Characterization of combustion in a gas engine ignited using a small un-scavenged pre-chamber

Abstract

Prechamber ignition technology receives increasing attention due to its considerable improvement on engine combustion efficiency and stability. However, fundamental knowledge concerning flame propagation inside the pre-chamber and jet formation in the main chamber is still quite scarce. In this study, a small (<0.5% VTDC) un-scavenged pre-chamber was tested in a medium size gas engine with pressure transducers installed in both pre- and main chamber. Three-dimensional computational reactive fluid dynamics Reynolds-averaged Navier–Stokes simulations were carried out using a level-set combustion model –G-equation – towards improved understanding of the combustion processes occurring inside the pre and main chamber. The characteristics of the turbulence and the flame at locations just ahead of the propagating turbulent flame front were recorded and analysed by means of the well-known Borghi–Peters diagram. The results revealed that the characteristics of the flame inside the pre-chamber differed greatly from those inside the main chamber due to considerably reduced turbulent length scales. In addition, a wide range of turbulence intensity and length scales are covered throughout the combustion event, presenting a significant challenge to modelling of flame–turbulence interaction. Various turbulent flame speed ( ST) closures widely used in internal combustion engine simulation were therefore assessed and the ranges of their respective model constants explored. A correlation for ST is subsequently proposed by blending two formulations of Gülder developed for small and large scale turbulence, respectively, and compared to the well-known Peters correlation. With appropriate model constants, both successfully reproduce the pre and main chamber combustion for the reference case in terms of evolutions of cylinder pressure, heat release rate and pressure difference between pre and main chamber. Following successful calibration of the reference operating condition, variations in engine speed, load, spark timing and lambda were calculated using both correlations, demonstrating encouraging predictive capabilities of the proposed modelling strategy.

Numerical Simulations of Pre-Chamber Combustion in an Optically Accessible RCEM

“…[35]). Xu et al [12] provide an estimate of the temporal trajectory of the flame front on the turbulent premixed combustion regime diagram using RANS for an unscavenged pre-chamber. For LES, multiple realizations would be needed to reconstruct statistics of the turbulence characteristics.…”

“…Most of the works are carried out in a RANS context (e.g. [5][6][7][8][9][10][11][12]) and some LES studies start to appear (e.g. [13][14][15][16]).…”

Numerical Study of Turbulence and Fuel-Air Mixing within a Scavenged Pre-Chamber Using RANS and LES

“…Most of the work has been focused on RANS models (e.g. [4][5][6][7][8][9][10][11]) and some LES studies start to appear (e.g. [12][13][14][15]).…”

A Study of Lean Burn Pre-Chamber Concept in a Heavy Duty Engine

“…In recent studies, the emphasis shifted towards the physical phenomenon which occurs inside the pre-chamber during the compression stroke and events following the pre-chamber combustion. Fundamental studies have been conducted in combustion vessels using pre-chambers with optical access [13,14,15]. Such studies were performed under precisely controlled conditions, unlike engine experiments, and can provide explanation on the physical processes.…”

“…The flow field inside the pre-chamber is governed by the internal geometry of the pre-chamber and thus the geometrical effects have been a focus area in recent years. For example, Xu et al conducted 3D CFD study upon the flow behavior for different pre-chamber configurations [15]. Moreover, Thelen and Toulson carried out a CFD study based on the TJI Michigan design and they showed the importance of the spark plug location for a fast ignition [16].…”