I have studied the effect of air preheating on non-premixed combustion, keeping the mass flow rate and inlet tube diameter constant at inlet air-fuel stoichiometry. Only the fuel flow rate is always constant, the air volume flow rate changes (mainly velocity) with temperature ?

3 conditions are formulated:

• air preheated to 566 K,
• with no preheating, i.e. the air is at 295 K
• and air preheated to 1000 K.

All the Inlet condition are shown in the attached figure.

On comparing the overall stoichiometric conditions - So when there is a decrease in the temperature of air supplied, there is a simultaneous decrease in the amount/volume flow rate of air required as well. This happens due to ideal gas law;

My results are quite strange :

1. air preheated to 295 K i am getting the furnace temperature around 1500 K

2. air preheated to 566 K i am getting the furnace temperature around 1450 K

3. air preheated to 1000 K i am getting the furnace temperature around 1600 K

can anyone explain to me y is it happening? is this due to dilution of as less the preheating temperature - less will be the amount/volume of air going in so fuel dilution effect will be less no higher temperature development etc.

Few papers have also reported such phenomena as well. but with no explanation:

1. Effect of air preheating and fuel moisture on combustion characteristics of corn straw in a fixed bed Wei Zhao, Zhengqi Li *, Guangbo Zhao, Fangshi Zhang, Qunyi Zhu Energy Conversion and Management

2. The Effects of Air Preheating and Fuel/Air Inlet Diameter on the Characteristics of Vortex Flame Mostafa Khaleghi,1 S. E. Hosseini,1 M. A. Wahid,1 and H. A. Mohammed2 Journal of Energy

Any help will be highly regarded.........