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The government of India has decided to implement Bharat Stage VI (BS-VI) emissions standards from April 2020. This requires OEMs to equip their diesel engines with costly after-treatment, EGR systems and higher rail pressure fuel systems. By one estimate, BS-VI engines are expected to be 15 to 20% more expensive than BS-IV engines, while also suffering with 2 to 3 % lower fuel economy. OEMs are looking for solutions to meet the BS-VI emissions standards while still keeping the upfront and operating costs low enough for their products to attract customers; however traditional engine technologies seem to have exhausted the possibilities. Fuel economy improvement technologies applied to traditional 4-stroke engines bring small benefits with large cost penalties. One promising solution to meet both current, and future, emissions standards with much improved fuel economy at lower cost is the Opposed Piston (OP) engine.

After having tested basic transient maneuvers such as load-step changes on the 4.9L three-cylinder opposed-piston diesel engine [1], a similar test-engine was subjected to a more aggressive test-routine - a hot-start heavy-duty FTP (Federal Test Procedure) transient cycle for the on-road engines. The three main objectives of this exercise were: 1 To assess the ability of the engine to meet the transient cycle requirements while maintaining close to the cycle-average BSFC for the FTP cycle derived from steady-state torque-to-fuel map. 2 To attain engine-out brake-specific emission levels that are compatible with US2010 EPA requirements with a conventional after-treatment system consisting of a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF) and a selective catalyst reduction (SCR) system. 3 To compare hot-start FTP transient cycle fuel economy with a publicly available benchmark.

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].

Opposed-piston engines have been in production since before the 1930’s because of their inherent low heat losses and high thermal efficiency. Now, opposed-piston gasoline compression ignition (OP-GCI) engines are being developed for automotive transportation with stringent emissions targets. Due to the opposed-piston architecture and the absence of a cylinder head, fuel injection requirements and packaging are significantly different than conventional 4-stroke engines with central-mounted injectors. The injection process and spray characteristics are fundamental to achieving a successful combustion system with high efficiency, low emissions, and low combustion noise. In this paper, the fuel injection system for the Achates 2.7L, 3-cylinder OP-GCI engine is described. The fuel system was designed for 1800 bar maximum fuel pressure with two injectors mounted diametrically opposed in each cylinder.

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.

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 mounting pressure on Indian manufacturers to meet future fuel economy and emissions mandates-including the recently passed Corporate Average Fuel Consumption (CAFC) standards for light-duty vehicles-many are evaluating new technologies. However, to provide an economically sustainable solution, these technologies must increase efficiency without increasing cost. One promising solution to meet both current, and future, standards is the opposed-piston engine. Widely used in the early 20th century for on-road applications, use of the opposed-piston engine waseventually discontinued due to challenges with emissions and oil control. But advancements in computer-aided engineering tools, combined with state-of-the-art engineering practices, has enabled Achates Power to develop a modern opposed-piston diesel engine architecture that is clean, significantly more fuel efficient and less expensive to manufacture than today's four-stroke engines.

Renewable fuels, such as the alcohols, ammonia, and hydrogen, have a high autoignition resistance. Therefore, to enable these fuels in compression ignition, some modifications to existing engine architectures is required, including increasing compression ratio, adding insulation, and/or using hot internal residuals. The opposed-piston two-stroke (OP2S) engine architecture is unique in that, unlike conventional four-stroke engines, the OP2S can control the amount of trapped residuals over a wide range through its scavenging process. As such, the OP2S engine architecture is well suited to achieve compression ignition of high autoignition resistance fuels. In this work, compression ignition with wet ethanol 80 (80% ethanol, 20% water by mass) on a 3-cylinder OP2S engine is experimentally demonstrated. A load sweep is performed from idle to nearly full load of the engine, with comparisons made to diesel at each operating condition.