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CALENDAR YEAR M986-H1987—H1988-H1989-+-1990H

CALENDAR YEAR M986-H1987—H1988-H1989-+-1990H

Figure 2. Program Time Phase Chart.

the Advanced Integrated Propulsion System (AIPS) for TACOM.

The four work phases outlined above are scheduled over a fifty-seven- (57) month period and shown in Figure 2. Phase I "Selection of Concept" is now completed and we are engaged in Phase II, "Exploratory Development" of tribological systems and insulated in-cylinder components. Advanced tribological systems and insulated in-cylinder components have been selected which are expected to meet the program's objectives. All of the concepts appear viable with a high confidence level for success.

We are also currently engaged in Phase III "Single-Cylinder Engine Preparation" and expect to have this phase completed in February, 1988—nearly seven months ahead of the original schedule.

Work Scope

Selection of Concept, Phase I. The work scope for this first phase focused primarily on surveying, screening, and selecting the technologies which will have the highest level of probability to meet the objectives and targets of the program. This phase was basically a paper study with no hardware involved. It was intended to select technical concepts for investigation in Phase II.

Exploratory Development, Phase II. This phase primarily uses rig tests to further evaluate, rank, and screen materials, lubricants, and design concepts selected from Phase I. In addition, material characterization and analytical techniques are included in the screening process. The selected bench test rigs are intended to allow the use of simple, low cost specimens which will reduce the testing time and allow a greater volume of candidates to be assessed. Examples include a thermal shock fatigue rig and friction-wear test rigs. The most complex rig is composed of a small bore engine which will very closely simulate the program engine's environment but will require significantly less financial, time, and testing resources.

Single-Cylinder Engine Preparation, Phase III. This phase is conducted parallel with Exploratory Development and involves design, procurement, test cell installation, and shake-down testing of the single-cylinder engine to be used for tribological and insulated component assessment.

Single-Cylinder Engine Testing, Phase IV. This phase completes the program by taking all of the best tribological and insulating technologies previously screened and combining them in one package. This phase includes assessing structural design integrity, durability and heat rejection levels, and. lubricant compatibility.

(stress-strength), overall performance, available technology, and development time frame. The three major concepts which were selected and the applicable time frames are shown in Table 1.

The originally proposed program called for the selection of one best concept; however, the participants felt it presented lower risk to select three concepts for each time frame (before 1990, and after 1990) rather than a single, optimized concept for the whole time spectrum. The significance of the

Table 1. Selected Concepts.

Concept Time Frame

1. Thermal Barrier Coating Before 1990

2. Monolithic/Air Gap Before/After 1990

3. Advanced Cast-In Composite After 1990

Progress

The current activities are divided into three major tasks: in-cylinder components, tribological systems and single-cylinder engine preparation. Execution of the in-cylinder components and single-

cylinder engine preparation tasks are the responsibility of Adiabatics, Inc. which is also the prime contractor. Concept Analysis Corp. of Detroit, Michigan was responsible for the software work which includes cycle simulation and finite element analysis. Midwest Research Institute is responsible for the tribological systems activities.

In-cylinder Components. The candidate design concepts which were selected for Phase II "Exploratory Development" were screened from several concepts as discussed in Reference 1. The concepts were selected on the basis of insulating effectiveness, probability of success year 1990 is related to the TACOM AIPS program. For the developed technology to be available for AIPS, it must be fully proven by 1990. Thermal analysis has estimated that thick thermal barrier coatings can provide sufficient thermal insulation to meet the primary program heat rejection target of 12.0 Btu/bhp-min. The heat rejection target for the AIPS program is much more conservative. The on or before 1990 BSHR target is 21 Btu/bhp-min. THis target allows for intake air aftercooling and liner TRR spot cooling, but still requires a significant level of in-cylinder insulation. The target for the reduction of in-cylinder heat transfer is reduced to 42-percent. The liner TRR temperature target is reduced to 700 degrees F maximum.

The primary thrust selected for the program was aimed at thermal barrier coatings and capped air-gap insulated piston assemblies. A review of candidate piston base materials indicated that the major factors to be considered were thermal expansion, piston weight, temperature stability, elevated temperature strength, and thermal conductivity. The major reason for selecting an iron or steel piston was to reduce the thermal expansion difference between the base piston material and the plasma-sprayed zirconia. However, one of the major disadvantages was the large increase in weight. A review of materials not limited to the traditional engine component designer candidates shows that titanium alloys such as Ti6242 are the best overall selections. A review of Table 2 shows the titanium alloy to match the thermal expansion of zirconia, density 2/3 of that for iron, thermal conductivity 1/3 of that for iron, and the overall strength superior to other materials.

Proposals for titanium alloy material applications were not limited to the thermal barrier-coated piston; they were also considered for the capped design—primarily for weight considerations. A thermal analysis was conducted, and the results are included in Table 3. The basic piston designs are illustrated in Figures 3 and 4. The following observations were made from reviewing the results of Table 3:

1. The capped piston air gap seal resulted in high heat flow to the ring groove area.

2. The insulating disk added only a slight improvement in reducing heat loss over the simple air-gaps.

Table 2. Thermal Barrier-Coated Piston Substrate Material Candidates.

Physical Properties 2

Density (lbs/in ) Melting Temp. (deg. F) Kt (Btu/hr-ft-*F)

Mechanical Properties ^ (psi X 106) T.S. (ksi) Y.S. (ksi)

Ductile Iron

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