Large Marine Diesel Engines Are Started Using High Pressure Compressed Air

8/10/2019 Large Marine Diesel Engines Are Started Using High Pressure Compressed Air

1/4

Large Marine Diesel Engines are started using high pressure compressed air. Theair is admitted into the cylinder when the piston is just past TDC and continued

until just before the exhaust valve opens. There is always more than one air start

valve open: - a situation known as overlap. This ensures that the engine will startin any position. The opening of the main air start valves is controlled by a set of

pilot valves located in the air start distributor, which in turn are timed to operateby a drive linked to the main camshaft. In the example shown, a small camshaft

is used to control the opening and closing of the air start pilot valves.

The drawing shows the principle of operation of an air start system. Large air

receivers are used to store the compressed air. The diagram shows the isolating

valve open so air is being allowed as far as the automatic valve and the air startcontrol valve.

When the engine is required to start, a low pressure air signal is sent to the airstart control valve (which can also be hand operated in an emergency). The air

pushes a piston down which opens the valve and allows high pressure air to flowto the pilot valve and the automatic valve operating pistons. The pilot valve is

forced down onto the cam profile and the automatic valve opens and highpressure air is led to the main air start valves and the pilot valve. When the pilot

valve cam follower is on the lowest point on the cam, air flows to the operating

piston of the main air start valve for that particular cylinder, opening the valveand allowing high pressure air to flow into the cylinder.

When the pilot valve is lifted by the cam, the pilot valve vents and the main airstart valve closes. When the start air signal is taken off the air start control valve,the system vents and the automatic valve shuts.


2/4

The animation below shows the sequence of operations.

An interlock blocking valve will operate, for instance if the turning gear is left in,

and this will stop high pressure air from reaching the air start control valve andthus either the automatic valve or the pilot valve.

A slow turning valve is fitted. This will open instead of the main automatic valve

if the engine has been stopped for more than 30 minutes during maneuvering. Itwill only supply enough air to turn the engine over very slowly; This is a

precaution in case a cylinder has had oil or water leak into it which would causedamage to the engine when starting. If the engine completes a full revolution on

the slow turn, then the main automatic valve opens and the engine will start.(note: The operating system for the slow turning has been omitted for simplicity).

International Association of Classification Society rules state:In order to protect starting air mains against explosion arising from improper

functioning of starting valves, the following devices must be fitted:

i. An isolation non-return valve or equivalent at the starting air supply

connection to each engine.

ii. A bursting disc or flame arrester in way of the starting valve of each cylinder

for direct reversing engineshaving a main starting manifold. OR

ii. At the supply inlet to the starting air manifold for non-reversing engines

Devices under (ii) above may be omitted for engines having a bore not exceeding

230 mm.

The system may also be provided with a relief valve.


3/4

Mariner Polytechnic Colleges Foundation

Rawis Legazpi, City

PP1 A

(Detailed sequence of staring Marine DieselEngine,

Include Safety Precaution)

Submitted By:

Cete, Jessmar Q.

ME2A2 B


4/4

Safety Precautions:

Relief Valves

If a relief valve on an engine cylinder lifts (pops) several times, stop the engine

immediately. Determine the cause of the trouble and decide upon the correct solution.

Except in an emergency, NEVER lock a relief valve in the closed position. Pressure-

relief mechanisms are fitted on enclosures in which excessive pressures may develop.

Fuel

When fuel reaches the injection system, it should be absolutely free of water and

foreign matter. You must thoroughly centrifuge the fuel before using it, and you must

keep the filters clean and intact. Remember, fuel leakage into the lubricating oil

system will cause dilution of the lubricating oil with a consequent reduction in

viscosity and lubricating properties.

Cooling Water

Do NOT allow a large amount of cold water, under any circumstances, to enter a hot

engine suddenly. Rapid cooling may crack a cylinder liner and head or may cause a

piston to seize within a cylinder. Reduce the load or, when ordered to do so, stop the

engine when the volume of circulating water cannot be increased and the temperatures

are too high. In freezing weather, you must carefully drain all passages and pockets in

the engine that contain fresh water and that are subject to freezing, unless an

antifreeze solution has been added to the water.

Starting Air

When engines are stopped, you must vent all starting-air lines. Serious accidents may

result if pressure is left on. Intake air must be kept as clean as possible. Accordingly,

you must keep all air ducts and passages clean.

Cleanliness

Cleanliness is essential to efficient operation and maintenance of diesel engines. Youmust maintain clean fuel, clean coolants, clean lubricants, and a clear exhaust. You

must also keep the engines clean at all times, and take steps to prevent oil or fuel from

accumulating in the bilges or in other areas to prevent fire hazards.

Documents

Large Marine Diesel Engines Are Started Using High Pressure Compressed Air