Gas Turbine Igniter Plugs

IGNITER PLUG PLUGS S mixture when the engine is being started. ~ A component in a gas turbine engine used to ignite the fuel-air mixture when ~ Some igniters resemble spark plugs used in reciprocating engines, while others are glow plugs heated  yellow-hot  yellow-hot with electrical electrical current.

There are three three basic types of igniter plug: ~ typical annular-gap type ~ the constricted or constrained air gap type ~ the shunted surface discharge type ~ The typical annulargap type is  is  similar in operation to the conventional reciprocating engine spark plug , annular-gap - gap but has a larger air gap between the electrode and body for the spark to cross. ~ It is sometimes referred to as a long a  long reach igniter  because  because it projects it  projects slightly into the combustion chamber  to produce a more effective spark.  liner  to ~ The constricted or constrained air air gap centre electrode is set back into the insulator  so  so the spark jumps out past out past the end of the igniter . igniters. ~ These igniters do igniters  do not protrude into the combustion liner , so they run they  run cooler than annular-gap igniters. ~ The surface discharge igniter plug has the end of the insulator formed by a semi-conducting a  semi-conducting pellet  which  which permits an electrical leakage from the central high tension electrode to the body. path  for the energy stored in the ~ This ionises the surface of the pellet to provide a low resistance path for capacitor. ~ The discharge The  discharge takes the form of a high intensity flashover   from the electrode to the body and only  requires a potential difference of approximately 2000 volts for volts for operation. ~ see below and overleaf for picture between 60 and 100 sparks per minute. minute. ~ The normal The  normal spark rate of a typical ignition system is between ~ Periodic replacement Periodic  replacement of the igniter plug is necessary necessary due to the progressive erosion erosion of the igniter electrodes caused by each discharge.

PLUGS S (contd.) IGNITER PLUG ~ The third type of is the glowglow -plug igniter..  glow  -plug igniter engines . ~ This low-voltage turbine engine igniter used on some of the smaller engines. ~ Designed for extreme low temperature starting. ~ It consists of a coiled resistance element  (reminiscent  (reminiscent of a cigarette lighter), whose inner end is connected to an insulated pin to which the lead from the DC ignition exciter is connected. ~ The outer end of the coil is grounded to the igniter body. ~ Current flowing  through  through the resistance element and heats and  heats it until it glows orange-yellow, and  air flowing orange-yellow, and air through the coil produces a streak of flame that flame that ignites the fuel-air mixture in the combustor.

The surface discharge igniter plug