11-06-2013, 03:53 PM
PULSE DETONATION ENGINE
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INTRODUCTION
Pulse detonation engine is a propulsion technology that involves detonation of fuel
Thrust formed due to detonation is effiecient than current sytem by virtue of it’s mechanical simplicity and thermal efficiency (potentially at Mach 5) .
But the process needs refinement for the material used in engines due to high pressure & temperature it has to withstand.
Important aspect is that it has a potential application in many sectors of the aerospace, aeronautic &military industries.
HISTORY
Power obtained from explosions for propulsion applications date back to late17th–early 18th centuries.
First exposure of gaseous detonations dates back to 1870–1883 period when combustion mode propagating at a velocity ranging from 1.5 to 2.5 km/s discovered.
Theoretical estimates for the detonation parameters based on one-dimensional (1D)flow considerations and mass, momentum and energy conservation laws 1890,1899 &1904.
End of the 19th–the beginning of the 20th century significant progress has been made both in experimentation and analysis of detonations.
WORKING PDE
Air & fuel are drawn through individual inlets and combined as flammable mixtures.
Mixture in front of the detonation chamber is detonated creating high pressure.
Pressure increases tremendously creating shock wave travelling across the length of combustion.
The shock wave moves to rear end and combustion products are discharged thus pressure reduces suddenly inside the chamber.
The reduction in pressure allows the air to enter through inlet .
The cycle is repeated up to 100times /second.
DIRECT INITIATION:-
The detonation is initiated by very powerful ignitor more or less immeditely.
Hundreds of joules are required to obtain a direct initiation of a detonation in a mixture of the most sensitive hydrocarbons and air.
Deflagration to Detonation Transition (DDT) :-
DDT requires lengths on the order of several meters to be completed .
A common method of circumvent these difficulties is pre detonation
The detonation from the pre-detonator is then supposed to be transmitted to the main chamber and initiate the detonation there (oxygen carried)
DIFFERENCE & COMPARISON WITH OTHER ENGINES
PDE the combustion chamber is open and no piston is used to compress the mixture prior to ignition .
The efficiency of the cycle can be explained by the high level of precompression due to the strong shock wave in the detonation.
the simplicity of the device is a result of the fact that the shock wave - responsible for this compression – is an integrated part of the detonation.
Pulse-jet the pre-compression is a result of momentum effects of the gases, and is a part of the resonance effects of the engine.
The resonance effects are influenced strongly by the external conditions of the engine, and the thrust is drastically reduced at higher speeds .
In the ramjet, pre-compression is obtained through the ram effects as the air is decelerated from supersonic to subsonic.
The major drawback with this concept is that the engine is ineffective for speeds lower than around M=2.
Conclusions
The PDE has an inherently simpler mechanical design and a higher thermodynamic efficiency. As such, it is shown that the PDE is more efficient, in both specific thrust and specific fuel consumption, than current ramjet systems at speeds of up to approximately Mach 2.3.
This performance advantage makes the PDE an excellent choice for static thrust up to mid- Mach numbers
The PDE has applications to many aerospace industries: Quick and efficient intercontinental travel, safe and cost-effective spacecraft launch, and effective military operation.
However, the engineering of new materials to endure the intense physical environment of the detonation cavity is a problem that remains to be solved.