Gasoline - Ignition Improver - Oxygenate Blends as Fuels for Advanced Compression Ignition Combustion 2013-01-0529
Mixing is inhibited both by the relatively low volatility of conventional diesel fuel and the short premixing time due to high fuel reactivity (i.e. cetane number (CN)). Consequently, in this research two promising oxygenates which can be produced from 2nd generation biomass -ethanol from cellulose and anisole from lignin - will be blended to gasoline, further doped with ignition improver. This will result in a diesel-like CN, but with a higher gasoline-like volatility. There is, however, also a more practical motivation for this study. In Europe, the dieselization trend is resulted in a growing excess of gasoline, which is currently largely exported to the USA at additional transport costs. Boosting the cetane number of gasoline into the diesel range with ignition improvers is a promising route to more efficiently consume European refinery products within Europe. In such a scenario and given current biofuel mandates, it is likely that biofuels will be added to the improved CN gasoline. Experiments are conducted on a modified in-line 6-cylinder DAF heavy-duty diesel engine. The goal of this paper is to assess the impact of a) fuel oxygen and b) oxygenate molecular structure on the effectiveness of the aforementioned advanced combustion concept with respect to engine efficiency and emission behavior. The results suggest that certain blends of 2- Ethylhexyl Nitrate (EHN) and oxygenates with gasoline can improve fuel efficiency and the soot-NOx trade-off compared to neat diesel fuel in conventional compression ignition combustion. Anisole is added to suppress soot emissions, based on positive findings in conjunction with diesel fuel in earlier work. EHN is subsequently supplemented to boost the gasoline blend CN into the diesel range. Improved efficiency is believed to be linked to the higher volatility of the gasoline blend. The improved soot-NOx trade-off is attributed to both higher volatility and the presence of fuel oxygen.