Mobile ground test rig for evaluating small-scale turbojet in-flight performance and start reliability

Abstract

This paper presents the design and analysis of a mobile ground test rig for small-scale turbojet engines to simulate in-flight start reliability for design changes aimed at increasing the performance of the engine. One of the primary goals of these efforts was focused on the desired capabilities of the test rig, such as affordability, mobility, the capability of simulating a range of conditions such as total pressure, mass flow rate, and Mach number, whilst testing the effect of different fuels and equivalence ratios. Successful engine ignition can be a difficult task when operating at flight speed and higher altitudes. Developing an engine ignition envelope for the best chance of ignition would allow pilots to know what flight speed and altitude to fly at for best operability. To understand the influence of combustion characteristics on combustor ignition, a test rig was needed to analyze these attributes. This rig utilizes the fuel distribution system and engine control unit readily available from a KingTech K-160 turbojet to reduce complexity, although the test stand is adaptable to different engines. The ground test rig incorporates a portable compressor attached to a pressure chamber to simulate a range of operating conditions by altering the total pressure and mass flow rate into the engine. While simulating these conditions, combustion was then tested with different fuels to show their effect on start reliability, fuel consumption, exhaust gas temperature, and other performance parameters. Diesel required less fuel than Jet-A and consistently produced more thrust over a range of throttle conditions. This resulted in the engine having a thermal efficiency of 12% using Diesel and 11% using Jet-A. Successful ignition occurred more frequently and most notable at leaner equivalence ratios using Diesel.