COOLING CONCEPTS FOR A FAMILY OF SMALL, HEAVY-FUEL ROTARY ENGINES FOR USE IN AUXILIARY POWER UNITS

Military Ground Vehicle electric power demands continue to grow as new mission equipment is added. Using an Auxiliary Power Unit (APU) consumes less fuel than restarting the main engine frequently to charge batteries.

To meet the rising demand for powerful, L-3 Combat Propulsion Systems is developing a family of heavy-fuel rotary engines. Rotary engines offer superior power density making them a good choice for applications that require high power in a limited space. Heavy fuel capability simplifies logistical challenges in the field.

However, rotary engines have unique cooling challenges. Unlike a piston engine, the intake, compression, expansion, and exhaust events all take place at their respective fixed positions around the circumference of the rotor housing, leading to large temperature differences around the housing. The cooling system must be carefully developed to minimize these temperature differences in an effort to control thermal deformation, minimize thermal stress, and retain material strength.

This paper compares the advantages and disadvantages of a single-fluid cooling concept compared (oil) to a dual-fluid cooling concept (oil and water-ethylene glycol).