CEI CEI Fuel Systems & Engine Combustion 1 — Questions and Answers
Question 1: Which combustion byproduct is formed when carbon-based fuels burn incompletely due to insufficient oxygen?
- Carbon monoxide (CO) (Correct answer)
- Carbon dioxide (CO2)
- Nitrogen gas (N2)
- Water vapor (H2O)
Correct answer: Carbon monoxide (CO)
Carbon monoxide (CO) is produced during incomplete combustion when there is insufficient oxygen to fully oxidize carbon to CO2.
Question 2: What is the stoichiometric air-to-fuel ratio for a gasoline-powered internal combustion engine?
- 14.7:1 (14.7 parts air to 1 part fuel by mass) (Correct answer)
- 10.5:1 (10.5 parts air to 1 part fuel by mass)
- 17.0:1 (17.0 parts air to 1 part fuel by mass)
- 21.0:1 (21.0 parts air to 1 part fuel by mass)
Correct answer: 14.7:1 (14.7 parts air to 1 part fuel by mass)
The stoichiometric air-to-fuel ratio for gasoline is 14.7:1, meaning 14.7 grams of air are required to completely combust 1 gram of gasoline with no excess oxygen or unburned fuel.
Question 3: How do oxides of nitrogen (NOx) primarily form during internal combustion engine operation?
- At high combustion temperatures, atmospheric nitrogen reacts with oxygen inside the combustion chamber (Correct answer)
- From sulfur impurities in diesel fuel reacting with oxygen
- From the decomposition of nitrogen-containing fuel additives at low temperatures
- From the catalytic converter oxidizing nitrogen in the exhaust stream
Correct answer: At high combustion temperatures, atmospheric nitrogen reacts with oxygen inside the combustion chamber
NOx forms primarily through the thermal Zeldovich mechanism, where the high temperatures in the combustion chamber (above ~1,300°C) cause atmospheric nitrogen and oxygen to react.
Question 4: What does a rich air-fuel mixture (lambda < 1) typically produce in excess in vehicle exhaust compared to a stoichiometric mixture?
- Higher CO and HC emissions due to incomplete combustion from excess fuel (Correct answer)
- Higher NOx emissions due to increased combustion temperatures
- Higher CO2 emissions with no change in HC levels
- Lower CO and HC emissions because more fuel is burned completely
Correct answer: Higher CO and HC emissions due to incomplete combustion from excess fuel
A rich mixture (excess fuel) leads to incomplete combustion, producing elevated CO and unburned hydrocarbon (HC) emissions because there is insufficient oxygen to fully oxidize all the fuel.
Question 5: Which fuel system component is responsible for atomizing and injecting precise amounts of fuel into the engine's intake ports or combustion chamber?
- Fuel injector (Correct answer)
- Fuel pressure regulator
- Mass airflow sensor
- Throttle position sensor
Correct answer: Fuel injector
Fuel injectors are electronically controlled solenoid valves that atomize and deliver precise quantities of fuel into the intake port or directly into the combustion chamber based on ECU commands.
Question 6: What is the role of the exhaust gas recirculation (EGR) system in reducing vehicle emissions?
- It recirculates a portion of exhaust gases back into the intake to lower peak combustion temperatures, reducing NOx formation (Correct answer)
- It recirculates exhaust gases to increase fuel atomization and reduce HC emissions
- It captures unburned hydrocarbons in the exhaust and returns them to the fuel tank
- It lowers CO emissions by injecting fresh oxygen into the exhaust stream
Correct answer: It recirculates a portion of exhaust gases back into the intake to lower peak combustion temperatures, reducing NOx formation
The EGR system dilutes the intake charge with inert exhaust gases, lowering peak combustion temperatures and oxygen concentration, which reduces the thermal formation of NOx.
CEI CEI Fuel Systems & Engine Combustion 1
Which combustion byproduct is formed when carbon-based fuels burn incompletely due to insufficient oxygen?