CEI Fuel Systems & Engine Combustion Flashcards
6 cards from real CEI practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CEI Fuel Systems & Engine Combustion flashcards as text
Which ignition system problem is most likely to cause a significant spike in hydrocarbon (HC) emissions during an emission test?
Answer: Engine misfire due to a fouled spark plug or weak ignition coil, causing unburned fuel to exit through the exhaust
Engine misfire, whether from a fouled spark plug, weak coil, or damaged wire, sends raw unburned fuel into the exhaust, dramatically increasing HC emissions.
What is the purpose of the positive crankcase ventilation (PCV) system, and what emission does it help control?
Answer: It routes crankcase blowby gases (containing unburned HC) back into the intake manifold to be burned rather than venting them to the atmosphere
The PCV system draws combustion blowby gases—primarily unburned hydrocarbons—from the crankcase and redirects them into the intake to be burned, preventing direct HC emissions to atmosphere.
Fuel volatility, measured by Reid Vapor Pressure (RVP), is regulated seasonally in many US regions. Why is lower RVP fuel required during summer months?
Answer: Lower RVP reduces evaporative hydrocarbon emissions from fuel tanks and carburetors in hot weather, helping areas meet ozone standards
Higher temperatures increase fuel evaporation; requiring lower RVP fuels in summer reduces evaporative HC emissions (a VOC ozone precursor) from fuel systems and refueling operations.
What effect does engine operating temperature have on CO emissions during a cold-start emission test?
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
During cold start, the ECU enriches the mixture for driveability and the catalytic converter is below its light-off temperature (~250–300°C), so CO passes through unoxidized, causing a spike in CO emissions.
A vehicle equipped with a selective catalytic reduction (SCR) system uses what reductant to chemically reduce NOx in diesel exhaust?
Answer: Diesel Exhaust Fluid (DEF), a urea-water solution that decomposes to ammonia, which reacts with NOx to form N2 and H2O
SCR systems inject DEF (32.5% urea in water) into the exhaust; the urea hydrolyzes to ammonia, which reacts with NOx over a vanadium or zeolite catalyst to produce harmless nitrogen gas and water.
What is 'lambda' (λ) in the context of engine air-fuel mixture analysis during emission testing?
Answer: The ratio of actual air-fuel ratio to the stoichiometric air-fuel ratio; λ=1.0 is stoichiometric, λ1 is lean
Lambda (λ) is the normalized excess air factor: actual A/F divided by stoichiometric A/F (14.7:1 for gasoline), giving a dimensionless value where 1.0 is perfect stoichiometry.