What is Ramjet: Definition and 17 Discussions

A ramjet, sometimes referred to as a flying stovepipe or an athodyd (aero thermodynamic duct), is a form of airbreathing jet engine that uses the engine's forward motion to compress incoming air without an axial compressor or a centrifugal compressor. Because ramjets cannot produce thrust at zero airspeed, they cannot move an aircraft from a standstill. A ramjet-powered vehicle, therefore, requires an assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust. Ramjets work most efficiently at supersonic speeds around Mach 3 (2,300 mph; 3,700 km/h). This type of engine can operate up to speeds of Mach 6 (4,600 mph; 7,400 km/h).
Ramjets can be particularly useful in applications requiring a small and simple mechanism for high-speed use, such as missiles. The US, Canada, and UK had widespread ramjet powered missile defenses during the 1960s onward, such as the CIM-10 Bomarc and Bloodhound. Weapon designers are looking to use ramjet technology in artillery shells to give added range; a 120 mm mortar shell, if assisted by a ramjet, is thought to be able to attain a range of 35 km (22 mi). They have also been used successfully, though not efficiently, as tip jets on the ends of helicopter rotors.Ramjets differ from pulsejets, which use an intermittent combustion; ramjets employ a continuous combustion process.
As speed increases, the efficiency of a ramjet starts to drop as the air temperature in the inlet increases due to compression. As the inlet temperature gets closer to the exhaust temperature, less energy can be extracted in the form of thrust. To produce a usable amount of thrust at yet higher speeds, the ramjet must be modified so that the incoming air is not compressed (and therefore heated) nearly as much. This means that the air flowing through the combustion chamber is still moving very fast (relative to the engine), in fact it will be supersonic—hence the name supersonic-combustion ramjet, or scramjet.

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  1. Destroyer500

    Ramjet artillery shell of a big size

    I will copy paste a post i made on another forum.Its just a fun project i started and i hope people in here are going to be able to help.I am not an aerospace engineer but im studying electrical and electronic engineering so i am familiar with formulas math and physics (up to a degree of...
  2. R

    Electric fan to get ramjet airborne?

    Does anyone know of prior work on the use of an electric fan to supply input air to a ramjet until the air speed is sufficient (~0.2 M) for normal operation? It's obviously possible, but might not be practical. The objective being the simplicity of a pulse jet without the vibration issues.
  3. Julian Erickson

    I Rocket-Jet Hybrid, Rocket + Ramjet

    I read that a thrust augmentor can significantly increase the efficiency of a jet engine (http://www.pulse-jets.com/phpbb3/viewtopic.php?t=931). Now from my understanding, the thrust agumentor is sort of like a ramjet. Only, in this case, the cold air is being sucked in along with the hot air...
  4. BoeingJet

    Can a Railgun-Powered Ramjet Solve the Challenges of High-Speed Travel?

    Recently, I designed (in my head) a Hypervelocity Passenger Vehicle (just a cool name for really high speed transports). I immediately ran into engine design problems ( I like designing everything stand-alone), since regular jet engines can't get to Mach 8.8 without burning up into flames, and...
  5. Nivek Writer

    How to calculate the drag force of a Bussard ramjet?

    Hello everyone, I am making a paper on the possible applications for nuclear fusion. One of these possible applications is a Bussard ramjet. I'm trying to calculate if Bussard ramjets are feasible, based on their thrust and the drag they experience. A Bussard ramjet would use a very big...
  6. yangshi

    Low Air Compressor CFM Still Works?

    Halfway through my thesis on a mach 2 ramjet, and I unfortunately realize that I need 50-72 CFM to test it. The only ACs I have are 2 CFM portable pancakes. Is it possible to run say a 25 CFM AC at 50 CFM for a short period of 10-60 seconds? Is there a quantitative way to find how long the AC...
  7. onion3000

    Ramjet/Scramjet Propulsion on a Vertical Rocket?

    Is it possible (practical/efficient) to utilize ramjet (or scramjet) on a vertical rocket? By this I mean would it be at all practical to make a vertically traveling rocket which partially uses ramjet as a method of propulsion, or is there some property of ramjet propulsion that makes this...
  8. G

    Practical measurements of ramjet engine

    Hello everyone I am trying to design a ramjet engine. For that I need measurements of its parts. Does anyone know how to calculate them or have a link to a website where I could find more information?
  9. Andrew J

    How to Determine Parameters of a Valveless Pulse Jet Engine?

    Hello all, I am a new member. I am a manager by trade but I hold a bachelors of science in mechanical engineering and would like to work on jet propulsion as a hobby and potentially as a part of my professional career in the future. In particular I am interested in pulse jets and ramjets. I...
  10. Newb_Aero_Ninja

    Convergent Subsonic Ramjet Utilizing Shockwave Compression

    Hi, I am working on investigating an idea I proposed regarding a ramjet that operates in subsonic flow (of a fixed speed) with a convergent intake. That utilizes the pressure immediately behind a standing shock-wave for compression. I have posted a link to my initial report here and I now need...
  11. T

    Can We Calculate Ramjet Thrust Using Combustion Mach Number and Rayleigh Flow?

    For a ramjet engine, combustion occurs at a finite Mach number M. If we know the ambient conditions like free stream Mach number and pressure and the ratio between the stagnation temperature at the inlet and exit of the combustor, how can we derive the thrust? How can we incorporate the...
  12. R

    Revolutionize Air Travel with Electrothermal Ramjet Technology

    Time to propose another crazy idea: the electrothermal ramjet. I was reading about Project Pluto today. I find it interesting that there is no combustion involved; just the compression of air then the expansion by heat from a nuclear fission reaction. What if we could use coils (or some other...
  13. J

    Ramjet Ignition Airspeed: What You Need to Know

    What airspeed do I need to ignite a ramjet?
  14. F

    Is this rusty metal object a flame holder for a ramjet engine?

    Ramjet flame holder? Or?? Any ideas you have would be greatly appreciated. The pictures were posted on a forum and after hundreds of guesses by various forum members, one of the people that I queried, a rocket expert from Wyoming, seems to be very close in his assessment (see below)...
  15. T

    Ramjet Rocket engine hybrid?

    I wanted to get some opinions on this, I am serious considering designing a ramjet rocket hybrid engine for my 3rd year mechanical engineering degree project and have started doing the research to see exactly how much work it entails I still can't quite decide... is this a realistic project? (my...
  16. G

    Ramjet Engine: How Does It Work at Subsonic Speeds?

    I think i know how the ramjet works at supersonic speeds, because of the shock wave the air particles traveling through the inside of the tube converge and bump into each other and because the air cannot expand it slows down, increasing the pressure, so when the air escapes it expands very...
  17. S

    Can a Ramjet Operate Without a Diffuser?

    According to the information I have gathered on ramjets, a ramjet uses a diffuser to slow down the air thus increasing the pressure. The nozzle is used to maintain pressure in the combustion chamber. So my question is, why can't a ramjet (operating at low speeds) simply not have a diffuser at...