A comparative exergetic performance and emission analysis of pilot diesel dual-fuel engine with biogas, CNG and hydrogen as main fuels

In this experimental study coupled with exergy analysis, a small compression ignition engine is modified to operate in dual fuel (DF) mode with biogas, CNG and hydrogen as main fuels, and diesel as pilot fuel. Injection timing (IT) advance is studied as a strategy to improve the low load performance and emission characteristics of DF engine. Experiments were performed at ITs of 20, 23, 26, 29 and 32 degree crank angles before top dead center (degrees BTDC) for two engine loading conditions of low and full loads at the operating points corresponding to maximum diesel substitutions. It was found that maximum diesel substitution was considerably affected by the type of main fuel and engine load, however, relatively less affected by IT advance. Highest maximum diesel substitution was observed with CNG, and lowest with hydrogen as main fuels in DF mode. It was also found that IT that gave highest performance or lowest emission varied with both the type of gaseous main fuels and engine loads. At low load, ITs of 32, 29 and 26 degrees BTDC showed highest exergy efficiencies of 8.5%, 11.1% and 11.9% for biogas, CNG and hydrogen DF operations respectively, compared to 12.6% for diesel only operation. At these operating conditions, exergy destructions of 73.67%, 64.86% and 60.96% (% of total input exergy) were found for DF operations compared to 62.98% for diesel only operation. At full load condition, hydrogen DF operation exceeded exergy efficiency by 2% compared to that with the diesel only operation. On the emissions side, HC, CO and smoke emissions were found to be reduced with advanced ITs; however, NOx emissions were significantly increased.