LEC Emissions Control Systems 2 — Questions and Answers
Question 1: Which EPA tier standard applies to newly manufactured locomotive engines after January 1, 2015?
- Tier 2
- Tier 3
- Tier 4 (Correct answer)
- Tier 5
Correct answer: Tier 4
EPA Tier 4 standards, effective January 1, 2015, set the most stringent emissions limits for newly manufactured line-haul and switch locomotives.
Question 2: What does NOx stand for in the context of locomotive emissions?
- Nitrogen oxides (Correct answer)
- Nitrous oxide only
- Non-oxidizing exhaust
- Nitrogen in exhaust
Correct answer: Nitrogen oxides
NOx is the collective term for nitrogen oxides (primarily NO and NO₂) produced during high-temperature combustion in diesel engines.
Question 3: A locomotive's diesel oxidation catalyst (DOC) primarily reduces which pollutant?
- NOx
- Carbon monoxide and hydrocarbons (Correct answer)
- Particulate matter only
- Sulfur dioxide
Correct answer: Carbon monoxide and hydrocarbons
The diesel oxidation catalyst oxidizes carbon monoxide (CO) and unburned hydrocarbons (HC) into carbon dioxide and water.
Question 4: Under the EPA's smoke opacity standards, what is the maximum allowable exhaust opacity during a full-load acceleration for a Tier 0 locomotive?
- 20%
- 30%
- 40% (Correct answer)
- 50%
Correct answer: 40%
Tier 0 locomotives are allowed a maximum smoke opacity of 40% during full-load acceleration under EPA regulations.
Question 5: What is the primary reason diesel particulate filters (DPFs) require periodic regeneration?
- To cool the exhaust system
- To burn off accumulated soot and restore filter flow (Correct answer)
- To replenish the DEF fluid
- To recalibrate the EGR valve
Correct answer: To burn off accumulated soot and restore filter flow
DPF regeneration burns off trapped soot at high temperatures to restore normal exhaust backpressure and filter efficiency.
Question 6: Which component in a selective catalytic reduction (SCR) system converts NOx into harmless byproducts?
- Diesel particulate filter
- Diesel oxidation catalyst
- Urea injection and catalyst substrate (Correct answer)
- Exhaust gas recirculation valve
Correct answer: Urea injection and catalyst substrate
In SCR systems, injected urea (DEF) decomposes into ammonia, which reacts with NOx over the catalyst substrate to produce nitrogen and water.
Question 7: During a pre-departure inspection, you notice the DEF tank level is at 10%. What is the correct action?
- Depart and refill at the next terminal
- Refill DEF before departing to maintain SCR system function (Correct answer)
- Bypass the SCR system temporarily
- Contact dispatch only if the warning light activates
Correct answer: Refill DEF before departing to maintain SCR system function
Operating with critically low DEF will cause the SCR system to deinerate, increasing NOx emissions beyond legal limits and potentially triggering engine derate.
LEC Emissions Control Systems 2
Which EPA tier standard applies to newly manufactured locomotive engines after January 1, 2015?