The impact of spray quality on the combustion of a viscous biofuel in a micro gas turbine

Highlights: • Combustion of straight vegetable oil was tested in a micro gas turbine. • The study is focused on the effect of fuel viscosity on combustion efficiency. • A linear relation between viscosity and CO emissions was found. • The pressure-swirl atomizer showed limited tolerance to increased viscosity. - Abstract: The relation between spray quality and combustion performance in a micro gas turbine has been studied by burning a viscous biofuel at different fuel injection conditions. Emissions from the combustion of a viscous mixture of straight vegetable oils have been compared to reference measurements with diesel No. 2. The effect of fuel viscosity on pollutant emissions is determined by adjusting the injection temperature. The measurements confirm that a reduction in fuel viscosity improves the spray quality, resulting in faster droplet evaporation and more complete combustion. CO emission levels were observed to decrease linearly with viscosity in the tested range. For the pressure-swirl nozzle used in the tests, the upper viscosity limit is found to be 9 cP. Above this value, droplet evaporation seems to be incomplete as the exhaust gas contains a considerable amount of unburned fuel. Additionally, the influence of increased injection pressure and combustor temperature is evaluated by varying the load. Adding more load resulted in improved combustion when burning diesel. In case of vegetable oil, however, this trend is less consistent as the decrease in CO emissions is not observed over the full load range. The outcome of this study gives directions for the application of pyrolysis oil in gas turbines, a more advanced biofuel with high viscosity