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Technical Paper

Influence of Autoignition and Behavior of Pressure Wave on Knocking Intensity by using Multipoint Pressure Measurement and In-cylinder Visualization of the End-gas

In this study, the effect of autoignition behavior of unburned region on pressure wave formation and knock intensity were investigated. In the experiment, a single-cylinder gasoline engine capable of high-speed observation of the end gas was used. Visualization in the combustion chamber and light absorption spectroscopic measurement of the end gas were carried out, and the autoignition behavior of the unburned portion and the reaction history before autoignition were analyzed. By analyzing the multi-point pressure histories, the process of autoignition and pressure wave growth was analyzed. As a result, it was found that knocking intensity increases by autoignition and pressure wave interaction each other.
Technical Paper

Study of Knocking Intensity Determinant by High-Speed Observation of the End-Gas Autoignition Using Optically Accessible Engine

The purpose of this study was to investigate how autoignition leads to the occurrence of pressure oscillations. That was done on the basis of in-cylinder visualization and analysis of flame images captured with a high-speed camera using an optically accessible engine, in-cylinder pressure measurement and measurement of light emission from formaldehyde (HCHO). The results revealed that knocking intensity tended to be stronger with a faster localized growth speed of autoignition. An investigation was also made of the effect of exhaust gas recirculation (EGR) as a means of reducing knocking intensity. The results showed that the application of EGR advanced the ignition timing, thereby reducing knocking intensity under the conditions where knocking occurred.
Journal Article

Analysis of Interaction between Autoignition and Strong Pressure Wave Formation during Knock in a Supercharged SI Engine Based on High Speed Photography of the End Gas

Engine knock is the one of the main issues to be addressed in developing high-efficiency spark-ignition (SI) engines. In order to improve the thermal efficiency of SI engines, it is necessary to develop effective means of suppressing knock. For that purpose, it is necessary to clarify the mechanism generating pressure waves in the end-gas region. This study examined the mechanism producing pressure waves in the end-gas autoignition process during SI engine knock by using an optically accessible engine. Occurrence of local autoignition and its development process to the generation of pressures waves were analyzed under several levels of knock intensity. The results made the following points clear. It was observed that end-gas autoignition seemingly progressed in a manner resembling propagation due to the temperature distribution that naturally formed in the combustion chamber. Stronger knock tended to occur as the apparent propagation speed of autoignition increased.