Performance and emission of a SI engine using different isopropanol/n-butanol/ethanol (IBE) and gasoline fuel blends: optimization of fuel additive formulation via response surface methodology (RSM)

The environmental damage caused by the fossil fuels makes the application of renewable fuels such as alcohols (e.g., ethanol and n-butanol) necessary. Since the purification of alcohols in the production process is expensive, the intermediate fermentation products including isopropanol/n-butanol/ethanol (IBE) are sometimes used as fuel additive. This study employed the mixture design as a subset of response surface methodology for the first time to examine the effect of changing the alcohol ratio of isopropanol and n-butanol from 30 to 60% (v/v) and increasing the concentration of ethanol as the gasoline fuel additive on the engine performance and pollutant emissions. In the present study, the fuel additives were mixed with the neat gasoline in the following composition (10% (v/v) fuel additive/90 (v/v) % gasoline) to produce different fuel blends. It was found that the engine performance parameters such as power, thermal efficiency, and specific fuel consumption were improved for the fuel blends containing alcoholic mixture additives compared to the neat gasoline. Also, a decrease in the NO_X emission was observed for all fuel samples containing alcoholic mixture additives. The unburned hydrocarbon (UHC) emission was also decreased for the majority of the examined fuel samples containing alcoholic mixture additives. After the multi-objective optimization of the fuel additive formulation, it was found that IBE 4.5:4.5:1 is the best additive formulation considering the engine performance parameters and exhaust emission. The application of the best additive formulation in the fuel blend resulted in a reduction of 12.66% in NOx emission, 24.28% in UHC emission, 5.66% in CO emission, and 4.83% in the specific fuel consumption compared to the neat gasoline. Moreover, the engine power and thermal efficiency parameters increased by 4.79% and 8.35% compared to the neat gasoline, respectively.