Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Patent
1987-09-15
1989-10-17
Koczo, Michael
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
123316, F02B 3700, F02B 4110
Patent
active
048738255
DESCRIPTION:
BRIEF SUMMARY
This invention relates to prime movers comprising a positive displacement engine compounded with a turbine/turbocompressor set, designated herein, with reference to the former component, as turbocompounded positive displacement engines. The invention further relates to operating cycles for such engines.
In general terms, it is already well known to link a turbine/turbocompressor set to a positive displacement engine, such as a reciprocating piston or rotary piston engine, so that the exhaust gases of the latter drive, or help to drive, the turbine, which drives the turbocompressor, which in turn turbocharges the positive displacement engine. Compound engine arrangements are also known in which the turbine/turbocompressor set, through exchanging air for combustion gases from the positive displacement engine, is actually part of a gas turbine engine capable of operating independently of the positive displacement engine. The present specification deals with improvements in both these types of prime movers.
It has been long considered desirable to turbocharge positive displacement engines, or to compound a positive displacement engine with a gas turbine engine, in order to maximise power output and fuel efficiency while minimising specific weight. Examples of turbocompounded piston engines are too numerous to mention, and many are very well known, particularly in the field of automotive technology.
A good early example of this type of engine as applied to aircraft propulsion was the "Napier Nomad", described for example, in the magazine "Flight", vol. 65, no. 4, April 1954, pp. 543-551. It consisted of a turbocharged 12-cylinder, 2-stroke diesel with the turbine/turbocompressor set driven off the diesel's exhaust, the two parts of the engine being interconnected through a variable gear which allowed the two shaft speeds to be optimally matched over the flight regime of the aircraft in which it was installed. It was not commercially successful, because it was heavier and more complex than equivalent turbojets; also turbojets offered higher speeds, while fuel at the time was relatively cheap so that the higher fuel consumption of the turbojet was not very much of a penalty.
Since then, numerous other studies on turbo-compounded positive displacement engines for aircraft propulsion have been carried out as technology has advanced. For example, NASA Technical Memorandum TMX-71906 entitled "Preliminary Evaluation of a Turbine/Rotary Combustion Compound Engine for a Subsonic Transport" by K. C. Civinskas et al, March 1976, shows what is essentially a high pressure ratio turbofan which has had its combustor replaced by a rotary piston engine, the compressor and turbine being on the same main shaft as the rotary piston engine and the fan also being geared to that shaft. The rotors of the rotary piston engine orbit directly about the main shaft. In terms of aeroengines this was not considered a successful design at the time, the improved fuel consumption obtained being insufficient to compensate for increased engine weight as compared with the reference turbofan.
More recently, U.S. Pat. No. 4,449,370 discloses a compound engine for aircraft use in which a low compression turbocharged diesel engine has a turbocharger which can be operated independentlv of the diesel. This is possible because although the turbine receives the exhaust gases from the diesel, they first pass through a catalytic combustor inserted in the cycle before the turbine, so that whenever needed, fuel and air can be supplied to the catalytic combustor to provide additional heating of the exhaust gases; furthermore, a valve and ducting is provided so that the diesel engine can be selectively bypassed, the compressor (blower) air being passed straight to the catalytic combustion chamber to drive the turbine and hence provide power for auxiliary equipment during the starting sequence.
A survey of these and numerous other proposed examples of turbocompounded positive displacement engines seems to reveal that, though of varied type and construction, they
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AIAA-83-1338, "Compound Cycle Turbofan Engine", J. G. Castor, Jun. 27-29, 1983.
NASA Technical Memorandum 88879, USAAVSCOM Technical Report 86-C-37, "Compound Cycle Engine Program", Bobula et al, 1986.
SAE Paper No. 740723, "Hyperbar System of High Supercharging", Melchior et al, 1974.
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