Spark Plug Fouling: A Quick Engine Test

A quick and repeatable test procedure has been developed to investigate cold-start spark plug fouling using a single-cylinder test facility which is capable of quickly cooling the engine back to the test temperature. With a constant engine speed of 140 rpm, the fuel flow is controlled for a 5 minute start/idle period, followed by a 5 minute cool-down period with the fuel off. This facility dramatically reduces the cold-soak period of a cold start which would otherwise require hours. Under conditions where carbon fouling occurs, the effects of fuel calibration, fuel properties (aromaticity, vapor pressure, and surfactant additives), and spark properties (energy and gap size) on the number of cold starts, the spark waveforms, and the electrical-shorting mode were investigated. Fuel calibration had the strongest influence. The relative roles of soot and water and of different soot formation mechanisms are discussed.