The Heinkel HeS 40 ''(HeS - Heinkel Strahltriebwerke)'' was an experimental constant-volume

jet engine A jet engine is a type of reaction engine discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include Rocket engine, rocket, Pump-jet, water jet, and ...

Heinkel Heinkel Flugzeugwerke () was a German aircraft manufacturing company founded by and named after Ernst Heinkel. It is noted for producing bomber aircraft for the Luftwaffe in World War II and for important contributions to high-speed flight, with ...

starting some time in 1940 or 41. It was based on the mechanical layout of the HeS 30, but replaced the conventional

flame can A flame (from Latin '' flamma'') is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. When flames are hot enough to have ionized gaseous components of sufficient density they ...

s with oversized ones including large

poppet valve A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usua ...

s that sealed off the chambers during firing. Constant-volume combustion, similar to the

Otto cycle An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines. The Otto cycle is a description of what hap ...

used in most piston engines, is considerably more fuel efficient than the constant-pressure combustion used in a typical jet engine.Kay 2007, p.

Design

The design was based on the HeS 30 not only to make parts more readily available as well as to make direct comparisons between the two easier. The main changes were to reduce the compression ratio of the compressor to about 2:1 (from 2.8:1), and add the new combustion chambers. The new chambers were considerably larger than the originals, forcing a reduction in the number from ten to six burners. The valve stems projected forward into streamlined fairings in the intake area behind the compressor. The operational cycle of the engine is somewhat similar to a conventional six-cylinder engine, except the compressor did all the compressing instead of a piston stroke, and the chamber only served as a combustion chamber, rather than a compression, combustion and expansion chamber as in a piston engine. Compressed air, similar to an automobile equipped with a

turbocharger In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

, but at a hgiher pressure ratio, was channeled into the cylinders in turn, closed off with the poppet valves, and then burned. By the time the combustion was complete the pressure in the flame cans would be much higher, although the actual expansion ratio is not specified. The hot gas was then released, and flowed through a turbine to extract power, instead of forcing a piston to move (although most of the output in the expected

turbojet The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, a ...

engine format - as opposed to a

turboshaft A turboshaft engine is a form of gas turbine that is optimized to produce shaftpower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust ...

- would be extracted as

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

, and the turbine only acted to power the compressor to continue the cycle). Although there would be some loss of charge during the burning period, and thus the design would be less efficient than the true Otto cycle, it would nevertheless be somewhat more efficient than a traditional jet engine, at the cost of some complexity.

History

It appears the HeS 40 was never built, and remained a paper design. Nevertheless, work on the design was ended by 1942, by which point the HeS 30 was making good progress.

References

Bibliography

* * {{Hirth aeroengines Centrifugal-flow turbojet engines Heinkel aircraft engines 1940s turbojet engines