CEI CEI Fuel Systems & Engine Combustion 3

Question 1

Which ignition system problem is most likely to cause a significant spike in hydrocarbon (HC) emissions during an emission test?

Accepted Answer

Engine misfire due to a fouled spark plug or weak ignition coil, causing unburned fuel to exit through the exhaust

Answer

A lean misfire at idle caused by a clogged fuel injector reducing HC levels

Answer

An advanced ignition timing condition producing excess NOx but reducing HC

Answer

A failed crankshaft position sensor causing the engine to run on fewer cylinders

Question 2

What is the purpose of the positive crankcase ventilation (PCV) system, and what emission does it help control?

Accepted Answer

It routes crankcase blowby gases (containing unburned HC) back into the intake manifold to be burned rather than venting them to the atmosphere

Answer

It pressurizes the crankcase to prevent oil leaks and reduce CO emissions

Answer

It cools the engine oil by circulating fresh air through the crankcase, reducing NOx

Answer

It filters particulate matter from crankcase ventilation gases before releasing them outside

Question 3

Fuel volatility, measured by Reid Vapor Pressure (RVP), is regulated seasonally in many US regions. Why is lower RVP fuel required during summer months?

Accepted Answer

Lower RVP reduces evaporative hydrocarbon emissions from fuel tanks and carburetors in hot weather, helping areas meet ozone standards

Answer

Lower RVP fuel has a higher octane rating that reduces engine knock and NOx emissions in summer

Answer

Lower RVP reduces CO tailpipe emissions by improving combustion efficiency at high ambient temperatures

Answer

Lower RVP fuel contains less ethanol, which reduces formaldehyde emissions during summer ozone season

Question 4

What effect does engine operating temperature have on CO emissions during a cold-start emission test?

Accepted Answer

Cold engines produce significantly more CO because the ECU runs a rich fuel mixture during warm-up and the catalytic converter is not yet at operating temperature

Answer

Cold engines produce less CO because fuel combustion is more complete at lower temperatures

Answer

Cold starts have no measurable effect on CO emissions since fuel trim adjusts immediately

Answer

Cold engines produce higher NOx because combustion temperatures are suppressed during warm-up

Question 5

A vehicle equipped with a selective catalytic reduction (SCR) system uses what reductant to chemically reduce NOx in diesel exhaust?

Accepted Answer

Diesel Exhaust Fluid (DEF), a urea-water solution that decomposes to ammonia, which reacts with NOx to form N2 and H2O

Answer

Diesel fuel injected into the exhaust stream to catalytically reduce NOx over a platinum substrate

Answer

Recirculated exhaust gas mixed with ammonia stored onboard in a high-pressure tank

Answer

Hydrogen gas produced by an onboard reformer to reduce NOx over a rhodium catalyst

Question 6

What is 'lambda' (λ) in the context of engine air-fuel mixture analysis during emission testing?

Accepted Answer

The ratio of actual air-fuel ratio to the stoichiometric air-fuel ratio; λ=1.0 is stoichiometric, λ<1 is rich, λ>1 is lean

Answer

The percentage of oxygen remaining in the exhaust after catalytic converter treatment

Answer

The rate of fuel evaporation from the intake manifold measured in grams per second

Answer

The difference between intake manifold pressure and atmospheric pressure indicating engine load