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 CFD results are shown to predict the measured performance and emissions characteristics with very good correlation. Using the CFD model results, hot spot areas on the piston surfaces-resulting from impingement of the injection plumes during the combustion event-are computed. A proprietary telemetry system using thermocouples at key locations on the piston is deployed to measure the effects of injector clocking and injection spray angle on the piston temperatures. It is demonstrated that the trends in the computed hot spot areas for different injection patterns correlate well with trends in the measured temperatures. Furthermore, the investigations show that the clocking angle and the spray angle are two critical levers that can be optimized using CFD simulations for piston thermal management in the OP2S configuration. The results of this investigation demonstrate the effectiveness of experimentally correlated combustion-CFD simulations to unlock the potential of the OP2S configuration for improved piston thermal management.
he opposed piston two-stroke (OP2S) engine architecture is widely recognized for its improved fuel efficiency relative to a four-stroke engine. Achates Power Inc. seeks to demonstrate the market readiness of the OP2S engine by proving competitive in other important areas, one of which is oil consumption. Achieving oil consumption competitive to modern four-stroke engines is thus a key step in bringing OP2S technology to market. Two-stroke engines have historically suffered from higher engine lube oil consumption and subsequent emissions and durability challenges. This is primarily due to two main features of traditional two-stroke engines; the direct interaction of the piston skirt and rings with the intake and/or exhaust ports, which results in a direct leak path for lube oil to the combustion chamber and/or exhaust manifold, and crankcase-scavenged architectures which entrain oil into air being pumped through the crankcase. The OP2S engine architecture directly addresses these concerns by utilizing intake and exhaust manifolds, a closed crankcase system, and oil control rings which operate outboard of the ports. Previous work has shown the importance of careful consideration of cylinder liner, piston, and ring design in minimizing oil consumption of the OP2S architecture. This work evaluates further refinements in cylinder form, hone texture and oil retention, port sealing ring design, and oil control ring design. A Da Vinci DALOC sulfur-trace analyzer for real-time oil consumption measurement was used to generate speed vs. load maps of oil consumption of an Achates Power OP2S A48 development engine, operated under typical medium-duty conditions. The engine demonstrated oil consumption levels competitive with modern four-stroke benchmarks and completed a 100-hour durability test with no measured performance loss or increase in oil consumption. This work represents a key step towards proving the potential of the Achates Power OP2S engine architecture in the commercial and passenger vehicle markets.
The oscillating combustion, which takes place in the closed vessel when certain colloidal gun propellants are fired has been investigated. The amplitude of the oscillation depended on the geometry and flame temperature of the propellant. For propellants having the same composition but different geometry, the amplitude of the oscillation varied inversely with the maximum pressure in the vessel. This was tentatively ascribed to vortex formation during combustion.
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