Principles of naval engineering - Historic Naval Ships Association

Chapter 23. -GAS TURBINECOMBUSTIONCHAMBERHOUSINGCOMBUSTIONCHAMBERLINERCOMBUSTIONCHAMBERCOVERCOMBUSTIONCHAMBERINLET DUCTFigure 23-8,— Elements of tubular or can-type combustion chamber.147.142Since each of the combustion chambers has itsown separate burner, each one operating independentlyof the others, there must be some wayto spread the flames during starting. This requirementis met by interconnecting all thechambers so that, as the flame is started by thespark ignition plugs in the lower chambers, theflame passes through the interconnector tubesand ignites the combustible mixture in the adjacentchambers. Once ignition is obtained, thespark igniters are automatically cut off.The annular combustion chamber is moreefficient than the can-type chamber. Althoughdetails of design may vary, the annular combustionchamber consists essentially of a singlechamber which completely surrounds the engine.Fuel enters the combustion chamber through aseries of nozzles which are mounted equidistantfrom each other on a ring at the front end of thecombustion chamber; because of this arrangement,the flame is distributed evenly around theentire circumference of the combustion chamber.Diffusion of air and an efficient flamepattern are maintained by means of rows ofholes which are punched in the outer liner orbasket of the combustion chamber.The can-annular combustion chamber combinesfeatures of both the can-type chamberand the annular chamber. The can-annularchamber allows an annular discharge from thecompressors, from which the air flows to individualburners where the fuel is injected andburned.- The can-annular combustion chambersare arranged radially around the axis of theengine— the axis in this instance being the rotorshaft housing. Figure 23-9 shows the arrangementof can-annular combustion chambers.The can-annular combustion chambers areenclosed by a removable steel shroud whichcovers the entire burner section. This featuremakes the burners readily accessible for anyrequired maintenance.The can-annular combustion chambers areinterconnected by means of projecting flametubes. These flame tubes facilitate starting,as previously described in connection with thecan-type combustion chamber.Each of the can-annular combustion chamberscontains a central, bullet-shaped, perforatedliner. The size and shape of the holes aredesigned to admit the correct quantity of airat the required velocity and angle. Cutouts areprovided in two of the bottom chambers for theinstallation of the spark igniters.Each can-annular combustion chamber receivesfuel through duplex nozzles installed atthe forward end of the chamber. Guide vanesaround the fuel nozzles direct the primary airand cause it to enter the combustion chamberwith a swirling motion which mixes the fueland air and thus leads to even and completecombustion.TurbineIn theory, design, and operating characteristics,the turbines used in gas turbine enginesare quite similar to the turbines used in asteam plant. The gas turbine differs from thesteam turbine chiefly in the type of blading601