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Feyza Kazanç

on 4 November 2014

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Transcript of COMBUSTION

Fuel+Air Products


Stoichiometric Oxygen
Chemical formula of a fuel
Oxygen requirements for the combustion
- Stoichiometric
- Fuel Lean
- Fuel Rich
COMBUSTION and Thermochemistry
Heating Value
- HHV (Higher Heating Value)
- LHV (Lower Heating Value)
Adiabatic Combustion Temperature
Chemical formula of a fuel:
Element/Atoms Molar Mass (kg/kmol)
Carbon (C) 12.0112
Hydrogen (H) 1.0080
Nitrogen (N) 14.0067
Oxygen (O) 15.9994
Sulfur (S) 32.0460
1 mol of a compound corresponds to 6.022*10^23 molecules
What are the stoichiometric numbers of v, w, x, y, and z???
What is the molecular weight of the compound???
Minimum Oxygen needed???
if more than a stoich. quantity of oxidizer supplied
Fuel Lean
if less than a stoich. quantity of oxidizer supplied
Fuel Rich
stoichiometric air-fuel ratio:

where CxHy + a(O2+3.76N2)
Equivalance ratio:
Equivalance ratio:
phi=1 ...stoichiometric
phi<1 ...fuel lean
phi>1 ...fuel rich
Absolute Enthalpy and Enthalpy of Formation
Absolute enthalpy
Enthalpy formation
@Tref, P
Sensible enthalpy change
from Tref to T
Tref = 25 C
Pref = 1 atm
Enthalpy of Combustion
First Law Energy Balance - Control Volume
exiting combustion
incoming fuel and
air streams
(Stoichiometric fuel-air mixture at standard state conditions)
(complete combustion at standard state condition)
q (control volume)
enthalpy of combustion (reaction) --> q = h products - h reactants
Heating Value (Heat of the combustion)
Higher Heating Value (HHV): heat of combustion calculated assuming that all of the water in the products has condensed to liquid
Lower Heating Value (LHV): corresponds to the case where none of the water assumed to condense
if liquid-->HHV
if vapor-->LHV
enthalpy of combustion:
Heating Value (Heat of combustion) is numerically equal to enthalpy of combustion, but with opposite sign
Adiabatic temperature of the combustion
Enthalpy of Combustion
T = 25 C
P = 1 atm
2 adiabatic flame temperatures;
1- Constant pressure adiabatic flame temperature
2- Constant volume adiabatic flame temperature
Figure: Illustration of constant-pressure adiabatic flame temperature on h-T coordinates
Calculation with the assumptions
Computational results with the software
Chemical Equilibrium
Ideal Combustion
: CO2, H2O, O2, and N2
: H2, OH, CO, H, O, N, NO
Second Law Consideration is needed!!!
const. mass
const. volume
adiabatic reaction
T and P increases until equil. reached
CO+1/2 O2=CO2
İf T is high enough CO2 dissociate
Flue gas recirculation
Figure: Illustration of chemical equilibrium for a fixed mass isolated system
constant u, v, m
No heat and work interaction
second law
the condition for equilibrium
Gibbs function
second law
For a mixture of ideal gases, gibbs function for the ith species
equilibrium condition
in the case of no FGR
Full transcript