CEI CEI Fuel Systems & Engine Combustion 2

Question 1

Which sensor provides feedback to the engine control unit (ECU) to maintain the air-fuel ratio near stoichiometry and is critical for three-way catalytic converter efficiency?

Accepted Answer

Oxygen (O2) sensor / lambda sensor

Answer

Crankshaft position sensor

Answer

Intake air temperature sensor

Answer

Manifold absolute pressure sensor

Question 2

A vehicle shows high positive fuel trim values (e.g., +25%) at idle. What does this most likely indicate?

Accepted Answer

An unmetered air leak (vacuum leak) causing the ECU to add extra fuel to compensate for a lean condition

Answer

A rich running condition caused by a stuck-open fuel injector

Answer

A faulty catalytic converter causing exhaust backpressure

Answer

A failed oxygen sensor providing a false rich signal

Question 3

What type of fuel system does a 'direct injection' gasoline engine use, and what emission challenge is uniquely associated with it?

Accepted Answer

Fuel is injected directly into the combustion chamber, which produces higher particulate matter (PM) emissions compared to port injection

Answer

Fuel is injected into the intake manifold, which produces higher NOx due to leaner combustion

Answer

Fuel is mixed with air before the throttle body, which produces higher EVAP emissions

Answer

Fuel is carbureted at idle and injected at high loads, which causes high CO at part throttle

Question 4

What is 'engine knock' (detonation), and how does it affect exhaust emissions?

Accepted Answer

Uncontrolled auto-ignition of the air-fuel mixture before the spark plug fires, causing incomplete combustion and increased HC and CO emissions

Answer

Excessive lubrication oil burning in the combustion chamber, increasing PM and HC emissions

Answer

Misfiring caused by a weak ignition spark, producing elevated NOx emissions

Answer

Exhaust valve flutter at high RPM causing HC spikes in the exhaust

Question 5

In a diesel engine, what is the primary pollutant of concern that is significantly higher than in gasoline engines due to the nature of diesel combustion?

Accepted Answer

Particulate matter (PM) and NOx

Answer

Carbon monoxide (CO) and hydrocarbons (HC)

Answer

Carbon dioxide (CO2) and sulfur dioxide (SO2)

Answer

Ammonia (NH3) and nitrous oxide (N2O)

Question 6

What is the function of a diesel particulate filter (DPF) in reducing vehicle emissions?

Accepted Answer

It traps and periodically burns off soot particles from diesel exhaust to prevent PM from being released into the atmosphere

Answer

It absorbs NOx from the exhaust stream using a urea-based chemical reaction

Answer

It oxidizes unburned hydrocarbons and CO in the exhaust using a platinum catalyst

Answer

It recirculates exhaust gases back into the intake manifold to lower combustion temperatures