Impact of compression ratio on combustion behavior of hydrogen enriched biogas-diesel operated CI engine

This experimental study investigated hydrogen-enriched biogas (gaseous fuel) and diesel (pilot fuel) in a compression ignition engine at variable compression ratios. A fumigation technique was employed to inject simulated hydrogen-enriched biogas (0.5 kg/h) in a 3.5 kW dual-fuel compression ignition engine. Experimentation was carried out by varying the brake mean effective pressure in the range between 0 and 3.5 bar at engine speed of 1500 rpm. Results illustrated that the ignition period decreased from 22.9 to 18.5 degrees CA with an increased compression ratio (16:1 to 18:1), specifically at brake mean effective pressure of 3.5 bar. Under the same loading conditions, the peak cylinder pressure and thermal brake efficiency continuously increasing w.r.t. compression ratio and attained a maximum value of 54.1 bar and 36.1 %, respectively, at a compression ratio of 18:1. Contrary, the continual decrement in HC, CO, and smoke opacity was identified concerning compression ratio; however, NOx formation was found to be higher at elevated compression ratio. Further, at 3.5 bar (BMEP), the tailpipe emissions assessed were: HC (8.2 g/kWh), CO (0.09 %), smoke opacity (37 %), and NOx (16.5 g/kWh), corresponding to the compression ratio of 18:1. It is inferred from this study that using hydrogen-enriched biogas at a higher compression ratio improves the engine performance to a great extent, along with emissions reduction.