Natural gases arc rarely pure methane; they usually also contain other light hydrocarbons and nitrogen. Determine on expression for the standard heat of combustion as a function of composition for a natural gas containing methane, ethane, propane, and nitrogen. Assume liquid water as a product of combustion. Which of the following natural gases has the highest heat of combustion?
(a) ycH4 = 0.95, yc2H6 = 0.02, yc3H8 = 0.02, yN2 = 0.01.
(b) ycH4 = 0.90, yc2H6 = 0.05. yc3H8 = 0.03, yN2 = 0.02.
(c) ycH4 = 0.85, yc2H6 = 0.07, yc3H8 = 0.03, yN2 = 0.05.