How to add Combustion efficiency

[arushkumarsingh]

The code is calculating HOF of fuel to calculate the FAR. But generally the LHV of fuel is used in cycle calculation, and for adding combustion efficiency we simply multiply the LHV value to eff. So now the real combustor the fuel adds LHV*eff amount of enthalpy per Kg.

But in this case as the enthalpy is being balanced between compressor inlet and combustor vitiated flow to calculate the FAR. I am not able to formulate the efficiency addition to combustor. In this code nowhere there comes an expression for enthalpy added by fuel. So how can I add the combustion efficiency property here.

[jackeylookie]

Have you solved this problem? I have the same question. If you have already solved it, can you provide me with some ideas? Thank you very much！！！

[arushkumarsingh]

Hi, According to my understanding:

In the CEA paper: https://ntrs.nasa.gov/api/citations/19950013764/downloads/19950013764.pdf page 25 section 4.1 there is a line "For each species heats of formation (and, when applicable, heats of transition) were combined with sensible heats to give assigned enthalpies."

So CEA enthalpy equation also take heat of formation in account, the more fuel you add in the system the enthalpy of the system will decrease more, as the enthalpy of formation of fuel is negative.

If you understand it like system and surrounding, the fuel is a imaginary system and the surrounding is the flow. When we add the fuel in the imaginary system and burn it, the enthalpy of the surrounding will increase, but the enthalpy of the system will remain constant in ideal case(full combustion).

Here in every engine they have balanced the enthalpy across combustor, i.e, the enthalpy in kJ/kg will be same before and after combustor, and then did the enthalpy-mass averaging after that. So in ideal combustion, the fuel will burn full and all the energy will go to surrounding and the system enthalpy will remain same. But in non-ideal case some of the energy will go into system and increase its enthalpy, hence the enthalpy after combustor will be little bit higher.

This is my understanding, but I have not formulated it. Please let me know the equations if you formulate it.

Also as explained in the issue #46 the LHV of fuel(with heat of formation) would be some negative value and you can take it while doing mass averaging, but as of now you can take it 0, it wouldn't make any significant difference.