Experimental investigation on combustion and emissions of a two-stroke DISI engine fueled with aviation kerosene at various compression ratios

Recent years, piston engines for unmanned aerial vehicles (UAVs) are currently undergoing a transition from gasoline to diesel or aviation kerosene. This study aims to evaluate the combustion characteristics and emissions of a two-stroke direct injection spark-ignition (DISI) engine under various compression ratios with aviation kerosene (RP-3) as fuel. The tested engine was operated under three compression ratios (7.2, 6.2, and 5.2) and four throttle openings (30%, 50%, 70%, and 100%), at a fixed speed of 4000 rpm, and with an excess air ratio of 1.0. The spark timing was adjusted to knock limited spark advance (KLSA) or maximum brake torque (MBT). The results indicate that using aviation kerosene in an spark ignition engine increases the knock intensity and power loss at medium/wide throttle openings (50%, 70%, and 100%) compared to gasoline under the original compression ratio. Decreasing the compression ratio can effectively suppress knocking and make MBT/KLSA significantly advanced. No knocking tendency is observed at a small throttle opening (30%), but lower brake power (BP) and brake thermal efficiency (BTE) are observed with a lower compression ratio. At medium/wide throttle openings, reducing the compression ratio to 6.2 can yield higher BP and BTE. However, when the compression ratio is further decreased to 5.2, the BP and BTE decreased. The HC emission level is higher and the CO and NO emissions are lower compared to gasoline at a compression ratio of 7.2. As the compression ratio is decreased, the HC and NO emissions are decreased and CO emissions are increased.