Comparison of Different Fuel Operations of a Multi-Fuel Single-Disk Rotary Engine through Thermodynamic Analysis

Abstract

Today unmanned aerial vehicle applications are powered by Wankel rotary engines due to their high power-to-weight ratio and smooth operation. Most of modern propulsion units for unmanned aerial vehicles are designed to run on high volatile fuels such as aviation gasoline (AvGas). However, the refueling infrastructure in aviation is geared toward the most used aviation fuel, kerosene. This and other reasons, such as significantly lower price and easier fire protection regulations, lead to the desire to be able to operate these propulsion units with kerosene. Opposed to reciprocating engines, the low compression ratio of rotary engines prevents the implementation of compression ignition combustion processes. Therefore, the purpose of this paper is to discuss the operation of a spark-ignited rotary engine on different fuels. In detail, different qualities of kerosene as well as gasoline/kerosene blends are compared together. In this respect, a thermodynamic analysis of the individual operations is undertaken. In order to make a statement about the efficiency and quality of the combustion, the investigation is carried out to determine the optimal rotor angle range for the center of combustion, with maximal efficiency and torque. On the basis of measurement data, it was possible to show that rotary engines also have an optimal rotor angle for the center of combustion, almost regardless of the operating point and mixture composition. Only the fuel used has little influence on the location of the optimal center of combustion. In addition to the comparison of the combustion characteristics of the individual fuels, the problems of operating with kerosene are examined in detail. Due to the low knock resistance of kerosene, restrictions in the operational area can be observed. Nevertheless, despite the different properties of the fuels, approximately similar torques and power outputs can be generated.