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MINKNOCK Sintesi della relazione

Project ID: ENK6-CT-2002-00643
Finanziato nell'ambito di: FP5-EESD
Paese: Portugal

Fundamental experiments

The work developed by this partner within the Fundamental Experiments workpackage was related with the detailed experimental analysis of a flame-wall interaction. A flame-wall interaction process is controlled by a competition between thermo-diffusive and aerodynamic processes which may lead to premature flame extinction, resulting in a deficient or non-burned fuel, or rapid consumption of the fuel trapped between flame and wall with consequences on engine efficiency. Due to the flame-flow complex process inside an IC combustion chamber, and in order to gain physical insight into the process, experiments were designed to study the freely propagating flame approaching a wall, inside a combustion chamber filled with a propane-air mixture.

Experiments were conducted with a planar and inclined walls and a PIV with temporal resolution was developed in this work. The main objective in this sub-task was to quantify experimentally the flow field that develops in between the flame and the wall, as the flame is approaching, in the presence of irregularities on the flame front. Post processing data software was also developed in this task and includes the determination of flame velocity in the flame reference (Sd) and flame stretch factor (K). Three types of flames were studied: hemispherical, symmetrical and non-symmetrical flames.

It is shown generically that the flow field in between the flame and the wall is not stagnant and, contrary to what is present in literature, there are free stagnation points in the flow field. In general three distinct flame patterns were found which generates different unburned flow topology. The undisturbed-concave flame generates a central stagnation point and the flow diverges to the sides. The symmetric-concave deformed flame traps the unburned gas and induces a stagnation point in the meddle of the flow field. This stagnation point move upwards and at the final instant the flow velocity points upwards. For the asymmetric flame propagation the flow generated in the unburned gas region has a topology close to a tangential wall flow.

Further analysis of the flame front structure showed that there is a high correlation between the flame stretch factor and the resultant flame velocity. The most important result is that the flame can survive to very high negative and positive stretch without extinguishing during the time propagation.

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Instituto Superior Tecnico-DEM/SAE-IN+
Av. Rovisco Pais
1049-001 Lisboa
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