Emissions Control Systems Flashcards

Which EPA tier standard applies to newly manufactured locomotive engines after January 1, 2015?

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.

What does NOx stand for in the context of locomotive emissions?

Answer: Nitrogen oxides

NOx is the collective term for nitrogen oxides (primarily NO and NO₂) produced during high-temperature combustion in diesel engines.

A locomotive's diesel oxidation catalyst (DOC) primarily reduces which pollutant?

Answer: Carbon monoxide and hydrocarbons

The diesel oxidation catalyst oxidizes carbon monoxide (CO) and unburned hydrocarbons (HC) into carbon dioxide and water.

Under the EPA's smoke opacity standards, what is the maximum allowable exhaust opacity during a full-load acceleration for a Tier 0 locomotive?

Answer: 40%

Tier 0 locomotives are allowed a maximum smoke opacity of 40% during full-load acceleration under EPA regulations.

What is the primary reason diesel particulate filters (DPFs) require periodic regeneration?

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.

Which component in a selective catalytic reduction (SCR) system converts NOx into harmless byproducts?

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.

During a pre-departure inspection, you notice the DEF tank level is at 10%. What is the correct action?

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.