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 opposed-piston 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.