Combustion

flow is defined as change of position in time. Combustion is chemical reaction of fuel with air that releases energy from fuel as heat. To improve combustion it is only to vaporize fuel, but vaporized fuel reacts fast producing detonation and that is why fuel is usually supplied as mist premixed with air in carburetor. When fuel droplets enter into cylinder some of them, when in contact with hot internal parts, split into carbon and hydrogen. Hydrogen burns fast and complete and carbon burns neither fast nor complete. Unburnt part of carbon deposits as black engine deposits or is released as black particulates that if inhaled can penetrate through lung tissue into blood, which initiates reaction of immune system that causes clotting leading to stroke or heart attack sometimes deadly. The split wastes up to 6% of fuel. Researchers try to prevent detonations in engines, because detonation creates higher pressure and temperature that devastate today's engines. Instead of preventing detonation the research should rather concentrate on developing methods to replace combustion with detonation as detonation creates better conditions for energy conversion and efficiency. Also if one droplets caught fire it burns on surface and flames ignite neighbor droplets, so flames propagate from droplet to droplet, relatively slow. but power available from fuel is defined as energy release in time, so speeding up burning would produce more power from less fuel. The direction of research is totaly wrong and the entire field of engine research stagnates, while engines consume more that 15 times fuel than they should if properly designed.

I didn't know the gun engine could also replace the Scramjet.

It's definitely too good to be true

"Instead of preventing detonation the research should rather concentrate on developing methods to replace combustion with detonation as detonation creates better conditions for energy conversion and efficiency."

If that's the case then why is a diesel engine that burns fuel more efficient that a petrol engine that ignites the fuel causing what is in effect explosive combustion?

That is down to the thermodynamics of the cycle which basically says the higher the compression ratio the higher the efficiency. Diesel engines run at much higher compression ratios than petrol.

Detonation VS combustion: It has been tried many times, I guess is still on the design board of many R+D companies.

Problem is a mechanical integrity of the combustion chamber. The Power to weight ratio becomes un-acceptable.

There are so many inaccuracies and irrelevances here that it is hard to know where to start. It is completely irrelevant to the discussion of fuel economy to mention where carbon particles end up in the human body, and it is untrue to say that the carbon particles end up in the bloodstream. They do not; there is no mechanism for them to pass from the lungs into the blood.
It is not true that one can improve the combustion cycle in an internal combustion engine by fully vaporising the fuel. It is true that fully vaporising the fuel will increase the speed of combustion, and indeed produce detonation, but the combustion process in an IC engine is most efficient when it progresses over a short period of time as the piston descends. The proper design of the inlet valve and the compression chamber allows the gas flow to circulate and for the flame front to propagate in a controlled fashion. The delivery of the fuel from an injector rather than as a mixture with air from a carburetor makes this a more controllable process.
The fuel is not first broken down to carbon and hydrogen by heat before each component is burnt. This is a piece of other-universe chemistry. Carbon residues are the product of incomplete combustion of the whole molecule. If sufficient air is in the mixture and the flame front takes in all the fuel, combustion is complete and there are no carbon residues.
Finally, again, the idea that detonation rather than controlled combustion leads to more efficient use of fuel is completely mistaken.

Is that you, DaS? There can only be one person who is smarter than everyone else!!

As you have started with supersonic flow I assume you are talking about jet propulsion as this is normally where this sort of condition occurs.

With supersonic flow into the combustors (cans) and carefully arranged fuel injection a high shear mixing zone is created leading to rapid & complete combustion instead of the relatively slow burn which occurs in subsonic mixing.

Could you elaborate on 'high shear mixing zone' and its effect on combustion.

That does fly in the face of the standard divergent ducting philosophy. Sounds like a good topic for research.