What type of ignition system does the APU use?

• A. Continuous spark ignition system
• B. Battery ignition system
• C. Capacitor discharge type ignition system
• D. Magnetic ignition system

Answer: (C)

The correct answer is that the Auxiliary Power Unit (APU) uses a capacitor discharge type ignition system. This system is designed to ensure reliable ignition under a variety of operational conditions. The capacitor discharge ignition system works by storing electrical energy in a capacitor and then discharging it to produce a high voltage spark at the ignition plug. This high-energy spark is capable of igniting the fuel-air mixture in the combustion chamber, which is important for starting the APU efficiently.

The advantage of using a capacitor discharge ignition system lies in its ability to produce a high-intensity spark that can ignite the fuel just as well in adverse conditions, such as cold starts or when the engine is operating at altitude. Additionally, this type of ignition system helps reduce the weight and complexity compared to other ignition systems, making it ideal for use in aviation applications.

Understanding the APU's ignition system is crucial for troubleshooting and maintenance, as it directly impacts the starting and operational reliability of the APU.