Homogeneous charge compression ignition versus dual fuelling for utilizing biogas in compression ignition engines

In this work, biogas was used in a compression ignition (CI) engine in the homogeneous charge compression ignition (HCCI) mode as well as in the dual-fuel mode together with diesel. In the HCCI mode, the charge temperature and amount of diesel injected into the intake manifold were used to control combustion. The presence of carbon dioxide in biogas suppresses the high heat release rates normally encountered in neat-diesel-fuelled HCCI engines. Efficiencies close to diesel operation together with extremely low levels of nitric oxide (NO) and smoke were attained in a brake mean effective pressure (BMEP) range from 2.5 bar to 4 bar in the biogas-diesel homogeneous charge compression ignition (BDHCCI) mode. Proper control over the charge temperature was essential. Thermal efficiency was higher and NO, hydrocarbon, carbon monoxide, and smoke levels were lower than in the biogas-diesel dual-fuel mode. Thus, the BDHCCI mode is a viable option for using biogas in Cl engines in the medium-load ranges. Operation of the engine in the Cl mode with diesel below a BMEP of 2.5 bar, then in the HCC1 mode up to a BMEP of 4 bar, and in the dual-fuel mode at higher BMEPs could lead to good overall performance and low emissions.