Evaluating high volume blends of vegetable oil in micro-gas turbine engines

Vegetable oil was examined to determine if high volume blends with No. 2 ultra-low-sulfur diesel could be successfully utilized in micro gas turbine engines. Property data, and atomization and micro-gas turbine engine studies were examined for blends of up to 75% by volume soybean oil with No. 2 ultra-low-sulfur-diesel (ULSD). Kay's and Grunberg-Nissan mixing rules were found to predict specific gravity and viscosity, respectively, based on composition to a high level of accuracy. For Kay's mixing rule the AADs were below 1%, while AADs for the Grunberg-Nissan equation stayed under 4%. Atomization tests showed an increase in cone angle of 18° for a 30-degree nozzle with a mixture of 50% soybean oil/ULSD over that of pure soybean oil. The pour point for blends of V50 and V75 were found to meet the ASTM D2880-13b Fuel Oil Specifications for gas turbine engines. For a V50 blend the spray angle was increased by 50% over that of pure SBO. The micro-gas turbine engine performed well for fuel blends up to 75% vegetable oil, with comparable engine efficiencies to that of ULSD. Engine efficiency and thrust increase with increasing RPM. The studies indicate that high volume blends of straight vegetable oil with ULSD are suitable in micro-gas turbine engines.