Diesel engine combustion of biomass pyrolysis oils

To investigate their ignition delay and combustion behavior, experiments wi th two biomass pyrolysis oils and No. 2 diesel fuel were performed in a dir ect injection diesel engine. It was found that while the indicated thermal efficiency of both pyrolysis oils equaled that of the diesel fuel, they exh ibited excessive ignition delays and required a moderate degree of combusti on air preheating to ignite reliably. Despite the longer ignition delays as sociated with the pyrolysis oils, the cylinder pressure rise rates were sig nificantly less than with No. 2 diesel fuel. Experimental ignition delay an d heat release rates were interpreted using a phenomenological spray combus tion model. Using a three parameter fit for vaporization, ignition, and com bustion rate, the model showed that the longer ignition delays of the bio-o ils result from slow chemistry relative to diesel fuel. The model also show ed that the heat release profiles of the bio-oils are consistent with slow combustion chemistry and rapid mixing relative to diesel fuel. As a result, whereas diesel combustion is predominantly mixing limited, pyrolysis oil c ombustion is predominantly limited by chemistry through much of the process .