Question

(a) What is the best air/fuel ratio for an automobile engine? (b) If the mixture is made leaner, what happens to the hydrocarbon emissions? (c) If the fuel mixture is richer, how does this affect NOx emissions

Answer 1

a)The best air/fuel ratio for an automobile engine is that, which has the correct amount of air and fuel to produce a chemically complete combustion event.

There are different types of fuels for automobile engines. For e.g. diesel, gasoline, and ethanol, so air/fuel ratio depends on fuel type. For gasoline engines, air/fuel ratio is 14.7: 1, which means 14.7 parts of air to one part of fuel.

For alcohol air/fuel is 6.4: 1 and for diesel 14.5: 1

b) A higher air/fuel ratio contains more air and therefore it is a leaner mixture. Lean mixtures improve the fuel economy and decrease in hydrocarbon emissions. If the mixture becomes too lean, the engine may fail to ignite, causing misfire and a large increase in unburned hydrocarbon emissions.

(c) If the fuel mixture is richer, NOx emissions can be significantly reduced.

If the fuel mixture is richer, there are more hydrocarbon emissions. There is no free oxygen to combines with nitrogen and NOx emissions can be reduced.