A comprehensive study of a reactivity-controlled compression ignition engine fueled with biogas and diesel oil

Abstract

Reactivity-controlled compression ignition (RCCI) engines have been introduced as a promising alternative to compression ignition engines, especially in reducing emissions. It is common practice in an RCCI engine to use two fuels with distinctly different reactivity to control the combustion process. Also, abundant biogas fuel could be considered as a potential and suitable alternative to conventional fuels. Biogas can easily be derived from renewable resources and is basically composed of methane (CH4), carbon dioxide (CO2), a small amount of hydrogen (H2), nitrogen (N2), oxygen (O2) and hydrogen sulfide (H2S). In this paper, biogas as an alternative fuel together with diesel oil is used for reactivity-controlled compression ignition in a modified heavy-duty engine. The biogas fuel with low reactivity is fed through the inlet port and diesel oil with high reactivity directly injected into the engine cylinder. Then, a detailed study of biogas composition, engine speed, intake temperature, fuel metering and injection strategies on combustion characteristics such as engine efficiency and emission levels is carried out. It is demonstrated that the amount of CO2 in biogas composition plays a significant role in combustion and emission processes. Typically, at IMEP = 9.4 bar, as the amount of CO2 in biogas composition is changed from 0 to 40%, the maximum in-cylinder temperature and pressure are reduced about 143 K and 4.6 bar, respectively, while NOx emission is reduced drastically by 75%.