Question

Dodecane (C2H26) burns completely with 150% of theoretical air. Determine (a) the air-fuel ratio on a molar and mass basis. (b) the dew point temperature of the combustion products, in C, when cooled at 1 atm. Ans: (a) 132.1, 22.41 (b) 44.8 deg C

Answer 1

Answer:

Given that,

Dodecane (C ₁₂ H ₂₆) burns completely with 150% of theoretical air

- Consider the reaction for theoretical combustion of B C2 H2o. Ca tota CO2 +3.76 N2 J aco + b Hotch s) Applying congewaffon of mass principle to all the constituents. Equating the carbon citom coefficients 26 = 2b b=18 Equating the oxygen atom coefficients. 22 = zatb 29th Q e 2(12) +13 Equating the nitrogen atom coefficie 2* 3, 76x2 = 20 C= 18.5x3.76 -69-56. Thorebosie the balanced chemical equation theoretical combution is for - C2H26 + 18-5 (02+3.76 N₂J 12 CO2t 13 H₂O+69.56N Consider the reaction for complete combution of the with iso % of theoretical aich, (12H₂6 + (1-5)/8.5 (O2 + 3.76N2) BCO₂ + 8 H₂O + 2q + ON2

Applying conservation of mass -poincipal to all the 2 dovdi tuonts. • Equating the courbon atom coefficients. 12 =B Equating the hydagen odom coefficients. 26=27 8 = 13 Equating the nitrogen Oxygen atom coefficients, 55,5# 28+8+21 d = 55.5-(2B+8) 2 - 55.5 - (20 × 12 +13) 2 Equating the nitrogen atom coefficients (1.5X8.5) X 2,76 X 2 =2W W=TomBn. The balance chemical equation.is, C2H26+(1.5) (18.5) (o 43.769N2. - 12/02+12420 +9=250+10mling a) . The air fuel ratio on mokor basis. AF moles of avia Simoles of fuel, AF = 27.75*( 13 76) 132.09 Kalotas kmal Cruel)

..The cior fuel ratio on molar basis is (32.09. Emal Cuisi knol(fuel) - The air fuel ratio on mass basis. AF = moles of air s mairt moles of fuel l. rifuel - AF Maid 7 LM Fuel / Ho, Mais molecular weight of the au WO1226 - molecwca weight of the fuel. AF - AE Mair . . Mfuel [ 28.97 =, 132.09% 12x1201) + (26X1.008) AF 22.1.466 kg Cao) Kal-fuel) forom the 5) The mole foraction of water vapor combustion proESS, products.. : nontothoa thN2 13 12+13+4.25 +IOH-3H = 0.0938

The peutral possue of water vapor. Pr=yP Pr=(0.0938) X (1.01325). o oarbar *) the dew point tenperatur at vapor pporessurot O. 095 berfrom saturated steamtables by inteapolation Ool-0.095 15.81 - Thew 45.81-468 0.1-0.08 Therefore the clewpoint temperaturure of the combustion Procluct is the 4,7350]