Revision Paper

Jaisson Vidal
July 2019

1 Introduction
2 Combustion characteristics of H2 and H2 blends flames
2.1 Combustion stability
Kim et al. [7] in an experimental study, investigated the hydrogen effects on the combustion stability
of a turbo gasoline direct injection engine in various air-fuel ratios. They evaluated that the addition of
hydrogen mass fraction from 0 to 5% improved the stability of combustion in leaner conditions from 1.0
to 1.5. In a similar study was evaluated by Ji and Wang [9], where they analyzed the effects of hydrogen
addition on spark ignition engine at lean conditions, and showed that with 6% hydrogen volume fraction
addition to gasoline maintained the combustion variation cycle-to-cycle nearly to 1% from 1.0 to 1.6
air/fuel ratios, while the pure gasoline increases sharply the combustion variation with the increase of
excess air-fuel ratio, nearly to 10% at 1.45 excess air/fuel ratio. Hence, showing that the engine fueled with
gasoline-hydrogen can work at leaner conditions improving thermal efficiency and emissions performance.

2.2 Laminar flame speed

The flame velocity can be defined as the speed that unburned gases move through the combustion
wave, where for hydrogen the laminar flame speed is very high. Many reasons help the high value for H2 ,
as a thermal diffusivity of H2 , that is very higher than hydrocarbons, and the oxidation kinetics is too
very quickly than hydrocarbons, facts that explain the high flame speed for H2 , and due the hydrogen
to be a non-hydrocarbon [12]. Nilsson et al. [11] investigated the effects of hydrogen addition on the
laminar flame speeds of methane and its blends. The experimental procedure was developed in a burner
plate and showed that an addition of 50% hydrogen fraction improved laminar flame speed of CH4 /H2
blend nearly to 60 cm/s, while the laminar flame speed of pure methane was 36 cm/s, both at same
excess air/fuel ratio 1.1.

2.3 Ignition delay time

Yousufuddin and Masood [6], studied the effect of ignition timing on the performance of a hydrogen-
ethanol fuelled in a single cylinder direct injection diesel engine, with hydrogen addition from 0 to 80%
by volume, and they evaluated that all percentage of hydrogen volume fraction reduces the specific fuel
consumption, and the best value was find aroud 25o BTDC spark timing at 11:1 compression ratio, nearly
to 0.097 kg/kW-h, while the same hydrogen volume fraction at 10o BTDC spark timing the value was
0.22 kg/kW-h, with 80% hydrogen. This fact is due the high burning velocity of hydrogen fuel, shortening
the combustion duration, increasing the cylinder gas temperature.

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2.4 Diffusion coefficient
2.5 Quenching distance

3 H2 addition on spark ignition engines

3.1 Fuel consumption and lean limit
In a recent study by Yilmaz and Tastan [3] show the effects of addition hydrogen on methanol-gasoline
blends, where an addition of 15% hydrogen volume fraction on G95M5 (95% gasoline - 5% methanol) the
specific fuel consumption decreases nearly 13% in stoichiometric conditions. Another study by Elsemary
et al. [4] investigated the performance of single cylinder spark ignition engine fueled with hydrogen-
gasoline blend. The procedure show that the addition of hydrogen reduces the gasoline consumption
until hydrogen percentage 31%, after this the addition of hydrogen percentage the gasoline consumption
increases. Karagoz Y et al. [8] in a experimental study, studied effects of pure hydrogen in a spark
ignition engine, single cylinder, 8.5:1 compression ratio. The results show that the maximum reduction
in BSFC was 3.53% for pure hydrogen when compared with pure gasoline at 3450 rpm engine speeds.

3.2 Thermal efficiency

Zhang et al. [2] investigated the effects of addiction of hydrogen in a spark-ignition engine and evaluated
hydrogen volume fractions are 0% and 3%, and maximum air-fuel ratios of 1.30 and 1.49, respectively.
Hence, revealed that he engine highest thermal efficiency achieves 36.7% after blending 3% hydrogen
volume fraction, while of pure ethanol is nearly 34%. In another study, Akansu et al. [1] proved that
the thermal efficiency has been increased from 25.6 to 30.9% with hydrogen mass fraction addition up to
45.1% to gasoline-ethanol blend. Another experimental procedure by Yilmaz and Tastan [3] investigated
the effects of hydrogen addition to methanol gasoline blends in a SI engine, the results obtained that the
addition of 15% of hydrogen mass fraction on G90M10 (90% gasoline - 10% methanol) increases nearly
11,7% in thermal efficiency. In a different study by Gonca [5], show the effects of different kinds of fuel on
a spark ignition engine, and evaluated hydrogen fuel operating with different residual gas fraction from
0,10 to 0,18 the thermal efficiency remains unchanged nearly 22%. Yousufuddin and Masood [6] show
the brake thermal efficiency versus ignition timing for various percentages of hydrogen volume 0-80%,
varying ignition timing from 10 to 30o CA BTDC, and evaluated that the best value for thermal efficiency
was measured nearly 27%, for 60% hydrogen at 11:1 compression ratio at 1500 rpm, while the value for
pure ethanol, in the same conditions, was measured nearly 23%. Karagoz Y et al. [8] investigated
hydrogen usage in a spark ignition engine, single cylinder, 8.5:1 compression ratio, and compares with
gasoline fuel. The study evaluated that the thermal efficiency of pure hydrogen was 3.7% higher than
pure gasoline, at stoichiometric conditions and 3450 rpm. Kim et al. [7] studied the effects of hydrogen
addition on combustion characteristics in various air/fuel ratios, and evaluated that the best value for
thermal efficiency was nearly 43.5%, with 5% hydrogen addition, at 8 bar, 2000 rpm and 1.3 air/fuel
ratio, while in the same conditions, but at 1.0 air/fuel ratio, the thermal efficiency of mixture was nearly
40.7%.

3.3 Peak cylinder pressure

Akansu et al. [1] disclosed higher pressure peaks with the addiction of 45,1% (mass fraction) of H2
with ethanol-gasoline blend (G80E20) in stoichiometric conditions, where the value produced was 64 bar,
while the value of peak pressure of pure gasoline (G100) demonstrated nearly 28 bar.

3.4 Compression ratio

Gonca [5] study the effects of different kinds of fuel and engine design parameters on spark ignition
engine. The procedures show that hydrogen as fuel increases thermal efficiency from 22% to nearly 26%
with compression ratios 10:1 to 20:1, respectively. Yousufuddin and Masood [6] in an experimental study
evaluated that the best operating conditions are find at 11:1 compression ratio combined with optimum
fuel combination 60-80% hydrogen volume substitution to ethanol, enhancing the brake thermal efficiency.

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3.5 Exhaust gas recirculation (EGR) strategy
The addition of hydrogen on gasoline engine improved the combustion stability, but the combustion
temperature of hydrogen is very higher than gasoline, then increases substantially the NOx emissions
[13]. To solve this problem the exhaust gas recirculation is normally used in combustion engines, where
the exhaust gas is introduced into the cylinder to retard the combustion, and reduces NOx emissions
[15]. The effect of EGR on the performance and emissions of hydrogen gasoline engine was studied by
[14], the study showed that addition of 5% hydrogen ratio on gasoline and 20% EGR ratio can improve
the engine torque output nearly to 20% and reduce the NOx emissions nearly 54.5% at air-fuel ratio 1.0.

3.6 Effects of water injection strategy

Another strategy, besides the EGR, for reducing N Ox emissions in a SI engine is a technique called
water injection. Woolley and Henriksen [20] studied the effects of water injection in a Dodge 440 CID V8
engine fueled with hydrogen. They reported that the water induction produces an exponential decrease
in N Ox emissions, and the thermal efficiency was not affected by water injection. In a recent and similar
experimental study, Dhyani and Subramanian [21] investigated the effects of water injection on N Ox
emissions in a SI engine hydrogen fueled, 4-cylinders and compared with EGR strategy. The experiment
was conducted on the SI engine varying the EGR rate from 0% to 28% by volume, and water injection
from 0 to 9.25 kg/h at 1500 rpm. They evaluated a significantly reduce with EGR, but a exponentially
decrease with water injetion, where for 25% EGR the N Ox emissions was reduced by 57%, while for 7.5
water injection was 97%, without affecting the performance of the engine. In another study Subramanian
et al. [22] studied the effect of water injection on a hydrogen fuelled spark ignition engine at constant
speed of 2500 rpm, and the results showed that for hydrogen flow rate at 0.78 kg/h, water injection varying
from 0 to 5.9 kg/h, thus the NO emissions reduced from around 7600 ppm to 2600 ppm, respectively,
without any reduction on thermal efficiency.

3.7 CO emissions
Zhang et al. [2] studied the CO emissions with the pure ethanol and 3% hydrogen-enriched ethanol in
a spark ignition engine, and evaluated that CO emissions are decreased when air-fuel ratio is increased.
Yilmaz and Tastan [3], in a experimental study, show the variation of CO emission with addition of
hydrogen fraction on methanol-gasoline blends. The procedure results a decreases nearly to 0.094% with
the G85M15H15 fuel (85% gasoline - 15% methanol - 15% hydrogen). Another study by Elsemary et
al. [4] investigated the effects of hydrogen addition in a spark ignition engine operating with gasoline,
and evaluated that the best hydrogen fraction is 31%, reducing amount of CO nearly to 0%, after this
percentage the CO emissions increases again, due the incomplete combustion. Karagoz Y et al. [8]
demonstrated in a experimental procedure, that the CO emissions reduced nearly to 11.5 times with pure
hydrogen fuel in a spark ignition engine in stoichiometric condition, single-cylinder, 8.5:1 compression
ratio at 3100 rpm engine speeds, when compared with pure gasoline fuel at same conditions.

3.8 CO2 emissions

Akansu et al. [1], showed that the CO2 values are significantly declining, nearly 50%, with an increase
in hydrogen fractions from 0% to 45.1%. Another study by Yilmaz and Tastan [3] measured CO2 emission
of hydrogen addition on methanol-gasoline blends in stoichiometric conditions. The minimum value of
CO2 emission was determined around 12,3%, at for G95M5H15 fuel (95% gasoline - 5% methanol - 15%
hydrogen), while for G95M5H0 fuel is nearly 13,9%.

3.9 N Ox emissions
Zhang et al. [2] evaluated that N Ox emissions are raised after the hydrogen addition, reducing from
3500 ppm to nearly 250 ppm, with air-fuel ratio 1.0 and 1.5, respectively. This fact is due the hydrogen has
a higher adiabatic flame temperature than the ethanol. Yilmaz and Tastan [3] show in an experimental
procedure, using methanol-gasoline blends in a SI engine, with addition hydrogen fraction from 0 to 15%,
where the addition of hydrogen on G95M5 (95% gasoline - 5% methanol) tends a increase N Ox emissions

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from 1149 ppm to 2250 ppm, with 0% and 15% of hydrogen volume fraction, respectively. Kim et al. [7]
studied the effects of hydrogen addition in a turbo gasoline direct injection in various air/fuel ratios, and
evaluated that the N Ox emissions decreased strongly when the air/fuel ratio increases. They used 5%
hydrogen with gasoline, at 2000 rpm and 10 bar, where the N Ox emission value for 1.1 air/fuel ratio was
nearly to 18 g/kW-h, while at same conditions but at 1.55 air/fuel ratio is nearly to 0%, due the N Ox
emissions depend strongly on oxygen concentration. In a similar study T. Su et al. [19] investigated the
effects of hydrogen addition on gasoline rotary engine at part load and lean conditions, with hydrogen
volume fraction at 0%, 3% and 6% in gasoline, varying the excess air-fuel ratio from 1.0 to 1.5, they
evaluated that N Ox emissions decrease strongly with increase air-fuel ratio, where at 1.5 air-fuel ratio
with 6% hydrogen addition the N Ox emissions was nearly to 0 ppm, while the same conditions but at
1.0 air-fuel ratio the value for N Ox emissions was around 350 ppm. This fact is due the reduction of
cylinder temperature in highs excess air-fuel ratio.

3.10 HC emissions
The emissions of HC was investigated by Zhang et al. [2] where emissions from the 3% hydrogen-blended
ethanol engine vary smoothly and increase gently with air-fuel ratio. Yilmaz and Tastan [3] investigated
the hydrogen addition of gasoline-methanol blends in a SI engine in stoichiometric conditions, and the
results showed a reduction nearly to 16% with 15% hydrogen fraction. In another study Kim et al. [7]
evaluated that the HC emissions increased with air/fuel ratio, in a turbo gasoline direct injection fueled
with hydrogen-gasoline blend. They evaluated the value for HC emissions nearly to 27 g/kW-h at 2000
rpm, 5% hydrogen and 1.55 air/fuel ratio, while at same conditions, but at 1.00 air fuel ratio the value
was nearly 7 g/kWh, because the combustion became more unstable with air/fuel increased. Karagoz Y
et al. [8] studied the effects of pure hydrogen addition in a spark ignition engine, single-cylinder, 8.5:1
compression ratio,in stoichiometric conditions, and the results was obtained values nearly to 0 g/kWh of
HC for pure hydrogen at various engine speeds, from 3100 rpm to 3450 rpm, while HC emissions values
for pure gasoline, at same conditions, was from 5.5 g/kWh to 9.8 g /kWh, from 3100 rpm to 3450 rpm,
respectively.

4 H2 addition on compression ignition engines

4.1 Fuel consumption and lean limit
Hamdan et al. [18] studied the effects of hydrogen addition under various engine speeds, from 1080 rpm
to 1800 rpm, in a compression ignition engine. Two cases was analyzed, pure diesel and diesel with 4 liter
per minute of hydrogen, injected into the air-intake manifold at atmosphere pressure. The results showed
that the presence of H2 reduces the specific fuel consumption due the lower heating value of hydrogen is
two and half times higher than diesel, and the best values was observed at low engine speeds, where at
1080 rpm the specific fuel consumption with hydrogen addition was nearly to 0.17 g/kWh, while for pure
diesel was 0.29 g/kWh.

4.2 Thermal efficiency

4.3 Peak cylinder pressure

4.4 Compression ratio

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4.5 Exhaust gas recirculation (EGR) strategy
The hydrogen is a promising alternative fuel for a clean combustion, but the N Ox emissions is a
particular threat to hydrogen fuelled engines, due the peak combustion temperature inside the combustion
chamber. In the other hand, exhaust gas recirculation (EGR) helps to reduce the N Ox emissions. In this
context Nag. et al [16] investigated the effects on engine emissions for hydrogen diesel dual fuel. The
experiments were conducted for 25%, 50%, 75%, and 100% loads, with hydrogen addition 0%, 10%, 30%,
and EGR rates from 0%, 5%, 10%. Was observed a decrease in N Ox emissions at high loads, where the
best value was nearly to 6.5 g/kWh, with 30% hydrogen addition, at 100% load and EGR rate of 10%,
while the same load and the same hydrogen addition, but at EGR rate 0% the value for N Ox emissions
was nearly to 11 g/kWh. Saravanan et al. [17] in a similar study, investigated the characteristics on
hydrogen as a dual fuel for diesel engine with EGR technique. The experimental setup was conducted
without EGR, with 15%, and 25% EGR rate, and the flow rate of hydrogen was set at 20 l/min. The
results showed that the N Ox formation is high without EGR, nearly to 600 ppm, when compared with
25% EGR rate where was observed a reduction to 450 ppm, at same full load 100%.

4.6 Effects of water injection strategy

4.7 CO emissions

4.8 CO2 emissions

4.9 N Ox emissions

4.10 HC emissions
Unburned hydrocarbons emissions are originated of incomplete combustion of the hydrocarbon fuel.
The amount of hydrocarbon emissions in exhaust gases is a useful measure of combustion inefficiency [24].
In a experimental study, Kumar et al. [23] investigated the effects of hydrogen addition on vegetable oil
fuelled compression ignition engine, at 1500 rpm, 3.7 kW output power. The experiment was conducted
at various loads from 20% to 100%, with hydrogen mass share from 0% to 40% addition on Jatropha
oil, and evaluated that unburned hydrocarbon level increases with load for neat oil, but decreases with
hydrogen addition. For 18% H2 addition the unburned HC was around 70 ppm, at 100% load, while for
the same conditions, but without H2 addition the HC value was nearly to 130 ppm.

5 Strategies to co-injection H2
Yu et al. [10] studied effects of hydrogen direct injection strategies on spark ignition engines with
hydrogen-gasoline blend. In this context, they evaluated strategies with hydrogen fraction addition of
10%, where the hydrogen injection pressures were varied at 2, 3, 4, 5 and 6 MPa, and the hydrogen
injection timings varied at 75o , 90o , 105o , 120o , and 135o CA BTDC, and the ignitions timings varying
from 10 to 30o CA BTDC. The best strategie in this experimental procedure was 4 MPa injection pressure,
105o CA BTDC injection timing, and 20o CA BTDC ignition timing, with improving thermal efficiency
of 4,5% at lean conditions of 1.5 excess fue/ratio. Due the improvement combustion stability of hydrogen
addition.

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References
[1] Selahaddin Orhan Akansu, Selim Tangoz, Nafiz Kahraman, Mehmet Ilhan Ilhak, Salih Acıkgoz. Exper-
imental study of gasoline-ethanol-hydrogen blends combustion in an SI engine. International Journal
of Hydrogen Energy 42 (2017); 25781-25790.
[2] Bo Zhang, Changwei Ji, Shuofeng Wang. Performance of a hydrogen-enriched ethanol engine at un-
throttled and lean conditions. Energy Conversion and Management 114 (2016) 68–74.
[3] Ilker Yilmaz, Murat Tastan. Investigation of hydrogen addition to methanol-gasoline blends in an SI
engine. International Journal of Hydrogen Energy 43 (2018) 20252-20261.

[4] Ismail M.M. Elsemary, Ahmed A.A Attia, Kairy H. Elnagar, Ahmed A.M. Elaraqy. Experimental
investigation on performance of single cylinder spark ignition engine fueled with hydrogen-gasoline
mixture. Applied Thermal Engineering 106 (2016); 850-854.
[5] Guven Gonca. Influences of different fuel kinds and engine design parameters on the performance
characteristics and NO formation of a spark ignition (SI) engine. Applied Thermal Engineering 127
(2017); 194-202.
[6] Syed Yousufuddin, Mohammad Masood. Effect of ignition timing and compression ratio on the per-
formance of a hydrogen-ethanol fuelled engine. International Journal of Hydrogen Energy 34 (2009);
6945-6950.

[7] Joonsuk Kim, Kwang Chun, Soonho Song, Hong-Kil Baek, Seung Woo Lee. Hydrogen effects on
the combustion stability, performance and emissions of a turbo gasoline direct injection engine in a
various air/fuel ratios. Applied Energy 228 (2018); 1353-1361.
[8] Yasin Karagoz, Ozgun Balci, Hasan Koten. Investigation of hydrogen usage on combustion char-
acteristics and emissions of a spark ignition engine. International Journal of Hydrogen Energy,
https://doi.org/10.2016/j.ijhydene.2019.01.147
[9] Changwei Ji, Shuofeng Wang. Effect of hydrogen addition on combustion and emissions performance
of a spark ignition gasoline engine at lean conditions. International Journal of Hydrogen Energy 34
(2009) 7823–7834.
[10] Xiumin Yu, Yaodong Du, Ping Sun, Lin Liu, Haiming Wu, Xiongyinan Zuo. Effects of hydrogen direct
injection strategyon characteristics of lean-burn hydrogen-gasoline engines. Fuel 208 (2017) 602-611.
[11] Elna J.K. Nilsson, Astrid van Sprang, Jenny Larfeldt, Alexander A. Konnov. The comparative and
combined effects of hydrogen addition on the laminar burning velocities of methane and its blends with
ethane and propane. Fuel 189 (2017) 369–376.

[12] Stephen R. Turns. An introduction to combustion: concepts and applications. 2nd-Ed. McGraw-Hill,
ISBN 0-07-230096-5. 2000.
[13] Irvin Glassman, Richard A. Yetter. Combustion. Fourth edition. Ed. Elsevier, 2008. ISBN: 978-0-12-
088573-2.
[14] Yaodong Du, Xiumin Yu, Lin Liu, Runzeng Li, Xiongyinan Zuo, Yao Sun. Effect of addition of
hydrogen and exhaust gas recirculation on characteristics of hydrogen gasoline engine. International
Journal of Hydrogen Energy 42 (2017) 8288-8298.
[15] Verhelst S, Maesschalck P, Rombaut N, Sierens R. Increasing the power output of hydrogen internal
combustion engines by means of supercharging and exhaust gas recirculation. International Journal of
Hydrogen Energy 34 (2009) 4406–4412.

[16] Sarthak Nag, Priybrat Sharma, Arpan Gupta, Atul Dhar. Experimental study of engine performance
and emissions for hydrogen diesel dual fuel engine with exhaust gas recirculation. International Journal
of Hydrogen Energy 44 (2019) I2163-I2175.

6
[17] N. Saravanan, G. Nagarajan, K.M. Kalaiselvan, C. Dhanasekaran. An experimental investigation on
hydrogen as a dual fuel for diesel engine system with exhaust gas recirculation technique. Renewable
Energy 33 (2008) 422–427.
[18] Mohammad O. Hamdan, Mohamed Y.E. Selim, Salah-A.B. Al-Omari, Emad Elnajjar. Hydrogen
supplement co-combustion with diesel in compression ignition engine. Renewable Energy 82 (2015)
54-60.
[19] Teng Su, Changwei Ji, Shuofeng Wang, Lei Shi, Jinxin Yang, Xiaoyu Cong. Investigation on per-
formance of a hydrogen-gasoline rotary engine at part load and lean conditions. Applied Energy 205
(2017) 683–691.
[20] R.L. Woolley, D.L. Henriksen. Water induction in hydrogen-powered IC engines. International Jour-
nal of Hydrogen Energy (1977) 401-412.

[21] Vipin Dhyani, K.A. Subramanian. Control of backfire and NOx emission reduction in a hydrogen
fueled multi-cylinder spark ignition engine using cooled EGR and water injection strategies. Interna-
tional Journal of Hydrogen Energy 44 (2019) 6287-6298.
[22] Subramanian, J.M. Mallikarjuna, A. Ramesh. Effect of water injection and spark timing on the nitric
oxide emission and combustion parameters of a hydrogen fuelled spark ignition engine. International
Journal of Hydrogen Energy 32 (2007) 1159–1173.
[23] M. Senthil Kumar, A. Ramesh, B. Nagalingam. Use of hydrogen to enhance the performance of a
vegetable oil fuelled compression ignition engine. International Journal of Hydrogen Energy 28 (2003)
1143 – 1154.
[24] Heywood, John B. Internal Combustion Engine Fundamentals. McGraw-Hilll. 1988.