A rectilinear droplet stream in combustion: Droplet and gas phase properties

A basic experiment has been designed to improve the understanding of certai n phenomena like droplet interaction occurring in dense sprays. The interac tion effect in a stream of monosized ethanol droplets on the drag coefficie nt (Cd) for non evaporating and reacting conditions is investigated. Also t he burning rate is studied. The spacing parameter C (ratio of interdroplet distance to droplet diameter) is the main parameter retained here to repres ent the interaction effects. Non intrusive optical techniques have been dev eloped to measure, simultaneously along the droplet path, the droplet size, velocity and mean temperature. The stream is first studied in non evaporat ing conditions. The data compiled for a large range of parameters (drag coe fficient Cd, Reynolds number Re, spacing parameter C) permit to establish a new correlation for the drag coefficient taking into account the spacing p arameter. The first experimental results are compared with those previously published. Then the stream is ignited by an electrically heated coil to in vestigate close coupled droplets (C<6) under reacting conditions. The previ ous optical methods are applied for those conditions. The CARS thermometry technique is used to determine the temperature fields around the droplets f or different values of the spacing parameter. The detailed analysis of the two phases in the burning droplet stream allows to improve the knowledge of the fundamental mechanisms on droplet/droplet interactions. For example, t he evolution of the drag coefficient with the spacing parameter is preponde rant to compute the droplet trajectory in dense sprays. Particularly, the r esults show an important effect of droplet spacing on the burning rate and the drag coefficient Cd for this basic configuration.