A tractor diesel engine operates under part-load with an actual operating air-fuel ratio of $(A/F)_{act} = 22.5$. If the stoichiometric air-fuel ratio is $(A/F)_{st} = 15.0$, the fuel-air equivalence ratio ($\phi = \frac{(A/F)_{st}}{(A/F)_{act}}$) of the mixture is ________ (round off to 2 decimal places).
Answer Key:
0.67
Step-by-Step Solution & Explanation
The fuel-air equivalence ratio $\phi$ is defined as:
$\phi = \frac{(F/A)_{act}}{(F/A)_{st}} = \frac{(A/F)_{st}}{(A/F)_{act}}$
Given $(A/F)_{st} = 15.0$ and $(A/F)_{act} = 22.5$:
$\phi = \frac{15.0}{22.5} = \frac{2}{3} \approx 0.6667 \approx 0.67$
(Note: $\phi < 1.0$ indicates a lean combustion mixture, typical for diesel engines).