Class 4 (4th Engineer) MEKM 📅 Feb 2026

Exam Question

With reference to turbochargers:

(a) Explain the term surging, stating how it occurs, its effect on the turbocharger and how it can be avoided. (8)

(b) Describe the procedures for cleaning EACH of the following and explain the precautions which should be taken: (8)

(i) Suction air

(ii) Turbine blades and nozzle ring

Reference Answer

### (a) Turbocharger Surging
#### Definition and Mechanism of Surging
Surging is a phenomenon of unstable aerodynamic operation in the compressor side of a turbocharger. It is characterized by a complete breakdown of steady flow, leading to violent pulsations and a momentary reversal of air flow back through the compressor impeller.
Fundamentally, surging occurs when the engine's demand for air (mass flow rate) is too low for the discharge pressure the compressor is generating. Each compressor has a characteristic performance map that plots pressure ratio against mass flow rate for different rotational speeds. The **Surge Line** on this map represents the boundary of stable operation. If the operating point of the engine moves to the left of this line (i.e., lower mass flow for a given pressure ratio), surging will occur.

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