Which type of igniter plug is utilized in the low-tension ignition system of an aircraft turbofan engine?

The shunted-gap type plug is specifically designed for low-tension ignition systems, which are commonly used in turbofan engines. In such systems, the igniter plug has a unique configuration that allows it to operate effectively with lower ignition voltages, typically ranging from 8 to 14 volts. This is essential because low-tension ignition systems rely on a smaller amount of voltage to ignite the fuel-air mixture efficiently during engine start-up.

The shunted-gap design facilitates the creation of a spark arc between the electrodes even under the lower voltage conditions, ensuring reliable ignition. Additionally, this type of plug consistently provides a more stable flame propagation, crucial for the efficient operation of turbofan engines during the critical phases of start-up and operation.

The other options, while related to igniter technologies, serve different purposes. High-voltage type plugs are used in high-tension systems that require significantly higher voltages for ignition. Ceramic type plugs may be utilized in other applications but do not specifically pertain to low-tension systems. Metal sheathed plugs are also utilized in different ignition scenarios but are not the typical choice for low-tension applications.