Numerical study of fuel and turbulence distributions in an automotive-sized scavenged pre-chamber

Abstract

This article presents a numerical study of the fuel and turbulence distributions in a pre-chamber at spark-time. The study has been conducted in the framework of the H2020 Gas-On project, dealing with the development of a lean-burn concept for an automotive-sized gas engine equipped with a scavenged pre-chamber. The test case considered studies a 7-hole pre-chamber with circumferentially-tilted orifices mounted on the cylinder head of a rapid compression-expansion machine (RCEM), consistent with the experimental test rig installed at ETH Zurich. An accurate description of turbulence and fuel distributions are key quantities determining the early flame development within the pre-chamber. Both quantities have an influence on the overall combustion characteristics and therefore on the engine performance. For this purpose, computational fluid dynamics (CFD) is employed to complement experimental investigations in terms of data completeness. The performance of the Reynolds-averaged Navier-Stokes (RANS)-based turbulence model is compared with large-eddy simulation (LES) through ensemble averaging of multiple LES realizations, in which the fuel injection rate evolution into the pre-chamber has been perturbed. Overall, RANS results show that the distributions of the turbulent kinetic energy and fuel concentration at spark-time agree well with the LES ensemble-averaged counterparts. This constitutes a prerequisite in view of the combustion phase and the accuracy reported provides further confidence in this regard.

Effect of spark ignition location on the turbulent jet ignition characteristics in a lean burning natural gas engine

“…37 Moreover, RANS can predict the fuel and turbulence distributions in the TJI system and describe the turbulent jet development process. 38,39 For LES, it could provide more details of the turbulent flow, but which goes beyond the focus of this paper. Meanwhile, the large computational expense of LES exceeds our available computational resources, which makes it difficult to use it in the study of the flow inside the pre-chamber natural gas engine.…”

Experimental comparison of efficiency and emission levels of four-cylinder lean-burn passenger car-sized CNG engines with different ignition concepts

“…Prechamber geometries are designed and optimized using CFD tools by Volkswagen Konzernforschung, Ricardo Software and ETH Zürich [3,4,10,11,15]. The performance of different prechamber designs was tested on a rapid compression and expansion machine at ETH Zürich and on a single cylinder engine at Poznan University of Technology with focus on prechamber performance [9,13].…”