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This study presents a preliminary application of Large-Eddy Simulations (LES) of a speed transient performed on a motored single-cylinder engine. The numerical setup follows a methodology which has been validated and optimized for stabilized operating points in previous work, and adapted to run a speed transient of 31 cycles, from 1000 to 1800 rpm. Analysis of the results contributes to characterize the impact of the transient on the engine charge, tumble motion and velocity distribution. These simulations, which have never been performed in the past (to the best of our knowledge), represent a decisive step towards modeling and understanding transient in GDI engines, and particularly their impact on soot particle emissions in real driving conditions.

Increasingly restrictive emission standards and CO2 targets drive the need for innovative engine architectures that satisfy the design constraints in terms of performance, emissions and drivability. Downsizing is one major trend for Spark-Ignition (SI) engines. For downsized SI engines, the increased boost levels and compression ratios may lead to a higher propensity of abnormal combustions. Thus increased levels of Exhaust Gas Recirculation (EGR) are used in order to limit the appearance of knock and super-knock. The drawback of high EGR rates is the increased tendency for Cycle-to-Cycle Variations (CCV) it engenders. A possible way to reduce CCV could be the generation of an increased in-cylinder turbulence to accelerate the combustion process. To manage all these aspects, 1D simulators are increasingly used. Accordingly, adapted modeling approaches must be developed to deal with all the relevant physics impacting combustion and pollutant emissions formation.

In spark-ignition engines, Cycle-to-Cycle Variations (CCV) limit the optimization of engine operation since they induce torque variations and the occurrence of misfire and/or knock. A mean for limiting the related negative impact of CCV on fuel consumption and emissions would be control strategies able to address them. At present, engine simulation codes used for control purposes can only describe CCV linked to variations of gas exchanges in the air loop. CCV of the in-cylinder flow motion cannot be naturally captured by classical quasi-dimensional combustion chamber models. A convenient way to mimic CCV is to impose stochastic distributions of the combustion model parameters. Nevertheless, it is not always clear if these perturbations have physical bases as well as realistic ranges of variation.

Large Eddy Simulation (LES) appears today as a prospective tool for engine study. Even if recent works have demonstrated the feasibility of multi-cycle LES, they have also pointed out a lack of detailed experimental data for validation as well as for boundary condition definition. The acquisition of such experimental data would require dedicated experimental set-ups. Nevertheless, in future industrial applications, unconditional dedicated experimental set-ups will not be the main stream. To overcome this difficulty, a methodology is proposed using system simulation to define fluid boundary conditions (crank-resolved intake/exhaust pressures and temperatures) and wall temperatures. The methodology combines system simulation for the whole experimental set-up and LES for the flow in the combustion chamber as well as a part of the intake and exhaust ducts. System simulation provides the crank-resolved temperature and pressure traces at the LES mesh inlet and outlet.

A full 3D Large Eddy Simulation (LES) of a four-stroke, four-cylinder engine, performed with the AVBP-LES code, is presented in this paper. The drive for substantial CO₂ reductions in gasoline engines in the light of the global energy crisis and environmental awareness has increased research into gasoline engines and increased fuel efficiencies. Precise prediction of aerodynamics, mixing, combustion and pollutant formation are required so that CFD may actively contribute to the improvement/optimization of combustion chamber, intake/exhaust ducts and manifold shapes and volumes which all contribute to the global performance and efficiency of an engine. One way to improve engine efficiency is to reduce the cycle-to-cycle variability, through an improved understanding of their sources and effects. The conventional RANS approach does not allow addressing non-cyclic phenomena as it aims to compute the average cycle.

The LES technique has been applied to the simulation of 9 consecutive complete engine cycles of a single cylinder, spark-ignited 4valve engine. The simulations have been realized with the AVBP code, jointly developed by IFP and CERFACS. An extended coherent flame model approach (ECFM-LES) has been used to model spark ignition and turbulent combustion, and is shortly presented, along with the used turbulence models. The engine was fuelled with gaseous propane injected far upstream from the intake, so that fuel injection was not simulated, the fresh charge being assumed to be homogeneous. After a description of the numerical set-up, results obtained with LES are compared with experimental findings on cycle to cycle cylinder pressure evolutions. It is shown that LES indeed captures qualitatively the observed cyclic variability of the engine, even with only 9 cycles simulated.

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.

The purpose of the 4-SPACE (4-Stroke Powered gasoline Auto-ignition Controlled combustion Engine) industrial research project is to research and develop an innovative controlled auto-ignition combustion process for lean burn automotive gasoline 4-stroke engines application. The engine concepts to be developed could have the potential to replace the existing stoichiometric / 3-way catalyst automotive spark ignition 4-stroke engines by offering the potential to meet the most stringent EURO 4 emissions limits in the year 2005 without requiring DeNOx catalyst technology. A reduction of fuel consumption and therefore of corresponding CO2 emissions of 15 to 20% in average urban conditions of use, is expected for the « 4-SPACE » lean burn 4-stroke engine with additional reduction of CO emissions.