Development and Implementation of a Thermal Signature Testing Protocol for a Fuel Cell Auxiliary Power Unit (APU) on a Diesel Tractor

Thermal signature is one of several factors that will determine the applicability of fuel cell auxiliary power unit (APU) technology to military vehicles. Thermal characterization is important for military applications in particular because it is a common mode of identification and detection. Fuel cell APU thermal characteristics are a unique case for which standardized testing procedures have yet to be established. The objective of our study was to develop and implement a protocol for quantifying the thermal characteristics of a fuel cell-equipped tractor operating under representative load conditions. Initial testing was conducted on a fuel cell APU-equipped Freightliner tractor using a high-performance radiometric infrared system. The testing protocol calls for a series of infrared images of the APU to be collected at three different viewing angles and two different elevations while the APU is under various loads. The diesel engine was studied under similar load conditions using seven different viewing angles and two different elevations. Simulation of various operating modes and power takeoff operations was performed because thermal profile of the fuel cell was expected to vary as a function of load. Thermal analysis of both the methanol-fueled fuel cell and the diesel tractor were conducted using box averaging and line analysis. We found that the APU had a unique, load-varying thermal profile; however, a metal cover significantly filtered radiation resulting in a measurable but not easily identifiable profile.