An experimental investigation of hydrogen-enriched air induction in a diesel engine system

Diesel engines are the most trusted power sources in the transportation industry. They intake air and emit, among others, the pollutants _NOX${\mathrm{NO}}_X$ and particulate matter. Continuous efforts and tests have tried to reduce fuel consumption and exhaust emissions of internal combustion engines. Alternative fuels are key to meeting upcoming stringent emission norms. We study hydrogen as an air-enrichment medium with diesel as an ignition source in a stationary diesel engine system to improve engine performance and reduce emissions. Stationary engines can be operated with less fuel than neat diesel operations, resulting in lower smoke levels and particulate emissions. Hydrogen (_H2)$({\mathrm{H}}_2)$-enriched air systems in diesel engines enable the realization of higher brake thermal efficiency, resulting in lower specific energy consumption (SEC). _NOX${\mathrm{NO}}_X$ emissions are reduced from 2762 to 515 ppm with 90% hydrogen enrichment at 70% engine load. At full load, _NOX${\mathrm{NO}}_X$ emission marginally increases compared to diesel operation, while both smoke and particulate matter are reduced by about 50%. The brake thermal efficiency increases from 22.78% to 27.9% with 30% hydrogen enrichment. Thus, using hydrogen-enriched air in a diesel engine produces less pollution and better performance.     

Statistically discussing impacts of knock type on the heat release process in hydrogen-fueled Wankel rotary engine

Hydrogen-fueled internal combustion engine is proposed to resist the threat of global warming. Wankel rotary engine (WRE) has been proven to be an excellent hydrogen-fueled power device, which can overcome the shortcomings of hydrogen, such as poor power, serious backfire and large storage volume, to some extent when it is used as fuel in the internal combustion engine. However, due to its unique structure, WRE suffers from severe knock. Therefore, the goal of this work is to investigate the impacts of knock type on the heat release process in hydrogen-fueled WRE. This present work is conducted at 2000 r/min and wide-open throttle. The main results are as follows: In hydrogen-fueled WRE, the peak knock pressure of knock caused by rapid and unstable combustion of hydrogen is usually earlier than CA50 and that of knock caused by spontaneous combustion of end gas is usually later than CA50. The sequence between the crank angle of peak knock pressure and CA50 combined with knock intensity can be used to determine the knock type in hydrogen-fueled WRE. Besides, a means for knock detection is proposed according to the distribution of crank angle corresponding to peak knock pressure. In addition, the distribution of CA0-10, CA50 and CA10-90 of 1000 consecutive cycles under two kinds of knock in hydrogen-fueled WRE are discussed in detail, and regular conclusions are drawn. In particular, the limitation of CA50 as a metric for evaluating knock level is also demonstrated.     

Recent studies on hydrogen usage in Wankel SI engine

In this study, investigations on the hydrogen usage in spark ignition (SI) rotary engines are reviewed to assess trend researches. Many scientists conducted various studies to investigate performance, emission and combustion characteristics of hydrogen technology. The studies generally focused on their usage as an additive fuel. It can be seen that hydrogen usage in SI engine are very promising for their lower emissions, more efficient combustion, and higher power output. Nevertheless, hydrogen utilization may cause combustion problems such as back fire, auto and pre-ignition. Moreover, because of their small molecular structure hydrogen storage is another issue. Especially, hydrogen blending is a particular solution and this makes hydrogen gas tolerable for storage and transporting problem. In the recent studies, hydrogen usage in rotary engine is found well suited and feasible by scientists. Combustion difficulties caused by long and narrow shaped combustion chamber and long quenching distance of this type of engine can be solved by hydrogen addition. However, absence of a light, safe and low cost storage technology are still bottlenecks for their usage and waiting for solution.     

Improving the combustion performance of a gasoline rotary engine by hydrogen enrichment at various conditions

The combustion process within the cylinder directly influences the thermal efficiency and performance of the engines. As for the rotary engine, the long-narrow combustion chamber prevents the mixture from fully burning, which worsens the performance of the rotary engine. As a fuel with excellent properties, hydrogen can improve the combustion of the original engine. In this paper, improvements in combustion of a gasoline rotary engine by hydrogen supplement under different operating conditions were experimentally investigated. The experiment was conducted on a modified hydrogen-gasoline dual-fuel rotary engine equipped with an electronically-controlled fuel injection system. An electronic control module was specially made to command the fuel injection, excess air ratio and hydrogen volumetric fraction. Integral heat release fraction (IHRF) was employed to evaluate the combustion of the tested engine. The tested engine was first run at the idle speed of 2400 rpm and then operated at 4500 rpm to investigate the combustion of the hydrogen-blended gasoline rotary engine under different hydrogen volume fractions, excess air ratios and spark timings. The testing results demonstrated that the combustion of the gasoline rotary engine were all improved when the hydrogen was blended into the chamber under all tested conditions.     

An experimental analysis of hydrogen enrichment on combustion characteristics of a gasoline Wankel engine at full load and lean burn regime

In this paper, a gasoline Wankel engine was modified and equipped with self-developed hybrid electronic control unit to experimentally investigate the effect of hydrogen-enrichment level on combustion characteristics of a gasoline Wankel engine at wild open throttle position and lean burn regime. Testing were carried out under constant engine speed of 3000 rpm and the lean operating limit of the original gasoline engine. The spark timing was set at 15 °BTDC. The hydrogen energy fraction in the intake was gradually increased from 0% to 10%. The results showed that hydrogen enrichment was effective on improving the combustion process through the shortened of the flame development and the flame propagation periods, advancing the central heat release, increasing the HRRmax and reducing the cyclic variation proportionally to the amount of hydrogen added to the air fuel mixture. Furthermore, increasing hydrogen fraction in the intake improves the engine economy by reducing the cooling loss.     

Investigation of the gas injection rate shape on combustion,knock and emissions behavior of a rotary engine with hydrogen direct-injection enrichment

The application of hydrogen direct-injection enrichment improves the performance of gasoline Wankel rotary engine, and the hydrogen injection strategy has a significant impact on combustion, knock, and emissions. The Z160F Wankel rotary engine was used as the investigated compact engine, and the simulation model was developed using CONVERGE software. The combustion, knock and emissions characteristics of the engine were studied with the different mass flow of hydrogen injection, i.e., the trapezoid, wedge, slope, triangle and rectangle type of gas injection rate shape. In the numerical simulations, the in-cylinder pressure oscillations were monitored using monitoring points, and the knock index (KI) was used as an evaluation indicator. The study revealed that the gas injection rate shape significantly affected the mixture of hydrogen and air, thus impacting combustion, knock and emissions. When the injection rate shape was rectangle, the flame speed was faster, the peak pressure in the cylinder was higher, and the corresponding crank angle was earlier, which led to higher pressure oscillations in the cylinder and larger KI. Based on the rectangle injection rate shape, the KI decreased by 75.81%, 33.47%, 26.46% and 76.58% for trapezoid, wedge, slope, and triangle, respectively, and the indicated mean effective pressure increased by 15.68%, 5.07%, 0.56% and 14.98%, respectively. Due to the small difference in maximum temperature, which resulted in very little variation in nitrogen oxides for each injection rate shape, the total hydrocarbon emissions of the trapezoid and triangle injection rate shape was high due to the delayed combustion phase. This paper provides a solution for direct hydrogen injection to improve the combustion, knock and emissions behavior of the rotary engine.     

Investigation on the cold start characteristics of a hydrogen-enriched methanol engine

This paper experimentally investigated the effect of hydrogen addition on the cold start performance of a methanol engine. The test was conducted on a modified four-cylinder gasoline engine. An electronically controlled hydrogen injection system was applied to realize the hydrogen port injection. The engine was started at an ambient temperature of 25 °C with two hydrogen flow rates of 0 and 189 dm³/s, respectively. The results demonstrated that hydrogen addition availed elevating the peak engine speed and cylinder pressure during the cold start. Both flame development and propagation periods are shortened after the hydrogen addition. When the hydrogen volume flow rate was raised from 0 to 189 dm³/s, HC, CO and total number of particulate emissions within 19 s from the onset of cold start were reduced by 68.7%, 75.2% and 72.4%, respectively. However, because of the enhanced in-cylinder temperature, NO_x emissions were increased after the addition of hydrogen.     

Improving the performance of a gasoline engine with the addition of hydrogen-oxygen mixtures

The limited fossil fuel reserves and severe environmental pollution have pushed studies on improving the engine performance. This paper investigated the effect of hydrogen-oxygen blends (hydroxygen) addition on the performance of a spark-ignited (SI) gasoline engine. The test was performed on a modified SI engine equipped with a hydrogen and oxygen injection system. A hybrid electronic control unit was adopted to govern the opening and closing of hydrogen, oxygen and gasoline injectors. The standard hydroxygen with a fixed hydrogen-to-oxygen mole fraction of 2:1 was applied in the experiments. Three standard hydroxygen volume fractions in the total intake gas of 0%, 2% and 4% were adopted. For a given hydroxygen blending level, the gasoline injection duration was adjusted to enable the excess air ratio of the fuel-air mixtures to increase from 1.00 to the engine lean burn limit. Besides, to compare the effects of hydroxygen and hydrogen additions on the performance of a gasoline engine, a hydrogen-enriched gasoline engine was also run at the same testing conditions. The test results showed that the hydroxygen-blended gasoline engine produced higher thermal efficiency and brake mean effective pressure than both of the original and hydrogen-blended gasoline engines at lean conditions. The engine cyclic variation was eased and the engine lean burn limit was extended after the standard hydroxygen addition. The standard hydroxygen enrichment contributed to the decreased HC and CO emissions. CO from the standard hydroxygen-enriched gasoline engine is also lower than that from the hydrogen-enriched gasoline engine. But NOx emissions were increased after the hydroxygen addition.     

Reducing the idle speed of a spark-ignited gasoline engine with hydrogen addition

Reducing idle speed is an effective way for decreasing engine idle fuel consumption. Unfortunately, due to the increased residual dilution and dropped combustion temperature, spark-ignited (SI) gasoline engines are prone to suffer high cyclic variation and even stall at low idle speeds. This paper investigated the effect of hydrogen addition on the performance of an SI gasoline engine at reduced idle speeds of 600, 700 and 800 rpm. The test results shows that cyclic variation was raised with the decrease of idle speed but reduced obviously with the increase of hydrogen energy fraction (βH₂)$\left({\text{β}}_{{\text{H}}_2}\right)$. Decreasing idle speed and adding hydrogen were effective for reducing engine idle fuel consumption. The total fuel energy flow rate was effectively dropped from 30.8 MJ/h at 800 rpm and βH₂${\text{β}}_{{\text{H}}_2}$ = 0% to 17.6 MJ/h at 600 rpm and βH₂${\text{β}}_{{\text{H}}_2}$ = 19.9%. Because of the dropped fuel energy flow rate causing the reduced combustion temperature, both cooling and exhaust losses were markedly reduced after decreasing idle speed and adding hydrogen. HC and CO emissions were dropped with the increase of βH₂${\text{β}}_{{\text{H}}_2}$, but increased after reducing idle speed. However, NOx emissions were decreased after reducing idle speed and adding hydrogen, due to the dropped peak cylinder temperature.     

Efficiency comparison between hydrogen and gasoline,on a bi-fuel hydrogen/gasoline engine

The combustion characteristics of hydrogen compared to gasoline offer the potential of an increased engine efficiency, especially at part load. Here, results are presented of the brake thermal efficiency of a bi-fuel hydrogen/gasoline engine, at several engine speeds and loads. Results on hydrogen are compared to results on gasoline. Hydrogen offers the possibility of a more flexible load control strategy. Where possible, results are compared between the wide open throttle, lean burn strategy and the throttled stoichiometric strategy.     

Reducing the idle speed of a gasoline rotary engine with hydrogen addition

This paper presented an experimental study about the idle performance of a rotary engine fueled with hydrogen and gasoline blends. The idle speed was reduced from original 2400 to 2300 and 2200 rpm, and hydrogen energy percentage (β_H2) was varied from 0% to 35.0%. Test results showed that cyclic variation was raised with the decrease of idle speed whereas reduced with the increase of β_H2. Both decreasing idle speed and increasing β_H2 were effective on reducing engine fuel consumption. Total fuel energy flow rate was effectively dropped from 22.4 MJ/h under “2400 rpm and β_H2 = 0%” to 20.01 MJ/h under “2200 rpm and β_H2 = 35.0%”. Combustion duration was reduced through increasing β_H2. HC and CO emissions were dropped with the increase of β_H2, but increased after reducing idle speed. CO₂ emission was decreased after reducing idle speed and adding hydrogen.     

Investigation on combustion and emissions characteristics of a hydrogen-blended n-butanol rotary engine

In this paper, a rotary engine equipped with an n-butanol and hydrogen port-injection system was developed to investigate the combustion and emissions characteristics of a hydrogen-blended n-butanol rotary engine at part load and stoichiometric conditions. A self-developed hybrid electronic control unit was adopted to adjust the injection durations of n-butanol and hydrogen. The rotary engine was run under the conditions of 4000 rpm, a manifold absolute pressure of 35 kPa and a fixed spark timing of 45 °CA before the top dead center during the whole testing operation. The hydrogen volumetric fraction in the total intake was varied from 0% to 6.30%. The test results manifested that the brake thermal efficiency and chamber temperature were simultaneously increased with hydrogen addition. The hydrogen supplement obviously shortened flame development and propagation periods. Both chamber pressure integral heat release fraction versus crank angle were increased when the hydrogen fraction was enhanced. HC emissions were reduced by 54.5% when hydrogen volume fraction was raised from 0% to 6.30%, CO and CO₂ emissions were also reduced after increasing hydrogen blending fraction. NOx emissions were mildly elevated due to the improved chamber temperature.     

Effect of hydrogen addition on the idle performance of a spark ignited gasoline engine at stoichiometric condition

With regard to the improvement of efficiency, combustion stability, and emissions in a gasoline engine at idle condition, an experimental study aimed at improving engine idle performance through hydrogen addition was carried out on a 4-cylinder gasoline-fueled spark ignited (SI) engine. The engine was modified to be fueled with the mixture of gasoline and hydrogen injected into the intake ports simultaneously. A self-developed electronic control unit (DECU) was dedicatedly used to control the injection timings and injection durations of gasoline and hydrogen. Other parameters, such as spark timing and idle valve opening, were controlled by the original engine electronic control unit (OECU). Various hydrogen enrichment levels were selected to investigate the effect of hydrogen addition on engine speed fluctuation, thermal efficiency, combustion characteristics, cyclic variation and emissions under idle and stoichiometric conditions. The experimental results showed that thermal efficiency, combustion performance, NO_x emissions are improved with the increase of hydrogen addition level. The HC and CO emissions first decrease with the increasing hydrogen enrichment level, but when hydrogen energy fraction exceeds 14.44%, it begins to increase again at idle and stoichiometric conditions.     

Idle performance of a hydrogen/gasoline rotary engine at lean condition

Because of the limit of properties of gasoline and irregular design of chamber, the pure gasoline rotary engine generally encounters partial burning, increased noxious emissions or even misfire at lean conditions. This situation could be deteriorated at idle because of the high variation in the intake charge and low combustion temperature. Hydrogen addition is proved to remit the deterioration of performance of sparked-ignited (SI) engines at idle and lean conditions. This paper conducted an experiment on a modified rotary engine equipped with gasoline and hydrogen port-injection systems to explore the performance of a hydrogen–gasoline rotary engine (HGRE) at idle and lean conditions. An electronic management unit (EMU) was invented to manage spark and fuel injection. Excess air ratio (λ) and hydrogen volumetric fraction in the total intake (${\alpha }_{{\text{H}}_2}$) were also governed through the EMU. For this study, the HGRE was operating at idle and ${\alpha }_{{\text{H}}_2}$ was kept at 0% and 3%, respectively. For a specific ${\alpha }_{{\text{H}}_2}$, gasoline flow rate was reduced to make the HGRE run at desired λ. Results indicated that engine fluctuation and fuel energy flow rate were both decreased after hydrogen addition. Combustion duration was cut down and central heat release point was advanced after hydrogen addition. Peak chamber temperature (T_max), pressure and heat release were enhanced after hydrogen blending. HC, CO and CO₂ emissions were simultaneously reduced because of hydrogen enrichment. Specifically, at λ = 1.00, HC, CO and CO₂ emissions were respectively reduced from 42,411 to 26,316 ppm, 1.86 to 0.78% and 9.96 to 8.58% when 3% hydrogen was added.     

Comparison of the performance of a spark-ignited gasoline engine blended with hydrogen and hydrogen–oxygen mixtures

This paper compared the effects of hydrogen and hydrogen–oxygen blends (hydroxygen) additions on the performance of a gasoline engine at 1400 rpm and a manifolds absolute pressure of 61.5 kPa. The tests were carried out on a 1.6 L gasoline engine equipped with a hydrogen and oxygen injection system. A hybrid electronic control unit was applied to adjust the hydrogen and hydroxygen volume fractions in the intake increasing from 0% to about 3% and keep the hydrogen-to-oxygen mole ratio at 2:1 in hydroxygen tests. For each testing condition, the gasoline flow rate was adjusted to maintain the mixture global excess air ratio at 1.00. The test results confirmed that engine fuel energy flow rate was decreased after hydrogen addition but increased with hydroxygen blending. When hydrogen or hydroxygen volume fraction in the intake was lower than 2%, the hydroxygen-blended gasoline engine produced a higher thermal efficiency than the hydrogen-blended gasoline engine. Both the additions of hydrogen and hydroxygen help reduce flame development and propagation periods of the gasoline engine. HC emissions were reduced whereas NOx emissions were raised with the increase of hydrogen and hydroxygen addition levels. CO was slightly increased after hydrogen blending, but reduced with hydroxygen addition.     

Reducing cyclic variation of a gasoline rotary engine by hydrogen addition under various operating conditions

In the present paper, the cyclic variations of a hydrogen-blended gasoline rotary engine operated under various conditions were experimentally investigated. The experiments were carried out on a modified hydrogen-gasoline dual-fuel rotary engine equipped with an electronically-controlled fuel injection system. An electronic control module was specially made to command the fuel injection, excess air ratio and hydrogen volumetric fraction. The tested engine was first run at idle condition with a speed of 2400 rpm and then operated at 4500 rpm to investigate the cyclic variations of a hydrogen-enriched gasoline rotary engine under different hydrogen volumetric percentages in the total intake, excess air ratios and spark timings. The experimental results demonstrated that the coefficient of variations (in peak pressure, engine speed, flame development period and flame propagation period) of the gasoline rotary engine were distinctly decreased with the increase of hydrogen volume fraction under all the tested conditions. In particular, at idle and stoichiometric conditions, the coefficient of variation in CA0-10 and CA10-90 were reduced from 9.25% to 5.01%, 15.40% to 8.70%, respectively.     

Effect of hydrogen addition on combustion and emissions performance of a spark ignition gasoline engine at lean conditions

Hydrogen has many excellent combustion properties that can be used for improving combustion and emissions performance of gasoline-fueled spark ignition (SI) engines. In this paper, an experimental study was carried out on a four-cylinder 1.6 L engine to explore the effect of hydrogen addition on enhancing the engine lean operating performance. The engine was modified to realize hydrogen port injection by installing four hydrogen injectors in the intake manifolds. The injection timings and durations of hydrogen and gasoline were governed by a self-developed electronic control unit (DECU) according to the commands from a calibration computer. The engine was run at 1400 rpm, a manifold absolute pressure (MAP) of 61.5 kPa and various excess air ratios. Two hydrogen volume fractions in the total intake of 3% and 6% were applied to check the effect of hydrogen addition fraction on engine combustion. The test results showed that brake thermal efficiency was improved and kept roughly constant in a wide range of excess air ratio after hydrogen addition, the maximum brake thermal efficiency was increased from 26.37% of the original engine to 31.56% of the engine with a 6% hydrogen blending level. However, brake mean effective pressure (Bmep) was decreased by hydrogen addition at stoichiometric conditions, but when the engine was further leaned out Bmep increased with the increase of hydrogen addition fraction. The flame development and propagation durations, cyclic variation, HC and CO₂ emissions were reduced with hydrogen addition. When excess air ratio was approaching stoichiometric conditions, CO emission tended to increase with the addition of hydrogen. However, when the engine was gradually leaned out, CO emission from the hydrogen-enriched engine was lower than the original one. NO_x emissions increased with the increase of hydrogen addition due to the raised cylinder temperature.     

Effects of hydrogen addition and cylinder cutoff on combustion and emissions performance of a spark-ignited gasoline engine under a low operating condition

Because of the low combustion temperature and high throttling loss, SI (spark-ignited) engines always encounter dropped performance at low load conditions. This paper experimentally investigated the co-effect of cylinder cutoff and hydrogen addition on improving the performance of a gasoline-fueled SI engine. The experiment was conducted on a modified four-cylinder SI engine equipped with an electronically controlled hydrogen injection system and a hybrid electronic control unit. The engine was run at 1400 rpm, 34.5 Nm and two cylinder cutoff modes in which one cylinder and two cylinders were closed, respectively. For each cylinder closing strategy, the hydrogen energy fraction in the total fuel (βH₂)$\left({\beta }_{{\text{H}}_2}\right)$ was increased from 0% to approximately 20%. The test results demonstrated that engine indicated thermal efficiency was effectively improved after cylinder cutoff and hydrogen addition, which rose from 34.6% of the original engine to 40.34% of the engine operating at two-cylinder cutoff mode and βH₂=20.41%${\beta }_{{\text{H}}_2}=20.41\%$. Flame development and propagation periods were shortened with the increase of the number of closed cylinders and hydrogen blending ratio. The total cooling loss for all working cylinders, and tailpipe HC (hydrocarbons), CO (carbon monoxide) and CO₂ (carbon dioxide) emissions were reduced whereas tailpipe NO_x (nitrogen oxide) emissions were increased after hydrogen addition and cylinder closing.     

Analysis of the particulate emissions and combustion performance of a direct injection spark ignition engine using hydrogen and gasoline mixtures

Three different fractions (2%, 5%, and 10% of stoichiometric, or 2.38%, 5.92%, and 11.73% by energy fraction) of hydrogen were aspirated into a gasoline direct injection engine under two different load conditions. The base fuel was 65% iso-octane, and 35% toluene by volume fraction. Ignition sweeps were conducted for each operation point. The pressure traces were recorded for further analysis, and the particulate emission size distributions were measured using a Cambustion DMS500. The results indicated a more stable and faster combustion as more hydrogen was blended. Meanwhile, a substantial reduction in particulate emissions was found at the low load condition (more than 95% reduction either in terms of number concentration or mass concentration when blending 10% hydrogen). Some variation in the results occurred at the high load condition, but the particulate emissions were reduced in most cases, especially for nucleation mode particulate matter. Retarding the ignition timing generally reduced the particulate emissions. An engine model was constructed using the Ricardo WAVE package to assist in understanding the data. The simulation reported a higher residual gas fraction at low load, which explained the higher level of cycle-by-cycle variation at the low load.     

Effect of hydrogen nanobubble addition on combustion characteristics of gasoline engine

Hydrogen is an attractive energy source for improving gasoline engine performance. In this paper, a new hydrogen nanobubble gasoline blend is introduced, and the influence of hydrogen nanobubble on the combustion characteristics of a gasoline engine is experimentally investigated. The test was performed at a constant engine speed of 2000 rpm, and engine load of 40, 60, and 80%. The air-to-fuel equivalence ratio (λ) was adjusted to the stoichiometric (λ = 1), for both gasoline, and the hydrogen nanobubble gasoline blend. The results show that the mean diameter and concentration of hydrogen nanobubble in the gasoline blend are 149 nm and about 11.35 × 10⁸ particles/ml, respectively. The engine test results show that the power of a gasoline engine with hydrogen nanobubble gasoline blend was improved to 4.0% (27.00 kW), in comparison with conventional gasoline (25.96 kW), at the engine load of 40%. Also, the brake specific fuel consumption (BSFC) was improved, from 291.10 g/kWh for the conventional gasoline, to 269.48 g/kWh for the hydrogen nanobubble gasoline blend, at the engine load of 40%.