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

During active regeneration, extra fuel is injected late in the combustion cycle; some of this unburned fuel can seep past the piston rings and into the crankcase, thinning the engine oil.

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

A DOC uses precious metal catalysts to oxidize CO, unburned hydrocarbons, and the soluble organic fraction (SOF) of diesel particulate matter into CO2 and water vapor.

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

Urban stop-and-go driving keeps engine loads and exhaust temperatures low, preventing passive regeneration from occurring, so soot accumulates rapidly and requires frequent active regeneration cycles.

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

SCR catalyst poisoning occurs when sulfur compounds or contaminants from oil or fuel deposits bind to the catalyst's active sites, reducing its ability to convert NOx into nitrogen and water.

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

When the DPF soot load reaches a critically high level that cannot be cleared by regeneration, the ECU activates limp mode, limiting engine power and speed to prevent DPF damage and force the driver to seek service.

Exhaust Practice Test

Exhaust Practice Test

Exhaust Diesel Exhaust & DPF Systems 3