Experiment on the Influence of Residual Exhaust Gas on the Combustion Characteristics of a Miniature Engine with Platinum Wire Ignition

[Image: see text] Affected by the scale effect, it is difficult for the gas exchange of a micro-internal combustion (IC) engine to reach the level of a conventional-size engine, resulting in excessively high residual exhaust gas content in the cylinder and serious deterioration of combustion. In order to verify the above point, experiments were carried out based on the variation characteristics of the residual exhaust gas content of the micro-engine during the starting process. The residual exhaust gas content of the micro-engine exhibits a gradually increasing change characteristic during the starting process. Through continuous monitoring of the in-cylinder pressure, the combustion characteristics of the first ignition cycle without residual exhaust gas were captured. Then, it was compared with that in the transitional combustion stage and the stable combustion stage. The latter two combustion stages have different residual exhaust gas contents. The results show that for micro-engines, the combustion cycle with different residual exhaust gas contents presents significantly different combustion characteristics. As the residual exhaust gas content increases, the combustion pressure and the heat release rate decrease, and the combustion duration extends. Excessive residual exhaust gas content is the main reason for the abnormal combustion characteristics of the micro-IC engine with platinum wire ignition. In addition, when there is no residual exhaust gas, the indicated work is the largest and the thermal efficiency is higher. As the in-cylinder residual exhaust gas content increases, the indicated work decreases significantly.