Predictive CFD Auto-Tuning Approach for In-Cylinder Simulations of Two Small-Bore LDD Engines

Abstract

Tightening emission regulations and accelerating production cycles force engine developers to shift their attention towards virtual engineering tools. When simulating in-cylinder processes in commercial LDD DI engine development, the trade-off between run time and accuracy is typically tipped towards the former. Highfidelity simulation approaches which require little tuning would be desirable but require excessive computing resources. For this reason, industry still favors low-fidelity simulation approaches and bridges remaining uncertainties with prototyping and testing. The problem with low-fidelity simulations is that simplifications in the form of sub models introduce multi variable tuning parameter dependencies which, if not understood, impair the predictive nature of CFD simulations.In previous work, the authors have successfully developed a boundary condition dependent input parameter table. This parameter table showed outstanding results for lab-scale experiments for over 40 varying operating conditions. The objective in this paper is first to identify the necessary considerations to adjust for the inherent differences between lab-scale and real engine conditions and then implement this parameter table into industry relevant conditions. With this approach the appropriate simulation setup for a real EU6 diesel engine can be predefined by the boundary conditions without previous tuning iterations. The performance of the simulation will be assessed based on its capability to match experimental heat release and chamber pressure data. The approach shown here has the potential to remove the necessity of lengthy tuning iterations and lays the groundwork for novel auto-tuned and predictive in-cylinder simulations.

Novel approach for adaptive coefficient tuning for the simulation of evaporating high-speed sprays injected into a high-temperature and high-pressure environment

“…Our most recent efforts on an optical single cylinder and a standard production engine (both small-bore direct-injected light-duty diesel engines with swirl and multi-hole injectors) using the tabulation only required small changes in the turbulence coefficients to show good agreement with a range of experimental data. 77 A long-term objective of the project is the adoption of the tabulation into an algorithm that can auto-tune simulations based on input boundary conditions.…”

A process for an efficient heat release prediction at the concepts screening stage of gasoline engine development

“…However, extensive experimental data was necessary to calibrate the model. In [41] an automated tuning procedure for diesel engines simulations was developed. The methodology showed good combustion predictions at limited operating points for a given engine overall structure.…”

“…CFD RoHR predictions at multiple operating points for each of the engine design screened during the concept stage of development remain unpractical. This is due to the limited time available to define the first engine concept [3], limited experimental data available to tune CFD models and the lack of consensus on how modelling coefficients should be set [10,41]. CFD analysis can be used later in the development process, once the concept design is defined [8,38,39,41].…”

“…In this research, default values for all the userdefined model constants available within the chosen turbulence model were used. A review of all constants effect of turbulence, including a sensitivity study, is available in[41]. Only the turbulence limiter, known as the realisable timescale bound limiter (TSB), was tuned.…”