It looks as though you are burning natural gas and getting about 17% w/w CO2 in your calculations: this is what one would expect. The temperatures look reasonable for a short-flame burner. I'm not sure what your problem is!!

Dear Prof. Jack,

Thank you very much for your time.

I am using acetylene as fuel and (21% O2 + 79% N2) as air inlet.

My problem is, I did not found any literature who used acetylene as fuel inlet, so I don't know the result generated for CO2 (21% mass fraction) is either correct or not?

I means how I will verify my result without any comparison to past work?

In most of the other studies either, methane, ethane, propane, ethylene etc, I did not see the combustor filled with CO2, the same as in my case. so its kind of strange.

I am very much worried, I tried hybrid initialization then change it to standard by air inlet also then as fuel inlet, tried to increase inlet temperature, tried to change k-epsilon from standard to realizable, but still getting the same result, even, my mesh and orthogonal quality is very good.

I don't know, in fluent, what parameter I should change/consider to procced and get better result for CO2 and H2O?

Stoichiometric combustion of acetylene in air produces about 11% v/v CO2 (or 17% w/w). The temperatures that you indicate would suggest some excess air being available in which case the CO2 is reduced unless the flame is losing heat to the enclosure. I do not see why the CO2 is increasing once you move beyond the flame front: possibly CO burning, but that should be a very small portion of the combustion: the increase looks large..

Dear Prof. Jack,

Yes, you are right, now, what possibly you suggest?

How to make this CO2 out of combustor?

Any increase or decrease in the inlet velocities etc?

I am using inlet velocity (0.96 m/s for air and 80 for fuel)

What seems odd to me is that the CO2 increases after the flame: it must peak at the tip of the flame, at close to the stoichiometric value. The combustion reaction that is generating the temperature field must also be generating a CO2 field. The CO2 would then be diluted by the excess air around the flame. It is very difficult to comment further without more info.

Dear Prof. Jack,

Yes, unfortunately, it is the case so.

To further comment, what information you need/or I shall provide?

The temperature profile indicates a diffusion flame, but the concentration profile seems like a pre-mixed flame where all the CO2 forms at the flame-front. To go further needs geometrical details of gas and air inlets and the enclosure as these determine the flame temperature and shape. However, my impression is that there is something wrong with the mathematical model used.