Characterization of Small-Scale Turbochargers for Unmanned Aerial Systems

Aircraft engine power is degraded with increasing altitude according to the resultant reduction in air pressure, temperature, and density. One way to mitigate this problem is through turbo-normalization of the air being supplied to the engine. Supercharger and turbocharger components suffer from a well-recognized loss in efficiency as they are scaled down in order to match the reduced mass flow demands of small-scale Internal Combustion Engines. This is due in large part to problems related to machining tolerance limitations, such as the increase in relative operating clearances, and increased blade thickness relative to the flow area. As Internal Combustion Engines decrease in size, they also suffer from efficiency losses owing primarily to thermal loss. This amplifies the importance of maximizing the efficiency of all sub-systems in order to minimize specific fuel consumption and enhance overall aircraft performance. The lack of published performance data for many commercially sold superchargers in the mass flow range of concern for this study makes selection of efficient turbo-normalization systems very difficult. This paper will present an experimental procedure for characterizing turbomachinery components for several small-scale turbochargers and superchargers of interest for the target engine, which is a small-displacement Diesel engine. Data were derived from testing these machines on an experimental stand of the authors’ design. Compressor and turbine maps created from the resulting data are presented, along with the calculated adiabatic compressor efficiencies.