Determination of the optimum biogas energy ratio in dual-fuel biodiesel used in cooking oil-biogas operation

This study aims to examine the effects of biogas input ratio on the engine performance, combustion characteristics, and emissions of dual-fuel mode diesel engines fueled by waste cooking oil biodiesel combined with biogas. The engine test was carried out in dual-fuel mode biodiesel-biogas operation with variations in the methane content of the biogas and biogas energy ratio in excess of 90%. The methane gas content was varied from 40%, 60%, 80%, and 100% with different applied loads. A constant engine speed of 2400 rpm is used for all tests. It has been shown that increasing the methane content of the biogas can improve the brake thermal efficiency, particularly at high loads. A maximum brake thermal efficiency of 29.3% can be achieved on dual fuel with 100% methane gas content. This value has increased by 7.51% compared to biodiesel fuel under the same load conditions. Biogas with 100% methane gas also reaches cylinder pressures of 8.07 MPa and rate of heat release of 35.8 J/deg-1 at high load operation. This study confirmed that the use of biogas with more than 90% biogas energy ratio can be operated in a dual fuel mode. At low and medium loads, nitrous oxide emissions are drastically reduced at biogas energy ratios of up to 90%, 82.8%, and 65.1%, respectively. The study also identified the optimum biogas energy ratio operating range of 60-90% for maximum thermal efficiency and low emissions.

Automated summary

This study confirms the feasibility of using waste cooking oil biodiesel combined with biogas as a dual fuel in diesel engines. Increasing the methane content of biogas improves engine performance, particularly at high loads, and can achieve higher brake thermal efficiency. By increasing the energy ratio, nitrous oxide emissions can be significantly reduced, with an optimum biogas energy ratio range of 60-90%.