The purpose of the fuel pump is to supply a certain amount of fuel under high pressure through the nozzle to the combustion chamber of the working cylinder . At the same time, it is necessary to ensure the constancy of the amount of fuel supplied for a certain duration and the established sequence of fuel injection into the engine cylinders Fuel pump.
According to the method of dosing fuel and other features distinguish fuel pumps: plunger spool and valve spool types with a gas pusher, etc .The greatest application for marine diesel engines received fuel pumps plunger (piston ) type.
Piston type Fuel pump
The steel body 6 of the pump is mounted on the cast iron bracket of the cylinder block . The pump plunger, located in the bushing 4 , receives upward movement from the pusher 17 when the roller 18 runs on the protrusion of the fist washer , the plunger is displaced downward by the spring 2 , resting on the end of the lock nut 3 , which secures the bushing 4 in the pump housing , at the bottom of the fitting 7 , the discharge valve 5 is placed perpendicular to which the safety valve is located on the left . The suction valve 10 is mounted vertically to the right of the discharge . The opening in the pump housing at the suction valve installation site is closed with a lock nut.
The fuel enters through the nozzle 9 and fills the working cavity of the pump with the suction valve open, which is controlled by a rod 12 located in the sleeve 11 and resting on the pusher 14. On the eccentric 15, impaled on the end of the cut-off roller (on this projection is not visible ) , the two-arm lever 16 rests , the left end of which is pivotally connected to the pusher 17 of the plunger , and the right rests against the pusher 14 of the valve stem .
The amount of fuel supplied to the engine cylinder for each operating cycle is determined by the stroke duration of the plunger 1 from the closing of the suction valve to . The moment the plunger reaches the upper dead position . The magnitude of this stroke depends on the gap between the suction valve shank and the rod 12 , The greater the load of the engine , the greater the gap , the earlier the suction valve closes and the longer the process of fuel injection through the nozzle into the working cylinder . To change the gap when reducing or increasing the load, turn the cut-off roller, and with it the eccentric 15 and thereby raise or lower the right end of the lever 16 , Individual adjustment of the gap in each pump C . the purpose of uniform distribution of fuel in the cylinders is achieved by rotation of the bolt 13, the head of which rests on the plate 12.
The symmetric Cam disc , from which it receives the movement of the push rod 17 , allows the engine to run on both the front and reverse . The use of the suction valve 10 as a bypass valve simplifies the design of the pump and increases the reliability of its operation.
Injector nozzle, or fuel valve, is to spray the fuel coming from the fuel pump , the mass of compressed air in the combustion chamber . The nozzles of modern diesel engines are divided into two main types : open and closed . In the open nozzle there is no shut-off body connecting the combustion chamber and the high-pressure fuel line . The advantage of open nozzles is the simplicity of design and low cost of production , and the disadvantage – _ leaking fuel from the atomizer , which leads to coke nozzle holes and stop the nozzle . Because of this, the indoor injectors have received very limited use ( in the pump injectors of high-speed diesels ).
In marine diesel engines, the most common closed nozzles that allow separating the combustion chamber from the high-pressure fuel line . The role of the locking body in them is performed by the nozzle needle, which is controlled automatically by the fuel pressure (hydraulic control ) or by means of a mechanical drive . A General view of the closed nozzle with hydraulic control is shown in figure 145, a.
The housing 8 of the injector is inserted into the Central hole of the cylinder cover and fastened with studs, the Fuel is fed into the nozzle through the nipple , screw in the threaded housing bore 8 in the direction of the arrow . Through channel 7 in the housing fuel enters the holder 3 needle G. Removable spray (nozzle) 1, having eight nozzle holes with a diameter of 0.30 mm, fixed nut 5, which forms a cooling cavity around it in this cavity is supplied oil flows out of it through two channels (not shown in the figure ) in the housing .
Closed nozzle and fuel spray device
There are different designs of nozzles : single channel , multi-channel , pin, etc. Most prevalent in marine engines received multi-channel spray nozzles number of holes from four to ten and a minimum nozzle diameter of 0.12 mm . The device of such a sprayer is shown in figure 145.6 fuel Pressure , at which the nozzle opens , the needle 2 is lifted by the force of the spring 12 located in the cap 9 , closed by the nut 11, and lifted by the plug 10, the Needle moves in the hole of the holder 3 , tightly adjacent to its walls .
The greatest lifting ( stroke ) of the needle is set about 0.5 – 0.6 mm and is limited to the hardened sleeve 4 , pressed into the nozzle body . The return of the needle to the place occurs under the pressure of the spring through the rod 6 . Pumping the nozzle with fuel in order to remove air from it is carried out on the right channel 15, closed bolt 13 with a ball valve 14 at the end.
Filters. The composition of the fuel pipeline ( see . rice. 142 )includes two fuel filters : low pressure ( coarse ) and high pressure ( fine). Low pressure fuel filter (Fig . 146 ) is used for fuel purification from mechanical impurities . Fuel from the supply tank enters the filter housing through the pipe 4 and fills the space between the walls of the housing and the filter bag . The latter consists of a set of thick 2 and thin 3 felt plates , which are put on the 10 mesh cylinder is the frame of the filter pack . Felt plates are made of high quality . The filter pack is put on the rod 11, screwed into the bottom of the filter housing , and closed from below and above with plates 9 and 13, the Spring 15 and the sleeve 14 serve to seal the gap between the rod and the hole in the plate 13 .
The filter housing is closed with a lid 8, which is pressed against the housing by special nuts 5 , 6 and 7, The air from the cylinder cavity is released through the channels at the top of the rod 11. The fuel, passing through the felt plates, is cleaned, fills the cylinder cavity, through the hole 12 the channel 16 of the rod enters , and from it into the discharge tube 1
Low pressure fuel filter
Mechanical inclusions and dirt are removed from the filter housing by its periodic cleaning or through a tap located at the bottom of the filter housing, a fine Filter is installed in front of the nozzle or sometimes in its housing . It serves to protect the nozzle of the nozzle holes from clogging with mechanical inclusions that have not been removed from the fuel by coarse filters for marine diesel engines , fine filters of the slit type are used, in which the filter element is a carefully polished cylindrical rod with longitudinal channels.
Engine lubrication and cooling systems . The lubrication system is used to supply oil to the friction parts of the engine in order to reduce friction losses and remove part of the heat generated during friction . The intensity of lubrication of the parts and mechanisms of the engine depends on the conditions of their work . The most abundant and continuous lubrication is required for crankshaft bearings , less abundant lubrication-for cylinder bushings and pistons ( to avoid the formation of carbon deposits on the bottom of the piston , piston rings and valves), for parts of the gas distribution mechanism , etc . Continuous oil supply to friction surfaces in modern marine engines is achieved by circulating oil under pressure in the circulating oil system . The oil tank in this system can be an engine crankcase ( in engines with wet sump ) or a special tank located outside the engine ( in engines with dry sump ) . Marine engines are mainly oil system with a wet sump, the schematic diagram of which (together with the cooling system )
Scheme of and cooling system of marine engine
The crankcase of the engine oil through the pipe 9 is taken by the gear pump 7 at a pressure of 300-400 kN / m2 ( 3-4 kgf / cm2 ) , pumped through the double filter 2 and through the pipe 1 is fed into the oil refrigerator 29 , where it is cooled with seawater Before the filter 2 and after it , pressure gauges 3 are installed , which control the difference in the oil pressure in the filter . If the difference in pressure gauge readings exceeds 50 kN / m2 ( 0.5 kgf / cm * ) this means contamination of one of the filters . In this case , the oil flow is switched to another filter, and the contaminated one is cleaned . At. an excessive increase in oil pressure before the filter is actuated by the safety valve 5, the excess oil is bypassed again into the suction line through the pipe 8.
The oil is pumped manually to all friction units of the engine before starting it or back the suction line is made by means of a piston pump 6, through 3 2 valves 4 and a pipe 8