Experimental investigation on the stable operating range of a two-stroke aviation kerosene engine at idle based on cyclic variation analysis

The excess air ratio and intake temperature significantly influence the cyclic variation of a two-stroke aviation kerosene engine under idle conditions. Characterizing their effects on combustion stability is essential for optimizing idle control strategies. Aiming at the problem of insufficient description of idle combustion stability of aviation kerosene two-stroke engine, this study experimentally investigated a two-stroke engine at 2300 r/min mounted on a dynamometer test bench, with intake temperatures ranging from 0 to 40 °C and excess air ratios from 0.7 to 0.9. Cylinder pressure was measured to calculate the coefficient of variation of indicated mean effective pressure (COVIMEP) and maximum cylinder pressure (COVPmax). Results demonstrate that COVIMEP first decreases and then increases as the mixture enriches, reaching a minimum at an excess air ratio of 0.8, whereas COVPmax increases monotonically with enrichment. Higher intake temperature improves mean IMEP and Pmax while reducing their COV values. Notably, the misfire boundaries identified by COVIMEP and COVPmax differ. The region with COVIMEP exceeding 10% occupies only 6% of the entire test range, while COVPmax-based unstable combustion occurs under two scenarios: high intake temperature with rich mixture, and low intake temperature with lean mixture. Therefore, appropriate evaluation parameters should be selected according to specific control objectives for idle speed regulation.