The Effect of Burned Residual Gases on Optimum Ignition Timing using Skip Fire Technique

In this paper the effect of burned residual gases on optimum ignition timing has been investigated using experimental data extracted from a single cylinder spark-ignition research engine at 1800 rpm and 0.9 equivalence ratio with CNG as fuel. To omit the residual gases, skip fire technique was utilized. The raw data including signals of in-cylinder pressure, inlet pressure, crank angle and TDC were recorded; then the data were processed by a program written in Fortran field; and variations of cylinder pressure versus crank angle, indicated mean effective pressures and peak pressures of identical cycles were calculated. Finally, from the obtained results at different timings, the optimum ignition timings of two cases, with and without burned residual gases, were determined and the peak pressures of the cases were compared. The obtained results showed that when burned residual gases were replaced by unburned gases, optimum advance was retarded about 9 degrees and peak pressure position of the equivalent cycle was appeared 4 degrees longer far away TDC. Cyclic variation of identical cycles in skip fire case showed that the configuration of the data distribution of Rimep-RPmax at optimum ignition timing had a considerable difference than those of the others