Comparing the Injection Strategy of Gasoline Compression Ignition vs. Alcohol Compression Ignition: A Partial Review and Experimental Comparison

Abstract

Abstract Gasoline compression ignition and compression ignition with a high cooling potential alcohol fuel, like wet ethanol 80 or methanol, are both promising alternatives to conventional diesel compression ignition that can improve efficiency and reduce criteria pollutants in the transportation sector. The fuel properties of gasoline are diametrically opposite of alcohol fuels and thus, the fuels behave differently in compression ignition. In this work the optimal compression ignition strategy with each fuel is studied. Data from the literature and experimental data presented in this work show that using a combination of partially-premixed and mixing-controlled combustion with gasoline in compression ignition enables robust control over the heat release process without incurring a significant efficiency penalty. Contrarily, the high cooling potential, of the alcohol fuels (∼6% of their lower heating value) means that heat absorption from evaporation and heating of the injected fuel can have a significant negative impact on efficiency if the fuel is injected near top dead center. However, the high cooling potential of the fuel enables robust control over the heat release process in a partially-premixed combustion strategy, which is not true of regular-grade gasoline (under all conditions). Overall, this work shows that on a light-duty diesel-engine architecture, compression ignition with gasoline, wet ethanol 80, and methanol can all achieve similar fuel conversion efficiencies. Compression ignition with gasoline resulted in a higher combustion efficiency compared to the alcohol fuels at the expense of higher engine-out NOx emissions and soot emissions. At 1500 rpm and 10 bar net indicated mean effective pressure, gasoline compression ignition achieved a net fuel conversion efficiency of 44.3% with an engine-out NOx level of 0.89 g/kWh and an FSN of 0.86. At the same operating condition, wet ethanol 80 compression ignition achieved a net fuel conversion efficiency of 44.0% with an engine-out NOx level of 0.21 g/kWh and an FSN of 0.03.