Combustion characterization of waste cooking oil and canola oil based biodiesels under simulated engine conditions

Abstract

Alternative fuels will come from a variety of feed stocks and refinement processes. Understanding the funda-mentals of combustion and pollutants formation processes of these fuels will be useful for their implementationin different combustion systems. In this work, optical diagnostics were performed to waste cooking oil (WCO)and canola oil (CAO) based biodiesel sprays to assess their combustion and soot formation processes.Conventional diesel was used as a reference fuel for comparison with the biodiesels. The experiments wereconducted in an optically-accessible constant-volume combustion chamber (CVCC) with simulated compression-ignition engine conditions, with different degree of exhaust gas recirculation. The liquid length and lift-offlengthresults indicate that there was no significant interaction between the liquid phases of the fuels and their com-bustion regions. Theflame lift-offlengths were found to be affected by both the chemical and physical propertiesof the fuels. It was observed that a larger difference between the lift-offlength and thefirst-luminosity distancewas correlated with lesser downstream soot formation, although the molecular structure of the fuel was found toaffect the process too. Assessing the sooting and combustion characteristics of the biodiesel and dieselflamesacross the varied ambient O2atmospheres revealed that the estimated soot contents of the biodiesel and dieselflames peaked at 15 and 21 vol.% O2concentration, respectively. The peak soot contents of the WCO and CAObiodieselflames were found be comparable, but lower than that of diesel, across the various O2environment.The results also demonstrated that the biodiesels have higher normalized peak pressure values than diesel at allO2conditions. Two-color pyrometry data demonstrated that the measured soot temperature and soot KL factorsof theflames were similar at 15 and 21 vol.% O2, but varied with further reduction of ambient O2concentration.Variations in the combustion duration andflame area were found to be fuel dependent.