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Stochiometry of Real Combustion
P M V SubbaraoProfessor
Mechanical Engineering Department
A First Step to Understand &Control Rate of Heat Release ….
Heat Addition Process of An Engine Cycle
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What is the optimal air/fuel ratio for Better HR ?
What Parameters control the HRR ?
Structure of Ford Research simulation.
Thermo Chemical Equilibrium
Fuel Model
• Ultimate Analysis of fuel: Gravimetric
• C : 84 -- 87% ; H : 11 -- 16% ; O : 0.3 -- 1.8% ; N : 0.1 -- 1.5% ; S : 0.1 -- 3%
• Percentage of carbon : x --- Number of moles, X = x/12
• Percentage of hydrogen : y --- Number of atomic moles, Y = y/1
• Percentage of oxygen: k --- Number of atomic moles, K = k/16
• Percentage of sulfur: z – Number of atomic moles, Z = z/32
• Equivalent chemical formula : CXHYSZOK
• Equivalent Molecular weight : 100 gms.
• Liquid and gaseous fuels generally have very little sulfur, oxygen and moisture.
• Generally popular chemical formulae: CXHY
Ideal combustion
CXHY + 4.773 (X+Y/4) AIR → P CO2 +Q H2O + R N2
Molecular weight of fuel : YXM fuel 008.1011.12
Homogeneous Mixture model for Air:
22 773.3 1 Air of 773.4 NofkmolesOofkmolekmoles
Molecular weight of Air : 96.28773.4
16.28773.332
airM
Air-fuel Ratio:1
008.1011.124
96.28773.4
stoistoi A
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YX
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Equivalence Ratio
• The equivalence ratio of a system is defined as the ratio as the ratio of the actual fuel/air ratio to the stoichiometric ratio.
• Mathematically
stoi
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i j
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Universal Law for Completion of Reaction
ji
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End of Reaction for an adiabatic system:
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Theoretical Prediction of Combustion Products: Pure Iso-Octane @ 5.0 MPa
Theoretical Prediction of Combustion Products: Pure Iso-Octane @ 5.0 MPa
Theoretical Prediction of Combustion Products: Pure Iso-Octane @ 5.0 MPa
Equilibrium Products at High Pressure 30 atm :Octane
Equilibrium Products at High Pressure 30 atm : Octane
Equilibrium Products at High Pressure 30 atm : Octane
Theoretical Prediction of Combustion Products: Pure Cetane
Real Combustion & Model Testing
Results of Model Testing.
• For a given fuel and required steam conditions.
• Optimum composition of Exhaust Gas.
• Optimum air flow rate.
• Optimum fuel flow rate.
• Optimum combustion configuration!!!
Molar Analysis of Dry Exhaust Products:• Mole fraction of CO2 : x1 • Mole fraction of CO : x2
• Mole fraction of O2 : x4
• Mole fraction of N2 : x5