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An analysis method for the characterization of fuel behavior during spark ignition engine start-up has been developed and applied to several sets of start-up data. The data sets were acquired from modem production vehicles during room temperature engine start-up. Two different engines, two control schemes, and two engine temperatures were investigated. The fuel accounting used was a cycle-by-cycle mass balance for the fuel, where the amount of fuel injected was compared with the amount burned or exhausted as unburned hydrocarbons. The difference was measured as "fuel unaccounted for". The calculation for the amount of fuel burned used an energy release analysis of the cylinder pressure data. The results include an overview of starting behavior and a fuel accounting for each data set. Differences between start-up strategies are discussed and areas for improvement are identified. Overall, starting occurred quickly, with combustion quality, manifold pressure and engine speed beginning to stabilize by the seventh cycle, on average. To facilitate this rapid starting at cold engine conditions, approximately five times the amount of fuel required for a stoichiometric mixture is injected during the first one or two cycles. A large portion of this fuel, equivalent to nearly ten injections at stoichiometric idle conditions, remains "unaccounted for" after ten cycles of this analysis. Close to 10% of the fuel injected during the initial overfueling that is "unaccounted for" at first, shows up later in underfueled cycles as burned fuel or as hydrocarbon emissions. Similar trends occurred with both engines, temperatures, and start-up strategies; although, during warm engine start-up conditions the overfueling is only 130% of stoichiometric, and the mass "unaccounted for" after ten cycles represents only one injection at idle. The most successful start-up strategies that were analyzed injected close to the stoichiometric requirement for each cycle after the initial overfueling. The stoichiometric requirement for a particular cycle is directly proportional to the manifold pressure at a given temperature and therefore it is recommended that methods for using manifold pressure in start-up strategies be investigated. 3 "And to love life through labour is to be intimate with life's inmost secret." K.G.

Analysis of Fuel Behavior in the Spark-Ignition Engine Start-Up Process