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In addition to the Spark Ignited and Compression Ignited modes of reciprocating internal combustion engine operation, a third option exists. In this class of engine, elevated charge temperatures and (in some cases) active chemical species are employed to achieve a Homogeneous Charge Compression Ignition (HCCI) mode of operation. This is typically accomplished using copious amounts of charge dilution by exhaust gases, which can elevate charge temperatures into autoignition regimes, yet simultaneously temper runaway combustion rates which would otherwise lead to destructive knocking. Engine operation in the HCCI mode has been described as efficient, stable, and low in the production of engine-out emissions. However, with the large amounts of charge dilution required, such engines to date suffer from relatively low energy density, and are difficult to control over wide ranging speed/load conditions.

This paper describes experimental studies carried out as part of a program to develop a neat methanol (M100) version of a GM 4-cylinder light truck engine. The engine was originally intended for variable fuel applications with fuels containing up to 80% ethanol. To permit M100 operation, a variable energy ignition circuit and special recessed surface gap ignitors have replaced the standard ignition components. This is referred to as a “plasma jet” ignition system, and is employed both to overcome the cold starting difficulties inherent with neat alcohol fuel and to permit less enrichment to be used during start-up in the interest of reduced hydrocarbon emissions. The plasma jet ignition systems used in previous related studies suffered from excessively high ignition energy requirements which would be detrimental to ignitor durability.