Effects of Elevated Diluent Contents on the Combustion and Emissions of Biogas-Diesel RCCI Engine at Full Load

Abstract

Difficulty in carbon dioxide (CO2) removal, coupled with the poor combustion due to diverse constituent of biogas, encouraged an investigation of the influence of high diluent (CO2, 25 – 45% vol) content and biogas fraction (40 – 70%) on the emissions of biogas/diesel dual-fuel reactivity-controlled compression ignition engine. The experiment was conducted at full load and a speed of 1600 rpm. The results showed distinct temperature trends for all the CO2 ratios and biogas fractions while radiation absorption effect of high CO2 content inhibits the combustion. Biogas with 35% CO2 proportion and a fraction of 50% produced the highest maximum temperature and heat released. The combustion resulted in a lower PPRR minimizing the higher-ringing strength tendency. At a 40% biogas fraction and 25% CO2, which simultaneously showed the highest ITE of 38.29%, the lowest BSFC of 7.41 g/kWh was achieved. An increase in the biogas fraction indicated a significant decrease in the nitrogen oxides (NOx) and particulate (PM) emissions by approximately 62.66, and 26.59%, respectively. Also, an increase in the diluent CO2 content decrease the carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions by approximately 20.30, and 38.83%, respectively. However, an increase in those parameters resulted in a severe UHC and CO emissions trade-off with the NOx and PM emissions, though a 70% biogas fraction indicated the potentials of reducing the impact of the trade-off.