Question

An average formulation for gasoline is C7H13. Complete combustion in air produces C7H13 + 10.25 O2 + 38.54 N2 = 7 CO2 + 6.5 H2O + 38.54 N2 Determine the Stoichiometric air to fuel ratio for complete combustion of gasoline. What is the effect of "rich" and "lean" air mixtures on emissions? Why is this ratio important to the operation of vehicle catalytic devices?

Answer 1

Air-Fuel Ratio (AF) = mass of air/mass of fuel

1 molecule of C7H13 has a molecular weight = 97 g

weigth of O2 molecule = 32g

thus oxygen to fuel ratio = 10.25*32/97 = 3.381

since 21 percent of air is oxygen so air required for 3.381 kg of oxygen = 3.381*100/21 = 16.102

thus AF = 16.102

rich mixture makes engine less efficient while lean mixture makes engine more efficient. but lean mixture produce high temperature which result in the formation of nitrogen oxides.When there is a change from rich to lean operation it will drop carbon monoxide emission.

This air - fuel ratio has a great sgnificance. when this ratio is high it will produce maximum power.