Exhaust Exhaust Emissions & Catalytic Converters 3

Question 1

What is the purpose of Selective Catalytic Reduction (SCR) in modern diesel exhaust systems?

Accepted Answer

To reduce nitrogen oxides using a urea solution

Answer

SCR systems inject diesel exhaust fluid (DEF, a urea solution) into the exhaust stream to chemically reduce NOx into harmless nitrogen and water.

Question 2

What is 'diesel exhaust fluid' (DEF) primarily composed of?

Accepted Answer

Urea and deionized water

Answer

DEF is a 32.5% solution of urea in deionized water, used in SCR systems to convert NOx emissions into nitrogen and water vapor.

Question 3

Which emission from gasoline engines is most directly associated with the formation of ground-level ozone (smog)?

Accepted Answer

Volatile organic compounds (VOCs)

Answer

VOCs react with nitrogen oxides in sunlight to form ground-level ozone, which is a major component of smog and a respiratory irritant.

Question 4

What does an EGR valve do in an emissions control system?

Accepted Answer

Recirculates a portion of exhaust gases back into the intake

Answer

An Exhaust Gas Recirculation (EGR) valve routes a portion of exhaust gas back into the intake manifold, lowering combustion temperatures and reducing NOx formation.

Question 5

Which OBD-II readiness monitor must be set before a vehicle can pass an emissions inspection?

Accepted Answer

Catalyst monitor

Answer

The catalyst monitor is a key OBD-II readiness monitor that must report 'ready' status, confirming the catalytic converter has been evaluated by the vehicle's computer.

Exhaust Practice Test

Exhaust Practice Test

Exhaust Exhaust Emissions & Catalytic Converters 3