46
votes
Accepted
How efficient is a Scramjet?
A scramjet is more efficient than a rocket engine for the same two reasons that all air-breathing engines are more efficient than (chemical) rocket engines:
Chemical rocket engines need to carry both ...
- 6,166
24
votes
Accepted
Is the compressor required on jet engines? Can air be rammed into the turbine?
Your questions
At what point (if any) does air stop getting sucked into the turbine and is just getting rammed in?
On a CFM56-7B engine (Boeing 737 NG) pressure is provided by the fan, the low ...
- 80.9k
13
votes
Is it possible for a ramjet to start from 0 velocity?
No, a ramjet can't be started at zero speed. Yes, there are missiles that use ramjet propulsion without any rotating parts: they use a rocket to accelerate the missile to high enough speed for the ...
- 17.3k
8
votes
Is it possible for a ramjet to start from 0 velocity?
No. A ramjet relies on stagnation pressure at the inlet in order to compress air prior to combustion. They are typically not effective until the speeds get quite high, somewhere in the Mach 2+ range.
...
- 75.1k
8
votes
How efficient is a Scramjet?
Scramjets use super compressed air from the atmosphere, while a rocket engine carries its own oxidiser. This main difference means that all weight and volume required for the oxidiser and reaction ...
- 62.9k
7
votes
Accepted
Are there any planes that have ramjet or scramjet engines?
Scramjets
There's only a couple flying examples. The early Soviet-born Kholod, the HyShot series, and the recent ISRO ATV all flew small scramjet engines, although none were designed for net thrust. ...
- 3,984
6
votes
Could hydrazine be used as a scramjet propellant?
Technically yes, you could use hydrazine in a scramjet.
But there's no reason to do so. The singular purpose of building a scramjet is to get air into the combustion chamber, so that you don't have ...
- 30.2k
5
votes
Could liquid alkali metal fuels be used for ramjet/scramjet propulsion?
How long does the lithium take to evaporate and then to react with oxygen? Air in a scramjet is moving extremely fast (supersonic by definition!), so there is very little time left for mixing and ...
- 237k
5
votes
What technical problems stopped scramjets from being used on hypersonic aircraft?
I'm don't research hypersonic flight, but I bet the primary barriers of hypersonic flight are less technological and more political/economical. After all, we pay money and conduct research in order to ...
- 1,068
4
votes
Are there any planes that have ramjet or scramjet engines?
René Lorin invented the ramjet in 1908, and his ideas were tried in flight for the first time from 1941 onwards. Different sizes were tried; below are two pictures, one of a Do-17 Z with a small Lorin ...
- 237k
4
votes
Are there any planes that have ramjet or scramjet engines?
Are you asking about current production or through out time?
The SR-71 was powered by a Pratt & Whitney J-58 engine which operated as a partial ram jet at high speeds. At lower speeds it ...
- 102k
4
votes
Accepted
Is there a viable alternative to liquid hydrogen as a fuel for scramjets?
To list possible alternatives, it is helpful to know why hydrogen is used for scramjets today. The key is the speed of propagation of a combustion in the hydrogen-oxygen mixture.
In order for ...
- 237k
4
votes
What mechanism or design aspect prevents jet blast from escaping the front of a Ramjet or scram jet?
Pressure is the greatest just before the combustor in both jet and ramjet engines - therefore air would have against the pressure differential for this to happen (turbine only has therefore an ...
- 2,544
4
votes
Accepted
Is the engine of 3M22 Zircon truly scramjet?
Speculatively possible.
I've searched if the manufacturer has made such a claim. However, they aren't making any claims. The only explicit claims they make is a press reprint about the specifications: ...
- 30.2k
3
votes
What is the effect of Mach number on efficiency, thrust and specific fuel consumption of a ramjet engine?
The thrust of a ramjet depends on the dynamic pressure of the airframe since this determines how high the pressure inside the ramjet can become. Thrust grows therefore initially with the square of ...
- 237k
3
votes
What mechanism or design aspect prevents jet blast from escaping the front of a Ramjet or scram jet?
Primarily the pressure differential between the stagnation pressure at the inlet and the ambient static pressure. Combustion takes place in an isobaric environment with the enthalpy of the exhaust ...
- 75.1k
3
votes
Is the compressor required on jet engines? Can air be rammed into the turbine?
Like any kind of vacuum system, vacuums cannot “suck“ anything. They just remove air from an enclosed space. This causes a pressure differential between the evacuated space and the surroundings. The ...
- 75.1k
3
votes
Accepted
why does the flow need to decelerate (by a thermal throat) in a scramjet?
I found an answer, for those who are curious. The thermal throat described in a scramjet is not an ideal case. Essentially, when the flow is supersonic, heat addition done in the combustion chamber ...
- 53
2
votes
Accepted
Rocket Thrust vs Air breathing jet engine why is a rocket better
It is simply the rate at which fuel can be burned. For instance, the Saturn V's first stage carried 1.37 million kg of liquid oxygen (along with the kerosene fuel), which it burned in about 165 ...
- 2,587
2
votes
Is the compressor required on jet engines? Can air be rammed into the turbine?
It is certainly possible to 'ram' air into a turbine. The maximum pressure that can be achieved is called the 'stagnation pressure', which is the point at which all incoming kinetic energy is ...
- 13.7k
2
votes
Is it possible for a ramjet to start from 0 velocity?
The OP clarified in a comment that they are talking about ground speed not air speed.
It is trivially possible to start a ramjet at zero ground speed, since ground speed is completely irrelevant. The ...
- 6,166
2
votes
Hypothetical Ramjet-Scramjet-Rocket Combination?
This is called a "combined cycle" engine and has been studied a lot, maybe flown a few times on experimental basis:
The RBCC, or rocket-based combined cycle propulsion system, was one of ...
- 2,912
1
vote
Is it possible for a ramjet to start from 0 velocity?
In theory you could have an engine that started in pulsejet operation and switched over to continuous combustion as the speed increased.
In practice, good luck with that. Pulsejets require very ...
- 111
1
vote
Could hydrazine be used as a scramjet propellant?
The Scramjet is an AIRbreathing engine.
Thus there's no reason to incorporate hypergolic fuels because that requires it's own oxidizer onboard weight.
Second, with an energy density of 19.5 Megajoules ...
- 129
1
vote
Could hydrazine be used as a scramjet propellant?
In addition to it's use as a monopropellant, hydrazine has been used as a fuel in bipropellant combinations, for example in a 30% by weight mix with 57% methanol and 13% water, with concentrated ...
- 1,169
1
vote
What mechanism or design aspect prevents jet blast from escaping the front of a Ramjet or scram jet?
Both ramjets and scramjets work on the principle of supersonic flow: a ramjet has supersonic flow before the intake, and a scramjet has supersonic flow throughout the engine.
When air encounters a ...
- 13.7k
1
vote
What is the effect of Mach number on efficiency, thrust and specific fuel consumption of a ramjet engine?
Thrust
For a given fuel, ramjet thrust vs mach number trend may be approximately(see note 1) given by
Thrust = flight mach number(sqrt(2000 / (air temperature * (1+(7 * flight mach ^ 2) / 40))) - 1)
...
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