COMBUSTION CHAMBER.—The efficiencyand performance of a turbine power unit depend on thetype of combustion system used. The basicrequirements for a satisfactory system are a high rate ofburning, minimum pressure drop, small bulk, and lightweight. The system must be consistent in operationover a wide range of loads and altitudes, with notendency to flood with fuel or suffercombustionblowout. Combustion blowout is a flame failure, and itis primarily a problem in high-altitude operation.Starting must be easy and positive, both on the groundand in the air. Combustion must be complete to avoidformation of carbon deposits.Fuel enters the front of the burner as an atomizedspray or in a prevaporized form. Air flows in around thefuel nozzle and through the first row of combustion airholes in the liner. Air near the burner nozzle stays closeto the front liner wall for cooling and cleaningpurposes. Air entering through opposing liner holesmixes rapidly with the fuel to form a combustiblemixture. Air entering the forward section of the linerrecirculates and moves upstream against the fuel spray.During combustion, this action permits rapid mixingand prevents flame blowout by forming a low-velocitystabilization zone. This zone acts as a continuous pilotfor the rest of the burner. Air entering the downstreampart of the liner provides the correct mixture forcombustion. This air also creates the intense turbulencenecessary for mixing the fuel and air and fortransferring energy from the burned to the unburnedgases.Since an engine usually has two igniter plugs, crossignition tubes are necessary in the can and can-annulartypes of burners. These tubes allow burning to start inthe other cans or inner liners. Axial-flow engines useeither an annular or the can-annular (fig. 6-10) type ofcombustion chamber. The igniter plug is usuallylocated in the upstream reverse flow region of theburner. After ignition, the flame quickly spreads to theprimary (combustion) zone. This zone contains thecorrect proportion of air to completely burn the fuel. Ifall the air flowing through the engine were mixed withthe fuel at this point, the mixture would be outside thecombustion limits for the fuel normally used.Therefore, only about one-third to one-half of the air isallowed to enter the combustion zone of the burner.About 25 percent of the air actually takes part in thecombustion process.6-6Figure 6-10.—Can-annular combustion chamber components and arrangements.
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
