Comparative Effects of Olefin Content on the Performance and Emissions of a Modern GDI Engine

The effects of different olefin contents in fuel (nominally 8.2 and 17.2% in volume) on the performance and exhaust emissions of a modem gasoline direct injection engine at speeds of 1500, 3500, and 5000 rpm under 10, 25, 50, 75, and 100% engine loads were investigated. The experimental results showed that reducing the olefin content had little impact on brake power, while it obviously increased brake-specific fuel consumption and decreased brake thermal efficiency at low and medium speeds. In addition, lower exhaust gas temperatures were observed at low speeds. The comparative results indicated that reducing the olefin content decreased CO emissions by -5.8 to 22.8%, but slightly increased (less than 5%) CO2 emissions. Likewise, total hydrocarbon emissions decreased, while NOx emissions also decreased by 5-15% under most of the operating conditions. Most importantly, great reductions in particle mass concentrations and particle number emissions were observed when lower olefin content gasoline was used, with decreases of up to 87.4 and 95.8%, respectively. Moreover, particle mass and particle number changes suggest that a lower olefin content facilitates the formation of larger soot particles. Therefore, although reducing the olefin content is disadvantageous to engine performance, it markedly reduces CO, total hydrocarbon, NOx, particle mass, and particle number emissions, in line with the latest national emission regulations.