Lubricant Induced Pre-Ignition in an Optical SI Engine

This work was concerned with study of lubricant introduced directly into the combustion chamber and its effect on pre-ignition and combustion in an optically accessed single-cylinder spark ignition engine. The research engine had been designed to incorporate full bore overhead optical access capable of withstanding peak in-cylinder pressures of up to 150bar. An experiment was designed where a fully formulated synthetic lubricant was deliberately introduced through a specially modified direct fuel injector to target the exhaust area of the bore. Optical imaging was performed via natural light emission, with the events recorded at 6000 frames per second. Two port injected fuels were evaluated including a baseline commercial grade gasoline and low octane gasoline/n-heptane blend. The images revealed the location of deflagration sites consistently initiating from the lubricant itself. With the high octane fuel (and the limited load adopted for safe optical work) lubricant induced pre-ignition was observed, but without knock. This pre-ignition was repeatedly the result of the lubricant deliberately introduced earlier on in the same cycle. With the lower octane fuel, the previously well reported “on-off” knocking nature of pre-ignited knocking combustion was observed during a sequence of cycles following a single injection of lubricant. In addition it was sometimes apparent that cycles with knock would result in oil subsequently being ejected from the piston top land area during the power stroke.