Large Eddy Simulation of a Motored Single-Cylinder Piston Engine: Numerical Strategies and Validation

Abstract

This paper describes a compressible Large Eddy Simulation (LES) used to investigate cyclic variations for nonreacting flow in an optical single cylinder engine setup. The simulated operating point is part of a large experimental database designed to validate LES for cycle-to-cycle prediction, and constitutes a first step towards the realization of fired operating points. The computational domain covers almost the whole experimental setup (intake and exhaust plenums, intake and exhaust ducts, cylinder) to account for acoustic phenomena. The assessment of the computation is performed in two regions of the domain: the intake and exhaust duct predictions are compared to the results of a Helmholtz solver and the experiment (pressure transducers and Particle Image Velocimetry (PIV)) while the in-cylinder dynamics are compared to PIV measurements. The ability of the B. Enaux · V. Granet (B) · O. Vermorel 154 Flow Turbulence Combust (2011) 86:153-177 developed methodology to capture the correct level of cycle-to-cycle variations is demonstrated considering in-cylinder pressure and velocity fields predictions. Cycleto-cycle variations in velocity are highlighted and localized using a proper orthogonal decomposition analysis.

Evaluating Large-Eddy Simulation (LES) and High-Speed Particle Image Velocimetry (PIV) with Phase-Invariant Proper Orthogonal Decomposition (POD)

“…Other examples of in-cylinder LES include LES of Diesel engine combustion with CHEMKIN and a flamelet time scale combustion model by Hu et al [27][28][29], validation of cycle-to-cycle variations for a motored singlecylinder piston engine using LES by Enaux et al [30], LES of Diesel engine combustion with a multi-mode combustion model by Banerjee et al [31] and LES of scalar dissipation rate in an IC engine by Zhang et al [32,33]. A recent review of LES applications in IC engines by Rutland [34] summarizes the status of this field.…”

“…This paper uses more traditional metrics for comparison, such as the ensemble average and RMS velocities, and mass-specific kinetic energies, as well as relevance indices to compare the flow structures in two velocity fields and phase-dependent and phase-invariant POD. Some prior work comparing PIV and LES velocity data has also used phase-dependent POD performed at several crank angles to analyze cyclic flow variations [30]. The ratio between the energy fractions of the first and second modes was used as a measure of cyclic flow variations.…”

Understanding the Influences of Thermal and Mixture Inhomogeneities on the Auto-Ignition Process in a Controlled Auto-Ignition (CAI) Engine Using LES

“…Within ICE simulations [22] the models are chosen according to the physics required for the given combustion mode. Accordingly, for spark ignition engines usually the Flame Surface Density (FSD) approach [23,24], the G-equation [25], or the Artificially Thickened Flame (ATF) model [26] are employed to treat the flame propagation. For applications with auto-ignition different mechanisms are dominating [2] and those simulations often use Probability Density Functions (pdf) to account for the unresolved scalar distribution and accordingly obtain a more accurate evaluation of the non-linear relations.…”

Numerical Methods and Turbulence Modeling for LES of Piston Engines: Impact on Flow Motion and Combustion

“…When dealing with sporadic or erratic phenomena such as CCV or abnormal combustions, an additional difficulty arises: since reliable trends and statistics may only be obtained by computing numerous cycles (typically 50), the solver must necessarily be robust and fast. A direct consequence of these issues (complexity, novelty, cost and robustness) is that classical ICE simulations do not generally use "high order" set-up compared to more academic LES configurations, such as turbulent pipe flows for instance [7], for which highly accurate set-up are the standard. In particular, ICE simulations usually use low order and/or dissipative numerical schemes as well as simple Sub-Grid-Scale (SGS) turbulence models.…”