Abstract
This research focused on the light emission behaviour of the OH radical (characteristic spectrum of 306.4 nm) that plays a key role in combustion reactions, in order to investigate the influence of the residual gas on autoignition. An exhaust pressure control valve was installed in the exhaust manifold of the test engine in order to forcibly apply internal EGR (Exhaust Gear Recirculation) by raising the exhaust pressure. When a certain level of internal EGR is forcibly applied, the temperature of the unburned end gas is raised on account of heat transfer from the hot residual gas and also due to compression by piston motion. As a result, the unburned end gas becomes active and autoignition tends to occur.