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Hydrogen engines are required to provide high thermal efficiency and low nitrogen oxide (NOx) emissions. There are many possible combinations of injection pressure, injection timing, ignition timing, lambda and EGR rate that can be used in a direct-injection system for achieving such performance. In this study, several different combinations of injection and ignition timings were classified as possible combustion regimes, and experiments were conducted to make clear the differences in combustion conditions attributable to these timings. Lambda and the EGR rate were also evaluated for achieving the desired performance, and indicated thermal efficiency of over 45% was obtained at IMEP of 0.95 MPa. It was found that a hydrogen engine with a high-pressure direct-injection system has a high potential for improving thermal efficiency and reducing NOx emissions.

A natural gas direct injection test engine equipped with a newly developed natural gas injector was built. High total hydrocarbon (THC) emission at part-load and high NOx emission at high-load remain as problems for direct injection natural gas engines. THC reduction and combustion improvement by throttling and NOx reduction by EGR were investigated. The following results were obtained: (1) the combustion at light and medium load conditions is improved by throttling. It is possible to improve the thermal efficiency at light-load in spite of the pumping loss by throttling. THC emissions are greatly decreased in this condition; (2) a large NOx reduction can be obtained without combustion deterioration by appropriate EGR at high-load conditions; and (3) it is possible to decrease both THC and NOx emissions by both throttling and EGR at part-load conditions.

A new ignition-combustion concept named PCC (Plume Ignition Combustion Concept), which ignite rich mixture plume in the middle of injection period or right after injection of hydrogen is completed, is proposed by the authors in order to reduce NOx emissions in high engine load conditions with minimizing trade-offs on thermal efficiency. In this study fundamental requirements of hydrogen jet to optimize PCC are investigated by using single and multi-hole nozzle with a combination of high speed laser shadowgraphy to visualize propagating flame. As a result, it was infered that igniting the mixture plume in the middle of injection period with minimizing jet penetration to chamber wall is effective reducing NOx formation even further.

In recent years, attention has focused on smokeless, sulfur-free dimethyl ethyl (DME) as a clean fuel for heavy-duty diesel vehicles [1]. In this development, the DME engine applied for 20-ton GVW truck was developed under the auspices of the Ministry of Land, Infrastructure and Transport of Japan, the first known instance worldwide. With careful design of the fuel system considering DME's unique fuel characteristics and suitable combustion improvement, higher torque was obtained with DME, compared to diesel fueling. and also use of the proper EGR and catalyst, exhaust emissions levels were generally less than one-fourth of new long-term regulation value promulgated in 2005 Japan.

Exhaust gas recirculation (EGR) was applied in a spark-assisted, direct-injection (Dl) neat methanol engine for light duty vehicles. An experimental study has been carried out to analyse for major factors of EGR that influence in the reduction of NOx mass emission and improvement in brake thermal efficiency. EGR on the Dl methanol engine alters intake charge, especially increasing the concentrations of H2O and unburned methanol with rising intake charge temperature. The results of qualitative analyses show that this phenomenon suppresses rapid heat generation at the initial combustion stage, therefore lowering the combustion temperature in the cylinders and leading to a reduction in NOx production.

In this study, we investigated the combustion technology for the direct injection (DI) methanol engine for a heavy-duty vehicle that makes use of the fuel characteristics of methanol and achieves smokeless burning with high efficiency and low NOx emissions under the heavy load condition. A 3.3-liter 4-cylinder spark-assisted DI methanol engine was tested to investigate the combustion and NOx emission characteristics under the full load condition with supercharging and/or EGR. We believe that supercharging suppressed the stratified charge combustion, but accelerated the premixed combustion to increase the indicated mean effective pressure. Moreover, supercharging was helpful in carrying out EGR under the full load condition without deteriorating the thermal efficiency. Furthermore, heavy EGR during supercharging reduced the NOx emissions dramatically while maintaining the high thermal efficiency and controlling the unburned hydrocarbons emissions.

Recently there has been much interest in Dimethyl Ether (DME) as a new fuel for diesel cycle engines. DME combines the advantages of a high cetane number with soot-free combustion, which makes it eminently suitable for compression engines. According to the latest engine test results, however, DME engine energy consumption was inferior to a diesel engine's under a heavy load. DME probably requires strong air-fuel mixing and short fuel injection. Some tests have reported that DME engine performance almost equals a diesel engine's by injecting high rail pressure DME into standard or slightly modified diesel common rail injection equipment. The effect, however, of higher injection pressure on the rates of heat release and spray distribution is unclear. In this study the rail pressure levels examined included 20, 25, 30, and 35 MPa. The results obtained from a single cylinder heavy-duty engine test show that the rate of heat release increases during the premixed combustion phase.

The effects of methanol and EGR on HCCI combustion of dimethyl ether have been tested separately in a diesel engine. The engine was equipped with a common rail injection system which allowed for random injection of DME. The engine could therefore be operated either as a normal DI CI engine or, by advancing the injection timing 360 CAD, as an HCCI engine. The compression ratio of the engine was reduced to 14.5 by enlarging the piston bowls. The engine was operated in HCCI mode with DME at an equivalence ratio of 0.25. To retard the combustion timing, methanol was port fuel injected and the optimum quantity required was determined. The added methanol increased the BMEP by increasing the total heat release and retarding the combustion to after TDC. Engine knock was reduced with increasing quantities of methanol. The highest BMEP was achieved when the equivalence ratio of methanol was around 0.12 at 1000 RPM, and around 0.76 at 1800 RPM. EGR was also used to retarding the timing.

Direct injection natural gas engines need to produce in the mixing process between the fuel jet and the air in the cylinder a “stratified” fuel-air mixture, with an easily ignitable composition near the spark plug at the time of ignition. Stratified-charge engines have a tendency to produce high NOx emissions due to the high temperature of burning areas at the start of combustion since the fuel-air mixture is not uniform. Therefore, it is necessary to reduce NOx emissions from direct injection natural gas engines. The objective of this study is to investigate measures to reduce emissions, especially NOx emissions, from direct injection natural gas engines. A single cylinder test engine was equipped with a newly developed high-pressure electromagnetic injector and a spark plug.

The planned development of a hydrogen ICE system for trucks is one of the technological candidates for air pollution reduction and global warming prevention for the large-sized (heavy-duty) trucks supporting Japanese freightage. This project is the first to develop a DISI multi-cylinder hydrogen ICE system aimed at combining high power output and low NOx generation.