Fuel and Emission Systems Flashcards

What is the stoichiometric air-fuel ratio for gasoline engines?

Answer: 14.7:1

The stoichiometric ratio of 14.7:1 (14.7 parts air to 1 part fuel by mass) provides the chemically ideal mixture for complete combustion and optimal catalytic converter efficiency.

What does a wideband oxygen sensor measure that a narrowband sensor cannot?

Answer: The exact air-fuel ratio across a wide range rather than just rich or lean of stoichiometric

Wideband (air-fuel ratio) sensors measure the precise lambda value across a wide range (typically 10:1 to 23:1), unlike narrowband sensors that only toggle between rich and lean near stoichiometric.

What is the function of the evaporative emission (EVAP) system?

Answer: To capture and store fuel vapours from the fuel tank and purge them into the engine for combustion

The EVAP system prevents hydrocarbon fuel vapours from escaping to the atmosphere by storing them in a charcoal canister and purging them into the intake manifold to be burned during normal driving.

What component controls the amount of fuel delivered by a port fuel injector?

Answer: The ECM controlling the injector pulse width (on-time)

The ECM controls fuel delivery by varying the injector pulse width — the duration the injector solenoid is energized. Longer pulse width delivers more fuel; shorter delivers less. Fuel pressure is held constant by the regulator.

What does a catalytic converter do to reduce harmful emissions?

Answer: It uses precious metal catalysts to chemically convert CO, HC, and NOx into less harmful CO2, H2O, and N2

A three-way catalytic converter uses platinum, palladium, and rhodium catalysts to oxidize CO and HC into CO2 and H2O, and reduce NOx into N2 and O2, significantly lowering tailpipe emissions.

What is the purpose of the exhaust gas recirculation (EGR) valve?

Answer: To reduce combustion temperatures and lower NOx emissions by introducing inert exhaust gas into the intake

The EGR valve meters a controlled amount of inert exhaust gas into the intake charge, displacing oxygen and lowering peak combustion temperatures, which reduces the formation of nitrogen oxide (NOx) emissions.