Allied & ICAR Exam Bank • ALLIED_1131NAT • 2 Marks
Section 3: Farm Power
Farm Power
Subtopic: Combustion Air-Fuel Ratio
Question Statement:
A diesel fuel has chemical composition $C_{12}H_{26}$. The stoichiometric air-fuel ratio (kg of air per kg of fuel) required for complete combustion is approximately: (Air is 23.2% O$_2$ by mass; atomic weights: C=12, H=1, O=16)
Answer Key:
14.9
Step-by-Step Solution & Explanation
$C_{12}H_{26} + 18.5 O_2 \to 12 CO_2 + 13 H_2O$. Molecular weight of fuel $= 12(12) + 26 = 170\text{ g/mol}$. Mass of $O_2$ required $= 18.5 \times 32 = 592\text{ g}$. Mass of $O_2$ per kg fuel $= 592 / 170 = 3.482\text{ kg}$. Air required $= 3.482 / 0.233 \approx 14.94\text{ kg air/kg fuel}$.