Utilization of primary alcohols in dual-fuel injection mode in a gasoline direct injection engine

Due to the higher octane rating of alcohols, they can be used in gasoline direct injection (GDI) engines at relatively higher compression ratios. However, relatively higher particulate matter (PM) emissions from GDI engines still remain a major challenge. To resolve this issue, this study is focused on exploring use of dual-fuel injection technology, in which alcohols are injected into the port and gasoline is injected directly in the engine combustion chamber. To investigate the effect of fuel properties on combustion, performance and emission characteristics of a dual-fuel engine, three different alcohols (methanol, ethanol and butanol) were injected in the intake port in different premixed ratios (15% and 30% energy replacement). All experiments were carried out at constant engine speed (2000 rpm), fixed engine load (22 Nm) and identical fuel injection parameters. Results showed that dual-fuel operation of alcohols (especially methanol and butanol) resulted in superior combustion and performance compared to baseline GDI engine. Injection of alcohol in the port reduced emissions of carbon monoxide (CO) and oxides of nitrogen (NOx), however, HC emissions increased slightly. Significant reduction in PM emissions from dual-fuel operation is an important finding of this study. Use of alcohols reduced both PM number as well as PM mass, however, emission of nanoparticles (NP) increased slightly (for ethanol and butanol). Increasing premixed ratio of alcohols in the port further improved the engine combustion, performance and PM emission characteristics of dual-fuel GDI engine. Overall, this study suggested dual-fuel operation as a potential solution for GDI engines in order to reduce PM emissions.