Components of an Auxiliary engine on ship

Fuel valve

1. Fuel Valve is also called the fuel Injector. It is fitted on cylinder head, which encompasses the combustion chamber. A fuel valve consists of a valve body or nozzle holder to which the nozzle is secured by a retaining nut. There is a spring and its compression nut within the valve body, along with an intermediate spindle if necessary. Mating surfaces between valve body and nozzle are ground and lapped to form an oil pressure-tight seal.

2. The fuel injection pump delivers high-pressure fuel to the fuel valve through high-pressure fuel pipe. The injector is mounted on the cylinder head by the integral flange in the holder and two studs with distance pieces and nuts.

3. Fuel valve operates hydraulically lifting a spring-loaded valve allowing the pressurised fuel to spray out through one or more orifices into the combustion chamber. The functions of a fuel injector are: 

• Open and close the passage of fuel to the combustion chamber

• Convert the high-pressure oil from the pump into a fine spray of desired pattern

4. The nozzle and needle are lapped together as a pair and cannot be replaced individually. The nozzle holder includes a threaded pipe stub for mounting the high-pressure pipe. On the uppermost part of the nozzle holder, there are three sealing rings. Between the two lowest O rings, the leak-off oil from the fuel valve is led out in to the spacing between the high-pressure piping and the protection tubing. The nozzle assembly and the fuel valve are cooled by the injected fuel.

Indicator and relief valves

1. Indicator and relief valve is a combination valve that is attached to each cylinder head by tow bolts. Indicator valve is opened when the engine is turned by a turning bar or when the engine is blown through before starting. It is also used for measuring peak pressure of the cylinder.

2. The relief valve releases excess pressure from the cylinder. Its approximate set valve is 10% of the combustion pressure inside the cylinder.

Cylinder head

1. Cylinder head is also known as cylinder cover. It forms the upper part of combustion chamber and seals the upper end of the combustion space. It carries mountings necessary for engine operation.

2. The cylinder head is made of one piece and has bores for various mountings such as:

Inlet and exhaust valves

• Fuel valve
•  Air starting valve
• Combined relief valve and indicator cock

3. The cylinder head is tightened down against the cylinder liner by means of studs. A thin ring made of soft iron provides the sealing between cylinder head and liner. Cylinder head is exposed to high mechanical and thermal loads. It is cooled by freshwater, which flow up from the cylinder liners.

Exhaust gas manifold

Exhaust manifold connects each cylinder head exhaust outlet to the turbine inlet of the turbocharger. Four-stroke engine uses pulse-type turbocharging.

The exhaust manifold in pulse-type turbocharging is grouped into two halves for a six-cylinder engine. This is to prevent exhaust gas from one cylinder entering another cylinder.

Cylinder block frame

Cylinder block or frame consists of number of cylinders cast in a single piece. The liners are inserted in the bores of the cylinder block. In between the liner and the cylinder block the cooling water is circulated. The complete cylinder block is located above the crankcase and is supported. They are of a monoblock structure, either vertical inline type or v type.

Inlet and exhaust valves

1. Air inlet and exhaust valves of the mushroom type are used in four-stroke engines. Inlet valves are of larger size than exhaust valves to handle large flow rates.

2. Exhaust valves have smaller diameter than inlet valves, because: 

• Exhaust valve open against higher pressures within cylinder.

• Unlike the inlet valve, the removal of the gases through open exhaust valve is assisted by exhaust gases.

• Being smaller it assist in keeping them cool, which is important as exhaust valve operate at higher temperatures.

3. The exhaust valve seats of engines burning heavy fuel oil are cooled to prevent high-temperature corrosion due to sodium and vanadium present in the fuel.

4. Valve spindles are subjected to high temperatures. Hence they are made of material which has good creep resistance.

5. Both valves open into the cylinder, so that high gas pressure in the cylinder holds the lids firmly against their seats. The springs which close the valves are strong enough to keep the lids on it seated during the low-pressure period of the engine cycle.

6. Two springs are fitted for each valve to avoid axial vibration. Even if one spring fails the valve does not fall inside the cylinder and damage the other components.

Cylinder liner

1. Cylinder liner is a cylindrical shaped sleeve mounted in openings of the frame. Top flange liner is pressed against the top of the frame by the cylinder cover. The bottom portion of the liner is free to expand, which accommodates thermal expansion.

2. There is a direct contact between the water and the outer surface of the liner. Hence it is called as the well liner. Two sealing rings seal water chamber and crankcase. The rings are fitted in grooves in the guide surface of the cylinder liner.

3. Sealing rings are also called O rings. They prevent water leaks into the crankcase and also prevent oil from the crankcase entering the water jackets.

4. A tell-tale leak off hole is provided between upper and lower rings to indicate leaks due to damaged or worn out O rings.

Bedplate

Bedplate is a box-shaped single construction. It constitutes the main structural members of the engine. The bedplate is used as lubricating oil reservoir and a dipstick is provided to ascertain the level. The bedplate is either welded or cast design. The engine frame is made of cast iron and turbocharger bracket houses an air cooler.

Piston

1. The Piston transmits the gas force to the crankshaft through a connecting rod. The piston is attached to the small end of connecting rod by a gudgeon pin. The piston pin is fully floating which means that it can turn freely in the pin bosses of the piston as well as in the connecting rod bush. The piston pin is kept in place in axial direction by two circlips.

2. The piston pin is equipped with channels and holes for lubrication of the pin bosses and for supply of cooling oil to the piston. The piston is cooled by oil and is of monobloc type made of aluminium alloy.

3. Close to the piston crown and the piston ring zone, the piston has a cooling oil space. Cooling oil is used oil from the engine's lubricating oil system. Oil is supplied to the cooling oil space through a channel

from an oil groove in piston pin bosses. By means of a duct, that is situated diametrically opposite to the inlet channel, the oil present in the cooling oil space is drained.

4. Piston is equipped with three compression rings and one oil scraper ring. Piston rings are designed for maximum sealing effect and minimum wear rate.

Lubricating oil pump

The lubricating oil pump is gear type or trochoidal pump. It is driven from the end of the crankshaft through a claw coupling or through a flexible gear wheel connection. Lubrication oil pump draws suction from sump through a suction strainer. It discharges oil to main bearings, connecting rod bearings and other running gear through set of discharge filters.

Connecting rod

1. Connecting rod connects piston to crankshaft and is drop forged. It has two ends namely, small end and big end. The small end is connected to piston, while the big end is connected to the crankshaft. At the big end, the joint faces on connecting rod and bearing cap are serrated.

2. This is to ensure precise location and to prevent relative movement of the parts. The connecting rod has bored channel for supply of oil from the big end to the small end eye. The big end bearing is of trimetal type, i.e. steel shells lined with lead bronze and coated with a thin running in and protection layer.

3. Lubricating oil for connecting rod bearing and piston is supplied from the adjacent main bearing through bores in crankshaft.

Rocker arm

1. The rocker arm has one end on the valve stem and the other end on the push rod through a hardened steel roller. It consists of a housing or a bracket that support a bush. Pivot pin rests inside the bronze bushing.

2. Rocker arm transmits the cam motion to the valve stem by a push rod. The rocker arm is pivoted at its center. The brackets are bolted to cylinder head. Rocker arm is connected to valve stem by a set screw, which is adjusted to provide clearance between the valve stem and rocker contact. This is called tappet clearance.

Air start valve

1. Air start valve is also called the starting valve and is fitted on the cylinder head, which encompasses the combustion chamber. The air distributor delivers high-pressure air to the air start valve through high-pressure pipe. The air start valve is mounted on the cylinder head by the integral flange in the holder and two studs with distance pieces and nuts.

2. Air start valve operates pneumatically moving down a spring-loaded valve and allowing the high-pressure air spray to enter into the combustion chamber. This high-pressure air pushes the piston down, causing the engine to turn on air.

3. The air start valve opens and closes the passage of high-pressure air into the combustion chamber.

Push rods

Push rod transmits the action of the cam to the valve stem through the rocker arm. Push rods translate the rotary motion of the cam to reciprocating motion of the valves.

These are hollow to obtain stiffness without unnecessary weight. The lower end of push rod carries a follower of mushroom shape, which rides on the cam. On one end of the valve rocker arm there is a cup into which a rounded head at the upper end gets fitted.

Air inlet manifold

An air inlet manifold directs the air/fuel mixture into the cylinders. The main function of the air inlet manifold is to supply the air/fuel mixture into each of the intake port in the cylinder head(s). The air/fuel mixture is distributed evenly for better performance and to improve the efficiency of engine.

Fuel injection pump

Each unit is provided with a fuel pump. It supplies pressurised fuel oil to the fuel injector. Fuel pump cams, mounted on the camshaft, operate the fuel pumps. Fuel cams are arranged such that the fuel is injected according to the firing order.

Fuel racks of the pump regulates the quantity of fuel delivered to the injector. Fuel racks of all the pumps are connected to the governor through linkages.

Camshaft

1. Camshaft is driven by crankshaft through a gear drive. The camshaft rotation follows the crankshaft rotation. The function of a camshaft is to drive the rocker arm and fuel pumps. Cams are accurately positioned on camshaft by shrunk fit.

2. The camshaft consists of a number of camshaft sections. The sections are assembled by flange couplings, which are joined together with fitted bolts and nuts. In addition to the flange couplings, the camshaft sections have the following, for each cylinder:

• One cam for operation of the fuel pump.
• One cam for the exhaust valve One cam for the inlet valve

3. The flange couplings, the fuel pump and exhaust valve cams are shrunk onto the shaft by heating. Dismantling of flanges is effected hydraulically by injecting lubricating oil in between the shaft and the flange.

4. Camshafts are heat treated and cams are surface hardened to take impacts. Camshafts are carried

by a series of camshaft bearings.

5. The bearings are thin shell type. The bearings are made of trimetal with steel back and fitted in the frame. Along the cam shaft the frame has large openings for inspection of fuel pump rollers, cams and bearings.

6. Adjustment of the engine timing is carried out by forcing lubricating oil in between the cam and the shaft, which enables the parts to be turned in relation to each other.

Gudgeon pin and bushes

Gudgeon pin rests in two bored holes in the piston and passes through the eye of the connecting rod, to join the two together.

Gears

The crankshaft drives the camshaft through the gear drive. The gear wheel drive for the camshaft is located at the flywheel end of the engine and enclosed by a two piece end shield or cover. Gear drive is driven by the crankshaft and it transmits the rotational motion to the crankshaft. It transmits the rotational motion to the crankshaft at the same speed of the engine or at half the speed of the crankshaft.

Main bearings and housing

1. The main bearings are traditional or underslung type. The bearing housings are fitted in the transverse girders of the frame and secured with bearing caps made of steel. The caps are provided with side guides and are held in place by means of studs with hydraulically tightened nuts. The bearing caps are additionally secured by means of pinching screws inserted horizontally through the engine frame.

2. The main bearings are of shell type. The running surface is made of trimetal coated with steel at the back. The bearing housing encloses the main bearing shells within which the crankshaft rotates. The bottom housing supports the crankshaft. Bolts transmit the reaction forces of the cylinder heads to the crankshaft main bearings via the cylinder block.

3. Oil is supplied to each individual main bearing through a bore present in the frame which is

connected to the lubricating oil system's external main pipe.

Jacket water pump

For the purpose of jacket cooling, the auxiliary engines are provided with mechanical pumps. Jacket water pump can be driven electrically or by engine. For this purpose the outlet temperature of the cooling water has to be maintained between 78-82° C. Water transported using Jacket water pump should be clean, without any solid particles. Jacket water pump is commonly used for supplying water and in drainage work in cities and mines.

Crankshaft

The crankshaft is solid forged and has ground main and crank pin bearing journals. The crankshaft is fitted with counterweights by two dovetail joints and secured by a centrally placed screw to ensure adjustable bearing pressure and balancing. The gear wheel for the camshaft drive is fitted to the aft end of the crankshaft. A claw type coupling for the lubricating oil pump is fitted to the aft end of the crankshaft. A claw type coupling for the lubricating oil pump is also fitted to the forward end. By means of main bearings, the crankshaft is supported.

Flywheel

Flywheel is attached to the crankshaft. The flywheel stores energy during power stroke from the engine and returns the energy during suction, compression and exhaust stroke. It acts as a power reservoir or an accumulator. Alternator is connected to the flywheel through coupling and coupling bolts. Markings are made on the flywheel circumference, with reference to top dead centre and timing of fuel injection.