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In an attempt to grab potential issues with a hydrogen direct injection lean burn engine to have similar power output to a gasoline-fuelled engine, emission characteristics of a hydrogen engine was investigated. It is demonstrated that low NOx emission can be achievable without any catalytic converter. Two major issues, however, have been recognized, that is, combustion instability at low load conditions and too low temperature of exhaust gas to get enough boosting pressure. Hydrogen concentration heterogeneous of the mixture was focused in the CFD and visualization study. Hydrogen jet design of an injector could contribute to improvement of mixing.

The purpose of this study was to find compatible specifications both of emission reduction and high power output with good throttle response for a sports utility motorcycle. In the emission reduction challenge, we examined equipping the exhaust system with a catalytic converter to achieve sufficient emission reduction. The catalytic converter, however, caused a temperature rise in the exhaust system, which caused a pressure propagation change. Additional muffler design optimization effectively maintained high performance and acceleration. The exhaust valve device was also optimized for emission reduction and high power output over a wide engine speed range. The optimized control of the exhaust valve was beneficial to preventing short-circuit of fresh mixture gas and early activation of the catalyst. Such comprehensive specifications could satisfy the performance and driveability characteristics required for sports utility motorcycles.