Bridging fundamental combustion analysis and engine knock behavior -1st report; CFR engine test for various RON fuels-

A collaborative study to bridge the gap between fundamental combustion analysis and the phenomena inside the engine has been conducted with the aim of understanding the knocking phenomenon in engines under various operating conditions. In the first and second reports, we conducted engine experiments and analyses to clarify the factors that determine the Research Octane Number (RON). This first report mainly addresses the engine tests and experimental analyses. To understand the characteristics of RON, a CFR engine was selected for our initial trial. A pressure sensor was installed in the CFR engine for measuring in-cylinder pressure histories. PRF80, PRF90, and PRF100 were used for engine tests. Here, Primary Reference Fuels for octane number measurement were used for enabling discussions across a wide range of RONs. The compression ratio of the CFR engine was adjusted for each fuel so that the knocking occurrence rates were approximately 50%. The unburned gas temperature histories were calculated based on the obtained pressure histories. The presence and timing of knocking occurrences were determined based on pressure oscillations. Comparisons were made of the unburned gas pressure and temperature at the timing just before knocking occurred. Based on the results of these experiments with the CFR engine, the relationship between the octane number of the PRFs and the temperatures and pressures of the unburned gas just before the occurrence of knocking was identified for the sake of novel analysis in the second report. This study provides a deeper understanding of the critical conditions leading to knocking, highlighting the significance of temperature and pressure conditions of unburned gases in the vicinity of knock onsets, influenced by varying RONs.