Neuro-separated meta-model of the scavenging process in 2-Stroke Diesel engine

The complexity of flow inside cylinder leads to develop new accurate and specific models. Influencing the 2-stroke engine efficiency, the scavenging process is particularly dependent to the cylinder design. To improve the engine performances, the enhancement of the chamber geometry is necessary. The development of a new neuro-separated meta-model is required to represent the scavenging process depending on the cylinder configuration. Two general approaches were used to establish the meta-model: neural networks and NTF (Non-negative Tensor Factorization) separation of variables. To fully describe the scavenging process, the meta-model is composed by four static neural models (representing the Heywood parameters), two dynamic neural models (representing the evolution of gases composition through the ports) and one separated model (the mapping of the flow path during the process). With low reduction errors, these two methods ensure the accuracy and the relevance of the meta-model results. The establishment of this new meta-model is presented step by step in this article

A Methodology to Develop and Reduce New Models: Application to the Scavenging in 2-Stroke Diesel Engines

The development of new reduced models implies the use of structured methodology: developing step by step, the user can control every parameter of its new models (its accuracy in particular) depending on its application. From the model definition to its reduction, the approach exposed in this paper allows the establishment of new qualified models directly usable to explore the space of solutions or to be integrated in a global model to improve its results

From functional analysis to energy harvesting system design: application to car suspension

In the context of global energy demand increase, working on energy efficiency is essential. This paper deals with energy harvesting on car suspensions. In order to have a real added value, some criteria must be considered: the need to design a system that would be easily integrated into cars, the possibility to locally use the recovered energy to add new functionalities that can improve the security or the comfort of the car, and the necessity to not degrade and, if possible, to improve (semi-active or active dampers) the performances of the suspension. From the mechanical point of view, the functional analysis is used to define and to characterize the main suspension parts, to investigate the connexions and the energy flows and to identify the key elements for energy recovery. Then, quarter car and half car models implemented with Matlab/Simulink software are presented in order to evaluate the quantity of energy that could be recovered. Three locations are presented and evaluated. Simulations results will finally give an overview on the implementation opportunities

A Methodology for a New Qualified Numerical Model of a 2-Stroke Diesel Engine Design

This paper presents a methodology to determine and to formalize all the variables involved in a CFD model of a 2-stroke diesel engine. The formalization includes the establishing of the values domain and the research of relations between the variables. The formalization can be followed by a reduction of the variables and the ranges of values. The methodology concludes on the qualification of the model. The methodology has to be used before solving the model. It helps not to forget any variable and to well understand the characteristics of the final model. It also provides the validity domain of the model and the limits of its exploitation. The methodology is applies to the 2-stroke Diesel engines to optimize its design and characterize the aerodynamics inside the combustion chamber

A new reduced model of scavenging to optimize cylinder design

This paper presents the development of a new scavenging model to optimize cylinder design. The developed model explicitly integrates some of the cylinder’s design and environmental variables to describe flows during the scavenging process. Then, based on the reduced model, an optimization phase was carried out in order to determine the optimal values of cylinder variables. From computational fluid dynamics (CFD) models to optimal cylinder design, all method steps used are described in this paper. Adaptable to any type of engine, here it is applied to the particular two-stroke diesel engine with ports only. In order to fully understand fluid flow, the methodology integrates a number of CFD calculations with different cylinder configurations to provide data. The CFD results are used as neural network outputs during the training phase, whereas the cylinder variables plus the crankshaft angle are the inputs. The trained network provides the analytical reduced model for gas composition transiting through ports, which characterize the scavenging process. Thanks to these, genetic algorithms are run to define the most suitable values of cylinder variables in order to improve scavenging. The entire process for establishing the reduced model and the optimal design of the chamber is presented in this pape

Scavenging Process Analysis in a 2-Stroke Engine by CFD Approach for a Parametric 0D Model Development

This paper presents a method to improve cylinder design of 2-stroke auto-ignition engine based on a CFD (Computational Fluid Dynamics) study of internal flows in the chamber and an unsteady global 0D parametric approach. In 2-stroke engine, scavenging process plays an important role regarding engine efficiency and pollutant emissions. Several geometrical and environmental parameters (like piston velocity and inlet/outlet thermofluid conditions) impact the scavenging process and most of them vary when the engine is running. To improve the scavenging process, an analytical model (integrating design parameter variations) is developed and will be implemented in 0D global model. CFD simulations are used to establish the analytical scavenging model. The CFD model includes species transportation, piston motion (remeshing), turbulent effectsbut it does not take into account the combustion process or the aerodynamics in the cylinder before the beginning of scavenging. After defining the influent parameters on the scavenging, multiple simulations with varying values of parameters were run and a data base was created. The data base will be used to develop a reduced model of the scavenging process which will be integrated in a global 0D model of the engine. Through a reference case, the in-cylinder flow is analyzed and the evolution of velocity, pressure, species and turbulent kinetic energy fields during scavenging are discussed. After a statistical treatment, the results of simulations highlight two main significant parameters: the advance of intake opening and the angle of the intake duct. The decoupling of these two parameters is particularly suitable for the optimization of engines

β-NTF reduction and fast kriging simulation of optimal engine configurations

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Etude numérique et expérimentale d'un modèle de balayage dans un moteur 2-temps à allumage spontané

Cet article présente une modélisation numérique 3D de l’aérodynamique interne d’un moteur 2 temps durant la phase de balayage. Cette modélisation est ensuite confrontée à des essais en soufflerie grâce à une maquette à l’échelle 1 du cylindre moteur pour 2 positions du piston et plusieurs conditions de pression en amont. L’approche RANS associée au modèle de turbulence k-e realizable fournit des résultats numériques proches de ceux obtenus de manière expérimentale, avec des écarts inférieurs à 5% pour le débit massique

Specialized Reduced Models of Dynamic Flows in 2-Stroke Engines

The complexity of scavenging by ports and its impact on engine efficiency create the need to understand and to model it as realistically as possible. However, there are few empirical scavenging models and these are highly specialized. In a design optimization process, they appear very restricted and their field of use is limited. This paper presents a comparison of two methods to establish and reduce a model of the scavenging process in 2-stroke diesel engines. To solve the lack of scavenging models, a CFD model has been developed and is used as the referent case. However, its large size requires a reduction. Two techniques have been tested depending on their fields of application: The NTF method and neural networks. They both appear highly appropriate drastically reducing the model’s size (over 90% reduction) with a low relative error rate (under 10%). Furthermore, each method produces a reduced model which can be used in distinct specialized fields of application: the distribution of a quantity (mass fraction for example) in the cylinder at each time step (pseudo-dynamic model) or the qualification of scavenging at the end of the process (pseudo-static model)

From functional analysis to energy harvesting system design: application to car suspension

International audienceIn the context of global energy demand increase, working on energy efficiency is essential. This paper deals with energy harvesting on car suspensions. In order to have a real added value, some criteria must be considered: the need to design a system that would be easily integrated into cars, the possibility to locally use the recovered energy to add new functionalities that can improve the security or the comfort of the car, and the necessity to not degrade and, if possible, to improve (semi-active or active dampers) the performances of the suspension. From the mechanical point of view, the functional analysis is used to define and to characterize the main suspension parts, to investigate the connexions and the energy flows and to identify the key elements for energy recovery. Then, quarter car and half car models implemented with Matlab/Simulink software are presented in order to evaluate the quantity of energy that could be recovered. Three locations are presented and evaluated. Simulations results will finally give an overview on the implementation opportunities