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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.

Degradation of the deNOx performance has been found in in-use heavy-duty vehicles with a urea-SCR system in Japan. The causes of the degradation were studied, and two major reasons are suggested here: HC poisoning and deactivation of pre-oxidation catalysts. Hydrocarbons that accumulated on the catalysts inhibited the catalysis. Although they were easily removed by a simple heat treatment, the treatment could only partially recover the original catalytic performance for the deNOx reaction. The unrecovered catalytic activity was found to result from the decrease in conversion of NO to NO2 on the pre-oxidation catalyst. The pre-oxidation catalyst was thus studied in detail by various techniques to reveal the causes of the degradation: Exhaust emission tests for in-use vehicles, effect of heat treatment on the urea-SCR systems, structural changes and chemical changes in active components during the deactivation were systematically investigated.

Fuel consumption rate (fuel economy) and exhaust gas emission regulations are being tightened around the world year by year. In Europe, the real driving emission (RDE) method for evaluating exhaust gas emitted from road-going vehicles was introduced after September 2017 for new types of light/medium-duty vehicles, in addition to the chassis dynamometer test using the worldwide harmonized light vehicles test procedure (WLTP). Further, the worldwide harmonized heavy-duty certification (WHDC) method was introduced after 2016 as an exhaust gas emission test method for heavy-duty vehicles. In each evaluation, the tests of vehicles and engines are initiated from cold states. Heavy-duty hybrid vehicles are evaluated using the vehicle simulation method. For example, the power characteristics of a engine model is obtained during engine warm operation. Therefore, various performances during cold start cannot be precisely evaluated by using simulator.