Ugo Sorge

CFD optimization for GDI spray model tuning and enhancement of engine performance

Coupling a 3D Computational Fluid Dynamics (CFD) tool with a rigorous method of decision making is becoming indispensable in the design process of complex systems, as internal combustion engines. CFD based optimization (CFD-O) is here carried out on a single cylinder, four-valve, four-stroke gasoline direct injection (GDI) engine, to enhance mixture formation under stratified charge operation, hence to choose between the single or double injection strategy maximizing the engine power output. A 3D engine model is coupled with the Simplex algorithm to find the optimal synchronization of both injection and spark timing within the working cycle. CFD-O is also addressed to perform the validation of the gasoline spray model, that otherwise reveals tedious and time-consuming. The Simplex algorithm is used to tune the constants entering a model developed by authors, as applied to three different high pressure GDI injectors, preliminary experimentally characterized. Fully automatic procedures are assessed to be exploited in the phase of engine design, whose contribution may be of great importance to reduce development costs and time-to-market of new technologies.

Numerical study of the mixture formation process in a four-stroke GDI engine for two-wheel applications

Abstract Guidelines for managing the mixture formation process in a high-performance four-stroke Gasoline Direct Injection (GDI) engine for two-wheel applications are discussed, as derived from a multidimensional modelling of the in-cylinder processes. Gasoline adduction from a multi-hole injector is simulated by resorting to a properly developed model that accounts for the dependence of the initial droplets size distribution upon injection pressure. The model portability is preliminary demonstrated by comparison with experimental measurements carried out on sprays entering a confined vessel at controlled conditions. The simulation of different engine operating conditions highlights the capability to work under the so-called “mixed mode” boosting with spray guided mixture formation.

CFD Modeling of a Mixed Mode Boosted GDI Engine and Performance Optimization for the Avoidance of Knocking

The paper applies simulation techniques for the prediction and optimization of the thermo-fluid-dynamic phenomena characterizing the energy conversion process in a GDI engine. The 3D CFD model validation is realized on the ground of experimental measurements of in-cylinder pressure cycles and optical images collected within the combustion chamber. The model comprehends properly developed submodels for the spray dynamics and its impingement over walls. This last is particularly important due to the nature of the mixture formation mode, being wall-guided. Both homogeneous stoichiometric and lean stratified charge operations are considered. In the case of stoichiometric mixture, the possible occurrence of knocking is also accounted for by means of a submodel able to reproduce the preflame chemical activity. The CFD tool is finally included in a properly formulated optimization problem aimed at minimizing the engine-specific fuel consumption with the avoidance of knocking through a non-evolutionary algorithm.

Modeling and performance optimization of a direct injection spark ignition engine for the avoidance of knocking

The paper applies simulation techniques for the prediction and optimization of the thermo-fluid-dynamic phenomena characterising the energy conversion process in an internal combustion engine. It presents the development and validation of a 3D CFD model for a GDI optically accessible engine operating either under stoichiometric homogeneous charges or under overall lean mixtures. The model validation is realized on the ground of experimental measurements of the in-cylinder pressure cycle and of the available optical images. The model comprehends properly developed sub-models for the spray dynamics and the spray-wall interaction. This last is particularly important due to the nature of the mixture formation mode, being of the wall-guided type. In the stoichiometric mixture case, the possible occurrence of knocking is also considered by means of a sub-model able to reproduce the pre-flame chemical activity. The CFD tool is finally included in a properly formulated optimization problem aimed at minimizing the engine specific fuel consumption with the avoidance of knocking. The optimization, performed through a non-evolutionary algorithm, allows determining the best engine control parameters (spark advance and start of injection).

Optimization of a GDI engine operation in the absence of knocking through numerical 1D and 3D modeling

Various solutions are being proposed and adopted by manufactures and researchers to improve the energetic and environmental performance of internal combustion engines within the transportation sector. For automotive spark ignition engines, gasoline direct injection is one of the presently preferred technologies, in conjunction with turbocharging and downsizing. One of the limiting phenomena of this kind of engines, however, still remains the occurrence of knocking, namely the self-ignition of the so-called end-gas zones of the mixture, not yet reached by the flame front. This phenomenon causes strong in-cylinder pressure oscillations, high stress levels and even damage to engine components.Present work focuses on a numerical and experimental study of a turbocharged GDI engine and is aimed at assessing CFD-O (computational fluid dynamics optimization) procedures to be used in the phase of design as a decision making tool for the development of control strategies for a smooth and efficient operation. A preliminary experimental analysis is performed in order to characterize the considered engine and to investigate the phenomenon of knocking that occurs under some circumstances as the spark advance is increased. The collected data are employed to elaborate a predictive criterion for the appearance of this kind of abnormal combustion, as well as to validate both a 1D and a 3D model for the simulation of the engine working cycle. Various numerical optimization procedures are then realized to increase the engine power output and simultaneously avoid conditions leading to undesired self-ignitions. These are either based on the use of a non-evolutionary algorithm or employ a genetic algorithm in the case multiple contrasting objectives are set. The response surface methodology is also explored as a way to reduce the computational effort.

Image Processing for Early Flame Characterization and Initialization of Flamelet Models of Combustion in a GDI Engine

Ignition and flame inception are well recognised as affecting performance and stable operation of spark ignition engines. The very early stage of combustion is indeed the main source of cycle-to-cycle variability, in particular in gasoline direct injection (GDI) engines, where mixture formation may lead to non-homogenous air-to-fuel distributions, especially under some speed and load conditions. From a numerical perspective, 3D modelling of combustion within Reynolds Averaged Navier Stokes (RANS) approaches is not sufficient to provide reliable information about cyclic variability, unless proper changes in the initial conditions of the flow transport equations are considered. Combustion models based on the flamelet concept prove being particularly suitable for the simulation of the energy conversion process in internal combustion engines, due to their low computational cost. These models include a transport equation for the flame surface density, which needs proper initialization. A flame collocation is indeed to be properly made when starting the calculations, often just based on the users skill and without resorting to any quantitative data derived from experiments. However, the way to define initial conditions for cyclic variability prediction is often based on just statistical considerations. This work aims at exploiting information derived from images collected in a single cylinder 4-stroke GDI engine to properly collocate the flame at the start of the combustion calculation. The considered engine is optically accessible through a wide fused-silica window fixed on the piston crown having a Bowditch design. Image processing methodologies are applied to evaluate local and integral luminous intensity, and flame morphology parameters. The collected data allows improving the numerical simulation and gaining hints about the main parameters defining the engine cyclic variability.

Analysis of the GDI Spray Dynamics Through Multidimensional Modeling and Flow Visualization in an Optically Accessible SI Engine

Present work is aimed at studying into detail mixture formation and combustion in a gasoline direct injection (GDI) engine working under stoichiometric mixture conditions. The study is performed both numerically and experimentally. From the experimental side, the engine, optically accessible, is characterized by collecting, for various injection strategies, in-cylinder pressure cycles and digital images. From the numerical side, a 3D engine model is developed, that includes proper sub-models for the spray dynamics and the spray-wall interaction. This last phenomenon is studied into detail by resorting to a preliminary 3D simulation of the spray impingement realized in a proper experiment, where the engine injector is mounted at a certain distance from a cold or hot wall.An interesting comparison between numerical and experimental images of the in-cylinder spray dynamics is presented, that also allows individuating the difference in the wallfilm deposition under various injection strategies. This opens the way to understand the difference in the combustion development arising as injection is anticipated or retarded in the engine working cycle.© 2014 ASME