In: Other
Calculate calorific value of E15 fuel. A car run by gasoline has highway mpg 33, if it runs by E15, calculate the new mpg. Ignore all other effects. If it runs only by ethanol what would be new mpg. (Points 10+10=20)
Basis 1 Litre of E15 :
Volume of Gasoline = Vol.fraction * Total volume = 0.85 * 1 = 0.85 L
Density of gasoline = 0.737 Kg/L
Mass of gasoline = Volume* density = 0.85 * 0.737 = 0.62645 Kg
Calorific value of gasoline = 46.4 MJ/Kg
Heat energy from 0.62645 Kg of gasoline = 0.62645 * 46. 4 = 29.067 MJ
Volume of Ehanol = 0.15 * 1 = 0.15 L
Density of Ethanol = 0.789 Kg/L
Mass of Ethanol = 0.15 * 0.789 = 0.11835 Kg
Calorific value of Ethanol = 29.7 MJ/Kg
Heat energy from 0.11835 Kg of Ethanol = 0.11835 * 29.7 = 3.515 MJ
Total energy from the 1 L of E15 = Enery from gasoline + energy fro ethanol = 29.067 + 3.515 = 32.582 MJ
1 litre = 0.264 gallon
Total energy from 0.264 gal of E15 = 32.582 MJ
Total energy from 1 gal of E15 = 32.582/0.264 = 123.417 MJ
b ) Given that car runs on gasoline at 33 mpg.
Calorific value of gasoline per litre = Calorific value of gasoline per Kg * Density in Kg/L = 46.4 * 0.737= 34.2 MJ /L
Total energy from 1 gal of gasoline = 34.2/0.264 = 129.545 MJ
Miles run per gallon of gasoline = 33 miles per gallon
Energy required per miles = energy from one gallon of gasoline / Total miles = 129.545 / 33 = 3.925 MJ / mile
Energy from 1 gallon of E15 = 123.417 MJ
Miles run using 1 gallon of E15 = Energy from 1 gallon of E15/Energy required per miles = 123.417/3.925 = 31.44 miles
If the car runs on E15, its highway mpg = 31.44 mpg
c) If ony run by ethanol.
Calorific value of Ethanol per litre = Calorific value of Ethanol per Kg * Density in Kg/L = 29.7 * 0.789= 23.433 MJ /L
Total energy from 1 gal of Ethanol = 23.433/0.264 = 88.76 MJ
Miles run using 1 gallon of ethanol = Energy from 1 gallon of Ethanol/Energy required per miles = 88.76/3.925 = 22.61 mpg