The effect of ignition timing on performance of LPG injected SI engine

Abstract

LPG injection systems are applied to spark ignited gasoline engines with a simple control strategy by taking the differences in heating values of gasoline and LPG into account only. But it is believed that the performance of engine can be improved if some additional parameters are considered in optimization such as ignition timing. In this study a four stroke LPG injected SI engine was run by using specially developed electronic control unit (ECU) which controls the ignition timings. 2 and 4 degrees retarded and advanced ignition timing values were applied besides the original values of gasoline engine. It was detected that the engine was run without any problem with up to 4 degrees advanced ignition timing values but on the other hand retarded values were causing improper combustion therefore some performance test steps failed or reliable results could not be obtained. Experiments were carried out at fixed throttle position of 25% of full opening and between 2000 - 4000 rpm engine speeds to determine performance parameters. Comparative results of performance emissions are presented for 2 and 4 degrees advanced ignition timing values from original. During the tests excess air ratio was not controlled for a specific value but it was kept between 0.91 and 1.1 CO, CO2 and HC emissions were in the intervals of 0.17 % - 3.41%, 10.70% - 12.22% and 83 - 225 ppm, respectively. The highest brake power and torque values were obtained as 31.67 kW at 4000 rpm and 96.64 Nm at 2000 rpm respectively with 2 degrees advanced ignition timing values. The lowest brake specific fuel consumption value was obtained as 240.14 g/kWh at 2500 rpm with 4 degrees advanced ignition timing value.