Experimental comparison of DI and PFI in terms of emissions and efficiencyrunning Ethanol-85

Abstract: It has in recent year become more and more important to find an alternative to fossil fuel in our vehicles due to the increasing fuel price and to reduce their negative impact on the environment. One alternative is already in widespread use around the world, namely ethanol. Ethanol has, besides its environmental qualities, properties that makes it a favorable fuel to use in Internal Combustion Engines (ICE). Its high octane rating combined with its high heat of evaporation makes it resilient against knock which allows for an engine with higher compression ratios and overall increased efficiency. The traditional SI engines use Port Fuel Injection (PFI) while modern engines are moving towards Direct Injection (DI). There are many advantages of the DI system, most notably increased efficiency and performance by increased volumetric efficiency and knock suppression while poorer air/fuel mixing and added complexity are the negatives. The positive effects of DI seem to be further increased when utilizing ethanol's improved charge cooling effect and its higher octane number. In order to investigate if an ethanol fueled SI engine is suitable for HD application both DI and PFI are evaluated in terms of efficiency and emissions on a Scania D12 HD engine. The engine is modified to accomedate a sparkplug. The Scania XPI is used as DI with some light modifications in order to run ethanol. The DI system is evaluated at two SOIs, stratified and homogenous, and a SOI sweep is performed for both DI and PFI in order to find the optimum SOIs. DI homogeneous and PFI are found to produce similar results while DI stratified stands out with its; low knock propensity, much faster combustion, lower HC emissions and lower CoV of IMEP. Railpressure is found to have little or no effect on homogeneous DI while it slightly increases the combustion speed, HC and CO emissions and efficiency as well as lowers the CoV of IMEP for stratified DI. No conclusions can be drawn about efficiency in this study due to a lack of reliable fuel flow measuraments.