Pulse detonation engines use explosions to create thrust and are more efficient than traditional jet engines at high speeds. They can drive an aircraft at four to five times the speed of sound. Researchers believe they can be combined with other engines for fuel efficiency and military reconnaissance.
A pulse detonation engine is a propulsion device that uses controlled explosions to create thrust. These types of engines have been investigated for use in supersonic aircraft. Theoretically, pulse detonation engines are more efficient than traditional jet engines at high speeds, and can drive an aircraft at four to five times the speed of sound.
Normal jet engines ignite fuel in a process known as “deflagration.” This means that as long as air is present, the fuel burns at a fairly constant rate. The expanding gases produced during the deflagration move slower than the speed of sound. This is an efficient use of fuel at low speeds, but it does not provide enough power for sustained supersonic propulsion.
Pulse detonation engines rely on a much more violent and vigorous expansion of gases. The fuel in this type of powertrain literally explodes, creating a shock wave that moves faster than sound. When these detonations are cycled or pulsed, thrust is created. A special valve is required to produce a recurring pulse of controlled explosions. The most common design for this valve is a rotating disc that allows air to enter a combustion chamber at a set interval.
It is important that the pulse timing is consistent. Too long an interval between detonations will prevent usable thrust from building up, while too short a time will result in a large unsustainable explosion. Due to the high pressure shock wave created by a pulse detonation engine, the materials must be much stronger and heavier than a traditional engine casing. High vibration and sound levels are also factors that must be minimized with dampers and insulation.
Several US research groups, including the National Aeronautics and Space Administration (NASA) and the Defense Advanced Research Projects Agency (DARPA), have experimented with different variations of pulse detonation engine technology. . The first flight of an aircraft powered by this type of propulsion occurred in 2008. However, this test aircraft did not reach supersonic speeds, and engine research continued.
Some researchers believe that pulse detonation engines can be combined with other types of engines. This type of hybrid system could allow an aircraft to use a fuel-efficient jet engine during takeoff, then switch to the more powerful firing engine for high-speed cruise. Many designers speculate that pulse detonation propulsion will allow the military to build advanced reconnaissance aircraft. At very high supersonic speeds, such an aircraft can evade and overcome enemy defenses. Efficient supersonic engines also have civil applications, and could lead to extremely fast inter-country or intercontinental flights.
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