INTERNAL COMBUSTION ENGINES LECTURER PROF.Dr. DEMIR BAYKA
FOR A MIXTURE OF GASES MOLECULAR WEIGHT: SPECIFIC GAS CONSTANT where R 0 =8.314 kJ/kmol-K
SPECIFIC HEAT OF A GAS MIXTURE
SPECIFIC HEAT RELATIONS units are kJ/kmol-K also
ALGORITHMS coefficients A ij can be obtained from pages 131 & 133 of your reference book
CHAPTER 3 COMBUSTION PROCESS 1. SPARK IGNITION ENGINES AIR + FUEL REACTANTS PRODUCTS
AIR = OXYGEN + NITROGEN (and some CO2 and Argon) CO2 and Argon may be assumed as part of Nitrogen such that
FOR UNIT VOLUME OF O units of AIR = O units of N 2 ’ O 2 is approximately 21% of AIR (on a volume basis)
FUEL IS MIXTURE OF HYDROCARBONS OTHER FUELS ARE ALCOHOLS, NATURAL GAS, LPG and HYDROGEN GENERAL FORMULA C N H M O L
MOLECULAR WEIGHT OF THE FUEL C N H M O L M f = 12N + M + 16L EXAMPLE : C 8 H 18 (octane) M f = 12 x = 114
ON A MASS BASIS CARBON PERCENT OF FUEL
ON A MASS BASIS HYDROGEN PERCENT OF FUEL
ON A MASS BASIS OXYGEN PERCENT OF FUEL
ASSUMING NO OTHER ELEMENT C + H + O f = 1
PRODUCTS OF COMBUSTION LEAN MIXTURE CO 2, H 2 O, O 2, N 2 COMPLETE COMBUSTION RICH MIXTURE CO 2, CO, H 2 O, H 2, N 2 INCOMPLETE COMBUSTION
STOICHIOMETRIC REACTION
ACTUAL REACTION
…..COMPLETE COMBUSTION
…INCOMPLETE COMBUSTION
TEMPERATURE OF THE PRODUCTS
n i = The number of moles of species u i = Molar specific internal energy of species (kJ/kmol)
LET US ASSUME FOR SIMPLICITY:
INTERNAL ENERGY OF THE REACTANTS
INTERNAL ENERGY OF THE PRODUCTS
INTERNAL ENERGY OF THE PRODUCTS
THE PROCEDURE FOR FINDING THE PRODUCT TEMPERATURE 1. COMPUTE T R ……... (= T 2 ) 2. COMPUTE LHS LHS = (Q R-P + U R ) 3. ASSUME T P and COMPUTE RHS 4. IF RHS<>LHS then ASSUME NEW T P and COMPUTE RHS 5. INTERPOLATE OR EXTRAPOLATE TO FIND T P