DEN326 / DEN426 / DENM021 - Combustion Coursework

Submission date: 17 April 2015, 3:30 pm (Electronic submission only)

Question 1

A certain fuel having a mass analysis of C 84%, H 15% and 1% incombustible

material is supplied to the combustion chamber of an engine. Air has 1 kmol Oxygen

for 3.76 kmol Nitrogen.

a. If the fuel is completely burned with air and there is no unburned oxygen in the exhaust gas, what is the expression that describes this situation? Find the corresponding air/fuel ratio by mass.

b. Determine the wet analysis by volume of the combustion products when 50 %

excess air is supplied with the fuel.

c. Determine the mass of water vapour formed per kg of fuel burned.

[30 marks]

Question 2

a. Define enthalpy of combustion, enthalpy of formation, LCV and HCV.

b. The general chemical equation for combustion can be written as:

)S(v)S(v i

N

1i

''

i

k

ki

N

1i

'

i

f

b

(i) Define the equilibrium constant Kc.

(ii) Write an expression for the reaction rate with respect to species (Si) as a

function of vi, vi kf, Kc and [Si].

c. The forward and backward reaction rates of the following reaction are 0.714

l/(mol2 s) and 2.8 l3/(mol4 s) respectively.

2

k

k24 H3COOHCH

f

b

Calculate the equilibrium constant and concentration of Methane in mol/l if at

equilibrium [H2O] = 0.02 mol/l, [CO] = 0.3 mol/l and [H2] = 0.1 mol/l.

[40 marks]

Question 3

Acetaldehyde, CH3CHO, decomposes into methane CH4 and carbon monoxide CO

with a rate constant of 0.334 mol-1 s-1 at 500 C.

a- What is the order of this reaction?

b- Calculate the amount of time it would take for 80% of CH3CHO to turn into the

above products if its initial concentration is 7.50 mol/m3.

c- Explain how the activation energy is obtained experimentally by measuring the

reaction rate constant at different temperatures.

[30 marks]