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A considerable amount of work was carried out in the mid-1980s to develop heavy-duty diesel engines that could meet limits on particulate emissions. These limits, although high by today’s standards, were considered very restrictive. Some manufacturers struggled to achieve the 0.6 g/bhp-h particulate matter limit with enough margin for production variabilities and to account for the deterioration factor. Significant progress was achieved in diesel emissions control through engine and fuel system design changes. This eventually made it possible to meet a particulate level of 0.25 g/bhp-h for 1991. The next target level for particulate emissions is 0.1 g/bhp-h for the 1994 heavy-duty engine. To meet the challenge, engine developers are not only considering engine and injection system design changes but also fuel improvements and exhaust aftertreatment. This paper includes a review of past and current strategies used to control emissions in the modern diesel engine.

This study was performed by the Department of Engine and Emissions Research under an SwRI® Internal Research and Development Program. The objective of the study was to evaluate the effectiveness of a system design that was an advancement over SwRI's patented Protection of Aftertreatment Systems from Sulfur (PASS) technology.[1,2] A Lean NO x Trap (LNT) was employed as the sulfur-sensitive emissions reduction device. Lean Sulfur Traps (LST) and Rich Sulfur Traps (RST) were formulated to provide the sulfur protection. Testing was performed to evaluate the efficiency of the LNT, the sulfur poisoning of the LNT, the efficiency of the LST, and the regeneration and protection characteristics of the PASS-2 system. The program successfully demonstrated that an LST upstream of an LNT does provide protection for the LNT from the adverse effects of fuel-borne sulfur. The work also demonstrated that the LST could be desulfurized, with all of the product sulfur species passing through the LNT, without adversely affecting its performance. These two results validated the PASS-2 advanced system design. The data also suggested that an LST could be effective at storing sulfur from 8 ppm sulfur diesel exhaust at very high efficiency for a minimum of 50,000 miles. A single desulfurization of the LST could release most of the stored sulfur in less than five minutes, with only a minor impact on fuel economy. A temporary deactivation of the LNT was reversed within five minutes, so the NO x emission impact would also be very minor. The lack of high temperature required to regenerate the LNT would result in significantly increased durability of the LNT. In essence, the PASS-2 system could be used to maintain emissions efficiency over 435,000 miles for heavy-duty applications, with an estimated nine desulfurizations of the LST during that period, when the system is fully developed.

The 2007 emission standards for both light-duty and heavy-duty diesel vehicles remain a challenge. A level of about 90% NOx conversion is required to meet the standards. Technologies that have the most potential to achieve very high NOx conversion at low temperatures of diesel exhaust are lean NOx traps (LNTs) and Selective Catalytic Reduction (SCR) of NOx using aqueous urea, typically known as Urea SCR. The LNT has the advantage of requiring no new infrastructure, and does not pose any new customer compliance issues. However, Urea SCR has high and durable NOx conversion in a wider temperature window, a lower equivalent fuel penalty, and lower system cost. On a technical basis, Urea SCR has the best chance of meeting the 2007 NOx targets. This paper reviews the results of some demonstration programs for both light-and heavy-duty applications.

The principal objective of this work is to determine the effect of cerium fuel additive on engine emissions characteristics. Emphasis is placed on obtaining a good baseline characterization of regulated and unregulated emission early in the study. Another objective is to uncover any operational problems during 1000 hours of durability. The study includes a post durability emission characterization to fulfill the objective of assessing the effect of cerium on emissions. 10 refs., 6 figs., 19 tabs.