Week 2: Analysing Combustion Processes

Question 1

What is the Equation for complete combustion and why does it happen

Answer 1

CH4 + 2O₂ ➡️ CO₂ + 2H₂O
Complete combustion occurs when there’s sufficient oxygen for conversion of carbon

Question 2

What is the name of mixture where there’s EXACTLY the right amount of oxygen for complete combustion

Answer 2

• Stoichiometric Mixture

Question 3

What is the name of the mixtore for complete combustion with excess oxygen over the Stoichiometric level and what’s the equation wolf this with some oxygen left over nfkvhr ehd

Answer 3

CH4 + 2.5O₂ ➡️ CO₂ + 2H₂O + 0.5 O₂
Lean mixture
Too little fuel to use up all the oxygen

Question 4

What is the equation for a rich mixture and what is it

Answer 4

• a rich mixture has an excess of fuel compared to oxygen
• might end up with unburned fuel

1.2 CH4 + 2O₂ ➡️ CO₂ + 2H₂O + 0.2 CH4

Question 5

What is incomplete combustion and its equation.

Answer 5

Wheee not all the carbon is converted to carbon dioxide .. instead get some carbon monoxide and elemental carbon

Question 6

What is the equivalence ratio

Answer 6

Ratio of fuel in the mixture to that required for the Stoichiometric quantity of oxidant.
Stoichiometric :
- e.g. CH4 + 2O₂ …. Has ø = 1
Lean:
- e.g. 0.5 CH4 + 2O₂ has ø = 0.5
Rich:
- e.g.1.2 CH4 + 2O₂ has ø = 1.2

Question 7

What is the air fuel ratio by mass equation

Answer 7

Mass of air in mixture / mass of fuel in mixture
BTW Mass of air is N and O reactants and mass of air is CH reactants

Question 8

What is relative air fuel ratio and the equation

Answer 8

λ = 1/ø
Ratio of air to fuel actually in the mixture to that in stoich. mixture

Question 9

What is mixture strength, MS, and equation

Answer 9

% of fuel in mixture to that required for complete combustion
100ø

Question 10

What is % excess air and the equation for it

Answer 10

% excess air over stoichiometric air (used for lean mixtures when excess air present to reduce temp, e.g turbines)
100( (1/ø) - 1 )