Wet Start

A wet start in aviation refers to a condition where fuel is introduced into a turbine engine, but ignition fails or is delayed, resulting in inadequate RPM without a corresponding increase in Exhaust Gas Temperature (EGT). While less dangerous than a hot start, it can still pose risks, including potential engine damage or fire if the excess fuel ignites later.

What is a Wet Start?

Fuel Introduction, Ignition Failure

A wet start occurs when fuel is pumped into the engine's combustion chamber, but the ignition system fails to ignite the fuel properly, leading to inefficient combustion.

YouTube Video

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Inadequate RPM and EGT

The engine fails to accelerate to normal speeds, as indicated by the N1 gauge, and the EGT (Exhaust Gas Temperature) does not rise as expected, even with fuel flow.

Potential Risks

The primary risk is the potential for a large, sudden ignition of the excess fuel, which can cause a mini-explosion in the combustion chamber, potentially damaging the engine and turbines.

Key Indicators of a Wet Start

Inadequate RPM

The engine's N1 gauge indicates low RPM, not reaching the expected idle or start-up values.

No Rise in EGT

Despite fuel flow, the EGT remains low, indicating a failure to ignite the fuel properly.

Historical Context (including "Wet Cranking")

Early Jet Engines

Water injection was used in early jet engines to increase thrust, especially in hot and high conditions, by cooling the air and allowing it to be ingested by the engine at higher density, Aviation Stack Exchange.

"Wet Cranking"

This term refers to a procedure where an engine is "wet cranked" (cranked with fuel) to check the oil circulation and fuel drain systems, particularly after a new engine installation, PPRuNe Forum.

Water Injection for Thrust

Some aircraft, like the Boeing 707 and 747, used water injection for thrust augmentation, particularly on hot and high airfields.