Sample Questions

Second Engineers Motor EKs


March 2002 Question 1.

  1. Describe, with the aid of a sketch, a charge air cooler. (6)

  2. Describe the procedures and precautions taken when cleaning both air and water sides of a charge air cooler. (7)

  3. State why it is necessary to maintain correct charge air temperature. (3)


The sketch illustrates a charge air cooler. The cooling water makes two passes to maximise cooling effect; the air makes a single pass to keep the pressure drop to a minimum. A manometer connected across the cooler will give an indication of any fouling on the  air side. The moving tube plate allows for expansion. Sacrificial anodes may be fitted in the water boxes to reduce corrosive attack, especially if the cooling medium is sea water. The flow of cooling water through the cooler is automatically controlled to keep the air inlet to the engine at optimum temperature.


Cleaning Air Side

On a large 2 stroke crosshead engine the air cooler may be cleaned by injecting an air cleaner chemical into the charge air while the engine is running. The chemical used is hazardous to health and thus protective clothing must be worn, and manufacturers instructions followed. Alternatively, a system using a chemical circulating tank, pump and built in sprays may be used when the engine is stopped. After circulating the chemical for a period of time as instructed, the air cooler must be rinsed using fresh water. Ensure drains from the air cooler to bilge are clear.

On a medium speed engine, the air cooler can be cleaned in situ (with the engine stopped) by blanking the air inlet and outlet and filling with a cleaning solution. However it will be necessary to support the air cooler, as the fastenings used may not be designed to cope with the extra weight. However it may be easier to remove the whole air cooler and place it in a bath of cleaning solution. Again protective clothing must be worn, and suitable ventilation provided. It is normal practise to pressure test the cooler stack when it is in the rinsing bath to check for leaking tubes.

Cleaning Water Side

This is normally done in situ with the engine stopped. After isolation and draining, the end covers on the cooling water boxes are removed and the cooler is rodded through or blasted using a pressure lance. In the case of the latter suitable protective clothing must be worn. Cleaning the water side is normally only carried out on air coolers using sea water. sacrificial anodes should be inspected and replaced as necessary.


It is necessary to maintain the correct charge air temperature for the following reasons:

  1. So that the correct mass of air is allowed into the cylinder for combustion of the fuel. (the higher the temperature the greater the specific volume)

  2. To keep the exhaust gas temperature at acceptable levels. (will rise if air temp is too high)

  3. To prevent water depositing on the liner surface destroying L.O. film if temp is too low.

  4. To prevent thermal shocking of liner if temp is too low.

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