Zero-stage
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Jet engine A jet engine is a type of reaction engine discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include rocket, Pump-jet, water jet, and hybrid propulsion, the term ...
s and other
gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directi ...
engines are often uprated by adding a zero-stage, sometimes written '0' stage, to the front of a
compressor A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
.Hooker, Sir Stanley (1984). ''Not much of an Engineer'', P. 153. Airlife Publishing Ltd, Shrewsbury, England . At a given core size, adding a stage to the front of the compressor not only increases the cycle
overall pressure ratio In aeronautical engineering, overall pressure ratio, or overall compression ratio, is the ratio of the stagnation pressure as measured at the front and rear of the compressor of a gas turbine engine. The terms ''compression ratio'' and ''pressure ...
, but increases the core mass flow. A further uprating may be done by adding another stage in front of the previously-added zero stage, in which case the new one may be known as a zero-zero stage. A comparison with other ways of uprating an existing engine without drastically redesigning the engine shows for a particular case, e.g. the
Rolls-Royce/SNECMA M45H The Rolls-Royce/SNECMA M45H is an Anglo-French medium bypass ratio turbofan produced specifically for the twin-engined VFW-Fokker 614 aircraft in the early 1970s. The design was started as a collaborative effort between Bristol Siddeley and S ...
, the thrust could have been increased by 25% with a zero-staged l-p compressor or 10% with either an improved HP turbine or with water injection. Zero-staging is also combined with other modifications to provide increased thrust or lower turbine temperature.""Rolls-Royce Aero Engines" Bill Gunston, Patrick Stephens Limited 1989, , p.141-142 It may be required for an existing aircraft weight increase, or for a new application, as shown by the following examples. A 15-stage
Rolls-Royce Avon The Rolls-Royce Avon was the first axial flow jet engine designed and produced by Rolls-Royce. Introduced in 1950, the engine went on to become one of their most successful post-World War II engine designs. It was used in a wide variety of ai ...
powered the Lightning F.1. A zero-stage, together with a new turbine, was added (total 16 stages) for the Caravelle III. A zero-zero stage was added (total 17 stages) for the Caravelle VI. The 7-stage Snecma Atar D was used in the Mystere II. A zero-stage was added (total 8 stages) for the E and G used in the Vautour and Super Mystere B.2. A zero-zero stage (total 9 stages), together with a 2-stage turbine was added for the Atar 8 and 9 used in the Mirage III. The
Rolls-Royce/Snecma Olympus 593 The Rolls-Royce/Snecma Olympus 593 was an Anglo-French turbojet with reheat (afterburners), which powered the supersonic airliner Concorde. It was initially a joint project between Bristol Siddeley Engines Limited (BSEL) and Snecma, derived ...
started with a 6-stage LP compressor. As the Concorde increased in weight during the design phase the take-off thrust requirement increased. The engine was given a zero-stage to the compressor, a redesigned turbine and partial reheat. Examples of zero-staging for land-based gas turbines are the aeroderivative GE LM2500+ and the heavy-duty GE MS5002B. An alternative to zero-staging used by some
OEM An original equipment manufacturer (OEM) is generally perceived as a company that produces non-aftermarket parts and equipment that may be marketed by another manufacturer. It is a common industry term recognized and used by many professional or ...
s is supercharging the compressor with a fan driven by an electric motor. Zero-staging is demonstrated by the following relationship: w_2 = (w_2 \sqrt/P_3) * (P_3/P_2) * (\sqrt) * (P_2/\sqrt) \, where: core mass flow = w_2 \, core size =(w_2 \sqrt/P_3) \, core total head pressure ratio = (P_3/P_2) \, inverse of core total head temperature ratio = T_2/T_3 \, i.e. (P_3/P_2 \,) core entry total pressure = P_2 \, core entry total temperature = T_2 \, So basically, increasing (P_3/P_2) \, increases w_2 \,. On the other hand, adding a stage to the rear of the compressor increases overall pressure ratio, and decreases core size, but has no effect on core flow. This option also needs a
Turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...
with a significantly smaller flow capacity to drive the compressor. Zero-staging a compressor also implies an increase in shaft speed: N_2 = (N_2 \sqrt) * (\sqrt) \, where: HP Shaft Speed = N_2 \, HP Compressor "Non-Dimensional" Speed (based on Exit Total Temperature) = (N_2 \sqrt) \, HP Compressor Exit Total Temperature = T_3 \, So if the "Non-Dimensional" Speed of the original compressor is to be maintained, increasing T_3 \, increases N_2 \,. This implies an increase in both the blade and disc stress levels. If the original shaft speed is maintained, then the increase in pressure ratio and mass flow from adding the zero stage will be severely reduced. Although the above equations are written with zero-staging an HP compressor in mind, the same approach would apply to an LP or IP compressor.


References

{{Reflist Jet engines