PM Characteristics of Low NOx Combustor Burning Biodiesel and its Blends With Kerosene

Particulate matter (PM) emissions from gas turbine engines have increasing attention due to their impact on global climate change, human health and local air quality. Most of the existing data for particle size distribution in aero engines is for diffusion or rich/lean type combustors where the rich zones generate solid nano particle carbon emissions. This work investigates well mixed lean low NOx combustion where mixing is good and generation of solid carbon particulate emissions should be very low. This work investigated the particulate number concentrations and size distributions of exhaust gases emitted from a radial swirler based low NOx gas turbine combustor. The tests were conducted using a radial swirler industrial low NOx gas turbine combustor under atmospheric pressure and 600K at reference Mach number of 0.017 and 0.023. A baseline of natural gas combustion was compared with a waste rape seed cooking oil methyl ester biodiesel (WME), its blend with kerosene B20, B50 and pure kerosene. The particulate emissions were compared as a function of the lean well mixed primary zone equivalence ratio. A SMPS with a Nano-Differential Mobility Analyzer (NDMA) was used to determine the number and concentration and size distribution of aerosols. The results showed that all WME particulates showed unimodal distribution characteristics with peak particle number at around 20nm. Conversion of the number distribution to mass showed very low mass emissions of around 1 mg/kg_fuel. Modern low NOx engines such as the Trent 970-84 has carbon mass emissions of 9 mg/kg_fuel based on the ICAO FOA-3 procedures. Thus, it is not unreasonable that in much lower NOx combustor designs the solid mass emissions will be lower than in current low NOx engines. Comparison is also made with particulate emissions from a diffusion flame APU gas turbine and much higher particle number emissions were demonstrated.