Index

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Turbocharger System

The turbocharger system of the engine, which is a constant pressure system, consists of an exhaust gas receiver, a turbocharger, a charging air cooler and a charging air receiver, the latter being integrated in the engine frame.

The turbine wheel of the turbocharger is driven by the engine exhaust gas, and the turbine wheel dri-ves the turbocharger compressor, which is moun-ted on the same shaft. The compressor sucks air from the engine room, through the air filters.

Turbocharger, see separate manual.

The turbocharger pumps the air through the charging air cooler to the charging air receiver. From the charging air receiver, the air flows to each cylinder, through the inlet valves.

The charging air cooler is a compact tube-type cooler with a large cooling surface. The cooling wa-ter is passed twice through the cooler, the end covers being designed with partitions which cause the cooling water to turn.

The cooling water tubes are fixed to the tube plates by expansion.

From the exhaust valves, the exhaust is led through a water cooled intermediate piece to the exhaust gas receiver where the pulsatory pressure from the individual exhaust valves is equalized and passed to the turbocharger as a constant pressure, and further to the exhaust outlet and silencer arrangement.

The exhaust gas receiver is made of pipe sections, one for each cylinder, connected to each other, by means of compensators, to prevent excessive stress in the pipes due to heat expansion.

In the cooled intermediate piece a thermometer for reading the exhaust gas temperature is fitted and there is also possibility of fitting a sensor for remote reading.

To avoid excessive thermal loss and to ensure a reasonably low surface temperature the exhaust gas receiver is insulated.

Compressor

Fouling of the airways depends primarily on the purity of the inlet air and thus, in turn, on the general maintenance condition of the machinery, i.e. mainly of the gas and oil tightness of the engines and on the fresh air ventilation system of the engine room.

Fouling of air filter, compressor or charging air cooler may be observed as changes in performance parameters:

-Decreasing charging air pressure.

-Decreasing turbocharger rotor speed.

-Increasing exhaust gas temperature.

-Severe fouling of airways may even result in compressor surge.

Regular cleaning during operation by injection of water before the compressor wheel will reduce the fouling rate considerably, and consequently prolong the intervals between dismantling necessary for mechanical cleaning.

L23/30H

Chemical cleaning will not improve the cleaning process as this primarily is based on the mechanical effect from the impact of the water droplets.

Certain types of fluid solvents can give formation of deposits on the compressor wheel, and should under no circumstances be used.

The intervals between cleaning by injection of water should be adjusted after assessing the degree and rate of fouling in the particular plant, i.e. based on observations and experience.

The tendency to fouling on the gas side of turbochargers depends on the combustion conditions, which are a result of the load on and the maintenance condition of the engine as well as the quality of the fuel oil used.

Fouling of the gas ways will cause higher exhaust gas temperatures and higher surface temperatures of the combustion chamber components and will also lead to a lower performance.

Tests and practical experience have shown that radial-flow turbines can be successfully cleaned by injection water into the inlet pipe of the turbine. The cleaning effect is based on the water solubility of the deposits and on the mechanical action of the impinging water droplets and the water flow rate.

The necessary water flow is dependent on the gas flow and the gas temperature. Enough water must be injected per time unit so that, not the entire flow will evaporate, but about 0.25 l/min. will flow off through the drainage opening in the gas outlet. Thus ensuring that sufficient water has been injected.

Service experience has shown that the above mentioned water flow gives the optimal cleaning effect. If the water flow is reduced the cleaning effect will be reduced or disappear. If the recommended water flow is exceed, there is a certain risk of a accumulation of water in the turbine casing, which can result in damage on the turbocharger.

The best cleaning effect is obtained by cleaning at low engine load approx. 20% MCR. Cleaning at low load will also reduce temperature shocks.

Experience has shown, that washing at regular intervals is essential to successful cleaning, as excessive fouling is thus avoided. Washing at intervals of 100 hours is therefore recommended. Depending on the fuel quality these intervals can be shorter or longer. However, the turbine must be washed at the latest when the exhaust gas temperature upstream of the turbine has risen about 20° C above the normal temperature.

Heavily contaminated turbines, which where not cleaned periodically from the very beginning or after an overhaul, cannot be cleaned by this method.

If vibration in the turbocharger occur after waterwashing has been carried out, the washing should be repeated. If unbalance still exists, this is presumably due to heavy fouling, and the engine must be stopped and the turbocharger dismantled and manually cleaned.

The washing water should be taken from the fresh water system and not from the fresh cooling water system or salt water system. No cleaning agents and solvents need to be added to the water.

To avoid corrosion during standstill, the engine must, upon completing of water washing run for at least 1 hour before stop so that all parts are dry.

Water Washing System

The water washing system consists of a pipe system equipped with a regulating valve, a manoeuvring valve, a 3-way cock and a drain pipe with a drain valve from the gas outlet, see illustration on working card 512-15.00.

The water for washing the turbine, is supplied from the external fresh water system through a flexible hose with couplings. The flexible hose must be disconnected after water washing.

By activating the manoeuvring valve and the regulating valve, water is led through the 3-way cock to the exhaust pipe intermediate flange, equipped with a channel to lead the water to the gas inlet of the turbocharger.

The water which is not evaporated, is led out through the drain pipe in the gas outlet.