Towards Large Eddy Simulation in Internal-Combustion Engines: Simulation of a Compressed Tumble Flow

Copyright © 2004 SAE International The development of the Large Eddy Simulation (LES) 3D CFD code AVBP to yield a CFD tool able to predict cyclic variability in Internal Combustion (IC) engines is reported. In a first step the implementation of an Arbitrary Lagrangian Eulerian (ALE) method into AVBP is described, allowing to move solid boundaries. Then the principles and implementation of the Conditioned Temporal Interpolation (CTI) mesh management technique is described, and some specific adaptations for LES simulations are discussed. Finally a first validation of the so obtained LES IC engine code is presented by comparing predictions with findings on the square piston experiment

Large-eddy simulation analysis of knock in a direct injection spark ignition engine

International audienceDownsized spark ignition (SI) engines running under high loads have become more and more attractive for car manufacturers because of their increased thermal efficiency and lower CO2 emissions. However, the occurrence of abnormal combustions promoted by the thermodynamic conditions encountered in such engines limits their practical operating range, especially in high efficiency and low fuel consumption regions. One of the main abnormal combustion is knock, which corresponds to an autoignition of end gases during the flame propagation initiated by the spark plug. Knock generates pressure waves which can have long term damages on the engine, that is why the aim for car manufacturers is to better understand and predict knock appearance. However an experimental study of such recurrent but non-cyclic phenomena is very complex, and these difficulties motivate the use of CFD for better understanding them. In the present paper, Large-Eddy Simulation (LES) is used as it is able to represent the instantaneous engine behavior and thus to quantitatively capture cyclic variability and knock. The proposed study focuses on the LES analysis of knock for a direct injection SI engine. A spark timing sweep available in the experimental database is simulated, and 15 LES cycles were performed for each spark timing. Wall temperatures, which are a first order parameter for knock prediction, are obtained using a conjugate heat transfer study. Present work points out that LES is able to describe the in-cylinder pressure envelope whatever the spark timing, even if the sample of LES cycles is limited compared to the 500 cycles recorded in the engine test bench. The influence of direct injection and equivalence ratio stratifications on combustion is also analyzed. Finally, focusing on knock, a MAPO (Maximum Amplitude Pressure Oscillation) analysis is conducted for both experimental and numerical pressure traces pointing out that LES well reproduces experimental knock tendencies

A conceptual model of the flame stabilization mechanisms for a lifted Diesel-type flame based on direct numerical simulation and experiments

This work presents an analysis of the stabilization of diffusion flames created by the injection of fuel into hot air, as found in Diesel engines. It is based on experimental observations and uses a dedicated Direct Numerical Simulation (DNS) approach to construct a numerical setup, which reproduces the ignition features obtained experimentally. The resulting DNS data are then used to classify and analyze the events that allow the flame to stabilize at a certain Lift-Off Length (LOL) from the fuel injector. Both DNS and experiments reveal that this stabilization is intermittent: flame elements first auto-ignite before being convected downstream until another sudden auto-ignition event occurs closer to the fuel injector. The flame topologies associated to such events are discussed in detail using the DNS results, and a conceptual model summarizing the observation made is proposed. Results show that the main flame stabilization mechanism is auto-ignition. However, multiple reaction zone topologies, such as triple flames, are also observed at the periphery of the fuel jet helping the flame to stabilize by filling high-temperature burnt gases reservoirs localized at the periphery, which trigger auto-ignitions

Éditorial: La simulation aux grandes échelles pour les écoulements dans les moteurs à combustion interne

International audienceNo abstract availabl

On the generalisation of high-order schemes for Large Eddy Simulations on moving meshes using an Arbitrary Lagrangian Eulerian approach

International audienceno abstrac

A PIV-Guided Large-Eddy Simulation of In-Cylinder Flows

A combination of Large-Eddy Simulation (LES) and Particle Image Velocimetry (PIV) was utilized to investigate the three-dimensional in-cylinder flow within an optically accessible Direct Injection Spark Ignition (DISI) engine at motored engine operation. The PIV measurements were used to guide the meshing procedure by identifying the regions were refinements and improvements were needed. From the iteratively optimized meshes LES results are shown from two selected meshes, an intermediate coarse mesh and the final optimized mesh, and compared to PIV measurements. The evolution of the intake flow and the tumble in the central tumble plane during compression are presented and discussed. Exploitation of the LES results allowed showing the influence of out-of-plane velocities along the cylinder liner impacting the formation of the tumble flow. The optimized mesh was then used to investigate the influence of the spark plug on the in-cylinder flow. For the studied engine the spark plug had a significant impact on the evolution of the tumble flow during compression. Finally 35 engine cycles were simulated using the optimized mesh with the spark plug in place. Velocity distributions in a region below the spark plug are shown and compared with PIV results. The two-sample Kolmogorov-Smirnov test revealed a strong similarity between the velocity distributions obtained by PIV and LES, thus validating the potential of LES for investigating cycle-to-cycle variability