A multi-parameter study of the extension of the stable operating range of a wet-ethanol-fueled engine using a microwave-assisted spark plug

A multi-parameter test matrix has been completed in an ethanol-fueled single-cylinder Waukesha ASTM-Cooperative Fuel Research (CFR) engine for studying microwave-assisted spark ignition performance under varied conditions, notably increased compression ratio, increased preheat, and increased charge dilution. Independent variables include compression ratio (9:1, 10.5:1, and 12:1); fuel water dilution by volume (0%, 20%, 30%, 40%); intake air temperature (22°C, 60°C); equivalence ratio (stoichiometric to lean-stability-limit); spark timing (advanced, maximum brake torque, retarded); and ignition strategy (spark only, spark with microwave). This report examines the extension of the stable operating range by a microwave-assisted spark plug, with data indicating that microwave-assisted spark ignition reduces cyclic variation as compared to spark-only ignition in highly-dilute mixtures at all tested compression ratios and intake air temperatures. Examination of the factors affecting microwave ignition performance shows diminished effects of microwave energy input when in-cylinder pressures are high at time of spark.