Experimental and Theoretical Comparative Study of Performance and Emissions for a Fuel Injection SI Engine with Two Octane Blends

Experimental and theoretical investigations are carried out to study and compare the effect of using two gasoline blends, namely octane 91 and octane 95, on the performance and exhaust emissions of a modern fuel injection SI engine at different engine speeds and loads. Theoretical combustion model is able to predict the engine performance when compared to the experimental findings. Results show that the engine performances of both fuels are comparable, with marginal differences, under the tested operating conditions, practically for engine speeds less than 3500 rpm. Higher power and less specific fuel consumption are observed when octane 91 fuel is used compared with octane 95 blend. Both blends do not show a tendency of knock occurrence. In general, both fuels show similar trends for CO, CO₂ and NO_x concentrations in the exhaust, whereas the unburned hydrocarbons are slightly higher when octane 91 fuel is used. In the higher speed range between 3500 and 5000 rpm, a noticeable decrease in CO₂ concentration, an increase in specific fuel consumption and CO concentration are observed.