Christopher A. Sharp

Technical advantages of urea SCR for light-duty and heavy-duty diesel vehicle applications

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.

Heavy-Duty Diesel Engine Emissions Tests Using Special Biodiesel Fuels

A 2003 heavy-duty diesel engine (2002 emissions level) was used to test a representative biodiesel fuel as well as the methyl esters of several different fatty acids. The fuel variables included degree of saturation, the oxygen content, and carbon chain length. In addition, two pure normal paraffins with the corresponding chain lengths of two of the methyl esters were also tested to determine the impact of chain length. The dependent variables were the NO x and the particulate emissions (PM). The results indicated that the primary fuel variable affecting the emissions is the oxygen content. The emissions results showed that the highest oxygen content test fuel had the lowest emissions of both NO x and PM. As compared to the baseline diesel fuel the NO x emissions were reduced by 5 percent and the PM emissions were reduced by 83 percent.

Cold Start HD FTP Test Results on Multi-Cylinder Opposed-Piston Engine Demonstrating Rapid Exhaust Enthalpy Rise to Achieve Ultra Low NOx

The 2010 emission standards for heavy-duty diesel engines in the U.S. have established a limit for oxides of nitrogen (NOx) emissions of 0.20 g/bhp-hr., a 90% reduction from the previous emission standards. However, it has been projected that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with the 2010 emission standards, the upcoming National Ambient Air Quality Standards (NAAQS) requirement for ambient particulate matter and ozone will not be achieved in California without further significant reductions in NOx emissions from the heavy-duty vehicle fleet. Given this, there is potential of further reduction in NOx emissions limit standards for heavy duty engines in the US. Recently there have been extensive studies and publications focusing on ultra-low NOx after treatment technologies that help achieve up to 0.02g/bhp-hr. at tailpipe [1]. To achieve ultra-low NOx emission levels over the composite HD FTP cycle, rapid heat energy must be provided to the diesel exhaust after-treatment system during cold start portion of the cycle, and peak NOx reduction efficiency must be maintained during the hot-start portion of cycle. Delivering this has been the challenge for conventional four-stroke heavy duty diesel engines as these are competing demands. Ultra-low NOx system solutions involving the implementation of supplemental heat sources downstream in the exhaust system comes at CO2 penalty and adds significant cost and complexity. The Achates Power Opposed-Piston Engine design provides an ideal solution to this challenge. The opposedpiston engine has several inherent advantages over conventional four-stroke engines, like higher BTE [2], low BMEP and internal EGR facilitating low engine out NOx and ability to provide rapid engine out temperature rise [3] for emission system while maintaining low engine out NOx. This paper highlights the results from cold-start HD FTP testing with the 4.9L Opposed-Piston Engine. The target of this testing was to evaluate the ability of the Achates Power Opposed-Piston Engine to provide rapid engine out temperature rise by operating the engine in the mode designed to deliver exhaust enthalpy, aiding fast catalyst light-off which enables early and peak NOx conversion in the exhaust after treatment system. Rapid exhaust heat and temperature rise that was delivered exceeded SCR catalyst light-off temperature thresholds (200°C) within the first 40 seconds in the cycle while controlling the engine out NOx levels.