Aerodynamics and Energetics Modeling

Heterogeneous multiphase flows

The spray in the combustion chamber of an aeronautical engine

The mission of the research unit "Heterogeneous multiphase" is to understand and model the phenomena involved in fuel injection in aeronautical engines in space or on Earth.

In the heart of the engines

One common characteristic of a number of liquid-fueled industrial systems (boilers, combustion chambers, engines) is the combustion of a dispersed phase (solid particles or droplets) in a gaseous phase. This type of multiphase combustion involves physical-chemical phenomena which are still imperfectly understood, whether the formation of spray by injection, the turbulent interaction between phases, or the combustion process itself: combustion of individual particles or droplets, package burning , etc.

Physical phenomena involved:

• disintegration
• turbulent dispersion
• interaction between droplets
• droplet collisions
• droplet-wall interaction
• secondary breakup
• evaporation
• auto-ignition
• combustion

Example: Inside a Turbojet

Localization of the combustion chamber in a turbojet

Vizualisation of the spray formed by the fuel injection in the annular chamber of the turbojet

Example: Piston Engine

Localization of the combustion chamber within the piston engine

Vizualisation of the spray formed by the fuel injection in the cylinder of the piston engine

Two-phase phenomena

Two-phase phenomena are common in combustion.

They have an effect on:

• efficiency of the combustor
• level of pollution
• stability of operation of the engine

They imply researches on two scales:

• on the scale of particules / droplets
• on a macroscopic scale: flows

The main challenges are:

• optical diagnostics
• modelling
• databases under real conditions

Manufacturers' needs in aeronautical propulsion

• Enhancement of injection systems
• Reduce polluting emissions
• Ignition at high altitude
• Control of high-frequencies combustion instabilities
• Widening of the operating range of the engines

The modeling process and its objectives

1^st phase: Fine modeling of the following:

• Fuel atomization: liquid sheets or jets under real conditions
• Dense two-phase flows (changes in turbulence as a function of loading)
• Unsteady flows

2^nd phase

• Fine modeling of the spray
• Detailed understanding of the spray
• Enhancement of injection systems under real conditions for both supply lines and ignition

Objectives

• Reduce polluting emissions
• Control combustion instabilities
• Improve the stability envelope (at high altitude)

Research organization for multiphase flows

Basic studies
Cold-gas experiment on reduced-scale models		LACOM Basic studies of injection systems under real conditions (T, P)
Test benches for injectors: Simulation fluids and kerosene		Bi-liquid test cells: injection and unsteady combustion
Modeling of steady and unsteady multiphase flows Development and validation of models
Integration to multiphase codes ex: Onera's CEDRE code

Last Update: February 5, 2007 - © ONERA 2009 - Terms of use