Gasoline engines ignition timing

The operation of a spark ignition gasoline engine above the stoichiometric point reduces the fuel consumption and therefore the CO2 emission of the engine. At the same time, the engine-out emissions of CO, NO t and up to some defined A/F-ratio,... 

Another condition to keep gasoline engines running smoothly is that the fuel-air mixture start burning at a precise time in the combustion cycle. An electrical spark starts the ignition. The remainder of the fuel-air mix should be consumed by a flame front moving out from the initial spark. 

The engine was the first to incorporate compression ignition of alcohols (7). Low cetane fuels can autoignite, however, provided the in-cylinder temperature is high enough and fuel injection correcdy timed. This compression ignition works for methanol as well as ethanol and gasoline. 

When ethanol is used in a standard spark ignition or compression ignition engine designed to bum conventional hydrocarbon-based fuels, ethanol performance varies substantially if no engine modifications are made, and it becomes difficult to rate the value of ethanol as an effective fuel. Consequently, flexible fueled vehicles (FFVs) or variable fueled vehicles (VFVs) have been developed to operate on either gasoline or alcohol-based fuels. These vehicles are equipped with on-board sensors and controls to adjust the spark advance and the fuel injector timing to help correct for the differences in fuel performance. 

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