Search Results

In practical lean burn engines used to date, the use of a stratified air-fuel configuration, with a comparatively rich mixture in the vicinity of the spark plugs, has resulted in the stable combustion of an overall lean mixture. However, because a comparatively rich mixture is burned during the first half of combustion, NOx emissions are not reduced sufficiently. This research focused on a form of lean burn with homogeneous premixture that would be able to balance low NOx emissions with combustion controllability. It is widely known that homogeneous lean premixed gas has poor flame propagation characteristics. To determine the dominant cause of this, this study investigated the combustion properties of a single-cylinder engine while changing the compression ratio and intake temperature. As a result, the primary cause of combustion fluctuation, the abnormal cycle has a low TDC temperature compared to that of other cycles.

It is a well-known fact that the exhaust emission characteristics of hydrogen fueled engines are extremely good. The external mixture formation - a hydrogen fuel supply method - has the merit of practically zero NOx emission level in the lean mixture range with the excess air ratio λ set at 2.0 or greater as well as the merits of simple mechanism and easy operation. However, the practical use of such engines has been impeded partly due to the occurrence of backfire where the excess air ratio λ is 2 to 3. In order to allow the practical use of the hydrogen fueled engines with external mixture formation, it is vital to determine the causes of backfire and to establish proper countermeasures. It is found through a recent study conducted on the mechanism of backfire that the abnormal electric discharge in the intake stroke is one of the causes of backfire.