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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 comparing the peak ignition voltage requirements of natural gas and gasoline in a typical bi-fuel vehicle application. Chassis dynamometer tests were carried out in which the vehicle was subjected to different types of transient wide open throttle events to create “worst case” voltage requirements. In addition to measurements of ignition voltage, other factors known to influence voltage requirements (such as cylinder pressure, electrode temperature, and fuel/air ratio) were recorded during the transient tests in order to obtain a better understanding of the underlying reasons for observed differences in voltage requirements between the two fuels and between the different transient test procedures. The results presented in this paper quantify the increased peak voltage requirements (relative to gasoline) for reliable ignition of natural gas under various operating conditions.