TUTORIAL – COMBUSTION (CHAPTER 5 – MEC551)

1)

In a combustion chamber, liquid propane C3H8 at 25°C, flow at rate of 1.0 kg/min is mixed and

burned with 50 percent excess air. The temperature of the incoming air is 17°C. If the combustion

is complete, and the exhaust temperature of the combustion product is 1500K. Determine;

i) the stoichiometric air-fuel ratio,

ii) air fuel ratio with 50% excess air and

iii) the rate of heat transfer from the combustion chamber.

(20 marks)

APRIL 2009

2) Propane C3H8 is burned in 100% theoretical air. Combustion is complete and takes place

at 1 bar. Determine:

i) the chemical reaction for propane burned in both oxygen only and air,

ii) the dew point temperature of the products of combustion, and

iii) the mole of water condensed per mole of fuel if the products of combustion are cooled

to 25°C.

(20 marks)

OCTOBER 2009

3) Liquid octane enters an internal combustion chamber operating at steady state

with a mass flow rate of 1.8 x 10"3 kg/s and is mixed with the theoretical amount

of air. The fuel and air enter the engine at 25°C and 1 atm. The mixture burns

completely and combustion products leave the engine at 890 K. The engine

develops a power output of 37 kW. Determine the air-fuel ratio and the rate of

heat transfer from the engine, in kW, neglecting kinetic and potential energy

effects.

(20 marks)

APRIL 2010

4) Ethane gas (C2H6) enters a combustion chamber at 25 °C at a rate of 6.5 kg/h

where it is mixed and burned with 5 percent deficiency of air. The amount of air is

preheated to 227 °C before entering the combustion chamber. An analysis of the

combustion gases reveals that all the hydrogen in the fuel burns to H20 but part of the

carbon burns to CO. If the products leave the combustion chamber 727 °C, determine:

i) the mole fraction of the CO in the products (%),

ii) the air fuel ratio,

iii) the equivalence ratio,

iv) the rate of heat transfer from the combustion chamber (kW), and the percentage of

excess air IF the fuel burns in air at an equivalence ratio, Ø = 1.

(20 marks)

OCTOBER 2010