A representative interactive linear-eddy-model (RILEM) for simulating spray combustion

Detta är en avhandling från Chalmers University of Technology

Författare: Tim Lackmann; Chalmers Tekniska Högskola.; Chalmers University Of Technology.; [2017]

Nyckelord: TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; turbulent combustion; engine simulation; regime independent;

Sammanfattning: Engine development aims at reducing pollutant emissions (e.g. NOx , soot,
UHC) while maintaining high efficiencies. Detailed experimental results
in combination with precise numerical predictions are of great importance
in order to develop combustion systems for new clean and efficient inter-
nal combustion engines. Computational fluid dynamics (CFD) tools must
be able to deal with multi-mode (premixed, partially premixed and non-
premixed) and multi-regime (from kinetically controlled to mixing con-
trolled) turbulent combustion under various conditions (low temperatures,
high pressures, high EGR rates). Work on laboratory flames [1, 2] clearly
demonstrates the strong need to account for the impact of unresolved tur-
bulent fluctuations of temperature and composition on chemical reaction
rates in Reynolds-averaged and large-eddy simulations (LES) of turbulent
combustion. Combustion models that neglect this so called turbulence-
chemistry interaction (TCI) cannot predict fundamental physical phenom-
ena like local or global extinction and re-ignition, possibly leading to in-
precise predictions of essential quantities including heat release rates, tem-
peratures and emissions. In order to maximize volumetric combustion ef-
ficiency and minimize pollutant formation, it is desirable to maximize the
rate of combustion subject to the limits of overall flame stability. These
limits of flame stability are determined by the rate of local extinction. Es-
pecially in new combustion concepts for engines, including stratified charged
compression ignition (SCCI), lean stratified premixed combustion, and the
use of high levels of exhaust gas recirculation (EGR) the impact of the flow
field on the chemistry plays an important role.
This thesis is divided into two parts. The first part deals with the intro-
duction of a new regime independent combustion model for engine applica-
tions, which is able to predict turbulent combustion under the beforemen-
tioned challenging conditions, while the second part deals with the extension
of existing knowledge about extinction in non-premixed combustion.

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