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Ramjets are a type of jet engine that make use of the forward motion of an aircraft in order to compress air into the intake of the jet engine’s combustion chamber. This air is then heated by combusted fuel making thrust possible. These types of jet engines are unique because they are engines built solely for speed.
This engine isn’t the normal workhorse jet propulsion we normally associate with the commercial airplanes – they’re too slow. Ramjets operate at peak efficiency at the speed of Mach 5 or 5 times the speed of sound. This is a speed at which the forward motion of the aircraft allows it to scoop up and compress air as it flies.
The ramjet has a long history in aeronautics. The ramjet was first conceived by René Lorin in 1913. He attempted to build and test it but failed to get it working. Over the next 50 years various nations such as Russia and France developed and tested Lorin idea. The first Ramjet powered aircraft to fly was built by René Leduc and was called the Leduc 0.10. It made its first successful flight in 1949. The French owned Nord Aviation would later build on his success with the Nord 1500 Griffon which successfully achieved a flight speed of Mach 2.19 in 1958.
So what makes a ramjet operate? It works on a different application of Bernoulli’s principle. Just like with other aircraft, the flow of air creates an area of high pressure and low pressure around the wings. In the case of ramjets the difference between the high air pressure in front of the ramjet engine and the low pressure behind it forces air to be sucked through the front portion of the engine called the inlet and into the combustion chamber. As I stated before this air is then heated by the burning of jet fuel to create thrust.
The ramjet engine has both advantages and weaknesses. First, a ramjet engine is quite simple in design. It consists of the inlet, the cone the diverts air into the engine, the combustion chamber, fuel injector, the flame holder, which ignites the fuel, and the nozzle which directs the heated heated exhaust to create thrust.
Second due to its simplicity it can under certain condition operate quite efficiently. This leads to a discussion of the engine’s weaknesses. First there is the fact that it needs high speed forward motion to operate. Without assistance from a regular jet engine, an aircraft with a ramjet engine can not take off from a standstill. Ramjet engines can only operate with at least a speed of Mach 1. A ramjet engine also has a limited window of efficiency. The engine top level of efficiency is at Mach 5 any faster and the inlet can’t properly direct airflow into the engine.
Ramjets are now being considered as a possible solution for finding new ways to propel space craft. This type of Ramjet, called a Bussard ramjet would work on the same principle as an atmospheric ramjet but would make use the interstellar cosmic winds instead.
If you enjoyed this article of Universe Today there are others you might like to read. The is an book review on solar sails that talks about the application of Bussard ramjets as interstellar propulsion. There is another great article about the unveiling of a new European space jet.
If you want to learn more about ramjets there are some great resources on the web you can check out. The NASA website has an article with more detailed information on ramjets. You might also find more information on the Purdue University engineering page.