Experimental Measurements of Ignition Delay Times of Iso-octane/n-Butanol Blend Mixtures in Rapid Compression Machine (RCM)

Among oxygenated alternative fuels, n-butanol is considered as a promising alternative biofuel which can partially (or fully) replace conventional transportation fuels currently in use. However, before n-butanol can be commercially utilised, its fundamental combustion characteristics need to be fully understood. In this work, the effect of adding n-butanol on autoignition property of iso-octane was studied. Measurements of ignition delay times for the two blends of n-butanol proportions of 30% and 50% by mole weight were made in a Rapid Compression Machine for stoichiometric mixtures at 2.0 MPa and temperature range 651-918 K. n-butanol increased ignition delay times of iso-octane at lower temperatures and hence acted as an octane enhancer, while at higher temperatures delay times were reduced. In the intermediate temperatures there was visually no difference in delay times between the two blends. Throughout the temperature range studied, the delay times of both blends were much closer to those of pure n-butanol which suggests that the combustion chemistry of n-butanol was dominant over that of iso-octane. These results have shown that n-butanol can enhance fuel octane rating and therefore can potentially improve thermal efficiency of SI engines, whilst CI engines can benefit from the reduced delay times at higher temperatures.