Effect two grades of octane numbers on the performance, exhaust and acoustic emissions of spark ignition engine

This study presents a comparative analysis of performance, exhaust and noise emissions for a one-cylinder, four-stroke, spark-ignition engine powered by gasoline fuels of two different grades of research octane numbers (RONs), namely octane 90, and octane 95. During the experimental works, each fuel test was performed by varying the engine speed within the range from 1000 to 3600 rpm. The SI engine was connected to eddy current dynamometer with electronic control unit (ECU), an exhaust gas analyzer and the sound level meter (SLM) to determine engine performance, exhaust emissions, and measuring the sound pressure level (SPL) in decibels (dBA) and one octave frequency bands in the audible human range at different engine speeds, respectively. The experimental results showed that the using gasoline with octane grades higher than the requirement of an engine will decrease the engine performance. On average, the brake power and thermal efficiency for the SI engine fuelled with octane 90 is higher than that of gasoline octane 95 by 6% and 11% respectively, and improvement of BSFC by 14%, which is mainly due to higher heating value. Even though, the volumetric efficiency of octane 95 is more 5% than octane 90 due to higher latent heat and heat capacity. In general, the exhaust emission profiles for NOx and CO of the engine improved for octane 95 by 11% and 17% respectively. On the other side, the HC and CO² emissions concentration of gasoline octane 90 is lower than that of gasoline octane 95 by 18% and 12% respectively. Finally, the noise levels showed a trend of the increase of disturbing for higher octane number and the increase of divergence between the two values of SPL at higher speed for both fuels.