Chemical Reactions

Example 15.1 Balancing the combustion equation
One kmol of octane (C 8 H 18 ) is burned with air that
contains 20 kmol of O 2 , Assuming the products
contain only CO 2 , H 2 O, O 2 , and N 2 , determine the
mole number of each gas in the products and the airfuel
ratio for this combustion process.
Solution Chemical reaction equation:
C 8 H 18 +20 (O 2 + 3.76 N 2 ) xCO 2 + yH 2 O + zO 2 + wN 2
Balance of each element : @ ReactantS = @ ProductS
C: 8 = x x = 8
H: 18 = 2y y = 9
O: (20x2) = 2x +y + 2z z = 7.5
N 2 : 20*3.76 = w w = 75.2
Air Fuel Ratio, AF = m air /m fuel = (NM) air /(NM) fuel
= 24.2 kg air/kg fuel
Theoretical and Actual Combustion
Processes
Complete combustion: 1) all C burns to CO 2
, and 2) all
HC burns to H 2
O
Incomplete combustion: Products contains Unburned
fuel or components สาเหตุหลัก: 1)Insufficient O 2
2)
Insufficient mixing. 3) Dissociation
Stoichiometric Air or Theoretical Air:
• = minimum amount of air needed for complete
combustion.
• no unburned and no O 2
left in products
• = Chemically correct amount of air or 100%
theoretical air
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