BENG3 THERMAL & FLUIDS ENGINEERING (THER305)
TUTORIAL EXAMPLES in COMBUSTION 2
1.
1 kg of a particular hydrocarbon fuel
when burnt in air gave the following:-
0.171 kg CO2
0.020 kg CO
0.700 kg N2
0.050 kg O2
Find the dry gas analysis by percentage volume. [12.5%,
2.3%, 80.2%, 5.0 %]
2.
A gaseous fuel consists of 50% methane,
25% hydrogen, 12% carbon monoxide, 3% oxygen, 6% carbon dioxide and 4%
nitrogen. Calculate the stoichiometric air-fuel ratio by volume. [5.5]
3.
A fuel for a petrol engine consists of
86% carbon (C) and 14% hydrogen (H2) by mass. Calculate the
stoichiometric air-fuel ratio by mass. [14.71]
4.
If the same fuel as in Q.3 is burnt with
10% excess air, calculate the dry volumetric analysis of the exhaust products. [CO2 13.7%; O2 1.9%; N2
84.4%]
5.
A dry analysis of the exhaust gas of a
reciprocating combustion engine gave the following results CO2 10%;
O2 8% with no CO. The fuel has a mass analysis of 88.8%C and 11.2% H2.
Calculate the air-fuel ratio used. [22.3]
6.
A dry analysis of the exhaust from a
diesel engine gave the following results CO2 9%; O2 6%;
CO, 1%. Calculate the percentage excess air used in the combustion process. [32.8%]
7.
If the HCV of methane gas (CH4)
is 37.80 MJ/m3 (at SSL conditions), determine its LCV. [34.08 MJ/m3].
8.
A fuel gas has a composition by volume: H2
40%, CO2 6%, N2 4%, 50%, CO
What volume of air (m3/m3 is required for complete
combustion? [2.14]
If the dry exhaust gas contains 9.2% by volume of CO2 and no CO,
what air/gas ratio by volume has been used? [4.95]
9.
Petrol, with a gravimetric analysis of
0.85 C, 0.15 H, burns in a car engine at 13:1 air/fuel ratio by mass. What is
the gravimetric proportion of CO in the wet exhaust gases? [5.48%]
10. The
gravimetric analysis of coal in a boiler trial was:
C 0.83, H 0.036, O 0.048, ash 0.086. The flue-gas volumetric analysis was CO2
0.109, CO 0.010, O2 0.071, N2 0.810. Determine:
a) the proportion of C burned to CO; [8.4%]
b) the actual air required for combustion of 1 kg of coal (consider N2
and C masses per kmol of flue-gas) ; [17.19 kg]
c) the mass of wet flue-gas and the mass of dry flue-gas per kg of fuel burned.
[18.10 kg,
17.78 kg ]
11. In
a test of gas turbine combustion chamber aviation kerosene (gravimetric
analysis 0.86 C, 0.14 H) is burned at an air/fuel ratio of 80:1 by mass. The
lower calorific value of the fuel is 44 MJ/kg. The fuel enters at 25°C, the air
at 100°C and combustion is adiabatic and complete. Determine:
a) the percentage excess air; [446%]
b) the gravimetric analysis of the wet products of combustion;
[CO2 3.90%, O2 18.8%, H2O
1.55%, N2 75.75%]
c) the mean molecular weight of the wet products; [28.85]
d) the mean Cp of the wet products between 25°C and tprod
assuming as a first approximation that tprod is 650°C. [1.077 kJ/kgK]
e) the specific enthalpy of the reactants, above 25°C, at entry to the
combustion chamber; [74.4 kJ/kg]
f) the temperature of the products, using the first approximation to Cp
[598°C]