Question

A fuel contains 84% carbon and 16% hydrogen by mass. The necessary air- fuel ratio for chemically correct combustion is _______

(a) 10.42: 1

(b) 15.30: 1

(c) 20.36: 1

(d) 31.08: 1

I have been asked this question during a job interview.

My enquiry is from I.C Engine topic in chapter Internal Combustion Engine of Farm Machinery

Answer 1

The correct answer is (b) 15.30: 1

The explanation: Let CxHy be the fuel

Molecular weight of CxHy = 12x+y

According to question: \(\frac{12x}{12x+y}\)*100 = 84

And \(\frac{y}{12x+y}\)*100 = 16

By solving the above equations, we get; x=7 and y=16

Thus, formula for fuel is C7H16

C7H16 (12*7 + 1*16=100) + 11O2(11*16*2=352) = 7CO2 + 8H20

\(\frac{Air}{Fuel} = \frac{352}{100*0.23}\) = 15.3:1