Investigation of biogas composition effects on combustion characteristics of an RCCI engine

Fuel reactivity controlled compression ignition (RCCI) engines are promising approaches to achieve high efficiency and clean combustion. Using biogas as a primary fuel in the engines causes better control of the combustion process due to its reactivity gradient with diesel fuel. In this study, biogas is inducted into the engine through an inlet port, and diesel as a high reactivity fuel is injected into the engine. At a constant engine speed of 1300 rpm and a fixed amount of diesel mass, a broad range of indicated mean effective pressure from 5.6 to 13.5 is studied. Also, the effects of different compositions of biogas and biogas to diesel ratio on combustion characteristics and emission levels are studied. Results show that changes in the amount of CO2 in biogas composition lead to drastic changes in maximum pressure, temperature, and emission levels. In other words, increasing the amount of CO2 in biogas and also the ratio of biogas to diesel both significantly decrease maximum pressure, temperature, and NOx emission.