Diesel Exhaust & DPF Systems Flashcards
6 cards from real Exhaust practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Diesel Exhaust & DPF Systems flashcards as text
What does the term 'oil dilution' mean in the context of diesel DPF regeneration?
Answer: Engine oil becoming contaminated and thinned by unburned diesel fuel from post-injection during regeneration
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.
What is the primary purpose of a Diesel Oxidation Catalyst (DOC)?
Answer: To oxidize carbon monoxide, hydrocarbons, and soluble organic fraction of particulates
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.
Why do diesel trucks used primarily for short-haul city driving experience DPF problems more frequently?
Answer: Low-speed urban driving produces insufficient exhaust heat for passive regeneration, causing soot accumulation
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.
What is 'SCR catalyst poisoning' in diesel exhaust aftertreatment systems?
Answer: Sulfur or oil-based contaminants deactivating the SCR catalyst's ability to reduce NOx
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.
What causes a diesel engine to enter 'limp mode' related to the DPF?
Answer: The DPF reaching maximum allowable soot load with no successful regeneration clearing it
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.
What is 'diesel particulate matter' (PM) classified as in terms of health risk?
Answer: A known carcinogen and significant respiratory hazard, particularly PM2.5
Diesel particulate matter, especially fine particles (PM2.5), is classified by the EPA and WHO as a carcinogen and serious respiratory health hazard linked to lung cancer, cardiovascular disease, and premature death.