What Causes Compressor Surge?

Compressor surge occurs when the pressure of air delivered by the compressor is higher than the pressure that the compressor can maintain. A turbocharger is a centrifugal compressor that increases air flow, which produces more horsepower. Because surging occurs when the turbocharger is producing too much air flow, it must be considered when a driver wants maximum power.

During a compressor surge, there is an imbalance due to the reverse in pressure which causes vibration and damage to the compressor parts. There are other instances where surge can occur, such as a sudden change in load or speed, faulty injectors, dirty turbo nozzle ring, faulty impeller blades, dirty or choked filter and if the turbocharger is too large for the engine, according to Bright Hub Engineering.

There are three things that are required for a turbocharger to operate: pressure ratio, air volume and speed. The air that enters the turbocharger follows a path of diffuser vanes. The radial velocity produced by the impeller is converted into pressure by the diffuser which increases pressure on the outlet side of the turbocharger. With the increased pressure, surging occurs, and due to the reverse air flow, the velocity angles are disrupted, which causes the breakdown of the boundary layers. Turbulence that occurs near the boundary restricts air flow, causing resistance. When the turbulence reaches a certain limit, diffusion of the air is reduced, causing pressure to be reduced. The pressure downstream of the diffuser is greater than the diffuser pressure, leading to reverse air flow.