森吉 泰生

Experimental methods and numerical analysis were used to investigate the mechanism of high-speed knocking that occurs in small two-stroke engines. The multi-ion probe method was used in the experiments to visualize flame propagation in the cylinder. The flame was detected by 14 ion probes grounded in the end gas region. A histogram was made of the order in which flames were detected. The characteristics of combustion in the cylinder were clarified by comparing warming up and after warming up and by extracting the features of the cycle in which knocking occurred. As a result, regions of fast flame propagation and regions prone to auto-ignition were identified. In the numerical analysis, flow and residual gas distribution in the cylinder, flame propagation and self-ignition were visualized by 3D CFD using 1D CFD calculation results as boundary conditions and initial conditions. Flame propagation calculated by 3D CFD was found to be directional due to in-cylinder flow caused by scavenging flow. The calculated direction of flame spread was matched with the experimentally measured direction. It was also found that the first auto-ignition occurred in the high temperature region where the concentration of residual gas was high. Finally, numerical analysis was performed for the high compression ratio engine specifications. As a result, the mechanism of knocking was clarified as the first auto-ignition caused by the high-temperature residual gas, followed by the pressure wave inducing continuous auto-ignition. The flow formed during the scavenging process and the subsequent compression process determine the directionality of flame propagation and residual gas distribution at top dead center. Thus, the possibility of knocking avoidance by scavenging air shape and combustion chamber shape was suggested.

For the survival of internal combustion engines, the required research right now is for alternative fuels, including drop-ins. Certain types of alternative fuels have been estimated to confirm the superiority in thermal efficiency. In this study, using a single-cylinder engine, olefin and oxygenated fuels were evaluated as a drop-in fuel considering the fuel characteristic parameters. Furthermore, the effect of various additive fuels on combustion speed was expressed using universal characteristics parameters.

Liquid fuel attached to the wall surface of the intake port, the piston and the combustion chamber is one of the main causes of the unburned hydrocarbon emissions from a port fueled SI engine, especially during transient operations. To investigate the liquid fuel film formation process and fuel film behavior during transient operation is essential to reduce exhaust emissions in real driving operations, including cold start operations. Optical techniques have been often applied to measure the fuel film in conventional reports, however, it is difficult to apply those previous techniques to actual engines during transient operations. In this study, using MEMS technique, a novel capacitance sensor has been developed to detect liquid fuel film formation and evaporation processes in actual engines. A resistance temperature detector (RTD) was also constructed on the MEMS sensor with the capacitance sensor to measure the sensor surface temperature. The response and the sensitivity of the developed sensor were examined at the atmospheric conditions at first. As a result, it was found that though the sensor shows less sensitivity to pure commercial gasoline, it has enough sensitivity to gasoline fuel containing 20% ethanol (E20 gasoline). After the sensitivity test, the sensor was installed into the intake pipe of the single cylinder engine and examined to detect the liquid fuel film on the wall of the intake pipe. The engine was operated at a constant speed of 2000 rpm with E20 gasoline fuel. The sensor performed well during the engine operation, and the liquid fuel impingement and evaporation process could be monitored.

Following Part 1 of the previous study, this paper reports the structure's exciting force and summarize the overall research results. An experimental study was conducted to clarify the relationship between engine combustion and vibration, and to establish technology to suppress it. This study focused on the vehicle interior noise caused by combustion in which vibration transmission is the main component at high speed and high load region. A phenomenon in which both the combustion's exciting force and the structure's exciting force are combined is defined as vehicle interior noise caused by combustion. Conventionally, combustion and vibration are often discussed in terms of the average cycle, but considering the nonstationary property of vibration, in this paper analyzed the structure's exciting force characteristics for vibration in cycle-by-cycle. Analysis was conducted using the combustion indicators clarified in the previous study. The engine vibration is affected by piston specifications even with the same heat release characteristics. Based on the analysis results, the piston rotation angle and translational displacement are defined as indicators of the structure's exciting force. In this paper, after discussing the piston motion characteristics as the structure's exciting force and the indicators of vibration suppression, the results clarified by the research combined with the previous study are summarized.