temperature engine must be minimized by high efficiency turbomachinery and innovative design.

On the positive side, an adiabatic engine possesses the potential for dramatically reducing the engine's cooling system and for moving to a single fluid design (i.e., a waterless, "oil only" configuration). Fuel economy improvements are possible because of improved piston expansion characteristics and increased exhaust energy recovery opportunities. In addition, and perhaps most significantly, fuel economy gains (particularly at part load) result on an installed basis because of a reduction of parasitic losses (i.e., fans, pumps, grilles, etc.).

Further, from a military system standpoint, propulsion system volume of a combat military vehicle can be reduced by over 40% through the utilization of this technology. Elimination of the conventional engine cooling fans, radiators, hoses and shrouds would produce a significant increase in reliability and mairtainability. The engine would not be as vulnerable to most conventional cooling system damage and extreme environmental conditions. Fuel economy improvements translate into increased range and reduced logistics concerns. Specific weight reductions allow improved vehicle response, while less vehicle volume allows reduced armor cover requirements, reduced : vehicle weight, and new innovative designs with improved. ■ survivability characteristics. The reduced signature of such an engine in terms of smoke and noise provides increased survivability to the combat vehicle, while high temperature operation provides a wider range of acceptable fuels to be utilized. With this engine type, the entire philosophy of combat vehicle design becomes far less restrictive. Concerns regarding satisfactory locations for cooling grilles, air passages, and associated equipment are eliminated. Applications of an adiabatic type engine to commercial activities provide similar advantages to those discussed above and in addition include improvements in the areas of emissions, simplicity, vehicle aerodynamics, operating costs, and maintenance. It should be noted that 50% of commercial and military field failures are cooling system related.


In the U.S., key research efforts within the adiabatic engine area include: high temperature tribology, brittle material fracture analysis, stochastic finite element stress analysis, transient heat transfer, and methods of designing engine components with ceramic/metal interfaces. Careful characterization of ceramic materials, techniques for low cost machining/processing of the ceramics, and non-destructive evaluations are also underway. In Japan, the monolithic ceramic engine has been the predominant approach. However, at high output engine conditions, current monolithic ceramics have not currently livèd up to expectations with respect to reliability and cost. In the U.S. and Europe, ceramic coatings are drawing greater interest because of low cost and high reliability potential. The trend toward ceramic material/engine manufacturer consortiums appears to be growing on a worldwide basis, with success in the future most likely achieved, by those working toward a common goal.


Having been pioneered by TACOM, low heat rejection "adiabatic type" engines form a critical building block for future

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