO emission around the stoichiometric ratio. When the
Table 2
Engine specification.
Specification
WRE
RPE
Number of rotors
Cooling method
Ignition source
Intake method
Exhaust method
Bore × stroke/ mm
Generating radius /mm
Width of rotor/mm
Displacement /L
Compression ratio
Eccentricity /mm
Power output
2
Water-cooled
Spark plug
Side-ported, natural aspiration
Side-ported
\
105
80
0.654
10
15
121 kW /5500 rpm
4
Water-cooled
Spark plug
Natural aspiration
\
77 × 84.5
\
\
0.4
9.5
\
132.4 kW/5500 rpm
3
H. Meng et al.
Fuel 318 (2022) 123675
Fig. 1. The brake power (top), BTE (middle) and NO emission (bottom) of HWRE (left) and GWRE (right).
one in Fig. 4 that at 2500 r/min, the maximum PPD of GWRE, which is
27.22 kW/L, is about 1.5 times the maximum PDD of GRPE, which is
18.26 kW/L. Besides, the BTE of GWRE is obviously lower than GRPE, in
particular at high-load or wide-open throttle conditions. It is worth
noting combined with Fig. 1 that although HWRE has a lower maximum
PDD than GWRE, it can achieve a maximum PPD about 1.23 times
compared to GWRE at 2500 r/min. In addition, comparing HWRE to
GRPE, there is only a 3.06% absolute reduction in maximum BTE at
2500 r/min. Hence, considering the combination of efficiency, dynamics
and carbon-based emissions, HWRE is an excellent alternative to GRPE.
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H. Meng et al.
Fuel 318 (2022) 123675
Fig. 2. The PPD (left), BTE (middle) and NO emission (right) of HWRE (pointed line) and HRPE (dashed line) at different engine speeds.
abnormal combustion that knock would increase the in-cylinder ther­
modynamic states, which in turn induces stronger knock and further
pre-ignition and even backfire. Due to the continually cumulative incylinder thermodynamics state, the timing of pre-ignition is gradually
advanced.
However, a similar situation is not observed in HWREs even if the
knock is violent. The pre-ignition in HWRE may be caused by the high
temperature of spark plugs due to untimely cooling of the cylinder body.
Fig. 5 shows pre-ignition in-cylinder pressure profiles of HWRE at 3000
r/min, 1.4 λ and 4◦ CA ATDC ignition timing. By calculation, the preignition timings of the 8th and 10th cycles, which are also the most
common pre-ignition within our test, are the timing of the leading spark
plug connected to the combustion chamber. Hence, the conclusion can
be drawn that the leading spark plug is a significant hot spot causing preignition, which can be explained by the fact that the high thermal load
near the spark plug has been addressed in the previous section and the
thermal load is particularly higher near the leading spark plug, which is
the main combustion zone due to the in-cylinder turbulence direction
[40], therefore, high temperature of the leading spark plug is prone to
lead to pre-ignition. Besides, compared to the results in Szwaja’s work
[39], the pre-ignition profiles of HWRE have some wrinkles, which are
caused by the unstable combustion of hydrogen. This is partly because
the engine speed is higher in this work, which helps to accelerate
hydrogen combustion, and partly because WREs have stronger incylinder turbulence. In addition, it also can be observed from Fig. 5
that there are some much violent knock caused by multi-point preignition, such as 35th, 40th, 45th, 54th and 59th. The hot spots may be
two spark plugs or leading spark plug and residually unburned lubri­
cating oil.
Fig. 3. The MBT ignition timing of HWRE and HRPE at varying λ at 2500
r/min.
4.2. Abnormal combustion
4.2.1. Pre-ignition
The pre-ignition of HICEs is usually caused by the in-cylinder hot
sources, such as spark plug, carbon deposition, suspending lubricating
particles, etc [5]. Szwaja et al. [39] found from the study about HRPEs
Fig. 4. The PPD (left) and BTE (right) of GWRE and GRPE at different engine speed.
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Fuel 318 (2022) 123675
super-fast flame velocity and the two are positively correlated. In WRE,
when the apex seal scratches through the spark plug hole, there is a
transient connection between the cylinder in the power stroke and the
cylinder in intake stroke as shown in the right one of Fig. 6. For the cycle
of normal combustion or weak knock, the flame is quenched by the apex
seal before it reaches the next cylinder, while for the violent knock, such
as 1 in the left one of Fig. 6, super-fast flame velocity gives the flame the
ability to propagate to the next cylinder, thus causing pre-ignition in the
next cylinder. Meanwhile, the pre-ignition cylinder is in intake stroke
and the flame propagates further to the intake port, thus generating the
backfire. The combustion pressure of the cylinder in intake stroke is
balanced with the manifold absolute pressure so that it behaves like
misfire pressure during the compression stroke.
To sum up, the backfire mechanisms of HWREs and HRPEs are
completely different and the backfire in HWRE only occurs after the
violent knock. Fortunately, the tested WRE is designed for gasoline
combustion, and hydrogen has wider flammability limits and shorter
quenching distance, hence, the backfire in HWRE can be eliminated by
reducing the aperture of the spark plug hole.
Fig. 5. The pre-ignition in-cylinder pressure profiles of HWRE.
4.2.3. Knock
In HICEs, the knock is usually divided into two types: caused by rapid
and unstable combustion of hydrogen and caused by the spontaneous
combustion of end gas, which is several times more intense than the
former [43]. Fig. 7 shows the knock in-cylinder pressure profiles of
HWRE and HRPE at 2000 r/min. It should be specifically stated that the
knock in-cylinder pressure of HWRE is selected from one of the most
violent knocks within 1000 continuous cycles, while the knock incylinder pressure of HRPE corresponds to the most violent knock
within 1000 continuous cycles. It can be found from Fig. 7 that HWRE
has more violent knock than HRPE at the same engine speed even if a
more advanced ignition timing and stoichiometric ratio, which are
prone to cause more violent knock [44], are adopted in HRPE. Knock
depends mainly on the type of fuel and the shape of the combustion
chamber. Since both HWRE and HOPE use hydrogen as fuel, the main
difference in knock of HWRE and HRPE comes from the shape of the
combustion chamber. Due to the elongated combustion chamber of
WRE, the end gas has more opportunities to speed the ignition delay.
Besides, high thermal load in the combustion side of WRE is conducive
to shortening the ignition delay. Hence, the high propensity for spon­
taneous combustion-induced knock makes HWREs prone to more vio­
lent knock compared to HRPEs.
The geometry of the combustion chamber and arrangement of spark
plugs has a significant influence on the acoustic resonance modes. Fig. 8
shows the FFT amplitude for HWRE knock. Limited by the lack of the
study of acoustic resonance modes of WRE combustion chamber, the
In short, compared with HRPE, the pre-ignition of HWRE is not
caused by the knock, but rather it causes the knock. Besides, the leading
spark is significantly responsible for the pre-ignition of HWRE.
4.2.2. Backfire
Backfire in engines is means that the fresh charge in intake stroke is
ignited by a hot source and causes the flame to flow into the intake port.
A comprehensive review of backfire in PI HRPEs was presented by Gao
et al. [41], which will not be discussed here.
In WRE, as mentioned above, the intake stroke occurring at low
temperature is not prone to generate backfire. In the work shown in
Figs. 1 and 2, no backfire occurs in the HWRE, while HRPE occurs
backfire at 2500 r/min. Morimoto et al. [33] also prove this opinion by
their work. However, while the knock study in HWREs was conducted,
the backfire appeared with a certain law. The backfire in HWRE is only
observed after a violent knock. Fig. 6 shows the backfire in-cylinder
pressure profiles (left) and the schematic of the backfire mechanism
[42] (right) in HWRE. In the left one of Fig. 6, the number in the legend
is the sequence and 2 is the backfire cycle, which is after a violent knock
cycle. The reasons are as follows: In the tested WRE, the in-cylinder
pressure sensor is combined with the leading spark plug and it can’t
measure the in-cylinder pressure throughout the cycle. Hence, for the
backfire cycle, only the misfire in power stroke can be observed but not
the pre-ignition in the intake stroke. Knock is usually accompanied by
Fig. 6. The backfire in-cylinder pressure profiles (left) and the schematic of backfire mechanism [42] (right) in HWRE.
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Fuel 318 (2022) 123675
Fig. 7. The knock in-cylinder pressure profiles of HWRE (left) and HRPE (right).
analysis in this work is based on the cylindrical combustion chamber
[45]. It can be found that the acoustic resonances of HWRE are more in
line with (1,0), (1,1) and (0,1), while that of HRPE are more in line with
(1,0) and (2,0) [46].
Overall, knock is a more prominent issue in HWREs and has different
characteristics from the knock in HRPEs, which needs to be studied in
more depth.
5. Conclusions
The goal of this work is to investigate the difference between
hydrogen-fueled Wankel rotary engines (HWREs), which is the focus of
this work, and hydrogen-fueled reciprocating piston engines (HRPEs)
from combustion, emissions and abnormal combustion. Also, some re­
sults with gasoline as fuel are provided for comparison. Based on the
experimental results, the main conclusions are as follow:
(1) Although there is a reduction of power in WRE when the fuel is
transformed from gasoline to hydrogen, HWRE can achieve
higher power per displacement (PPD) than REP fueled by
whether gasoline or hydrogen. When engines are operated with
maximum power at 2500 r/min, HWRE achieves 82%, 166% and
123% PPD compared to GWRE, HRPE and gasoline-fueled RPE
(GRPE), respectively.
(2) HWRE can achieve a 4.9% absolute improvement in maximum
BTE than GWRE. Compared to the RPE, WRE has lower brake
thermal efficiency (BTE) whether fueled by gasoline or hydrogen.
When engines are operated with maximum BTE at 2500 r/min,
HWRE has a 4.96% and a 3.06% reduction in absolute value in
BTE compared to HRPE and GRPE, respectively. In addition, due
to uneven thermal load, HWRE has a poorer NO emission than
HRPE at the stoichiometric ratio.
(3) The characteristics and generated mechanism of abnormal com­
bustion, which includes pre-ignition, backfire and knock, in
HWREs are significantly different from that in HRPEs. In HWREs,
the backfire can be eliminated, while the knock is more violent.
Fig. 8. The FFT amplitude for HWRE knock.
CRediT authorship contribution statement
Hao Meng: Conceptualization, Methodology, Writing – original
draft, Investigation. Changwei Ji: Funding acquisition, Formal analysis,
Resources. Gu Xin: Writing – review & editing, Investigation, Funding
acquisition. Jinxin Yang: Investigation. Ke Chang: Investigation.
Shuofeng Wang: Writing – review & editing, Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgments
This work was supported by National Natural Science Foundation
(Grant No. 51976003), Beijing Lab of New Energy Vehicles (Grant No.
JF005015201901, JF005015201801).
In summary, considering the combination of power, efficiency and
emission, HWRE is an excellent alternative to the current GRPE. How­
ever, some aspects need to be further investigated to the development of
hydrogen-specific WRE, for instance, how to improve the thermal effi­
ciency, how to reduce the thermal load while ensuring thermal effi­
ciency, how to prevent the knock.
References
[1] Gao J, Tian G, Sorniotti A, Karci AE, Di Palo R. Review of thermal management of
catalytic converters to decrease engine emissions during cold start and warm up.
7
H. Meng et al.
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
Fuel 318 (2022) 123675
Appl Therm Eng 2019;147:177–87. https://doi.org/10.1016/j.
applthermaleng.2018.10.037.
Falkner ROBERT. The Paris agreement and the new logic of international climate
politics. Int Aff 2016;92(5):1107–25. https://doi.org/10.1111/1468-2346.12708.
Sun Z-y, Liu F-S, Liu X-H, Sun B-G, Sun D-W. Research and development of
hydrogen fuelled engines in China. Int J Hydrogen Energy 2012;37(1):664–81.
https://doi.org/10.1016/j.ijhydene.2011.09.114.
Wang L, Yang Z, Huang Y, Liu D, Duan J, Guo S, et al. The effect of hydrogen
injection parameters on the quality of hydrogen–air mixture formation for a PFI
hydrogen internal combustion engine. Int J Hydrogen Energy 2017;42(37):
23832–45. https://doi.org/10.1016/j.ijhydene.2017.04.086.
Verhelst S, Wallner T. Hydrogen-fueled internal combustion engines. Prog Energy
Combust Sci 2009;35(6):490–527. https://doi.org/10.1016/j.pecs.2009.08.001.
Gao J, Tian G, Ma C, Xing S, Jenner P. Performance explorations of a naturally
aspirated opposed rotary piston engine fuelled with hydrogen under part load and
stoichiometric conditions using a numerical simulation approach. Energy 2021;
222:120003. https://doi.org/10.1016/j.energy.2021.120003.
Yang J, Meng H, Ji C, Wang S. Comparatively investigating the leading and trailing
spark plug on the hydrogen rotary engine. Fuel 2022;308:122005. https://doi.org/
10.1016/j.fuel.2021.122005.
Ma Y, Wang XR, Li T, Zhang J, Gao J, Sun ZY. ScienceDirect Hydrogen and ethanol:
production, storage, and transportation. Int J Hydrogen Energy 2021. https://doi.
org/10.1016/j.ijhydene.2021.06.027.
Gao J, Xing S, Tian G, Ma C, Zhao M, Jenner P. Numerical simulation on the
combustion and NOx emission characteristics of a turbocharged opposed rotary
piston engine fuelled with hydrogen under wide open throttle conditions. Fuel
2021;285:119210. https://doi.org/10.1016/j.fuel.2020.119210.
Das LM. Hydrogen-fueled internal combustion engines. Elsevier Ltd. 2016. https://
doi.org/10.1016/b978-1-78242-363-8.00007-4.
John Heywood. Internal Combustion Engine Fundamentals 2018.
Yang Z, Zhang F, Wang L, Wang K, Zhang D. Effects of injection mode on the
mixture formation and combustion performance of the hydrogen internal
combustion engine. Energy 2018;147:715–28. https://doi.org/10.1016/j.
energy.2018.01.068.
Welch A, Mumford D, Munshi S, Holbery J, Boyer B, Younkins M, et al. Challenges
in developing hydrogen direct injection technology for internal combustion
engines. SAE Tech Pap 2008. https://doi.org/10.4271/2008-01-2379.
Qin Z, Yang Z, Jia C, Duan J, Wang L. Experimental study on combustion
characteristics of diesel–hydrogen dual-fuel engine. J Therm Anal Calorim 2020;
142(4):1483–91. https://doi.org/10.1007/s10973-019-09147-y.
Verhelst S, Wallner T, Sierens R. Hydrogen-fueled internal combustion engines.
Handb Hydrog Energy 2014;35:821–902. https://doi.org/10.1201/b17226.
Lee J, Lee K, Lee J, Anh B. High power performance with zero NOx emission in a
hydrogen-fueled spark ignition engine by valve timing and lean boosting. Fuel
2014;128:381–9. https://doi.org/10.1016/j.fuel.2014.03.010.
Yang Z, Li D, Wang L. Research on the hot surface ignition of hydrogen-air mixture
under different influencing factors. Int J Energy Res 2018;42(12):3966–76.
https://doi.org/10.1002/er.4132.
Yang Z, Wang L, Zhang Q, Meng Y, Pei PuCheng. Research on optimum method to
eliminate backfire of hydrogen internal combustion engines based on combining
postponing ignition timing with water injection of intake manifold. Int J Hydrogen
Energy 2012;37(17):12868–78. https://doi.org/10.1016/j.ijhydene.2012.05.082.
Fan B, Zhang Y, Pan J, Wang Y, Otchere P. Experimental and numerical study on
the formation mechanism of flow field in a side-ported rotary engine considering
apex seal leakage. J Energy Resour Technol Trans ASME 2021;143:1–15. https://
doi.org/10.1115/1.4047787.
Fan B, Zeng Y, Pan J, Fang J, Adeniyi Salami H, Wang Y. Evaluation and analysis of
injection strategy in a peripheral ported rotary engine fueled with natural gas/
hydrogen blends under the action of apex seal leakage. Fuel 2022;310:122315.
https://doi.org/10.1016/j.fuel.2021.122315.
Taskiran OO, Calik AT, Akin Kutlar O. Comparison of flow field and combustion in
single and double side ported rotary engine. Fuel 2019;254:115651. https://doi.
org/10.1016/j.fuel.2019.115651.
Ji C, Meng H, Wang S, Wang Du, Yang J, Shi C, et al. Realizing stratified mixtures
distribution in a hydrogen-enriched gasoline Wankel engine by different compound
intake methods. Energy Convers Manage 2020;203:112230. https://doi.org/
10.1016/j.enconman.2019.112230.
Fan B, Wang Y, Pan J, Zhang Y, Zeng Y. Numerical study on flow field in a
peripheral ported rotary engine under the action of apex seal leakage. J Fluids Eng
Trans ASME 2021;143:1–14. https://doi.org/10.1115/1.4049117.
Fan B, Wang Y, Zhang Y, Pan J, Yang W, Zeng Y. Numerical investigation on the
combustion performance of a natural gas/hydrogen dual fuel rotary engine under
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
8
the action of apex seal leakage. Energy Fuels 2021;35(1):770–84. https://doi.org/
10.1021/acs.energyfuels.0c03498.
Taskiran OO. Improving burning speed by using hydrogen enrichment and
turbulent jet ignition system in a rotary engine. Int J Hydrogen Energy 2021;46
(57):29649–62. https://doi.org/10.1016/j.ijhydene.2020.11.142.
Fan B, Zeng Y, Zhang Y, Pan J, Yang W, Wang Y. Research on the hydrogen
injection strategy of a direct injection natural gas/hydrogen rotary engine
considering apex seal leakage. Int J Hydrogen Energy 2021;46(13):9234–51.
https://doi.org/10.1016/j.ijhydene.2020.12.214.
Zambalov SD, Yakovlev IA, Maznoy AS. Effect of multiple fuel injection strategies
on mixture formation and combustion in a hydrogen-fueled rotary range extender
for battery electric vehicles. Energy Convers Manage 2020;220:113097. https://
doi.org/10.1016/j.enconman.2020.113097.
Fan B, Pan J, Yang W, Chen W, Bani S. The influence of injection strategy on
mixture formation and combustion process in a direct injection natural gas rotary
engine. Appl Energy 2017;187:663–74. https://doi.org/10.1016/j.
apenergy.2016.11.106.
Meng H, Ji C, Wang S, Wang Du, Yang J. Optimizing the idle performance of an nbutanol fueled Wankel rotary engine by hydrogen addition. Fuel 2021;288:
119614. https://doi.org/10.1016/j.fuel.2020.119614.
Zambalov SD, Yakovlev IA, Skripnyak VA. Numerical simulation of hydrogen
combustion process in rotary engine with laser ignition system. Int J Hydrogen
Energy 2017;42(27):17251–9. https://doi.org/10.1016/j.ijhydene.2017.05.142.
Wang H, Ji C, Su T, Shi C, Ge Y, Yang J, et al. Comparison and implementation of
machine learning models for predicting the combustion phases of hydrogenenriched Wankel rotary engines. Fuel 2022;310:122371. https://doi.org/10.1016/
j.fuel.2021.122371.
Stutzenberger H, Boestfleisch V, van Basshuysen R, Pischinger F. Suitability of
rotary engines for hydrogen operation. Mot Z;(Germany, Fed Repub Of) 1983;44.
Morimoto K, Teramoto T, Takamori Y. Combustion Characteristics in Hydrogen
Fueled Rotary Engine 2014.
Meng H, Ji C, Yang J, Wang S, Chang Ke, Xin Gu. Experimental study of the effects
of excess air ratio on combustion and emission characteristics of the hydrogenfueled rotary engine. Int J Hydrogen Energy 2021;46(63):32261–72. https://doi.
org/10.1016/j.ijhydene.2021.06.208.
Ji C, Xin Gu, Wang S, Cong X, Meng H, Chang Ke, et al. Effect of ammonia addition
on combustion and emissions performance of a hydrogen engine at part load and
stoichiometric conditions. Int J Hydrogen Energy 2021;46(80):40143–53. https://
doi.org/10.1016/j.ijhydene.2021.09.208.
Amrouche F, Erickson PA, Varnhagen S, Park JW. An experimental study of a
hydrogen-enriched ethanol fueled Wankel rotary engine at ultra lean and full load
conditions. Energy Convers Manag 2016;123:174–84. https://doi.org/10.1016/j.
enconman.2016.06.034.
Wang Du, Ji C, Wang S, Yang J, Wang Z. Numerical study of the premixed
ammonia-hydrogen combustion under engine-relevant conditions. Int J Hydrogen
Energy 2021;46(2):2667–83. https://doi.org/10.1016/j.ijhydene.2020.10.045.
Meng H, Ji C, Yang J, Wang S, Xin Gu, Chang Ke, et al. Experimentally
investigating the asynchronous ignition on a hydrogen-fueled Wankel rotary
engine. Fuel 2022;312:122988. https://doi.org/10.1016/j.fuel.2021.122988.
Szwaja S, Cupiał K, Grab-Rogaliński K. Anomalies in combustion of hydrogen in a si
engine modified to work as a supercharged one. J KONES Powertrain Transp 2012;
19(3):437–42. https://doi.org/10.5604/12314005.1138159.
Spreitzer J, Zahradnik F, Geringer B. Implementation of a Rotary Engine (Wankel
Engine) in a CFD Simulation Tool with Special Emphasis on Combustion and Flow
Phenomena. SAE Tech Pap Ser 2015;1. https://doi.org/10.4271/2015-01-0382.
Gao J, Wang X, Song P, Tian G, Ma C. Review of the backfire occurrences and
control strategies for port hydrogen injection internal combustion engines. Fuel
2022;307:121553. https://doi.org/10.1016/j.fuel.2021.121553.
Analyzing characteristics of knock in a hydrogen-fueled Wankel rotary engine
(submitted) n.d.
Szwaja S, Naber JD. Dual nature of hydrogen combustion knock. Int J Hydrogen
Energy 2013;38(28):12489–96. https://doi.org/10.1016/j.ijhydene.2013.07.036.
Zhen X, Wang Y, Xu S, Zhu Y, Tao C, Xu T, et al. The engine knock analysis – An
overview. Appl Energy 2012;92:628–36. https://doi.org/10.1016/j.
apenergy.2011.11.079.
Shi H, Uddeen K, An Y, Pei Y, Johansson B. Statistical study on engine knock
oscillation and heat release using multiple spark plugs and pressure sensors. Fuel
2021;297:120746. https://doi.org/10.1016/j.fuel.2021.120746.
Szwaja S, Bhandary K, Naber J. Comparisons of hydrogen and gasoline combustion
knock in a spark ignition engine. Int J Hydrogen Energy 2007;32(18):5076–87.
https://doi.org/10.1016/j.ijhydene.2007.07.063.