Effect of using fuel with different octane numbers on performance and emissions in a spark ignation engine

Thermal efficiency of internal combustion spark ignition engines can be increased by increasing compression ratio. To increase compression ratio, quality of gasoline especially octane number of gasoline fuel should be increased. In this study, different octane number fuels were investigated in a spark ignition engine. In the experiments, 95, 97 and 100 octane gasoline fuels were used. Without changing design parameters, performance and emission behaviors of the engine were observed by using higher octane number fuels at the same compression ratio. The experiments were performed between 1500 rpm and 4500 rpm engine speeds with 500 rpm increments and four different engine loads (25%, 50%, 75% and WOT). In the tests, a four-stroke and four-cylinder spark ignition engine having 8.8 compression ratio was used. Optimum performance and emission parameters were obtained with 95 octane gasoline which is standard fuel of the test engine. However, higher NOx emissions were observed with 95 octane gasoline. This result was thought higher combustion temperatures.