The Effects of Oxygenated Fuels on DISI Engine Particle Emissions and Efficiency : Experimental investigation of the effects of oxygenated biofuels on particle emissions and engine performance

Sammanfattning: The transport sector is one of the main sources of greenhouse gas emissions.Replacing fossil fuels with renewable fuels can help reduce the impact oftransportation on the climate. Liquid, oxygenated biofuels show great potentialas a replacement in spark-ignited engines, as they exhibit similarcombustion behavior to gasoline, and are compatible with existing infrastructure.This thesis aims to expand the knowledge on how oxygenated fuelsaffect emissions and performance in direct-injected spark-ignited (DISI) engines.Experiments on a gasoline optimised DISI engine at low and mid loadconditions, were conducted to establish how these fuels affect engine efficiency,combustion propagation, and emissions. A thorough investigationon how the particle emissions change with different fuels was also performed.The research evaluated five different oxygenated fuels in comparison to gasoline:ethanol, methanol, n-butanol, iso-butanol, and methyl tert-butyl ether.The oxygenated fuels all increased engine efficiency, even at low loads wherethe engine was not knock limited. The most significant increase in efficiencywas observed for methanol, with up to 12% improvement in indicated thermalefficiency compared to gasoline. At low loads all oxygenated fuels decreasedthe emissions of unburned hydrocarbons, carbon monixde and nitrogenoxides. The results at mid load conditions show that fuels with lowvolatility will increase these emissions. The findings also indicate that fuelvolatility will have a more significant impact on the particle emissions levelsthan fuel oxygen content. This effect is more pronounced at lower enginespeeds and higher engine loads.This thesis work reveals great potential to use liquid, oxygenated biofuelsin DISI engines to decrease transport-associated carbon dioxide emissions.Even without engine modifications, oxygenated fuels yield improved engineefficiency compared to gasoline. Optimized injection for fuels with decreasedvolatility is needed to reduce emissions at higher engine loads.

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