III. Make up a sentence with the phrase “the drawbacks promise to be overcome”.

III. Make up a sentence with the phrase “the drawbacks promise to be overcome”.

IV. Say some definitions of the words from the text to make your group mates guess.

Operation of pulse detonation engine

A detonation propagating from the closed end of the tube is followed by an unsteady expansion wave (called Taylor wave), whose role is to bring the flow to rest near the closed end of the tube. When the shock wave reaches the rear of engine and exits, the combustion products are ejected in “one go”, the pressure inside the engine suddenly drops, and the air is pulled in front of the engine to start the next cycle.

PDE operation is not determined by the acoustics of the system and can be directly controlled. PDEs typically operate at a frequency of 50–100 Hz, which means that a typical cycle time is on the order of 10–20 ms. Since PDE produces a higher specific thrust than a comparable ramjet engines at low supersonic speeds, it is suitable for use as part of a multi-stage propulsion system. Single-tube supersonic impulse PDE with straight detonation has higher performance than ideal ramjet engines for flight Mach number up to 1.35.

The PDE can provide static thrust for a ramjet or scramjet engine or operate in combination with turbofan systems.

PDE can be classified as:

• Pure (standalone)

• Combined cycles

• Hybrid turbomachinery cycles

Pure PDE as the name implies consists of an array of detonation tubes, an inlet, and a nozzle. The applications of pure PDEs are mainly military, as they are light, easy to manufacture, and have higher performance around Mach 1 than current engine technologies. Their noise and the drop in efficiency at higher Mach number imply that pure PDEs will likely not to be used often for large-scale applications.

Combined-cycle PDEs may provide the most exciting possibilities for aviation. Adding a PDE to the flowpath of a ramjet or scramjet would make an engine capable of operating efficiently as high as Mach 5.5. These engines would seem initially suitable for high altitude, high-speed aircraft.

Hybrid PDE’s make use of detontative combustion in place of constant pressure combustion, usually in combination with turbomachinery. Hybrid engines are of two types, one in which the PDE replaces the conventional combustor, but has several disadvantages among which providing high temperature flow into turbine blades. An alternate approach involves arranging the PDE combustor in the bypass duct of turbofan engines and mixing the PDE exhaust with the turbine exhaust in a mixer located aft of the turbine, which resembles a mixed turbofan arrangements. In other researches of hybrid turbofan-PDE: The central core engine would still turn the large fan in front, but the bypass would flow into a ring of PDEs in an unmixed turbofan arrangement. The bypass air enters pulse detonation tubes that surround the standard combustion chamber. The tubes are then cyclically detonated; one detonates while the others fill with air or are primed with fuel. This combination promises to require simpler engine mechanisms and yield higher thrust with lower fuel consumption as examined by GE.

Hybrid PDEs will allow commercial aircraft powered by subsonic gas turbines to be faster, more efficient, and more environmentally friendly. Similarly, hybrid supersonic gas turbines can also be used in military applications. Generally, hybrid PDEs will deliver the same thrust of a turbofan engine but with less fuel consumption. Moreover, they would produce significantly more thrust without requiring additional fuel.

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