Question

There are 220 million motored vehicles in the USA, of which about 85% operating on gasoline-fired Otto engines. Gasoline can be assumed 100% octane (C8H18) with a heating value of 48,000 kJ/kg, specific gravity of 0.83, and price of $2.50/gallon. A typical vehicle uses 15% excess air in combustion, and is driven an average of 32 miles per day per vehicle, with an average fuel economy of 18 miles per gallon of gasoline. The averaged unburned Hydrocarbons, CO, and NOx, emissions amount to 0.3%, 0.05%, 0.05% of the exhaust gases respectively.

(a) Balance the combustion equation of C3H18 with 15% excess air, and fine the air-fuel ratio by mass.

(b) Estimate the total combustion air needed, carbon emission, and greenhouse gas CO2 generated from all gasoline engines of USA in Mton/year, and total sale of gasoline in USA in billion$/year.

(c) Estimate total emission of Pollutants: unburned HCs, CO, and NOx from mobile gasoline engines in USA per year.

Answer 1

a)

The chemical equation for propane burned with 15% excess air can be expressed as

C8H18+ 1.15 x 12.5(O₂ + 3.76 N₂) -> 8CO₂ + 9H₂O + 3.75 O₂ + 54.05 N₂

air to fuel ratio=mass of air/mass of fuel=1.15*12.5*(32+3.76*28)/114=17.31

b)consumption of gasolin=220*32/18*0.85=332.44 million gallon/year

Total sale of gasoline=2.5*332.44 million =$831.11 million/year=$8.3111 billion/year

Mass of gasoline=(332.44 million gallon=1258.42229 million litre)*830 Kg/m^3=1.044*10^9 Kg

moles of octane=9.1622*10^6 Kmol of octane

total combustion air needed=1.15*12.5*9.1622*10^6 =1.317*10^8 Kmoles

greenhouse gas generated=9.1622*10^6=7.329*10^7 Kmole=3.225*10^9 Kg/year=3.225*10^6 Mton/year

c)Exhaust gas=0.15*9.1622*10^6=1.37433 *10^6 Kmol

Hydrocarbons, CO, and NOx, emissions amount to 0.3%, 0.05%, 0.05% of the exhaust gases

Hydrocarbons=0.3/100*1.37433 *10^6 Kmol =4123 Kmol/year

CO=0.05/100*1.37433 *10^6 Kmol =687.165 Kmol/year

NOx=0.05/100*1.37433 *10^6 Kmol =687.165 Kmol/year