The effects of research octane number and fuel systems on the performance and emissions of a spark ignition engine: A study on Saudi Arabian RON91 and RON95 with port injection and direct injection systems

This research aims to experimentally analyze the performance and emissions of a single cylinder, four-stroke spark ignition (SI) engine fuelled by two grades of gasoline used in Saudi Arabia, RON91 and RON95 while operating with two fuel delivery systems; port injection (PI) and direct injection (DI). The experiments were conducted on a single cylinder research engine with pent-roof type cylinder head that can be interchangeably operated with either port injection or direct injection. Brake power, brake specific fuel consumption (BSFC) and exhaust emissions were measured at different engine speeds, loads and fixed compression ratio of 10:1. Cylinder pressure, mass burnt fraction and rate of heat release were analyzed. The experimental results showed that the brake power of the engine is higher with RON91 which is mainly due to higher heating value. The BSFC decreases with increasing in engine load and it increases with increasing engine speed. However, there are no noticeable differences between two tested gasoline fuels in the BSFC except at high speed and load, where BSFC of RON91 is higher than RON95. Combustion analysis showed a mixed response to different RON and fuel systems. Generally, combustion of RON95 is faster than RON91 in both PI and DI systems. In DI system, RON95 showed longer combustion duration at low speed and load. The concentrations of nitrogen oxides (NOX), carbon monoxide (CO) and total hydrocarbon (THC) emissions in the exhaust system were measured. It is observed that NOX emissions of RON91 are higher than RON95 in most cases except at high engine speed with DI system. It is also detected that CO emissions of RON91 are higher than RON95 in both injection systems at higher load. It is also noticed that RON91 system has higher THC emissions.