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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.

This paper describes an experimental study to determine the potential for fuel efficiency improvements offered by dedicated, high compression E85 engines with optimized powertrain calibration strategies. The study involved a prototype variable fuel engine that could operate using either gasoline or E85, and a high compression version of the same engine that was suitable only for E85. Fuel consumption and engine-out emissions were evaluated using steady-state engine dynamometer tests to represent urban and highway speed/load conditions. For each fuel and engine combination, the fuel efficiency and emissions trade-offs provided by varying Exhaust Gas Recirculation (EGR) levels were determined. For the high compression engine, operation at lower speed/higher load conditions (producing the same power as the standard speed/load settings) was also investigated.