Comparison of thermophysical properties and combustion characteristics of various biodiesels in a non-MILD ultra-low emission swirl burner

Abstract

All global decarbonization strategies increase the importance of biodiesels in the future. Presently, three representative biodiesels: coconut, oil palm, and waste cooking oil, were studied. The coconut methyl ester is the most volatile, while palm methyl ester is among the least volatile biodiesels. The waste cooking oil-based biodiesel has a highlighted presence in the circular economy. Firstly, the thermophysical properties of the three neat biodiesels and blends with commercial diesel fuel are presented. Density, surface tension, and kinematic viscosity affect atomization, and the distillation curve characterizes fuel evaporation, while the flash point is critical for mixture ignition. The fuels behaved similarly up to 25 V/V% biodiesel-diesel mixture. Secondly, all fuels are tested in a Mixture Temperature-Controlled burner, featuring distributed combustion without any low-oxygen technique. The flame shape was highly affected by fuel volatility and governed pollutant emissions. NO emission was evaluated due to practically complete combustion in all cases, concluding that distributed combustion may lead to nearly a magnitude reduction of this pollutant. The maximum value was below 14 mg/Nm3, fulfilling the current European gas turbine standard with an 80% margin. Our goal is to introduce the Mixture Temperature-Controlled combustion concept in boilers and gas turbines.