LN04 - Internal Combustion Engines ME422 Yeditepe...

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1 Internal Combustion Engines – ME422 Yeditepe Üniversitesi THERMODYNAMICS of COMBUSTION Prof.Dr. Cem Soru ş bay Internal Combustion Engines Thermodynamics of Combustion ¾ Introduction ¾ Properties of mixtures ¾ Combustion stoichiometry ¾ Combustion in IC-engines ¾ Chemical energy ¾ Heat of reaction ¾ Heat of formation ¾ Chemical equilibrium ¾ Adiabatic flame temperature ¾ Dissociation reactions
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2 Introduction Thermodynamics deals with equilibrium states and how chemical composition can be calculated for a system of known atomic/molecular composition if two independent thermodynamic properties are known. Systems undergoing chemical reactions are not in general, in chemical equilibrium - reactions are rate-controlled Chemical composition at a given instant in time is controlled by the thermodynamic properties, chemical reaction rates and fluid dynamics of the system. Introduction First Law of Thermodynamics for a thermodynamic system, the time rate of change of energy of the system is equal to the rate at which work is done on the system + the rate at which heat is transferred to the system. Neglecting PE and KE within system, energy consists of internal energy due to, - thermal energy due to translation, rotation and vibration of molecules - so called sensible energy , - chemical energy due to chemical bonds between atoms in the molecules, For system of mass m, work done W and heat transfer rate to the system q, first law can be written as, q W dt mu d + = & ) (
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3 Introduction mechanical work - power is, first law becomes, thermodynamic properties can be evaluated by assuming that the whole system is uniform or by dividing the system into subsystems that are assumed uniform, j number of cells with volumes V j dt dV p dt dx pA W = = & q dt dV p dt mu d + = ) ( = = J j j j j u V mu 1 ρ Introduction For a closed system energy balance can be obtained integrating first law equation with-respect-to time, where for constant pressure , integrating, 12 12 1 2 ) ( Q W u u m + = = 2 1 12 t t dt dt dV p W = 2 1 12 t t dt q Q q dt pV mu d = + ) ( q dt mh d = ) ( 12 1 2 ) ( Q h h m =
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4 Introduction If the chemical composition is constant, chemical energy does not change - for ideal gases, = 2 1 1 2 T T v dT c u u R c c v p + = = 2 1 1 2 T T p dT c h h Properties of Mixtures For mixtures of gases, system mass is obtained from the sum of masses of separate species, density of system is the sum of species densities, mass fraction is mass of species i, divided by total mass, and by definition = i i m m = i i ρ i i i m m y = = = i i y 1
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5 Properties of Mixtures Similarly mole fraction is mole of species i, divided by total number of moles, or ratio of molar concentration of species i to total molar concentration, and Molecular weight is, relation between mole fraction and mass fraction, n n N N x i i i = = = i i x 1 = = i i i i i M x N m M i i i i i i M y M M m M m N N x / / = = = Properties of Mixtures mixture internal energy and enthalpy per unit mass , internal energy and enthalpy per mole of mixture , pressure of mixture
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LN04 - Internal Combustion Engines ME422 Yeditepe...

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