what are ramjet. i need some technical information about it?

Question

it is a type of propulsion system. i wish to present a paper on that topic,hence i need some technical information.

Answer 1

Ram Jets
Many people confuse ramjets with pulsejets and are unaware that although both are quite simple and somewhat similar in design, they vary significantly in the way they operate and the tasks for which they are suitable.

Ramjets have no moving parts -- much like a valveless pulsejet but they operate with cotinuous combustion rather than the series of explosions that give a pulsejet its characteristic noise.

On the face of it a ramjet would seem to be the ideal kind of jet -- no spinning turbines, no vibrating valves and a seemingly ultra-simple construction.

Unfortunately there are two things that work against the ramjet:

Operating Speed
Unlike pulsejets and jet-turbine engines, the ramjet will not operate unless it is moving through the air at a speed of at least 400 mph.

If you attempt to start a ramjet while it's stationary or moving to slowly then it will give little or no thrust -- in fact you'll just get lazy, smokey flames billowing out both the intake and exhaust.

This is because a ramjet relies on heating a fast-moving stream of cold air as it enters the engine and then expelling that air at a higher speed out the back. Unless the engine is moving rapidly through the air there's nothing for the burning fuel to heat.

Fuel Consumption
As a general rule of thumb, the fuel-efficiency of an internal combustion engine is related to the compression ratio at which it operates. That is to say -- the more the air/fuel mixture is compressed before it is ignited then the more power you'll get from a given amount of fuel.

Diesel engines have a compression ratio of about 20:1, most car engines operate at compression ratios as high as 11:1, a pulsejet runs at a compression ratio of less than 2:1 and ramjets are about the same at low speeds.

As a result, the ramjet (like the pulsejet) is not a particularly fuel-efficient engine. What makes it worse is that since the ramjet needs to be operated at very high speed, it's going to have to burn a lot of fuel just to overcome the drag it creats at that speed.

Can Ramjets Be Home-built?
Yes -- it's quite possible to build a ramjet using the kind of tools you'd find in a reasonably well equipped home workshop -- but why bother?

Unless you're going to be using it at a minimum speed of 400 mph it will be nothing but a paperweight.

There are some companies that offer to sell you the plans for a ramjet and a helicopter which is powered by these jets affixed to the tips of the rotor blades.

Many people have bought these plans, few have built the engines or helicopters and, to the best of my knowledge, nobody has ever reliably flown one.

What is ignored by such designs are the problems of fuel-efficiency and the fact that the rotorblades of such a helicopter would have to be spun up to almost full RPMs before the ramjet would even operate. This would require significant power to "spin-up" the rotor system and add to the cost and complexity of such a project.

So, I'd advise readers that such projects are an interesting curiosity -- but don't expect that you will end up with a jet-powered craft capable of flying safely or reliably.

So Where Are Ramjets Actually Used?

Subsonic ramjets are seldom (if ever) used these days but more modern hybrid turbjet/ramjet engines have been used in the ultra-high speed SR71 Blackbird.

Many of the low-orbit reusable space vehicles are now considering the use of scramjets for their power-plant while still in the earth's atmosphere but even scramjets remain largely the domain of the drawing board.

Scramjets differ from ramjets insomuch as the airflow inside the engine remains supersonic -- whereas conventional ramjets slow the incoming air down to a much lower speed so that its pressure is increased and it is easier to burn regular fuels.


Thrust is the force which moves any aircraft through the air. Thrust is generated by the propulsion system of the aircraft. Different propulsion systems develop thrust in different ways, but all thrust is generated through some application of Newton's third law of motion. For every action there is an equal and opposite reaction. In any propulsion system, a working fluid is accelerated by the system and the reaction to this acceleration produces a force on the system. A general derivation of the thrust equation shows that the amount of thrust generated depends on the mass flow through the engine and the exit velocity of the gas. Engineers use a thermodynamic analysis of the ramjet to predict thrust and fuel flow for a particular design.

In the early 1900's some of the original ideas concerning ramjet propulsion were first developed in Europe. Thrust is produced by passing the hot exhaust from the combustion of a fuel through a nozzle. The nozzle accelerates the flow, and the reaction to this acceleration produces thrust. To maintain the flow through the nozzle, the combustion must occur at a pressure that is higher than the pressure at the nozzle exit. In a ramjet, the high pressure is produced by "ramming" external air into the combustor using the forward speed of the vehicle. The external air that is brought into the propulsion system becomes the working fluid, much like a turbojet engine. In a turbojet engine, the high pressure in the combustor is generated by a piece of machinery called a compressor. 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.

Shown above are pictures of an X-15 rocket-powered airplane with a ramjet slung underneath the body and a wind tunnel test of a ramjet inlet used on a missile. In both propulsion systems, a rocket is used to bring the ramjet up to speed before it produces thrust. Because the ramjet uses external air for combustion, it is a more efficient propulsion system for flight within the atmosphere than a rocket, which must carry all of its oxygen. Ramjets are ideally suited for very high speed flight within the atmosphere.

EngineSim is an interactive Java applet which allows you to test the design of ramjet engines. You can learn the fundamentals of ramjet engine propulsion with the EngineSim simulator.

Answer 2

Ramjet
A member of a class of high-speed air-breathing propulsion systems. These include subsonic combustion ramjets (RAM), supersonic combustion ramjets (SCRAM), dual-mode ram-scramjets (RAM-SCRAM), dual-combustor ramjets (DCR or DCRJ), and air-ducted rockets (ADR). In each case, air collected from the atmosphere is ducted into the engine to serve as the oxidizer for the burning of fuel that is stored on board. All the engines operate on a modified form of the basic Joule or Brayton cycle; that is, the air is compressed in the inlet, burned at near-constant pressure, and accelerated in an expansion nozzle. In accordance with Newton's, second law, thrust is produced by the increase in momentum as the gas passes from the inlet to the nozzle exit. Compression is produced by one or a multiplicity of compression waves generated on the inlet surfaces. The level of pressure that can be reached in these waves is insufficient to produce net thrust unless the air speed is greater than about Mach 0.9 (that is, the velocity is 0.9 times the local speed of sound). Thus the ramjet must be launched from a high-speed aircraft or brought up to speed by a booster rocket or another adjunct engine. The latter type are known as combined-cycle engines. A classic example is the combination of a turbojet and a ramjet, which is called a turboramjet. See also Brayton cycle; Mach number; Newton's laws of motion; Rocket propulsion; Turbojet; Turboramjet.

A subsonic combustion ramjet may be boosted to its operating speed by a solid-fueled rocket (see illustration). After the booster separates, the air entering the inlet is compressed through oblique shocks and a terminal normal shock. The flow aft of the normal shock and in the combustor is subsonic, but the velocity is high and flameholders are needed to anchor the flame and thereby produce high combustion efficiency. Passing from the combustor, the exhaust gases are reaccelerated in a converging-diverging nozzle to supersonic speed at the engine exit. See also Diffuser; Nozzle.


Diagram of a ramjet engine.

There are several characteristics that lead to the choice of one of the ramjet cycles for a variety of missions. Foremost are the engine performance as measured by specific impulse, light weight, and low cost. For applications up to about Mach 3, the turbojet has the highest specific impulse among hydrocarbon-fueled engines, which leads to its choice as the power plant for subsonic and supersonic aircraft. Most missile applications demand higher thrust which requires afterburning. For flight speeds between Mach 3 and 5, the subsonic combustion ramjet is optimal, and above Mach 5 the choice is among the supersonic combustion ramjet, the dual-mode ram-scramjet, and the dual-combustor ramjet. The solid rocket has much lower engine performance and is used only when high specific impulse is not the governing factor. Rocket-powered vehicles are used for relatively short-range missions or for near-to-vertical flight. See also Afterburner; Aircraft fuel.

Answer 3

By typing 'ramjet' into a search engine, I got over a million hits.

What's **your** problem?


Doug

Answer 4

Scramjet or ramjet?

Answer 5

search in google