Program Description

To meet the program objectives, DOE has defined several specific goals. The primary goal is to develop technology capable of producing engines which exhibit a 30% improvement in fuel consumption. That translates to a specific fuel consumption goal of .25 lbs. per brake-horsepower-hour. Since this program is directed toward the•development of'commercial transportation engines, several other goals must also be met. Engines using the technology must be able to meet emission and noise standards, be cost competitive in both capital and maintenance costs and be able to operate on minimal quality fuels.

DOE has also set several important guidelines in order to make the results of this program most effective and implemented by industry in as short a time as possible. First in importance is industry involvement in all phases of the program. This includes early planning as well as continuous liasion to insure proper direction and identification of technical barriers to implementation. Secondly, to assure early implementation, technology development will be directed toward more evolutionary rather than revolutionary approaches. Lastly, to assure that government funds will not be used for product development, research will be directed toward long term high risk technology where industry is "not willing to go it alone."

Technical management of the program has been delegated to NASA's Lewis Research Center in Cleveland, Ohio. NASA initiated it's effort planning to first develop the critical technology then demonstrate that technology in a series of proof-of-concept engine tests. Implementation of the program is being carried out primarily by research contracts with the diesel engine industry. Table 1 gives a listing of the present contractors in the program.

The program is focusing the majority of its research on key problem areas that have been identified as the critical barriers to the successful development of the low heat rejection (LHR) concept. Those problem areas are shown in figure 1.

In the LHR concept, the upper parts of the cylinder surfaces can run as hot as 2000°F. This necessitates the use of a high temperature insulation to protect the surrounding structure. In this case the preferred material is either a solid ceramic or a ceramic thermal barrier coating. In designing an engine, it is possible to use both the solid ceramic and the coating in combination, singularly, or combined with an "air gap" insulation in the metal. All of these approaches are being investigated.

The second critical technology barrier is the tribology problems associated with the high temperature piston lubrication and seals.

Solutions to these problems are being investigated in a variety of ways involving solid, liquid and gaseous lubricants as well as various high temperature wear resistant coatings. Solutions to the piston/cylinder problems must also consider the lubrication system in the rest of the engine. Friction and wear needs to be considered and minimized too. Reducing friction becomes a positive gain because it has a direct effect in reducing fuel consumption, particularly at part load.

Exhaust emissions of the low heat rejection engine must be able to meet legislated standards, since the concept is being developed for commercial applications. Tests run to date give conflicting evidence regarding the trends of the emissions. It is generally thought that HC, CO, and particulates will be reduced while NOX will increase. The program is first addressing the characterization of the emissions and then will use the results to guide research on combustion optimization and emission reduction.

In the LHR concept, the majority of the heat previously lost to the cooling system is now available as increased exhaust energy. The maximum gains to be made in reducing fuel consumption are through effective utilization of this energy. The program has evaluated several different methods for heat utilization. The two that have emerged as most promising are turbocompounding and the Rankine cycle bottoming system. The Rankine system removes upwards of 15% of the exhaust stream energy but is a complex system. The turbocompounding system is not as complex but it only extracts about 5% of the available energy. Several potential solutions to the problems are being addressed.

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