Ignition timing sensitivities of oxygenated biofuels compared to gasoline in a direct-injection SI engine

Abstract

Global concerns over atmospheric carbon dioxide (CO2) levels and the security of fossil fuel supply have led to the development of biofuels; a potentially carbon-neutral and renewable fuel strategy. One new gasoline-alternative biofuel candidate is 2,5-dimethylfuran (DMF). In this paper, the potential of DMF is examined in a direct-injection spark-ignition (DISI) engine. Focus is given to the combustion performance and emissions sensitivity around the optimum spark timing, especially at 10 crank angle degrees retard (SR10). Such spark retard strategies are commonly used to reduce catalyst light-off times, albeit at the cost of reduced engine performance and increased CO2. The results for DMF are compared to gasoline, ethanol, butanol and methanol so that its sensitivity can be positioned relatively. The overall order of spark sensitivity at the highest load (8.5bar IMEP) was: gasoline>butanol>DMF>ethanol>methanol. The four biofuels widen the spark window due to improved anti-knock qualities and sometimes increased charge-cooling. This allows the increase of CO2 to be better minimized than with gasoline. Furthermore, DMF is the only biofuel to produce high exhaust gas temperatures, similar to gasoline and helpful for fast catalyst light-off, whilst maintaining high combustion stabilities. This demonstrates the potentially favorable characteristics of DMF to become an effective cold-start fuel.