Rain Cannot Make a Jet Engine Flame Out

I recently received a question in my social media inbox. The person asking admitted to being a nervous flyer because he was told by some “maritess” that flying in the rain is dangerous since the water could extinguish the “flames” in the engines. Well, tell that “maritess” to go back to school again. This is completely untrue and far from happening. Rain is not sufficient to cause a jet engine to flame out, and let me explain why.

Jet engines operate on a fundamental principle: compressing air, mixing it with fuel, igniting the mixture, and using the hot exhaust gases to generate thrust. However, this combustion process doesn’t take place directly within the entire airflow path. Air entering the engine first encounters the fan blades, which compress it significantly. This compressed air then splits into two streams:

• Core Air: A portion of the compressed air is diverted into the combustion chamber. Here, fuel is injected, and the mixture ignites, generating intense heat.
• Bypass Air: The remaining compressed air bypasses the combustion chamber entirely. This bypass air serves two key purposes: it provides additional thrust by accelerating out the rear of the engine, and it helps cool the hot core air exiting the combustion chamber.

This separation of airflow plays a crucial role in rain resilience. Rainwater ingested by the engine primarily gets mixed with the bypass air, which never enters the combustion chamber. The bypass air simply carries the water through the bypass duct, located between the engine core and the outer cowling, eventually expelling it out the rear of the engine without impacting the combustion process.

Designed to Handle Water

Even a small amount of water entering the core airflow path could theoretically disrupt combustion. However, modern jet engines are designed with features specifically to prevent this from happening. One crucial element is the inlet design. The air entering the core makes a sharp turn before reaching the combustion chamber. Water droplets, being denser than air, have difficulty making this sharp turn and tend to remain in the bypass airflow. Additionally, some engines may employ other water separators at key locations within the core airflow path to further minimize water reaching the combustor.

But what if some water droplets do manage to slip past these initial barriers and enter the combustion chamber? Even in this scenario, the engine remains operational. The combustion chamber burns fuel at incredibly high temperatures – often exceeding 900°C (1650°F). This intense heat instantly vaporizes any water droplets upon contact, transforming them into steam. Steam, being a gas, doesn’t disrupt the combustion process the way liquid water could.

Furthermore, the combustion chamber operates under very high pressure. This high pressure prevents water from condensing or freezing on engine components, ensuring smooth operation.

Rigorous Testing

Modern jet engines undergo rigorous testing procedures before they are certified for commercial use. These tests include simulations and exposure to various weather conditions, including rain, snow, hail, and even clouds (which contain water vapor). Manufacturers ensure that their engines can operate safely and reliably even under challenging weather conditions.

In addition to these tests, engines are equipped with features that further minimize the effects of water ingestion. Heated intakes prevent ice formation on the engine inlet during freezing temperatures. Anti-icing systems can be activated to remove any ice build-up that might occur. Water separators within the engine core can further remove any water droplets that manage to bypass the initial separation mechanisms. Finally, drain valves allow for the removal of any accumulated water within the engine.

While heavy rain or thunderstorms might cause flight delays due to reduced visibility or turbulence, rain itself doesn’t pose a significant threat to jet engine operation. Modern engines are designed to handle water ingestion through a combination of airflow separation, high combustion chamber temperatures, and robust testing procedures.