Effects of direct-injected hydrogen addition on methane combustion performance in an optical SI engine with high compression-ratio

Natural gas is one of the most potential alternative fuel of clean combustion and anti-knocking property. However, slow-burning rate and obvious cyclic variations have become the major concerns for modern gas engines. Based on a high compression-ratio, optically accessible, single-cylinder spark-ignition engine, fundamental experiments were conducted to investigate the role of direct-injected hydrogen under from stoichiometric to lean combustion conditions. Synchronization measurement of in-cylinder pressure and optical flame imaging was conducted to analyze cycle-to-cycle variations, indicated thermal efficiency, and flame evolution. The results show that as the addition of direct-injected hydrogen, the cycle-to-cycle variations decrease and indicated thermal efficiency increases, with advanced combustion phase and shortened combustion duration. The combustion imaging indicates that the significant positive influence is from the direct-injected hydrogen, which promotes initial flame kernel formation and early flame propagation. Further, an empirical criterion for mass fraction burned combined with optical data was adopted for quantification and analysis of early flame evolution. It shows that the addition of direct-injected hydrogen mainly promotes the early-stage flame propagation, manifesting increased the burning rate and thermal efficiency. The results shall give useful information in the application of direct-injected hydrogen to improve natural gas engine performance while increasing flame speed and controlling cyclic variations.     

Effect of hydrogen direct injection on natural gas/hydrogen engine performance under high compression-ratio conditions

In traffic transportation, the use of low-carbon fuels is the key to being carbon-neutral. Hydrogen-enhanced natural gas gets more and more attention, but practical engines fueled with it often suffer from low engine power output. In this study, the inner mechanism of hydrogen direct injection on methane combustion was optically studied based on a dual-fuel supply system. Simultaneous pressure acquisition and high-speed direct photography were used to analyze engine performance and flame characteristics. The results show that lean combustion can improve methane engine's thermal efficiency, but is limited by cyclic variations under high excess air coefficient conditions. Hydrogen addition mainly acts as an ignition promoter for methane lean combustion, as a result, the lean combustion limit and thermal efficiency can be improved. As for hydrogen injection timing, late injection can increase the in-cylinder turbulence intensity but also the inhomogeneity, so a suitable injection timing is needed for improving the engine's performance. Besides, late hydrogen injection is more effective under lean conditions because of the reduced mixture inhomogeneity. The current study shall give some insights into the controlling strategies for natural gas/hydrogen engines.     

湍流射流点火对天然气发动机燃烧特性影响的试验研究

湍流射流点火（Turbulent Jet Ignition,TJI）是一种有效的燃烧增强技术,可提供更高的点火能量,使发动机稳定着火,且可以提高燃烧压力和燃烧速率,缩短燃烧持续期,是实现发动机稀薄燃烧的有效手段。基于一台带有预燃室的点燃式单缸试验机,开展了TJI模式下天然气发动机性能的试验研究。首先,研究了不同过量空气系数下TJI对天然气发动机动力性能、排放性能及燃烧特性的影响,并与火花塞点火（Spark Ignition,SI）模式进行对比;其次,在稀燃条件下分别探究了进气增压和预燃室喷氢对天然气发动机动力性、经济性及燃烧过程的优化作用。结果表明：TJI的使用可有效拓展天然气发动机的稀燃极限,且燃烧滞燃期和燃烧持续期均更短,放热率更高;过量空气系数1.5为甲烷TJI最佳稀燃工况,此时燃油消耗率最低,且可实现氮氧化物近零排放;此外,采用进气增压的方式可以提高TJI发动机在高负荷下的经济性;TJI模式下,相较于预燃室喷甲烷,预燃室喷氢气可进一步缩短滞燃期和燃烧持续期,提高放热率,达到提升TJI性能的效果。     

Progress in hydrogen enriched hydrocarbons combustion and engine applications

The paper summarized the work on hydrogen enriched hydrocarbons combustion and its application in engines. The progress and understanding on laminar burning velocity, flame instability, flame structure flame and chemical kinetics were presented. Based on fundamental combustion, both homogeneous spark-ignition engine and direct-injection spark-ignition engine fueled with natural gas-hydrogen blends were conducted and the technical route of natural gas-hydrogen combined with exhaust gas recirculation was proposed which experimentally demonstrated benefits on both thermal efficiency improvement and emissions reduction.     

Combustion and emissions performance of a hybrid hydrogen–gasoline engine at idle and lean conditions

Due to the narrow flammability of gasoline, pure gasoline-fueled spark-ignited (SI) engines always encounter partial burning or even misfire at lean conditions. Gasoline engines tend to suffer poor combustion and expel large emissions at idle conditions because of the high variation in the intake charge and low combustion temperature. Comparatively, hybrid hydrogen engines (HHE) fueled with the mixtures of hydrocarbon fuels and hydrogen seem to achieve lower emissions and gain higher thermal efficiencies than the original hydrocarbon-fueled engines due to the wide flammability and high flame speed of hydrogen. Since a HHE only requires a small amount of hydrogen, it also removes concerns about the high production and storage costs of hydrogen. This paper introduced an experiment conducted on a four-cylinder SI gasoline engine equipped with a hydrogen port-injection system to explore the performance of a hybrid hydrogen–gasoline engine (HHGE) at idle and lean conditions. The injection timings and durations of hydrogen and gasoline were governed by a hybrid electronic control unit (HECU) developed by the authors, which can be adjusted freely according to the commands from a calibration computer. During the test, hydrogen flow rate was varied to ensure that hydrogen volume fraction in the intake was constantly kept at 3%. For the specified hydrogen addition level, gasoline flow rate was reduced to make the engine operate at idle and lean conditions with various excess air ratios. The test results demonstrated that cyclic variations in engine idle speed and indicated mean effective pressure were eased with hydrogen enrichment. The indicated thermal efficiency was obviously higher for the HHGE than that for the original gasoline engine at idle and lean conditions. The indicated thermal efficiency at an excess air ratio of 1.37 was increased from 13.81% for the original gasoline engine to 20.20% for the HHGE with a 3% hydrogen blending level. Flame development and propagation periods were also evidently shortened after hydrogen blending. Moreover, HC, CO and NOx emissions were all improved after hydrogen enrichment at idle and lean conditions. Therefore, the HHE methodology is an effective and promising way for improving engine idle performance at lean conditions.     

Improvement of thermal efficiency and reduction of NOx emissions by burning a controlled jet plume in high-pressure direct-injection hydrogen engines

A new combustion process called the Plume Ignition Combustion Concept (PCC), in which the plume tail of the hydrogen jet is spark-ignited immediately after the completion of fuel injection to accomplish combustion of a rich mixture has been proposed by the authors. This PCC combustion process markedly reduces nitrogen oxides (NOx) emissions in the high-output region while maintaining high levels of thermal efficiency and power. On the other hand, as burning lean mixture of fuel and air is the conventional way to improve thermal efficiency and reduce NOx, a high λ premixed mixture of hydrogen and air formed by injecting hydrogen in the early stage of the compression stroke has been used in direct-injection hydrogen engines. It was recently reported, however, that this mixture condition does not always offer expected improved thermal efficiency under even lean mixture conditions by increasing unburned hydrogen emissions caused by incomplete flame propagation in the non-uniform and extremely lean portion of the mixture. In this study, the effect of retarding the injection timing to late in the compression stroke but slightly advanced from original PCC was examined as a way of reducing unburned hydrogen emissions and improving thermal efficiency. These effects result from a centroidal axially stratified mixture that positions a fairly rich charge near the spark plug. This stratified mixture is presumably effective in reducing incomplete flame propagation thought to be the cause of unburned hydrogen emissions and also promoting increasing burning velocity of the mixture that improve thermal efficiency. Finally, this research is characterized by measuring the hydrogen fuel concentration at the point and the time of spark ignition quantitatively by spark-induced breakdown spectroscopy in order to identify the changes in mixture ratio mentioned above caused by the parameters involved.     

Direct injection of hydrogen main fuel and diesel pilot fuel in a retrofitted single-cylinder compression ignition engine

Up to 90% hydrogen energy fraction was achieved in a hydrogen diesel dual-fuel direct injection (H2DDI) light-duty single-cylinder compression ignition engine. An automotive-size inline single-cylinder diesel engine was modified to install an additional hydrogen direct injector. The engine was operated at a constant speed of 2000 revolutions per minute and fixed combustion phasing of ?10 crank angle degrees before top dead centre (°CA bTDC) while evaluating the power output, efficiency, combustion and engine-out emissions. A parametric study was conducted at an intermediate load with 20–90% hydrogen energy fraction and 180-0 °CA bTDC injection timing. High indicated mean effective pressure (IMEP) of up to 943 kPa and 57.2% indicated efficiency was achieved at 90% hydrogen energy fraction, at the expense of NO_x emissions. The hydrogen injection timing directly controls the mixture condition and combustion mode. Early hydrogen injection timings exhibited premixed combustion behaviour while late injection timings produced mixing-controlled combustion, with an intermediate point reached at 40 °CA bTDC hydrogen injection timing. At 90% hydrogen energy fraction, the earlier injection timing leads to higher IMEP/efficiency but the NO_x increase is inevitable due to enhanced premixed combustion. To keep the NO_x increase minimal and achieve the same combustion phasing of a diesel baseline, the 40 °CA bTDC hydrogen injection timing shows the best performance at which 85.9% CO₂ reduction and 13.3% IMEP/efficiency increase are achieved.     

Improvement on the combustion of a hydrogen fueled engine

More and more attention is being paid to hydrogen as a future fuel. Hydrogen has the intrinsic physical—chemical characteristics of wide ignition limits, high flame propagation rate and low ignition energy. By using hydrogen, the combustion process in engines can be improved and the rapid burning of the lean mixture in them can be realized, thus leading to improvements both in fuel economy and in emission characteristics of the original engine. The experimental results of burning hydrogen fuel, hydrogen-gasoline mixed fuel and hydrogen-diesel oil mixed fuel in the engine to improve the combustion processes are discussed.     

Operation principles for hydrogen spark ignited direct injection engines for passenger car applications

The sustainable reduction of greenhouse gas emissions from road transport requires solutions to achieve net-zero carbon dioxide emissions. Therefore, in addition to vehicles with electrified powertrains, such as those implemented in battery electric of fuel cell vehicles, internal combustion engines fueled with e-fuels or biofuels are also under discussion. An e-fuel that has come into focus recently, is hydrogen due to its potential to achieve zero tank-to-wheel and well-to-wheel carbon dioxide emissions when the electrolysis is powered by electricity from renewable sources. Due to the high laminar burning velocity, hydrogen has the potential for engine operation with high cylinder charge dilution by e.g. external exhaust gas recirculation or enleanment, resulting in increased efficiency. On the other hand, the high burning velocity and high adiabatic flame temperatures pose a challenge for engine cooling due to increased heat losses compared to conventional fuels. To further evaluate the use of hydrogen for small passenger car engines, a series production 1 L 3 cylinder gasoline engine provided by Ford Werke GmbH was modified for hydrogen direct injection. The engine was equipped with a high pressure external exhaust gas recirculation system to investigate charge dilution at stoichiometric operation. Due to limitations of the turbocharging system, very lean operation, which can achieve nitrogen oxides raw emissions below 10 ppm, was limited to part load operation below BMEP = 8 bar. Thus, a reduction of the nitrogen oxides emission level at high loads compared to stoichiometric operation was not possible. At stoichiometric operation with external exhaust gas recirculation engine efficiency can be increased significantly. The comparison of stoichiometric hydrogen and gasoline operation shows a reduced indicated efficiency with hydrogen with significant faster combustion of hydrogen at comparable centers of combustion. However, higher boost pressures would allow to achieve even higher indicated efficiencies by charge dilution compared to gasoline engine operation.     

Effect of ignition timing and hydrogen fraction on combustion and emission characteristics of natural gas direct-injection engine

An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO₂ concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO₂ do not vary much with hydrogen addition. The exhaust NO_x increases with the advancing of ignition timing and the behavior tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction is over 10%.     

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.     

Study on combustion behaviors and cycle-by-cycle variations in a turbocharged lean burn natural gas S.I. engine with hydrogen enrichment

Lean burn is widely accepted as an effective approach to simultaneously improve spark-ignition engine's thermal efficiency and decrease exhaust emissions. But although lean burn has a lot of advantages it is also associated with several difficulties including slower flame propagation speed and increased cycle-by-cycle variations. Hydrogen addition is thought to be an ideal approach to tackle these problems. This paper presents an experimental work aimed at investigating the effects of hydrogen addition on the combustion behaviors and cycle-by-cycle variations in a turbocharged lean burn natural gas SI engine. The experiments were conducted over a wide range of hydrogen enhancement levels, equivalence ratios, spark timings, manifold absolute pressures and engine speeds.     

预燃室式天然气掺氢发动机燃烧及排放模拟

为探索掺氢对预燃室式大功率中速天然气发动机燃烧和排放的影响,采用计算流体动力学耦合化学动力学方法,在一台6ACD320型天然气发动机上,对氢气体积分数为0～ 30％的天然气-氢气混合燃料的燃烧过程进行了数值模拟.结果表明:在天然气中掺氢促使缸内产生了更多的0、OH等活性自由基,从而加速了缸内火焰传播,发动机的指示燃气消...     

Experimental study on combustion and emissions performance of a hybrid hydrogen–gasoline engine at lean burn limits

Lean combustion is an effective way for improving the spark-ignited (SI) engine performance. Unfortunately, due to the narrow flammability of gasoline, the pure gasoline-fueled engines sometimes suffer partial burning or misfire at very lean conditions. Hydrogen has many excellent combustion properties that can be used to extend the gasoline engine lean burn limit and improve the gasoline engine performance at lean conditions. In this paper, a 1.6 L port fuel injection gasoline engine was modified to be a hybrid hydrogen–gasoline engine (HHGE) fueled with the hydrogen–gasoline mixture by mounting an electronically controlled hydrogen injection system on the intake manifolds while keeping the original gasoline injection system unchanged. A self-developed hybrid electronic control unit (HECU) was used to flexibly adjust injection timings and durations of gasoline and hydrogen. Engine tests were conducted at 1400 rpm and a manifolds absolute pressure (MAP) of 61.5 kPa to investigate the performance of an HHGE at lean burn limits. Three hydrogen volume fractions in the total intake gas of 1%, 3% and 4.5% were adopted. For a specified hydrogen volume fraction, the gasoline flow rate was gradually reduced until the engine reached the lean burn limit at which the coefficient of variation in indicated mean effective pressure (COVimep) was 10%. The test results showed that COVimep at the same excess air ratio was obviously reduced with the increase of hydrogen enrichment level. The excess air ratio at the lean burn limit was extended from 1.45 of the original engine to 2.55 of the 4.5% HHGE. The engine brake thermal efficiency, CO, HC and NO_x emissions at lean burn limits were also improved for the HHGE.     

Effect of ignition timing and hydrogen fraction on combustion and emission characteristics of natural gas direct-injection engine

An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO₂ concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO₂ do not vary much with hydrogen addition. The exhaust NOx increases with the advancing of ignition timing and the behavior tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction is over 10%. __________ Translated from Transactions of CSICE, 2006, 24(5): 394–401 [译自:内燃机学报]     

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.     

Combustion and emission characteristics of a spray guided direct-injection spark-ignition engine fueled with natural gas-hydrogen blends

Combustion and emission characteristics of a spray guided direct-injection spark-ignition engine fueled with natural gas-hydrogen blends were investigated. Results show that the brake thermal efficiency increases with the increase of hydrogen fraction and it shows an increasing and then decreasing trend with advancing fuel-injection timing. For later injection timings, the beginning of heat release is advanced with increasing hydrogen fraction, while the beginning of heat release is advanced and then retarded with the increase of hydrogen fraction at earlier injection timings. The flame development duration, rapid combustion duration and total combustion duration decrease with increasing hydrogen fraction. Maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate show an increasing and then decreasing trend with the increase of hydrogen fraction. Brake NOx emission is increased and then decreased, while brake HC, CO and CO₂ emissions decrease with the increase of hydrogen fraction.     

Improving thermal efficiency by reducing cooling losses in hydrogen combustion engines

Hydrogen can be readily used in spark ignition engines as a clean alternative to fossil fuels. However, the higher burning velocity and shorter quenching distance of hydrogen compared with hydrocarbons cause a larger heat transfer from the burning gas to the combustion chamber walls. Because of this cooling loss, the thermal efficiency of hydrogen-fueled engines is sometimes lower than that of conventionally fueled engines. Therefore, reducing the cooling loss is a crucial element in improving the thermal efficiency of hydrogen combustion engines. Previous research by the author and others has proposed the direct injection stratified charge as a technique for reducing the cooling loss in hydrogen combustion and shown its effect in reducing cooling loss through experiments in a constant volume combustion vessel. However, it is known that a reduction in cooling loss does not always improve thermal efficiency due to a simultaneous increase in the exhaust heat loss. This paper explains the relation between cooling loss reduction and thermal efficiency improvements by the direct injection stratified charge in hydrogen combustion engines.     

Research on the hydrogen injection strategy of a turbulent jet ignition (TJI) rotary engine fueled with natural gas/hydrogen blends

Natural gas/hydrogen blends (NGHB) fuel is considered as one of the ideal alternative fuels for the rotary engine (RE), which can effectively reduce the carbon emissions of RE. Additionally, applying turbulent jet ignition (TJI) mode to RE can significantly increase the combustion rate. The purpose of this study is to numerically investigate the influence of hydrogen injection position (HIP) and hydrogen injection timing (HIT) on the in-cylinder mixture formation, flame propagation and NOx emission of a TJI hydrogen direct injection plus natural gas port injection RE. Therefore, in this paper, a test bench and a 3D dynamic simulation model of the turbulent jet ignition rotary engine (TJI-RE) fueled with NGHB were respectively established. Moreover, the reliability of the 3D simulation model was verified by experimental data. Furthermore, based on the established 3D model, the fuel distribution and flame propagation in the cylinder under different HIPs and HITs were calculated. The results indicated that the HIP and HIT could change the hydrogen distribution by altering the impact position, impact angle, and the strength of vortexes in the cylinder. To improve the flame propagation speed, more hydrogen should be distributed in the pre-chamber. Additionally, a higher concentration of hydrogen in the cylinder should be maintained above the jet orifice. This was not only conducive to the rapid formation of the initial fire core in the pre-chamber, but also significantly improved the combustion rate of the in-cylinder mixture. Compared with other hydrogen injection strategies, the hydrogen injection strategy by using the HIP at the middle of the cylinder block and the HIT of 190^oCA(BTDC) could obtained the highest peak value of in-cylinder pressure and the highest NOx emission.     

The utilization of hydrogen in hydrogen/diesel dual fuel engine

A hydrogen fueled internal combustion engine has great advantages on exhaust emissions including carbon dioxide (CO₂) emission in comparison with a conventional engine fueling fossil fuel. In addition, if it is compared with a hydrogen fuel cell, the hydrogen engine has some advantages on price, power density, and required purity of hydrogen. Therefore, they expect that hydrogen will be utilized for several applications, especially for a combined heat and power (CHP) system which currently uses diesel or natural gas as a fuel.A final goal of this study is to develop combustion technologies of hydrogen in an internal combustion engine with high efficiency and clean emission. This study especially focuses on a diesel dual fuel (DDF) combustion technology. The DDF combustion technology uses two different fuels. One of them is diesel fuel, and the other one is hydrogen in this study. Because the DDF engine is not customized for hydrogen which has significant flammability, it is concerned that serious problems occur in the hydrogen DDF engine such as abnormal combustion, worse emission and thermal efficiency.In this study, a single cylinder diesel engine is used with gas injectors at an intake port to evaluate performance swung the hydrogen DDF engine with changing conditions of amount of hydrogen injected, engine speed, and engine loads. The engine experiments show that the hydrogen DDF operation could achieve higher thermal efficiency than a conventional diesel operation at relatively high engine load conditions. However, it is also shown that pre-ignition with relatively high input energy fraction of hydrogen occurred before diesel fuel injection and its ignition. Therefore, such abnormal combustion limited amount of hydrogen injected. Fire-deck temperature was measured to investigate causal relationship between fire-deck temperature and occurrence of pre-ignition with changing operative conditions of the hydrogen DDF engine.