But there are no compressors in a ramjet. Therefore, ramjets are lighter and simpler than a turbojet. Ramjets produce thrust only when the vehicle is already moving; ramjets cannot produce thrust when the engine is stationary or static. Since a ramjet cannot produce static thrust, some other propulsion system must be used to accelerate the vehicle to a speed where the ramjet begins to produce thrust. The higher the speed of the vehicle, the better a ramjet works until aerodynamic losses become a dominant factor.
The combustion that produces thrust in the ramjet occurs at a subsonic speed in the combustor. For a vehicle traveling supersonically , the air entering the engine must be slowed to subsonic speeds by the aircraft inlet. Shock waves present in the inlet cause performance losses for the propulsion system. Above Mach 5, ramjet propulsion becomes very inefficient. The new supersonic combustion ramjet , or scramjet , solves this problem by performing the combustion supersonically in the burner.
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Combustion occurs in an open chamber akin to a giant afterburner, where liquid fuel is injected or solid fuel is ablated from the chamber's sides [sources: Ashgriz; Encyclopaedia Britannica ; SPG ; Ward ]. Ramjets' speed limitations gradually inspired hybrid engines that could fly at lower speeds and accelerate to supersonic velocities. The most famous example, the SR Blackbird, used a turbojet-ramjet hybrid called, appropriately, a turboramjet.
Such engines work like an afterburning turbojet until well past Mach 1, after which ducts bypass the turbojet and redirect the ram-compressed airflow into the afterburner, making the engine behave like a ramjet [source: Ward ]. Missile designs, meanwhile, gradually did away with boosters by moving them inside the ramjet itself, creating ramrockets , aka integral rocket ramjets.
During rocket acceleration, plugs temporarily seal the ramjet's intake and fuel injectors. Once the rockets are spent and the ramjet is up to speed, these pop off, and the empty rockets act as combustion chambers [source: Ward ]. Looking forward, crossing the Mach 5 line into hypersonic speeds will likely entail scramjets supersonic combusting ramjets. Unlike other ramjets, scramjets do not need to slow air to subsonic speeds in their combustion chambers. To pull off ignition and expansion in the 0.
Scramjets remained theoretical before the past few decades, and work remains mostly experimental. Some analysts believe the technology could reach Mach , but air travel at hypersonic speeds means overcoming forces unlike those faced by even the fastest supersonic craft.
One major obstacle to rocket-powered space travel is the exponential relationship between acceleration and fuel. The faster you go, the more fuel you need; the more fuel you carry, the more mass you add, the more additional fuel you need to overcome it [sources: Long ; NASA ].
With this in mind, physicists have proposed other solutions, including everything from solar sails to exploding ejected nuclear bombs. In , physicist Robert Bussard proposed an interstellar ramjet that would collect charged particles in space via an electromagnetic field, converge them, create a fusion reaction and use the energy for propulsion [sources: Long ; NASA ].
I'm often enchanted by stories of great innovations that failed to find an application when they were first invented. While writing this article, for example, I was repeatedly reminded of the laser, which was once called a solution looking for a problem. On the other hand, sometimes weird inventions make millions. Other times we invent things for one purpose that turn out to have unforeseen applications.
Among its many contributions, the American space program invented the ribbed swimsuit and changed diapers forever.
Today, materials scientists are discovering properties for which we have yet to find uses. With luck, they'll fare better than Lorin. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. How Ramjets Work. Ramjets: Making Mock of Mach. Detonations and Arrivals " ". A cameraman with a high-speed camera films the thrust augmentor flame of a ramjet I engine at the Lewis Flight Propulsion Laboratory in Cleveland.
The lab later became known as the John Glenn Research Center. Ramjets, Ahead of Their Time? Rudi Ramjet? Ramjets: Making Mock of Mach " ". The Blackbird parked at the Steven F. The Interstellar Ramjet. Read More. Lots More Information Author's Note: How Ramjets Work I'm often enchanted by stories of great innovations that failed to find an application when they were first invented.
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