The whole report of problem no. 13 "Gas flow" has been "recycled" for the 13th IYPT the year after. There was a similar problem (no. 3 "Plasma") which also concerned the flame of a candle. There the "Gas flow" was one of many relevant parameters and we decided to include the whole "Gas flow"-report in our "Plasma"-report. If you want to see the "Gas flow"-report look for the report of problem no. 3 "Plasma" of the 13th IYPT, because I don't want to present the same report twice.