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Reducing the greenhouse emissions from on-road freight vehicles to meet the climate change mitigation objectives, has become a prime focus of regulatory authorities all over the world. Besides India, the United States, the European Union, Canada, Japan, and China have already established or planned heavy-duty vehicle efficiency regulations addressing CO2 and NOX emissions. In addition, Argentina, Brazil, Mexico, and South Korea are all in various stages of developing policies to improve the efficiency of their commercial vehicle fleets. For CO2 emissions reduction standards, the U.S. mandates 27% reduction by 2027, EU is calling for 15% reduction by 2025, China for 27% by 2019 over 2012 levels, and India is mandating 10%-15% reduction by 2021 for phase 2 of the new standard. There has also been considerable focus on further reduction in NOX emissions from current levels (0.2 g/hp-hr), to the proposed ultra-low NOx standards (0.02 g/hp-hr) in the U.S. for heavy duty engines by 2024.

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].

In a recent paper, Opposed-Piston 2-Stroke Multi-Cylinder Engine Dynamometer Demonstration [1] published at the SAE SIAT in India in January 2015, Achates Power presented work related to the first ever opposed piston multi-cylinder engine fuel economy demonstration while meeting US 2010 emissions. The results showed that the research 4.9L three cylinder engine was able to achieve 43% brake thermal efficiency at the best point and almost 42% on average over the 12 modes of the SET cycle. The results from this test confirmed the modelling predictions and carved a very robust path to a 48% best BTE and 46.6% average over the cycle for a production design of this engine. With the steady state performance and emissions results achieved, it was time to explore other attributes.

With current and pending regulations-including Corporate Average Fuel Economy (CAFE) 2025 and Tier 3 or LEV III-automakers are under tremendous pressure to reduce fuel consumption while meeting more stringent NOx, PM, HC and CO standards. To meet these standards, many are investing in expensive technologies-to enhance conventional, four-stroke powertrains-and in significant vehicle improvements. However, others are evaluating alternative concepts like the opposed-piston, two-stroke engine. First manufactured in the 1890s-and once widely used for ground, marine and aviation applications-the historic opposed-piston, two-stroke (OP2S) engine suffered from poor emissions and oil control. This meant that its use in on-highway applications ceased with the passage of modern emissions standards.