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DNS ANALYSIS OF HEAT AND MASS TRANSFERS IN A DROPLET-LADEN TURBULENT JET

DOI: 10.1615/ICHMT.2008.CHT.1690
18 pages

Zakaria Bouali
UMR 6614 CNRS CORIA, Rouen University, bp 12−Site universitaire du Madrillet, 76801 St Etienne du Rouvray, France

Bruno Delhom
CORIA, University of Rouen, France

Karine Truffin
Institut Français du Pétrole - R102 1&4 avenue Bois Préau 92852 Rueil Malmaison, France

Hicham Meftah
CORIA, University of Rouen, France; Ibn Zohr University, GEMS Laboratory, ENSA, B.P 1136, Agadir-Morocco

Julien Reveillon
CORIA UMR 6614, University of Rouen, Technopole du Madrillet, BP 12, 76801 Saint-Etienne-du-Rouvray Cedex, France

Abstract

Nowadays, it is fundamental to decrease fuel consumption and pollution generated by cars by improving the engines' efficiency. The characterization, the prediction and the control of the physical phenomena interacting within the combustion chamber are necessary if one wants to improve the current systems and to develop new technologies. That is why, it is important to understand and control the whole of the physical processes taking place from the liquid injection and atomization down to combustion phenomena and gas exhaust.
In direct injection engines, modelling the evaporation of the liquid fuel is a very difficult phase. Experimental results have shown that the droplet presence amplifies the temperature fluctuations and modifies the mixing between the vapour of fuel and the oxidizer. If, up to now, the effects of evaporation on equivalence ratio and the velocity fluctuations have been taken into account in engines modelling, temperature exchanges between the spray and the gas phase have not been clearly evaluated. These fluctuations, however, could play a considerable role in the process of self-ignition and then pollutant formation.
The main objective of this work is to carry out direct numerical simulations (DNS) of an evaporating gasoline spray to estimate the effects of the droplets on the energy field and to study temperature and enthalpy fluctuations. We focus mainly on the vaporization sources terms found in the balance equation of the variance of the sensible enthalpy. DNS is a useful tool, which allows to solve exactly the Navier-Stokes equations by considering all the characteristic scales of the flow. When two-phase flows are considered, only a DNS of the carrier phase is carried out whereas a Lagrangian model is necessary to describe the liquid phase. The droplets are considered as local sources of vapour, momentum and energy, a two-way coupling is considered.

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