Question

Actual flame temperature is always lower than the adiabatic flame temperature, because there is ___________.
A) No possibility of obtaining complete combustion at high temperature.
B) Always loss of heat from the flame.
C) Both A) and B).
D) Neither A) nor B).

Answer 1

Hint: The answer to this question here is based upon the basic concepts of chemistry that deals with the terms constant volume adiabatic flame temperature and constant pressure adiabatic flame temperature.

Complete step by step answer:
The concepts of adiabatic process, isothermal process, isobaric process and many more are familiar to us in the thermodynamics chapter of physical chemistry.
We shall see in detail about the flame temperature that even relates to the adiabatic volume and pressure.
- Adiabatic flame temperature is the one when a combustion reaction takes place and energy is released due to this combustion reaction and if no heat is lost during this process, then that temperature will be called as adiabatic flame temperature.
- Thus, the constant volume adiabatic flame temperature is nothing but the temperature resulting from the complete combustion process without work, heat transfer or change in any energy.
Also, constant pressure adiabatic flame temperature is the one resulting from the complete combustion process with no heat transfer or change in energy and its temperature is lower than constant volume process as some energy will be utilised to change volume of the system.
Thus, the correct answer is that the actual flame temperature is lower than that of adiabatic flame temperature because some energy released during the combustion goes into changing the volume of the system.

Therefore, the correct answer is option C) Both A) and B).

Note: Adiabatic flame temperature is important because it allows temperature control by changing the air – fuel mixture and also gives us the sense of whether the unburned fuel is released into the environment or not.