To understand the occurrence of backfire in hydrogen fueled engines using an external (inducted) fuel supply, a fundamental study was completed using a modified experimental engine. A relation was found between the crevice volume in the combustion chamber and the occurrence of backfire. The results showed that the crevice around the spark plug electrode was not a major cause of backfire, but the combustion state of the mixture in the piston top land crevice, second land, and ring groove did have a direct affect on backfire occurrence. By increasing the top land crevice volume and the amount of blow-by gas, the equivalence ratio before backfire occurred was extended.

To achieve high power and high efficiency in a hydrogen fueled engine for all load conditions, the dual injection hydrogen fueled engine that can derive the advantage of both high efficiency from external mixture hydrogen engine and high power from direct cylinder injection hydrogen engine was introduced. For verifying the feasibility of the above engine, the high pressure hydrogen injector of ball valve type actuated by a solenoid was developed. A systematic experimental study was conducted by using a modified single cylinder dual injection hydrogen fueled engine which was equipped with both an intake injector and a high pressure in-cylinder injector. The results showed that (1) the developed high pressure hydrogen injector with a solenoid actuator had good gas-tightness and fine control performance, (2) the transient injection region, in which injection methods are changed from external fuel injection to direct-cylinder injection, ranged from 59 to 74 percent of the load, and (3) the dual injection hydrogen fueled engine had the maximum torque of direct-cylinder fuel injection and the maximum efficiency of external fuel mixture hydrogen engines.

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To achieve high power and high efficiency in a hydrogen-fueled engine for all load conditions, the dual-injection hydrogen-fueled engine, which can derive the advantages of both high efficiency from external mixture hydrogen engine and high power from direct cylinder injection was developed. For verifying the feasibility of the above engine, a high-pressure hydrogen injector of ball-valve type and actuated by a solenoid was developed. A systematic experimental study was conducted by using a modified single-cylinder dual-injection hydrogen-fueled engine, which was equipped with both an intake injector and high-pressure in-cylinder injector. The results showed that (i) the developed high pressure hydrogen injector with a solenoid actuator had good gas tightness and fine control performance, (ii) the transient injection region, in which injection methods are changed from external fuel injection to direct-cylinder injection, ranged from 59 to 74% of the load, and (iii) the dual-injection hydrogen-fueled engine had the maximum torque of direct-cylinder fuel injection and the maximum efficiency of external fuel mixture hydrogen engines.

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