Active pre-chamber ignition with supplemental air scavenging on a two-stroke UAV engine using gasoline and heavy fuels

An active pre-chamber ignition system with supplemental scavenge air, delivered via a poppet valve, has been implemented on a small-bore two-stroke engine for drone applications. The engine was operated either using the pre-chamber ignition mode or the standard spark ignition mode by swapping the cylinder head. Multiple fuels were examined, including pre-mixed gasoline and two kerosene-based military fuels with varying cetane ratings (30 and 50). During the pre-chamber tests, the fueling in the crankcase was reduced and instead delivered via the pre-chamber to reduce fuel short-circuiting. Fuel economy and emissions characteristics were assessed for both pre-chamber and traditional spark ignition modes. The results comparing the two ignition systems operating on gasoline revealed a 39.7% decrease in specific fuel consumption at low-speed conditions and a 30.9% decrease at cruising speed, while also reducing hydrocarbon emissions by up to 50%. When operating on the kerosene-based fuels, the pre-chamber ignition mode yielded up to a 44.6% decrease and 29.7% decrease in indicated specific fuel consumption at the low speed and cruising speed conditions, respectively. These results provide a foundation for future performance mapping and optimization of air-scavenged pre-chamber ignition systems for two-stroke applications. This study addresses a gap in the literature concerning the experimental application of active pre-chamber ignition systems in small-bore two-stroke engines. The system under study mitigates the limitations of passive concepts through active air and fuel scavenging of the pre-chamber.