This work presents a modeling approach for multidimensional combustion simulations of a highly dilute opposed-piston spark-ignited gasoline engine. Detailed chemical kinetics is used to model combustion with no sub-grid correction for reaction rates based on the turbulent fluctuations of temperature and species mass fractions. Turbulence is modeled using RNG k-ε model and the RANS-length scales resolution is done efficiently by the use of automatic mesh refinement when and where the flow parameter curvature (2nd derivative) is large. The laminar flame is thickened by the RANS viscosity and a constant turbulent Schmidt (Sc) number and a refined mesh (sufficient to resolve the thickened turbulent flame) is used to get accurate predictions of turbulent flame speeds. An accurate chemical kinetics mechanism is required to model flame kinetics and fuel burn rates under the conditions of interest. For practical computational fluid dynamics applications, use of large detailed chemistry mechanisms with 1000s of species is both costly as well as memory intensive. For this reason, skeletal mechanisms with a lower number of species (typically ∼100) reduced under specific operating conditions are often used. In this work, a new primary reference fuel chemical mechanism is developed to better correlate with the laminar flame speed data, relevant for highly dilute engine conditions. Simulations are carried out in a dilute gasoline engine with opposed piston architecture, and results are presented here across various dilution conditions.

Pinnacle is developing a multicylinder 1.2 L gasoline engine for automotive applications using high-performance computing (HPC) and analysis methods. Pinnacle and Oak Ridge National Laboratory executed large-scale multidimensional combustion analyses at the Oak Ridge Leadership Computing Facility to thoroughly explore the design space. These HPC-led investigations show high fuel efficiency (∼46% gross indicated efficiency) may be achieved by operating with extremely high charge dilution levels of exhaust gas recirculation (EGR) at a light load key drive cycle condition (2000 RPM, 3 bar brake mean effective pressure (BMEP)), while simultaneously attaining high levels of fuel conversion efficiency and low NOx emissions. In this extremely dilute environment, the flame propagation event is supported by turbulence and bulk in-cylinder charge motion brought about by modulation of inlet port flow. This arrangement produces a load and speed adjustable amalgamation of swirl and counter-rotating tumble which provides the turbulence required to support stable low-temperature combustion. At higher load conditions, the engine may operate at more traditional combustion modes to generate competitive power. In this paper, the numerical results from these HPC simulations are presented. Further HPC simulations and test validations are underway and will be reported in future publications.

Pinnacle is developing multi-cylinder 1.2 L gasoline engine for automotive applications using high performance computing (HPC) and analysis methods. Pinnacle and Oak Ridge National Laboratory executed large-scale multi-dimensional combustion analyses at the Oak Ridge Leadership Computing Facility to thoroughly explore the design space. These HPC-led investigations show high fuel efficiency (∼46% gross indicated efficiency) may be achieved by operating with extremely high charge dilution levels of exhaust gas recirculation (EGR) at a light load key drive cycle condition (2000 RPM, 3 bar BMEP), while simultaneously attaining high levels of fuel conversion efficiency and low NOx emissions. In this extremely dilute environment, the flame propagation event is supported by turbulence and bulk in-cylinder charge motion brought about by modulation of inlet port flow. This arrangement produces a load and speed adjustable amalgamation of swirl and counter-rotating tumble which provides the turbulence required to support stable low-temperature combustion (LTC). At higher load conditions, the engine may operate at more traditional combustion modes to generate competitive power. In this paper, the numerical results from these HPC simulations are presented. Further HPC simulations and test validations are underway and will be reported in future publications.

Pinnacle Engines, Inc., and researchers at Oak Ridge National Laboratory (ORNL) collaborated under the DOE Small Business Voucher program to perform high-fidelity engine simulations of Pinnacle's unique opposed-piston engine. In addition to the opposed-piston architecture, Pinnacle's design includes features such as variable valve timing and compression ratio which provide the potential for improved performance, efficiency, and emissions but also introduce many degrees of freedom in design and operation. The impact and complex interactions of these design and operating parameters must be well understood to direct and optimize the final design. Using DOE's flagship supercomputing resource, Titan, the team was able to perform an extensive set of numerical engine simulations to explore the impact of these parameters on predicted engine performance. Based on the learnings from this study, Pinnacle will build and experimentally evaluate a prototype engine for light-duty gasoline applications.