The atomised fuel spray is fed into the re-heat jet pipe and ignited by one of three methods:-• Spark Ignition• Hot Streak Ignition• Catalytic Ignition
a. Spark Ignition. Spark ignition for re-heat fuel is similar to normal engine ignition. Light-up is obtained by using a pilot fuel burner and an igniter plug. The igniter plug is fitted downstream of the pilot burner in a conical fitting that is a part of the re-heat system. The core provides airflow conditions suitable for light-up and when fuel is sprayed from the pilot burner, it is carried on to the igniter plug and ignition takes place. This method has been superseded by the other methods.
b. Hot Streak Ignition. The hot streak ignition system is more often called ‘hot shot' ignition. It consists of one or two fuel injectors; one sprays fuel into the engine combustion system and the other if fitted sprays fuel aft of the turbine as a relay system to keep the flame alight for a longer distance. Spraying additional fuel into the main combustion area causes an elongated flame and a ‘hot streak' flame reaches and ignites the re-heat fuel. The turbine blades are not damaged because the hot streak flame is of short duration. This method provides a very quick light up, however if it fails to light then reheat has to be reselected.
c. Catalytic Ignition. Catalytic ignition is achieved by use of a platinum/rhodium element. Atomised fuel is sprayed over the element and a chemical reaction causes spontaneous ignition.