Internal-combustion engines – Precombustion and main combustion chambers in series – Two-cycle
Patent
1987-09-16
1989-02-28
Myhre, Charles J.
Internal-combustion engines
Precombustion and main combustion chambers in series
Two-cycle
123 65VD, F02B 7502
Patent
active
048075795
DESCRIPTION:
BRIEF SUMMARY
This invention relates to turbocompounded 2-stroke piston engines and to improved cylinder head configurations for such engines.
By the term "turbocompounded 2-stroke piston engines" is meant a 2-stroke reciprocating piston engine adapted to be linked to a turbine-turbocompressor set so that the exhaust gases of the former drive, or help to drive, the turbine of the latter, which drives the turbocompressor, which in turn turbocharges the piston engine. The turbine/turbocompressor set may be part of a gas turbine engine capable of operating independently of the piston engine, or may operate merely as a turbocharger.
It has long been considered desirable to turbocharge piston engines operating on a 2-stroke cycle in order to maximise power output and fuel efficiency while minimising specific weight of the engine.
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, apparently 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.
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 independently 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 other proposed examples of turbocompounded 2-stroke piston engines seems to reveal that, though of varied type and construction, they follow convention for such engines in that the pressure at which the turbocharging air is delivered to the piston engine is lower than the pressure at which the combustion gases from the piston engine are exhausted to the turbine.
Furthermore, considering examples of 2-stroke piston engine operating cycles in the ordinary case where they are not turbocompounded, it can be observed that, as a general rule, their compression ratios are approximately the same as their expansion ratios. It appears to be a fact that this general rule has also been applied to them when they have been compounded with turbine/turbocompressor sets.
It is here contended that the facts mentioned in the above two paragraphs are disadvantageous because, for reasons which will be appreciated later, they result in the overall operating cycles of turbocompounded 2-stroke piston engines being less efficient and powerful than they could be.
It is an object of the present invention to provide turbocompounded 2-stroke piston engines which are adapted to utilise a more efficient and/or powerful operating cycle than hitherto.
Accordingly, the present invention provides a turbocompounded 2-stroke piston engine having a cylinder head incorporating, for each cylinder of said piston engine, an indirect combustion chamber, inlet valve means for admitting turbocharging air to the cylinder, and exhaust valve means for exhausting combustion gases from the cylinder, the piston engine being adapted to perform an operatin
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Myhre Charles J.
Okonsky David A.
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