Question

You work for a company that produces gas grills. A new design for a propane grill uses preheated air to improve its performance. The grill flame operates with an equivalence ratio of 0.9 and the air and fuel are heated to 450K prior to the burner. A ceramic plate is above the burner for radiating heat to the food on the grill. You are told that the plate is capable of withstanding 2200 K. Assuming that the flame directly impinges on the plate, are you comfortable with this design? Show calculations to back up your reasoning. (assume complete combustion and product specific heats evaluated at 1500 K)

Answer 1

Here the propane is the major combustion element so that we can write the propane equation as

in this given that the equivalence ratio = 0.9

that is (Actual fuel air ratio)/(stoichometric fuel air ratio)=0.9

For the stoichometric analysis says that for 1 mole of C3H8 we required 5 moles of O2

In 1 mole of air ---------------> 0.0094 moles of O2 is required

so x mole of air-----------------> 5 moles of O2

-> x = 531.914 moles of air

Therefore stoichometric fuel air ratio = (1 mole)/(531.914)

Therefore Actual fuel air ratio =

Therefore the actual sir = 1/0.00169 = 591.02 moles of air

531.914 moles of air ---------------------> 5 moles of O2

591.02 moles of air------------------------> ? moles of O2

=(5*591.02)/(531.914) = 5.556 moles of O2

Which is actual O2 is supplied.

Therefore the combustion reaction will be written as follows.,

  

  

Now the heat combustion =

2220 KJ = (1+5.556) * (205.89)*(T_2-450)

2220000 = 1349.61*(T_2-450)

T_2 = 2094.91 K

Maximum temperature of furnace which is capable is given as 2200K, So T_2 is less than furnace temperature threrefore this sheme of combustion is satisfactory to our given conditions.