Turbulence Intensity and Length Scale Effects on Premixed Turbulent Flame Propagation

Abstract

The effects of varying turbulence intensity and turbulence length scale on premixed turbulent flame propagation are investigated using Direct Numerical Simulation (DNS). The DNS dataset contains the results of a set of turbulent flame simulations based on separate and systematic changes in either turbulence intensity or turbulence integral length scale while keeping all other parameters constant. All flames considered are in the thin reaction zones regime. Several aspects of flame behaviour are analysed and compared, either by varying the turbulence intensity at constant integral length scale, or by varying the integral length scale at constant turbulence intensity. The turbulent flame speed is found to increase with increasing turbulence intensity and also with increasing integral length scale. Changes in the turbulent flame speed are generally accounted for by changes in the flame surface area, but some deviation is observed at high values of turbulence intensity. The probability density functions (pdfs) of tangential strain rate and mean flame curvature are found to broaden with increasing turbulence intensity and also with decreasing integral length scale. The response of the correlation between tangential strain rate and mean flame curvature is also investigated. The statistics of displacement speed and its components are analysed, and the findings indicate that changes in response to decreasing integral length scale are broadly similar to those observed for increasing turbulence intensity, although there are some interesting differences. These findings serve to improve current understanding of the role of turbulence length scales in flame propagation.

Analysis of an innovative combustion chamber with the wall guided fuel injection in a small diesel engine

“…In detailed chemical kinetic mechanisms, the reversible (or irreversible) reactions involving K chemical species can be represented in the general form 49,50 ;…”

“…The H term indicates the effects of ensemble averaging or filtering of the convection term. 49,50 The fuel assembly was aligned to the nozzles in the designed combustion chamber. A more balanced gas force distribution had been occurred with the combustion in the pockets.…”

Characterisation and Design of Direct Numerical Simulations of Turbulent Statistically Planar Flames

“…Several DNS designs from the literature have been positioned within the diagram. The indicated letters correspond to particular literature according to: (a)≙ [10]; (b)≙ [19]; (c)≙ [21]; (d)≙ [32]; (e)≙ [33]; (f)≙ [34]; (g)≙ [35]. The different positions indicate the design trade-offs made by the respective authors.…”

“…(b)≙ [19]; (c)≙ [21]; (d)≙ [32]; (e)≙ [33]; (f)≙ [34]; (g)≙ [35]. The different positions indicate the design trade-offs made by the respective authors.…”

“…The Pr in the numerator is added to the x variable, while the Pr in the denominator stays outside. The same step has been applied to derive Equations ( 32)- (34). For Equations ( 35)- (38), the added fraction is (Pr/Pr) 3 , and for Equations ( 39)-( 42), it is (Pr/Pr) −1 .…”