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Opposed-piston 2-stroke (OP-2S) engines have the potential to achieve higher thermal efficiency than a typical diesel engine. However, the uniflow scavenging process is difficult to control over a wide range of speeds and loads. Scavenging performance is highly sensitive to pressure dynamics, port timings, and port design. This study proposes an analysis of the effects of port vane angle on the scavenging performance of an opposed-piston 2-stroke engine via simulation. A CFD model of a three-cylinder opposed-piston 2-stroke was developed and validated against experimental data collected by Achates Power Inc. One of the three cylinders was then isolated in a new model and simulated using cycle-averaged and cylinder-averaged initial/boundary conditions. This isolated cylinder model was used to efficiently sweep port angles from 12 degrees to 29 degrees at different pressure ratios.

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.

Heavy-duty vehicles, currently the second largest source of fuel consumption and carbon emissions are projected to be fastest growing mode in transportation sector in future. There is a clear need to increase fuel efficiency and lower emissions for these engines. The Opposed-Piston Engine (OP Engine) has the potential to address this growing need. In this paper, results are presented for a 9.8L three-cylinder two-stroke OP Engine that shows the potential of achieving 55% brake thermal efficiency (BTE), while simultaneously satisfying emission targets for tail pipe emissions. The two-stroke OP Engines are inherently more cost effective due to less engine parts. The OP Engine architecture presented in this paper can meet this performance without the use of waste heat recovery systems or turbo-compounding and hence is the most cost effective technology to deliver this level of fuel efficiency.

This paper presents analytical and measured results on the effects of injection pattern design on piston thermal management in an Opposed-Piston, Two-Stroke (OP2S) diesel engine. The OP2S architecture investigated in this work comprises two opposing pistons forming an asymmetric combustion chamber with two opposing injectors mounted on the cylinder wall. This unique configuration offers opportunities to tailor the injection pattern to control the combustion heat flux and resulting temperatures on the piston surfaces while optimizing combustion simultaneously. This study utilizes three-dimensional (3D) computational fluid dynamics (CFD) with state-of-the-art spray, turbulence and combustion models that include detailed chemistry to simulate the in-cylinder combustion and the associated flame/wall interactions. In addition, the measurements comprise a real-time thermocouple system, which allows for up to 14 locations to be monitored and recorded on the intake and exhaust pistons.

The cooling system design for a two-stroke, opposed-piston (OP) engine is substantially different from that of a conventional four-stroke engine as the opposed-piston engine requires efficient cooling at the center of the cylinder where the heat load is highly concentrated. A thermally efficient design ensures engine durability by preserving the oil film at the top ring reversal zone. This is achieved by limiting the surface temperature of the liner to below 270°C at this location. Various water jacket designs have been analyzed with computational fluid dynamics (CFD) using a "discretized" Nusselt number approach for the gas side heat flux prediction. With this method, heat transfer coefficients are computed locally given the flow field of the combustion gases near the liner surface and then multiplied by the local gas/liner temperature difference to generate the heat flux distribution into the cylinder liner.