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ME 525: Combustion Session 1

Today

Course Administration

Introduction: Applications andFundamentals

Outline

Begin Review of Backgroundmaterial

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Course Administration

Instructor: Jay P. Gore gore@purdue.eduTeaching Assistants: Indraneel Sircar isircar@purdue.edu

Home Work: Ten Homework problems assigned with aone week to ten days gapanswers to be emailed tothe instructor with copies to TA

Instructor Office Visits: For one hour after class or byappointment

Encourage Study Groups: Will be formed after review ofstudent self-introductions. Submit names of up to 5classmates you would like in your study group.

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mailto:gore@purdue.edumailto:isircar@purdue.edumailto:isircar@purdue.edumailto:gore@purdue.edu

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Student Self-Introductions

Name and Email: .

Degree Objective (Ph.D. or M. S.): .

Advisor: .

Research Topic: .

Course Background: Circle the appropriate course numbers or theword equivalent and the word senior or the word grad

ME500 or ME300 or equivalent senior or grad thermodynamics

ME505 or ME315 or equivalent senior or grad heat transfer

ME509 or ME309 or equivalent senior or grad fluid mechanics

MA527 or MA 528 or equivalent senior or grad first year math

ME581 or equivalent senior or grad numerical methods

Names of five (or as many as you know) classmates who youwould like in your study group

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Grading

Two Midterm Examinations: 30%

Final Examination (Comprehensive): 30%

Text Book Home Work Problems: 20%.

Special Project(s): 20%.

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Text Book

An Introduction to Combustion: Concepts andApplications, Third Edition, McGraw Hill by Stephen R.

Turns

Download Software at www.mhhe.com/turns3e

Other software may need to be used for Homework

problems and special problems

Study groups will have opportunity to share combustion

related web links, combustion videos, interestingcombustion related news items with Professor Gore for his

screening, sharing with the class

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http://www.mhhe.com/turns3ehttp://www.mhhe.com/turns3e

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Applications of Combustion

Power plants

Coal, Diesel, Natural Gas

Manufacturing

Mining and ore melting, combustion synthesis, heattreatment, boiling and purification.

Transportation: Air, Space, Land, Rivers, Sea, and Ocean

Otto, Diesel, Rankine and Brayton cycles

HVAC and other Appliances Fire Safety

Forest, residential, automobile

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Combustion Design Issues

Fuel for a given power ratingefficiency, heat rejected, exhaust product composition

Oxidizer or air needed for a given power rating

Mining and ore melting, combustion synthesis, heat treatment,

boiling and purification. Pollutants produced and their long term and short term impact

Cost of pollutant and pollution control

Pressure and temperature rise and control and containmentdesign

Ignition, extinction, turndown, speed, pressure oscillation,noise, odor, and fire safety

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Combustion Fundamentals- 1

Combustion is an exothermic chemical reaction betweena fuel and an oxidizer in which chemical energy stored inmolecular bonds is released in the form of sensibleenergy.

Most fuels currently in use are hydrocarbon fossil fuelswith coal being the most used and most criticized fuel.

Most oxidizer currently in use is oxygen from air.

Combustion products generally include CO2, H2O, CO, H2,N2, and excess O2.

Soot, unburned HC and NOxpressure oscillation, noise,and odor.

Combustion may involve material in solid, liquid, vaporand superheated gas state.

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Stoichiometric Chemical Reaction

Generic fuel: CxHyOz, Molecular weight = (12x+y+16z) g/mol or

kg/kmol. eg. CH4and CH3OH Molecular weight of CH4= 12.011+4*(1.00794) =

12.011+4.03176=16.04876 kg/kmol

Saves a lot of time and effort to make engineering assumption

like: MWCH4= 16 kg/kmol

CxHyOz+ S (O2+ 3.76 N2) = xCO2 + y/2H2O + 3.76SN2

S = moles of O2from air needed for complete combustion of

CxHyOz.

S=x+y/4-z/2. So for CH4, S=2; for generic paraffin CnH2n+2,S=n+(n+1)/2=1.5n+0.5; and for a generic paraffin alcohol

CnH2n+1OH, S=n+(n+1)/2-1/2=1.5n

For Propane: S = 5; Propanol: C3H7OH, S = 4.5

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Combustion Fundamentals - 2

Fuel pyrolysis and vaporization must occur first for solid/liquid fuels.

Mixing at various length scales of the combustor, flow and molecular

scales occurs next prior to the molecular scale chemical reaction.

If mixing promoted first and then ignition and flame stabilization is

promoted, then a mode of combustion defined as premixedcombustion prevails.

If mixing occurs simultaneously with ignition and reaction then a

mode of combustion defined as non-premixed (diffusion) combustion

prevails.

Combination of premixed and diffusion combustion prevails in flame

stabilization region.

Flameless combustion may occur in certain devices.

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Combustion Fundamentals - 3

Combustion is an energy transfer process in which a portion of the storedmolecular bond energy of a working substance (reactants taken together) is

transformed into sensible energy of the chemically transformed workingsubstance, transferred in the form of heat and/or work for useful purposesand/or transferred to another working substance as heat.

The properties of the working substance that typically change as a result ofcombustion include: Internal energy: dus=cvdT,

enthalpy: dhs= dus+ vdP+ Pdv=cpdT; enthalpy including enthalpy change of state: dhs= dus+ vdP+ Pdv+ hfg enthalpy including enthalpy change associated with chemical bonds

Nomenclature and units

Us

= sensible internal energy kJ

us= specific sensible internal energy kJ/kg

Hs= sensible enthalpy kJ

hs= specific sensible enthalpy kJ/kg

T = temperature, K

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Combustion Fundamentals - 4

Nomenclature and units

P= pressure or force per unit area kN or kN/m2

= kPAUs= sensible internal energy kJ

us= specific sensible internal energy kJ/kg

Hs= sensible enthalpy kJ

hs= specific sensible enthalpy kJ/kg

Hfg= enthalpy change associated with phase change kJhfg= specific enthalpy change associated with phase change kJ/kg

cv = constant volume specific heat, kJ/kg-K

cP = constant pressure specific heat, kJ/kg-K

HHV= Higher heating value of a fuel, kJ/kg. Energy removed after complete combustionof the fuel to products to bring the products to the same temperature as thereactants and associated condensation of the resulting water vapor.

LHV= Lower heating value of a fuel , kJ/kg. Energy removed after complete combustionof the fuel to products to bring the products to the same temperature as thereactants but without condensation of the water vapor in the products.

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