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Hybrid electric propulsion has matured to the point that it is in production for small vehicle platforms. Work still needs to be done on adapting the technology for heavier weight classes. The dramatic increase in fuel efficiency, the exhaust emission reductions and the availability of an on-board source of high-power electrical energy for auxiliary systems are important for the commercial and military market. The U.S. Army's National Automotive Center (NAC) in Warren, MI, and United Defense L.P. (UDLP) in San Jose, CA, have developed a series hybrid 20-ton tracked military vehicle to explore this technology. This paper describes this work and its application to the other hybrid programs.

A cooperative research and development program was organized to determine the critical particle size of abrasive debris that will cause significant wear in rotary injection fuel pumps. Various double-cut test dusts ranging from 0-5 to 10-20 μm were evaluated to determine which caused the pumps to fail. With the exception of the 0-5-μm test dust, all other test dust ranges evaluated caused failure in the rotary injection pumps. After preliminary testing, it was agreed that the 4-8-μm test dust would be used for further testing. Analysis revealed that the critical particle size causing significant wear is 6-7 μm. This is a smaller abrasive particle size than reported in previously published literature. A rotary injection pump evaluation methodology was developed. During actual operation, the fuel injection process creates a shock wave that propagates back up the fuel line to the fuel filter.