Exhaust Diesel Exhaust & DPF Systems 3

Question 1

What does the term 'oil dilution' mean in the context of diesel DPF regeneration?

Accepted Answer

Engine oil becoming contaminated and thinned by unburned diesel fuel from post-injection during regeneration

Answer

The DPF releasing oil-based compounds into the exhaust stream

Answer

DEF fluid mixing with engine oil through a failed seal

Answer

Water vapor from combustion condensing in the oil sump

Question 2

What is the primary purpose of a Diesel Oxidation Catalyst (DOC)?

Accepted Answer

To oxidize carbon monoxide, hydrocarbons, and soluble organic fraction of particulates

Answer

To trap particulate matter from diesel exhaust

Answer

To reduce nitrogen oxides through urea injection

Answer

To recirculate exhaust gases to lower combustion temperatures

Question 3

Why do diesel trucks used primarily for short-haul city driving experience DPF problems more frequently?

Accepted Answer

Low-speed urban driving produces insufficient exhaust heat for passive regeneration, causing soot accumulation

Answer

City driving uses more fuel, overwhelming the DPF's capacity faster

Answer

Frequent braking damages the DPF substrate structure

Answer

City air quality filters penetrate the DPF more easily than highway air

Question 4

What is 'SCR catalyst poisoning' in diesel exhaust aftertreatment systems?

Accepted Answer

Sulfur or oil-based contaminants deactivating the SCR catalyst's ability to reduce NOx

Answer

DEF fluid freezing and cracking the SCR catalyst housing

Answer

NOx concentrations exceeding the SCR's design capacity

Answer

Soot from the DPF bypassing and coating the SCR substrate

Question 5

What causes a diesel engine to enter 'limp mode' related to the DPF?

Accepted Answer

The DPF reaching maximum allowable soot load with no successful regeneration clearing it

Answer

The DPF temperature sensor failing open circuit

Answer

The DOC overheating above design temperatures

Answer

An SCR DEF dosing error causing excessive NOx output

Question 6

What is 'diesel particulate matter' (PM) classified as in terms of health risk?

Accepted Answer

A known carcinogen and significant respiratory hazard, particularly PM2.5

Answer

A nuisance pollutant with only cosmetic air quality impacts

Answer

A greenhouse gas regulated primarily for climate impact

Answer

An irritant with only short-term health effects and no long-term risk