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This paper study the case of a heavy-duty spark ignition engine fueled with LPG, for which it was demonstrated that the thermal effect of the pre-knock reactions in the end-gas occur in the presence of alkenes, one of the commercial LPG main component. In this sense, the engine was operated at full load, with different spark advances generating different levels of knock, which was characterized in terms of angle and intensity. It was developed a classical two zone thermodynamic combustion model for predicting the end-gas pressure and temperature levels, which are cycle-by-cycle variables. It was made the comparison between the cycles with knock and without and it was find that in the knocking cycles case the end-gas temperature is higher, this situation being attributed to the presence of alkenes in the fuel composition.

In the present study, a relation for the evaluation of knock auto-ignition induction period was studied in the case of a spark ignition engine for heavy-duty transportation fueled with commercial LPG. Because the existing formulas for knock auto-ignition induction time were determined for quasi-steady mixture conditions and in general for pure hydrocarbons, it was considered interesting the establishing of a such a relation using pressure data recorded from a internal combustion engine; in this case being took in account the influence of combustion cyclic variability and also of using a mixture of hydrocarbons. The results obtained after knock was characterized in terms of intensity and onset crank angle and a two zone combustion model was developed and applied for obtaining the unburned zone temperature, were conducted in the way of determining and verifying possible relations for knock auto-ignition induction time.