ME 475/675 Introduction to

CombustionLecture 5

Constant-Volume Adiabatic Flame Temperature, Chemical Equilibrium

Announcements

• Due Now (before lecture starts)• X1, Extra Credit problem 2.15 and 2.30

• Please turn in HW on white or engineering paper• Grading based on solution (not solely on answers)

• Please bring you textbook to class

Adiabatic () Flame Temperature

• 1st Law, Steady Flow Reactor

• All chemical energy goes into heating the products• To find adiabatic flame temperature use• PP = PR and

StoichiometricReactants

TR PR

Complete Combustion ProductsCCO2 HH2OPP = PR, T = TAd

�̇�𝐼𝑁=0 �̇� 𝑂𝑈𝑇=0

Assume

• • Molecular constant pressure heat of combustion

Constant Volume Adiabatic Flame Temperature

• so • Use definition: (since standard internal energy U is not tabulated)

• Idea gas: ; ,

• Only and are unknown

V, m𝑄=0 𝑊=0

Assume

• ;

Example (turn in next time for EC)

• Estimate the constant-volume adiabatic flame temperature for a stoichiometric acetylene and air mixture initially at 298 K and 101.325 kPa = 1 atm. Use specific heats at 1400 K.

• Constant Volume

Example (Turn in next time for Extra Credit)• Find TAd for a 25°C Stoichiometric mixture of Acetylene and air. Use

specific heats at 1400 K.• Constant pressure• PP = PR, HP = HR

Ideal Combustion

• In real high temperature combustion the product species may dissociate (break apart) yielding• H2, OH, CO, H, O, N, NO, …. (no ?)

• How to find final molar fractions of each component for different temperatures and pressures?• Chemical Equilibrium