The activities of programs investigating various aspects of aircraft internal combustion engines are briefly described including developments in fuel injection technology, cooling systems and drag reduction, turbocharger technology, and stratified-charge rotary engines

Kempke, E. E., Jr.

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POSITIVE DISPLACEMENT TYPE GENERAL-AVIATION ENGINES:
SUMMARY AND CONCLUDING REMARKS
Erwin E. Kempke, Jr.
National Aeronautics and Space Administration
Lewis Research Center
During this session, the internal combustion engine program, its status and
accomplishments have been presented. Both the near and longer term technical
thrusts were discussed. Significant progress on both fronts has been made.
In the near term conventional engine area the integration of four
modifications in a test engine provides for a I0 percent improvement in the
high-performance-cruise fuel economy while meeting the emissions standards.
A new program aimed at improved cooling and drag reduction has been
established. The Phase I effort on improved-cylinder head-and-barrel cooling
will be underway at Teledyne Continental Motors, Aircraft Products Division, by
the end of this year.
The grant program to develop and verify a realistic Otto cycle computer
model shows significant progress at the two-thirds completion point. Today,
calculations of two-dimensional unsteady, turbulent, compressible flow with
moving boundaries are being made. The related ambitious experimental program to
develop advanced combustion diagnostic techniques has been completed.
In the fuel-injection technology program the contract to Spectron is
quantitively characterizing the performance of various injector nozzles. The
in-house flow visualization work is studying the same set of nozzles under
motored engine conditions by means of high-speed photography.
The effort to define the benefits and requirements of advanced but cost
effective turbocharger technology has been initiated. The RFP for Phase I is
expected to be issued in early 1980.
For the longer term the results of the on-going studies involving alter-
native engine configurations were presented. The advanced spark-ignition piston
engine study, which is 75 percent complete, shows 0.33 and 0.36 BSFC for the
stratified charge and lean burn concepts, respectively. The two-stroke diesel
shows 0.36 BSFC and 1.07 Ib/hp for the 250-hp cruise version. The
stratified-charge rotary engine study, which has been completed to the
technology assessment task, continues to be a viable candidate.
The airplane and mission studies by Beech and Cessna will soon be underway.
Results from these studies and the on-going Lewis effort will objectively
evaluate, rank, and compare the three study engines with each other, with
representative current-production engines, and with a highly advanced small
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turboprop in terms relevant to the industry. The result of these activities in
late FY 80 will be recommendations as to which concepts merit serious technology
enablement programs.
The supporting research and technology included both contract and in-house
elements. Diesel and rotary engine test cells at Lewis are now operational with
baseline mapping complete. Active research programs are underway in such areas
as supercharge versus compression ratio tradeoffs for optimum performance;
fuel-injection rate, timing, and other parameters; and ceramic combustion-
chamber insulation materials. A Curtiss-Wright program confirmed that
efficiency improvements in the RC2-75 could be achieved by increasing
compression ratio and relocating spark plugs: the BSFC at cruise was improved
from 0.54 originally to 0.47.
The University of Michigan, working under a NASA grant, recently completed
feasibility tests of a dieselized current-production spark ignition cylinder.
These tests indicated that moderate firing pressures at low compression ratio
resulted in improved cruise BSFC, thus indicating the possibility for
considerably reducing the specific weight of a diesel.
In conclusion, the results of the near-term conventional engine activities
have shown that it may soon be possible to improve both economy and cooling
efficiency. Since the technology is being developed in terms of current
production engines under the constraint of remaining compatible with existing
facilities, processes, etc., it can be incorporated into OEM production with
little adverse effect. By the same token this technology is potentially
available for incorporation by retrofit.
Farther into the future it appears that the internal combustion engines
discussed today are all viable candidates. They have the potential of improving
significantly on the present situation in terms of fuel economy, weight,
alternative fuels capability, and other characteristics. In addition to these
readily quantifiable benefits, there are further benefits in the areas of safety
and all-around utility. Over-the-weather cruise altitude capabilities could
eliminate up to 25 percent of all weather-related accidents at the same time it
is providing more efficient and comfortable flying conditions. Although the
candidate engine selection process will be difficult, it is anticipated that a
preliminary selection may be possible after comparative engine/airframe results
are in hand. However, regardless of which candidate is selected, the potential
powerplant advancements are synergistic with expected improvements in
structures, aerodynamics, materials, and avionics which together will result in
significantly improved airplanes for the 1990's and beyond.
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Positive displacement type general-aviation engines: Summary and concluding remarks

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