TURBOCHARGERS IN MARINE DIESEL ENGINE

The turbocharger consists of a single-stage axial-flow turbine and a centrifugal air compressor connected by a single rotor shaft supported on inboard bearings.

Turbocharger bearings are lubricated by engine lubricating oil. Turbochargers are equipped with cleaning devices for the compressor side. The rotor shaft rpm . is measured by a speed transmitter system installed at the compressor side and described in the sub-suppliers manual of the turbocharger. Maintain the turbocharger according to the instructions of the turbocharger manufacturer.

Turbocharger cleaning devices

The diesel engine efficiency is highly related to the efficiency of the turbocharger. The turbocharger efficiency is directly influenced by the degree of fouling of the compressor wheel, diffuser ring, nozzle ring, and turbine wheel. Regularly cleaning is essential during engine operation. The cleaning is not effective when the water cleaning is not carried out regularly scheduled. The following factors may influence the degree of fouling, e.g.:

• Environment
• Fuel quality
• Load pattern
• Poor combustion

Compressor side cleaning

The compressor should be cleaned by water injection during the engine operation. The cleaning process will have good results if the deposit formation has not gone too far. In this cleaning method, the water is not acting as a solvent but instead removes the deposits mechanically by the impact of the water droplets. Use clean water without additives. Daily cleaning of the compressor prevents or delays excessive build-up of dirt. If a very thick hardened crust of dirt is formed, the compressor must be dismantled for cleaning. The turbocharger is provided with a water container ( 1 ). During cleaning, the container is pressurized by the charge air via line (2), by which water is forced to the compressor inlet via line ( 3 ).

Cleaning procedure

Water injection is to be executed when the engine runs at normal operating conditions and with a load > 70 %. Record the charge air pressure, exhaust gas temperatures,and the turbocharger speed to ascertain the efficiency of cleaning.

• Loosen grip screw ( 4 ) and remove container ( 1 )
• Fill the container with clean water.
• Replace container and retighten grip screw ( 4 ).
• By opening valve ( 5 ), charged air enters the container via pipe ( 2 ). The water content is forced into the compressor wheel inlet via pipe ( 3 ).
• The complete water volume should be injected in 4-10 sec. The success of cleaning can be evaluated by comparing engine exhaust gas temperatures before and after
• cleaning. If unsuccessful, the cleaning process should be repeated earliest after 10 minutes.
• On completion of the cleaning process, the engine should at least run another 5 minutes under load.

Turbocharger by-pass and waste gate

General

To control at part load the turbocharging efficiency and to control at full load the firing pressure, the turbocharger is matched, and the system is equipped with an on / off controlled by-pass valve ( 1 ) and a proportional controlled waste gate valve ( 2 )
.

By-pass valve.

To increase the charge air pressure and flow and prevent the turbocharger compressor’s surging, the by-pass valve is opened between 20 % and 60 % load. Surge is the process at which compressed air flows back through the compressor and should be avoided as The required flow of air to the charge air receiver will be far insufficient for the required load. Large air speed variations will occur, causing extreme forces on turbine and compressor wheels, which can finally result in wheel damage.