Experimental and Numerical Study of Abnormal Combustion in Direct Injection Spark Ignition Engines Using Conventional and Alternative Fuels

In this paper, the potential of alternative fuels to reduce preignition in engines is primarily investigated. Two ketones (2-butanone and 3-methylbutanone), a furan (2-methylfuran), and five alcohols (ethanol, iso-propanol, 2-butanol, isobutanol, and 1-propanol) are compared to three conventional fuels (RON95E0, RON9SE10, and iso-octane). If the alternative fuels can reduce preignition significantly, the efficiency of spark-ignition engines can be potentially increased. One major aim is to categorize the fuels in terms of preignition resistance. Additionally, the distributions of the initial preignition kernels are measured by high-speed luminescence imaging to analyze the reason for preignition. Furthermore, the occurrence of measured preignition is compared with computed ignition delay times at the pressures and temperatures of the engine load points used to find out whether the mixture is prone to autoignition in the bulk gas phase. This is most likely the case for the three conventional fuels because of thermodynamically critical gas-phase conditions. Seemingly, preignition is not induced by droplets, presumably because of an improved injector targeting. Moreover, the preignition resistance of the alternative fuels is significantly higher (critical intake pressure difference: similar to 2 bar) compared to that of the three conventional fuels. It can also be concluded that 2-butanone is most resistant against preignition. Similarly, alcohols and 3-methylbutanone are highly beneficial compared to conventional fuels. Overall, the most important fuel properties for preignition appear to be research octane number and enthalpy of vaporization. Apparently, ignition is caused by glow ignition at a hot surface (spark plug) only for 2-methylfuran, iso-butanol, and 1-propanol.