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ME 475/675 Introduction to Combustion

ME 475/675 Introduction to Combustion. Lecture 4. Announcements. Extra Credit example due now HW 1 Due Friday Tutorials Wednesday 1 pm PE 113 Thursday 2 pm PE 113 Please bring you textbook to class Please turn in HW on white or engineering paper

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ME 475/675 Introduction to Combustion

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  1. ME 475/675 Introduction to Combustion Lecture 4

  2. Announcements • Extra Credit example due now • HW 1 Due Friday • Tutorials • Wednesday 1 pm PE 113 • Thursday 2 pm PE 113 • Please bring you textbook to class • Please turn in HW on white or engineering paper • Grading based on solution (not solely on answers)

  3. Example: • Last lecture (turned in today) • Problem 2.14, p 71: Consider a stoichiometric mixture of isooctane and air. Calculate the enthalpy of the mixture at the standard-state temperature (298.15 K) on a per-kmol-of-fuel basis (kJ/kmolfuel), on a per-kmol-of-mixture basis (kJ/kmolmix), and on a per-mass-of-mixture basis (kJ/kgmix). • Find enthalpy at 298.15 K of different bases • This time (turn in next lecture) • Problem 2.15: Repeat for T = 500 K

  4. Standard Enthalpy of Isooctane • Coefficients to from Page 702 • ; • Spreadsheet really helps this calculation

  5. Enthalpy of Combustion (or reaction) Products Complete Combustion CCO2 HH2O 298.15 K, 1 atm Reactants 298.15 K, P = 1 atm Stoichiometric • How much energy is released from a reaction if the product and reactant temperatures and pressures are the same? • 1st Law, Steady Flow Reactor • and Enthalpy of Reaction (< 0 for combustion) • Dependent on T and P of reaction • Heat of Combustion

  6. Stoichiometric Methane Combustion, CH4 • CH4 + __ (O2 + 3.76 N2)  __ CO2 + __ H2O + ___ N2 • @ 25C and 1 kmol CH4 p 688 p 692 p 701 (Heat in to system for TR = TP) Water Vapor

  7. Other Bases • Per kg fuel • Heat of Combustion • (Heat out for TR = TP) • See page 701, LHV = Lower Heating Value • Corresponds to water vapor in the products p 692 p 692 • p. 701: Higher Heating Value = HHV = 55,528 (slightly larger due to dissociation?)

  8. Per kg of reactant mixture • LHV =

  9. Adiabatic () Flame Temperature Complete Combustion Products CCO2 HH2O PP = PR, T = TAd Stoichiometric Reactants TR PR • 1st Law, Steady Flow Reactor • All chemical energy goes into heating the products • To find adiabatic flame temperature use • PP = PR and

  10. Adiabatic Methane Combustion TR = 25°C • CH4 + 2 (O2 + 3.76 N2)  1 CO2 + 2 H2O + 7.52 N2

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

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