OCR Text |
Show curve of the envelope is the border of the beginning of fluttering and high sound level effects. The bottom curve is formed by the beginning of smoky combustion and high CO levels in the burner exhaust. The ignition envelope is wider than the operational zone envelope at inputs lower than 30% of maximum, approximately the same in the range of 30 - 70%, and much narrower in the range of 70 - 100% of maximum input. It means that ignition is possible at low excess air, (below the smoke with high CO level emission conditions). Moreove_- , it is possible to ignite with a high excess air level where a flame is fluttering. At high fire condition, ignition of a 4.5" SER is possible at 90 - 110% excess air mix. At a maximum input of 19Kwt (65,000Btu/hr) ignition at > 110% excess air is unstable, which diminishes 100% possibility of ignition. An ignition is possible at < 90% excess air, but is accompanied to some extent by an explosion phenomenon and high sound levels. To obtain a stable ignition the position of the spark inside the nozzle is oriented to the burner axis ± 450. This positioning allows 100% reliability of igniting the mixture with a delay of no more than 5 seconds. A U.V. scanner signal has proved dependable in controlling the flame throughout all points of the operational and ignition zones in 3.25" and 4.5" SER's. Working with the 6.0" SER burner, the first tests were conducted with a UV scanner, however, as the furnace temperature increased, the UV scanner's signal became very weak and then approximately zero at 9270C/1700oF and higher furnace temperatures. That phenomenon can be explained by special conditions which are formed inside of the nozzle cone at high temperatures. As it has been mentioned above, the butane fuel has a much stronger tendency of soot release in the combustion process, especially in rich burning mixture where the air factor is less than 1.0. The higher the temperature level, the higher the carbon particle concentration -10- |