The current trend in automobiles is towards electrical vehicles, but for the most part these vehicles still require an internal combustion engine to provide additional range and flexibility. These engines are under stringent emissions regulations, in particular, for the reduction of CO2. Gas engines which run lean burn combustion systems provide a viable route to these emission reductions, however designing these engines to provide sustainable and controlled combustion under lean conditions at λ=2.0 is challenging. To address this challenge, it is possible to use a scavenged Pre-Chamber Ignition (PCI) system which can deliver favorable conditions for ignition close to the spark plug. The lean charge in the main combustion chamber is then ignited by flame jets emanating from the prechamber nozzles. Accurate prediction of flame kernel development and propagation is essential for the analysis of PCI systems. A modelling approach is proposed based on the Dynamic Discrete Particle Ignition Kernel model coupled with the G-equation combustion model. The model is validated for an air/methane academic benchmark. The approach is then applied to the investigation of performance of three pre-chamber designs developed within Horizon 2020 GASON project in conjunction with the experimental investigation of these pre-chambers mounted on Rapid Compression Expansion Machine (RCEM). The investigated prechamber designs vary with respect to the tangential nozzle angle and volume. The study focusses on a lean limit of the proposed system's operation with the main charge at λ=2.0 and a variation of prechamber design and scavenging level. The comparison of the simulation results with the experimental observations demonstrates good accuracy of the developed model. In addition, the combined experimental and modelling provides insights into the effect of prechamber geometry on potential performance.
20XX-01-XXXX Numerical study of turbulence and fuel-air mixing within a scavenged pre-chamber using RANS and LES Author, co-author (Do NOT enter this information. It will be pulled from participant tab in MyTechZone)
In this work, numerical simulations of an automotive-sized scavenged pre-chamber mounted in an optically-accessible rapid compressionexpansion machine (RCEM) have been carried out using two different turbulence models: Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES). The RANS approach is combined with the G-equation combustion model, whereas the LES approach is coupled with the flamelet generated manifold (FGM) model for partially-premixed combustion. Simulation results are compared with experimental data in terms of OH* chemiluminescence in the main chamber. Both RANS and LES results were found to qualitatively reproduce the main features observed experimentally in terms of spatial flame development. Simulation results are further analysed by means of early flame propagation within the pre-chamber (related to the fuel and turbulence intensity distributions) and the ignition process in the main chamber. During the turbulence jet ignition (TJI) process, the analysis of the LES progress variable variance reveals that during the intensive jet mixing the mixture in the main chamber is predominantly ignited by autoignition followed by a progressive transition to a deflagrative premixed flame propagation mode. For the lean fuel-air mixture considered (=2) the mixing of the additional fuel (previously injected into the pre-chamber) within the main chamber was found to play a major role on the ignition process.
When developing a turbocharged internal combustion engine, the choice of turbocharger is usually based on designer experience and existing hardware. However, proper turbocharger design relies on matching the compressor and turbine performance to the engine requirements so that parameters such as boost and back pressure, compressor pressure ratio, and turbine inlet temperatures meet the needs of the engine without exceeding its allowable operating envelope. Therefore, the ultimate measure of a successful turbocharger design is how well it is matched to an engine across various operating conditions. This, in turn, determines whether a new turbocharger is required, or an existing solution can be used. When existing turbocharger solutions are not viable, the engine designer is at a loss on how to define a new turbocharger that meets the desired performance requirements. A common approach in industry has been to scale the performance of an existing turbocharger (compressor and turbine maps) and take these requirements for Original Equipment Manufacturers to possibly match it with a real machine. However, the assumptions made in a basic scaling process are quite simplistic and generally not satisfactory in this situation. A better approach would be to use a validated meanline model for a compressor and turbine instead, allowing to perform an actual preliminary design of such components. Such approach allows to link the engine performance requirements in a very early stage of te component design project and it guides the designer for the design decisions, such as rotor size, variable geometry nozzles, diameter, or shroud trims and others. Therefore, a feasible solution is more likely with design less iterations. This paper describes a methodology for an integrated approach to design and analyze a turbocharged internal combustion engine using commercially available state-of-the-art 1D gas dynamics simulation tool linked to two powerful turbomachinery meanline programs. The outputs of this analysis are detailed performance data of the engine and turbocharger at different engine operating conditions. Two case studies are then presented for a 10-liter diesel truck engine. The first study demonstrates how the programs are used to evaluate an existing engine and reverse engineer an existing turbocharger based only on the available performance maps. Then a second study is done using a similar approach but redesigning a new turbocharger (based on the reverse engineered one) for an increased torque output of the same engine.
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