Pressure Coupling Of the Spherical Linear Eddy Model to RANS-CFDfor Internal-Combustion Engine Simulation.

Abstract

As a result of the increase of the use of combustion engines, more restrictive emission standards are applied. New combustion technologies are being constantly developed to enhance the internal combustion engine, this is motivated by overcoming issues that are relevant for both engine efficiency and the environmental aspects. To do that, turbulent combustion modelling is needed. In this paper, an updated version of the Linear Eddy Model (LEM) will be presented. LEM is capable of simulating premixed, nonpremixed and mixed mode combustion, and it is a regime independent model that runs under the assumption of finite-rate chemistry that is sensitive to turbulent chemistry interactions, which makes it suitable for prediction of pollutant formation. A New coupling scheme to the CFD-RANS simulation is proposed, the coupling is based on linking the two models via pressure. The benefits of pressure coupling are that the effects of wall heat losses and latent heat of evaporation that are modelled on the CFD side are an intrinsic part of the pressure term that is linking the two models, in contrast to volume coupling in which these relevant phenomena need supplementary modelling on the LEM side. The pressure coupling results in a radially uniform dilatation of the LEM domain reflecting the combined effects of pressure change, fuel addition, and cylinder volume change during the engine cycle. Consistency of the LEM cone volume and the CFD domain volume is maintained by adopting a split operator strategy involving a volume correction that adjusts the cone angle. A Spherical Stand-Alone Linear Eddy Model (SSALEM) has been created to conduct relatively fast simplified code development and parameter studies. SSALEM input parameters were drawn from a WSR-RANS simulation and a 1D slider-crank model that calculates the combustion chamber volume that corresponds to a given crank-angle. Model results show the capability to physically track the evolution of several scalars that are solved on the LEM line such as temperature, fuel, and intermediate species in the combustion process.

A Pressure-Coupled Representative Interactive Linear Eddy Model (RILEM) for Engine Simulations

“…That implies that all relevant physical processes, such as fuel injection and piston movement, must be modeled on the one-dimensional line. It also offers the possibility to utilize LEM as a computationally affordable stand-alone model to perform engine simulations with a realistic representation of all relevant physical processes as described in [32]. An important consequence of the representative character of the LEM line is the need for a volumetric formulation of the LEM, which is realized via a (double) solid cone geometry of the LEM domain with the assumption of spherical symmetry.…”

“…In this paper, we discuss further improvements of RILEM to address and overcome those shortcomings: First, to better utilize the detailed modeling of heat losses within the CFD flow solver on the LEM side, we introduce a pressure-based coupling for RILEM. The pressure coupling was implemented and tested for a Spherical Stand-Alone Linear Eddy Model (SSALEM) in [32], where the driving parameters were extracted from a MZWM reacting case. SSALEM can be considered a model among simpler models such as zone models [33] for CFD combustion simulations.…”