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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.

Lean burn gas engines are expected to reduce NOx emission while improving engine performances such as output and thermal efficiency. Recently, an ignition method using a small quantity of diesel fuel (pilot fuel) as an ignition source for lean-burn gas engines has introduced further improvement of their performance. Generally, this method has been used for pre-chamber engines because it could not successfully lead to reduce NOx and Particulate emissions when adopted for open-chamber engines. However, the possibility of improvement of performances of open-chamber engines with this ignition method has also been expected(1). An experimental study was conducted to investigate the performance of an open-chamber gas engine with pilot fuel for ignition source. Experiments were conducted by using a single cylinder gas engine equipped with a common-rail injection system.

Research and development of an advanced air/fuel ratio control system for stationary lean-burn gas engines for co-generation have been carried out. The unique feature of this control system is that the air/fuel ratio is controlled by the feedback from the fluctuation of engine speed. Air/fuel ratio is controlled as high as possible to achieve low NOx emission while maintaining the fluctuation of engine speed within its maximum tolerance. Experiments have been conducted by using a test engine equipped with the new control system. Superior performance of the system has been demonstrated.