Effects of Injection Pattern Design on Piston Thermal Management in an Opposed-Piston Two-Stroke Engine

Abstract

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.

Study of new prototype pintle injectors for diesel engine application

“…In these nozzles, three main components can be defined: the needle, the sac and the hole (or holes), which can vary in number and orientation depending on the particular nozzle design. In the case of the figure, a single-hole axi-symmetric hole geometry, as it could be used for side-injection combustion systems, is represented [24]. When the injector is closed, the needle separates the high-pressure region of the nozzle (corresponding to the internal channel where the needle is located) from the low-pressure region, which includes the sac and the discharge hole.…”

“…These architectures typically require combustion systems with side-injection layouts of one or more injectors with narrow plume angle nozzles. For example, Venugopal et al [24] explored side-injector orientation and control using conventional multiholed nozzles on a diesel 2-stroke opposed piston to study the impacts on combustion and piston thermal loading. The main difference between the pintle nozzles used in this study and other pintle nozzles studied in the literature [25] is the relative shape of the nozzle and the needle.…”

Meeting Stringent 2025 Emissions and Fuel Efficiency Regulations with an Opposed-Piston, Light-Duty Diesel Engine

“…Achates Power has developed a proprietary combustion system [9] composed of two identical pistons coming together to form an elongated ellipsoidal combustion volume where the injectors are located at the end of the long axis [10] (Figure 4).…”

“…• Excellent control at lower fuel flow rates because of two small injectors instead of a single higher flow rate • Multiple injection events and optimization flexibility with strategies such as injector staggering and rate-shaping [10] The result is no direct fuel spray impingement on the piston walls and minimal flame-wall interaction during combustion. This improves performance and emissions [1] with fewer hot spots on the piston surfaces to further reduce heat losses [10].…”

On the Effect of a Rail Pressure Error State Observer in Reducing Fuel Injection Cycle-to-Cycle Variation in an Opposed-Piston Compression Ignition Engine

“…Whereas fuel injection pressure oscillation and injected quantity cycle-to-cycle variation become more prominent in the OPCI, it is surprising to find that most previous studies on fuel injection of OPCI were concerned with spray layout [26,27] optimization and spray combustion characteristics [28]. Thus, it is necessary to analyze the effects of OBS application on the spray combustion characteristics.…”