ME 475/675 Introduction to

CombustionLecture 25

Finish Ex. 6.2 and its numerical solution

Announcements• HW 9 Due Friday, Oct. 23, 2015• Example 6.2 and its numerical solution

• For , plot product mass fraction versus mass flow rate• Plot blow out versus mass flow rate• At least 4 data points for each plot and compare to Fig. 6.8 of Textbook

• Due Friday, Oct. 23, 2015

Steady-State Well-Stirred Reactor• Mass Conservation for M species• One inlet and one outlet:

Accumulation = generation + net inflow• Since well-mixed properties leaving are same as

this inside CV

• Steady State

• Find molar concentrations [i] from mass fractions Yi (needed to find )

Energy Conservation (to find T)• Steady State:

• Residence Time

• ;

• All these conditions (equations) are algebraic (not differential) • Find and (M + 1 unknowns)• Linear in , nonlinear in

Example 6.2• Develop a simplified model of a well-stirred reactor using the same simplified

chemistry and thermodynamics used in Example 6.1 (equal and constant cp’s and MW’s, and one-step global kinetics). Use the model to determine the blowout characteristics of a spherical (80-mm-diameter) reactor with premixed reactants (C2H6-air) entering at 298 K. Plot the equivalence ratio at blowout as a function of mass flowrate for . Assume the reactor is adiabatic. • MWF= MWOx= MWP= 29; cp,F = cp,Ox = cp,Pr = 1200 J/kgK• The enthalpy of formation of the air and products are zero, and that of the fuel is • 4*107 J/kg

• The stoichiometric air-fuel ratio is 16.0 and restrict combustion to stoichiometric or lean conditions, .

• Constant pressure, constant volume, or well stirred reactor?

Last Lecture• Species Production

• Inlet Conditions

• • ;

Species Conservation

• Fuel• 1

• Oxidizer

• 2

• Product

• or• 3

Energy Conservation (to find T)

MathCAD Solution

Yoxin1

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16

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f T mdot( )mdot cpHff

T 298( ) MW Vol 6.19 109

exp15098T

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HffT 298( )

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T 298( )

1.65

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Ru T

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0

5 10 3

0.01.01

.005

f T2 mdot( )

0

3000298 T2

.

•