Heavy-duty diesel engine oil aging effects on emissions.

摘要

Diesel engines are highly reliable, durable and are used for wide range of applications with low fuel usage owing to its higher thermal efficiency compared to other mobile power sources. Heavy-duty diesel engines are used for both on-road and off-road applications and dominate the heavy-duty engine segment of the United States transportation market. However, diesel engine exhaust emissions affect the ambient air quality by producing higher levels of oxides of nitrogen (NOx) and particulate matter (PM) compared to other mobile sources. New diesel engines produce significantly lower levels of PM and NOx emissions to comply with 2010 EPA emission limits compared to just a decade ago. But, the reliability of an on-road diesel engine (over 1 million miles) results in a significant portion of the heavy-duty engine truck fleet containing many legacy diesel engines in operation and these engines are relatively high NOx and PM emitters. Various programs to introduce fuels, additives, and retrofit devices to reduce NOx and PM emissions from these legacy engines have been carried out in states such as California and Texas. In these programs, emissions are compared between a baseline condition and the candidate technology configuration using a representative legacy engine. However, a small variation in the emissions levels can lead to either pass or failure of the candidate technology. The motivation for this research study was to investigate how engine oil aging history in a legacy engine affects the emission levels which may cause these decisive small variations.A research study was undertaken to determine engine oil aging effects on gaseous and particulate matter emissions from a 12.7L 1992 Detroit Diesel Series 60 legacy heavy-duty diesel engine. Commercially available Shell Rotella RTM SAE 15W-40 engine oil was used to evaluate exhaust emission constituents up to 40 hours of oil aging, in two different test campaigns. The engine was exercised over transient and steady state test cycles. Apart from measurement of regulated gaseous and gravimetric PM emissions from the engine, PM number concentration levels were also measured. Oil samples were analyzed to study changes in its physical properties along with ash content, soot contamination, and metal content. Additionally, the oil samples were analyzed for determination of particle size distribution of suspended particles in the samples.From the research, no significant changes in regulated gaseous and PM emission were observed during either test campaigns that could be attributed to the lubricant oil. Analysis of the oil samples showed no significant change in viscosity and density within the aging time period, but showed increase in total acid number (TAN) by 21%, soot content and metal content, whereas decrease in total base number (TBN) by 14.5%. Investigation into particle sizing of suspended particles in the oil samples suggests contamination of the oil by larger diameter particles during the initial 15 hours of its use compared to particles found from the oil samples from later part of the aging time period.