Chaptet 7 Fuel system of the diesel engine
The fuel system is a major component of the diesel engine.
According to the requirement of the diesel engine working condition
modes, its function is to gush out the right amount clean fuel the
combustion chamber within regular hours ,with the proper atomized state ,
causing the advantage of mist to form and burn.
According to the different structure patterns and purposes of the
diesel engine,we have developed the fuel systems of different types. Their
performance characteristic lay respectively particular emphasis on to
some extent. The modern diesel engine adopts mechanical injection
system mainly. Among them with the fuel injection pump and fuel
injector to join with the high pressure fuel pipe, and when the fuel
injection pump plunger stroke is regular , with overflow bore or cutting
expenditureregulated the fuel system of plunger fuel injection pump is
most widely applied.In addition, We adopt the pumpfuel injector system
integrating the inject nozzle with the fuel injection pump too, Some
new-type fuel systems have appeared too recently,for example the
electronically controlled injection system.
The pumpfuel injector system is shown in the following diagram:
It is made up of the following parts：fuel tank,injection pump,low
pressure fuel pipe,fuel filter, fuel injection pump, high pressure fuel pipe,
fuel injector, return pipeline and so on. Fuel in the fuel tank is sent into
the fuel injection pump by the fuel filter with certain pressure (0.15～
0.4MPa) with the injection pump. The high-pressure fuel that is out
from the fuel injection pump gushes out the combustion chamber after the
high pressure fuel pipe flows into the fuel injector. Amount of fuel supply
of the injection pump is 3-8 times bigger than the fuel injection pump, the
surplus fuel will return to the fuel tank through relief valve in the fuel
filter (controlling the pressure of injection fule at the same time ).
If we assign relief valve outside the oil inlet cavity of fuel injection
pump,then all fuel will flow through the oil inlet cavity of fuel injection
pump, it has better cooling effect, but at the same time all fuel will flow
through the fuel filter too, so we must increase the size sometimes.
Leaky fuel from the fuel injector will get back to the fuel tank by
the return pipeline (it is also connected to the whole return oil pipe ).
Never allowing the return pipeline of the fuel injector to connect the
pipeline with certain pressure, for example connecting the pipeline
between the injection pump and fuel filter.
We had better make all pipelines of the fuel injector connect a
single return pipelines with no pressure,then fuel will flow back to the
fuel tank.
Some diesel engines have the device which enabling the system of
the whole fuel pipelines to get rid of the air automatically, namely there
must be a difference in height from the fuel filter to the fuel injection
pump, so as to ensure air in the pipeline and fuel vapor bubble can rise to
the top of fuel filter and then flow back to the fuel tank from there to the
overflowed pipelines.
We will study several main parts of the fuel system in the following.
Section 1 Injection pump
Function of the injection pump is to overcome the flow resietance of
pipelines when diesel engine is working, then deliver the fuel in the fuel
tank to the fuel injection pump.
The commonly used patterns of the injection pump are divided into
piston type, shaves stype and gear wheel type,etc., we will introduce their
structures and operation principles now.
一、Operation principles of the piston-injection pump
There is a double-acting type piston-injection pump of heavy
12V180 diesel engine,and its operation principles are shown in the
following diagram.
The partial wheel in the fuel injection pump camshaft passes the
rolling wheel and top rod, and presses the piston downwards, then
enables sucking the check valve and supercharger valve to open like this,
at the same time the piston spring is compressed. After the partial wheel
turning over the roller, the elasticity of the spring makes the piston go up,
at this moment, the check valve opens, and other two valves are
closed .The camshaft circles each time, the injection pump injects the fuel
twice.If fuel pressure of the discharge pipeline is bigger than elasticity of
the spring, then piston will stay in the underpart of injection pump, after
the fuel pressure reduced , continue supporting the fuel.
二、Operation principles of gear wheel-injection pump[Animation
Demonstration]
Installing two gear wheels clenching the teeth each other in the
shell, one is driving gear wheel, and another one is the driven gear wheel,
two gear wheels are rotated in different directions. Fuel is full of oil inlet
cavity and between two teeth when the gear wheel is rotating, and it is
delivered to the outlet oil cavity to increase the pressure.
The route that the fuel transportation is shown in animation.
1.Trapped fuel phenomenon
When the gear wheel rotates, some space is smaller and smaller that
the gear wheel clenches the teeth , the fuel pressure sealed among the
tooth increases, this makes load of the bearing of gear wheel increase.
2.Settlement of the trapped fuel phenomenon[Animation
Demonstration]
In order to prevent this kind of phenomenon,we mill the
decompression trough on the end wall of the shell , the extruded fuel will
be pushed into the oil outlet cavity along this trough.
3. The gear wheel-injection pump[Virtual model]
Section 2 Fuel filter
In order to guarantee the diesel engine works without stopping , the
fuel that comes out from the fuel tank must remove the impurity
carefully . If fuel filtrates badly, the matching parts of the fuel injection
pump and fuel injector will be worn and torn or blocked quickly. Wearing
and tearing of the matching parts, it is not even to cause every jar to
support the fuel, the consumption of the fuel will increase and the power
will drop.Generally all install two fuel filters in the diesel engines.
The first is a strainer filter, its installation is before the delivery pump,
filtering out the bigger impurity. The second is a thin filter which can
fileter out the small impurity , it is installed before the fuel injection
pump.
The strainer generally adopts the network type filter. The detailed
filter usually uses the quality type of the paper and felt type filter and
high-pressure chink type filter.
一、The paper quality element type filter [example picture]
Fuel filter which is used in the type 135 diesel engine is shown in the
following picture :
It is mainly made up of three parts :the filter element, the outer cover
and the filter seat. The fuel is sent into the fuel filter through the injection
pump, strains the paper quality element, removes the impurity in the fuel ,
enters the fuel filter tube cavity, and then passes the collection oil cavity
on the filter seat , leads to the fuel injection pump. There is a return
pipeline joint in the filter seat, which installed the relief valve inside,
when the fuel pressure of the fuel filter exceeds 0.08MPa, surplus fuel
will go back to the fuel tank through the return pipeline joint.
We should join the low pressure fuel pipe according to the arrow
point direction on the seat , can't connect by mistake .
The sealing washer which strains the element bottom is put in the spring
seat, spring sticks bottom surface in the nut closely sealing washer, which
playing a part in sealing.
Depend on the connection of the pull rod between filter seat and
outer cover , there are rubbers that are enclosed and sealed, there is
releasing gas screw on the filter top, which can loose releasing gas screw
to remove air in the fuel filter in the use.
二、Blankets type filter
Blankets type filter is mainly made up of the filter, straining the
element and filter cover 8 and so on.As the diagram shown.Straining the
element and putting it in the filter body, it is filtered slice and made up by
metal network , silk set and felt, it is relatively thick to strain slice by 7
slices, 8 slices are relatively thin, mounted on filter screen alternativly
each other.
There is a welded pressing plate on filter network and the welded
bottom base in underpart, it has nuts to top spin in the bottom base filter
the felt slice and press closely on the pressing plate in the top through
putting the tray.
There are oil inlet valve、outlet valve joints on the filter cover, and
cocks which equiped with defalting valves on the relasing gas pipe.Filter
body and filter cover are connected with the central rod,its end turns on
lathe into the screw plug of the filter body bottom, another end turns on
lathe into the nut, joining the two. Straining the element is fixed on the
filter cover when the spring of the screw plug is pressing tightly.Fuel
flows into the inside cavity of the element and shell through the fuel inlet
pipe 7, then flows into the inside cavity of the metal nets through the
blankets filter piece and silk clothing,and flows into the oil outlet
pipelines through the pipilines, the purpose to install oil pipe is to draw
clean air of no fuel, and the air is gathered in the top of the fuel filter. The
releasing gas cock is used to filter the air of the fuel from the oil
cavity.We must discharge the air before starting the diesel engine.
三、High-pressure chink type filter
Before the fuel flowing into the inject nozzle, there are still equipped
with the high-pressure chink type filter on a lot of diesel engines [the
graphic presentation ], doing the last filtration.
This kind of filter contains the grinding steel element rod, inserting
in the sleeve with very small interval (about a 0.02-0.04mm ),we mill
8-40 fuel troughs on the element rod, one half for the inlet fuel, another
one half for the outlet fuel, the two interlock each other, the fuel flows
into from one end, pass the interval, flows out from another end , making
some small impurity stay in trough and achieve the goal of filtering.
And it can lengthen the inject nozzle the period of revolution, when
the fuel quality is good, which may work for 400 一 500 hours ,then it is
needed to clean again.
Section 3 Fuel injection pump
一、Function of the fuel injection pump
The fuel injection pump is also called the high pressure fuel pump, it
is the most important part in the fuel system.The function of the fuel
injection pump is to improve the pressure of the fuel, and according to the
requirement of working conditions of the diesel engine , gushing out the
fuel of a certain amount the combustion chamber within accurate time.
The requisition for the fuel injection pump is:
(1) The amount of fuel supported of the fuel injection pump should
meet the need of the diesel engine under various kinds of working
conditions, namely the amount of oil supply increases when load is big,
the amount of oil supply reduces when load is small.
We should guarantee the amount of oil supply to every jar and be
equal at the same time .
(2) According to the requirement of diesel engines, the fuel injection
pump should be guaranteed supplying the fuel of every jar begin
constantly to be the same, namely every jar is for the fuel to advance the
angle unanimously, should be guaranteed to be for the fuel to extend time
the samly , and is for the fuel to meet an urgent need and begin rapidly, it
should be agile rapidly to stop the oil , avoid dripping the fuel
phenomenon.
(3) It is different methods according to the form of combustion
chamber and mixed air , the fuel injection pump must offer the fuel of
enough pressure to the fuel injector so as to ensure good atomized quality.
We have a look at the work animation of the fuel injection pump first
before studying the fuel injection pump.
The structure of the fuel injection pump
二、The structure of the fuel injection pump
The fuel injection pump can be divided into mono-pump and the
synthesized pump according to its ensemble architecture(the whole
pump).
1. Mono-pump [Assemble the animation to demonstrate] [The
synthesized pump virtual model]
Mono-pump is formed by one plunger and barrel mainly, itself don’t
bring camshaft and some even don’t bring roller transmission part.
Because this kind of mono-pump is easy to be fixed up in the position
close to cylinder head, making high pressure fuel pipe shorten greatly,it is
applied to the cylinder bore diameter above 200mm of the high-power
medium-speed、low-speed diesel engine at present.
2. The synthesized pump
The synthesized pump (Example pictures) [The whole pump virtual
model]is installated that cylinder numbers are equal to the plunger and
barrel assembly in the same pump body, every jar has a group of fuel
injection component , by every corresponding cam drive of the camshaft
in the body of the pump.
Among the synthesized fuel injection pumps , we take out the
synthesized fuel pump group to explain now. The structure chart is as
follows:
Its major parts are as follows, the camshaft, roller body, plunger and
barrel, plunger return spring, rotating sleeve and tooth ring, oil outlet
valve and valve seat ,compressing tightly and connecting pipes etc..
Barrel and plunger is a pair of main accurate matching parts in the fuel
injection pump, they are processed, ground and mixed each other
carefully, their diameter interval is 0.001-0.003mm only, this pair of parts
can only be changed in pairs, can't be changed alone .
There are two bores on the barrel, which making barrel inside cavity
communicate with oil pipes, there are vertical troughs on the right oil
bore place , among them stretching into the screw , which making barrel
fixed and can't be rotated in pump body.
The top of plunger has an annular trough , it communicates with terminal
surface on plunger with the vertical trough . The spiral hypotenuse begins
from the vertical trough and is used to regulate the amount of oil supply.
Plunger underpart has two protruding shoulders and flanges. The
protruding shoulder of plunger is inserted in the notch of rotating sleeve.
Rotating sleeve is installed on barrel freely. Tooth ring of opening is put
with screw in the rotating sleeve to fasten, and clenching the teeth by
rack.
Rack is put in the vertical bore of pump body and linked with
governor gear shift . While rack is moving to the axial direction under the
function of gear shift and governor, rotating sleeve and plunger of every
oil pimp will turn certain angle thereupon . Retainer of the plunger return
spring is equipped on plunger flange. Spring retainer is supported on
pump body. The function of spring is to make plunger fall. Cam on
camshaft acts on plunger through roller body, which making that go up.
Roller body is the transmission body among cam and plunger, it bears
side thrust and makes plunger only receive axial force by itself. Equipped
with roller on roller body underpart axle, it is mounted on rolling needle
bearing, twisting the adjusting screw and insurance nut on roller body.
The operation principle of the fuel injection pump
三、The
operation principle of the fuel injection pump
1. The course of sucking the oil and pressing the oil
Sucking the oil and pressing the oil of the fuel injection pump, is
finished by plunger reciprocating motion in barrel. When plunger lies in
the underpart position, two oil bores on barrel are opened, the inside
cavity of barrel communicates with oil passageway in pump body, the
fuel is filled with the oil chamber rapidly.
When cam is carried on roller of roller body, plunger rises. Upward
movement begins from the plunger to the oil bore and terminates before
blocking from top surface of the plunger. Within these periods, because of
movement of plunger, the fuel is pushed out of the oil chamber, flows into
the oil passageway. So this section lift is called the advance stroke. When
plunger blocks the oil bore, it begins to press the oil course. When
plunger goes up, the indoor oil pressure rises sharply. When the pressure
exceeds out spring elasticity of oil valve and top oil pressure, carrying
and opening the oil valve, the fuel is pressed the oil pipe and sent to fuel
injector.
The moment is called the initial point of supplying oil in theory when
oil inlet bore of plunger is totally blocked by the top surface of plunger.
When plunger continues upward movement, supplying the oil continues
all the time too, the pressing oil course is not over untill the spiral
hypotenuse of plunger gets out of the way the oil return bore of barrel, as
the oil bore is opened , the high-pressure oil flows back to the oil
passageway in pump body from the oil chamber through the vertical
trough and the oil return bore of barrel. The oil pressure of oil chamber in
barrel is reduced rapidly at this moment, oil outlet valve falls in the valve
seat within the function of spring and oil pressure in high-pressure oil
pipe, fuel injector stops gushing out the oil immediately. Though plunger
still continues upgoing at this moment, but the oil already stopped. The
moment is called the end point of supplying oil in theory when oil return
bore of barrel is opened by plunger hypotenuse.
[Animated demonstration of the entire process]
Seen from the sucking the oil and pressing the oil course since
above-mentioned, in the whole course of plunger upward movement, just
a section of stroke is pressing the oil course, this stroke is called the
effective stroke of plunger.
2. oil adjusting[Virtual model]
In order to meet the needs of diesel engine load, the amount of oil
supply of the fuel injection pump must be regulated in the range from the
amount of maximum fuel (full-load ) to zero amount of oil supply
(park ).For the regulation of oil quantity to realize is made all plungers of
the fuel injection pump rotate through rack , rotating sleeve at the same
time. ［Animation Demonstration］
Seen from the animation, when plunger is rotated, oil supply time
isn’t changed , but the oil supply end time alters, because position of
plunger hypotenuse to oil return bore of bareel is changed. As angle that
plunger turns being different, the effective stroke of plunger is different
too, therefore the change thereupon of the amount of oil supply.
The bigger angle what plunger is rotated to not supplying the oil level
is, the hypotenuse distance of the terminal surface which is opened to oil
return bore of barre is bigger,the bigger the amount of oil supply is, if
angle that plunger rotates relatively little, Disruption of oil supply
begins relatively early, the amount of oil supply is too relatively small. It
must be interrupted when the diesel engine parks, for this reason, we can
turn into and make the vertical trough on plunger be facing toward on
barrel oil return bore. At this moment, in the whole plunger stroke, the
fuel in barrel has been flowing back to oil pipes through vertical trough、
oil return bore all the time,there is not pressing the oil course, so the
amount of oil supply equals zero.
Therefore, as plunger rotates,we can regulate the amount of oil supply
by changing the terminal point of oil supply,this kind of method is called
for oil supply terminal point to regulate the law.
Changing the position of the hypotenuse on plunger, we can receive
other regulating methods. The plunger hypotenuse shpes of three kinds of
regulating method of oil supply is shown in the following diagram.
（a）Regulate the law of oil supply terminal point for
above-mentioned,it is suitable for applying to the diesel engine that the
rotational speed does not change and applying to the ship supercharged
diesel engine too.
（b）Regulate the law for some of supply beginning. Because the
spiral hypotenuse slopes upwards, the oil supply initial point isn’t
changed,but oil supply terminal point is changed while rotating plunger
amount of oil regulated. This adjustment method was once thought that it
would be suitable for driving the propeller directly on the diesel
engine,when it runs according to the promoting performance,load
increases with rotational speed, fuel injection advance angle should be
increased. But it is unfavorable when it works for low load in fact, so
higher turbocharged engines are already few application of marine
diesel,we still hope to adopt the first kind of regulation to oil supply
terminal point method.
（c）Method to change for initial point and end point of oil supply at
the same time . This kind of plunger meets the requirement of reducing
the amount of oil injection by properly moving backward initial point and
end point ahead of time, therefore, it can control the whole combustion
process and go on near the top dead centre no matter in low , high load.
This kind of regulating method is suitable for the marine diesel engine
that is in high pressurization and changed in rotational speed and load.
In the regulating mechanism of oil supply of the fuel injection pump,
besides above-mentioned rack type oil amount controlling organizations ,
there is a kind of shift fork type oil amount controlling organization.
There is one adjusting arm in plunger underpart , one of ball head's end of
adjusting arm is put in the trough of adjusting fork, adjusting fork is fixed
on pull rod by locking screw, moves pull rod, adjusting fork drives
plunger to rotate, so as to achieve the goal of changing oil supply. Its
advantage is processing simply, easy repair, oil pump is small in external
dimension, the serial pumps of our country No. 2 adopts this kind of
controlling organization. ［Animated demonstration］
In above-mentioned the fuel injection pump, the most key part is
plunger. There are a lot of structure forms of plunger, but its basic
structure is like the Fig:
The form has helix type (b and d ) and straight line type (a and c) in
the chute (the oil edge) on plunger. The chute of straight line type plunger
returns oil through centre bore, processing the advantage such as being
simple, the serial pumps of our country No. 2 adopts plunger of this
form .
Spiral troughs or straight line chutes on plunger, according to its
slope direction, we can divide it into dextrorotation (c and d ) and Left
deviation fastenned (a and b ). The trough direction of the spiral can be
judged with the tactics of controlling. The fastenning of spiral trough
turning towards direction relates to control the movement direction of the
tooth pole or arrangement. Spiral trough that dextrorotation turned
towards, oil supply reduces when rotating left, it is applied to the fuel
injection pump that the whole pump installs governor in the right side.
And the fuel injection pump installing governor in the left side fastens the
spiral trough with the left.
Oil supply adjustment
四、Adjustment of the fuel injection pump oil supply timing
The fuel injection pump of the multi-cylinder diesel engine should
begin to supply the oil after the same canshaft rotating angle. And the
time should be equal that every jar begins to supply oil, the general
deviation is 1 degree,We can make use of adjusting screw on roller body
to adjust when its deviation is greater (The picture demonstrated).
Adjusting screw is twisted outside while appearing, plunger enables
rising, its time to block oil return bore of barrel advances. If adjusting
screw is twisted inside, the beginning moment of oil supply will be late.
五、Homogeneity of every oil supply adjustment of oil pump
The adjustment of the homogeneity of every oil pump oil supply
makes use of rotating plunger to be realized. Generally requires that the
disparity of every oil pump oil supply does not to exceed 3%, if a certain
oil pump does not conform to the standard, we must adjust it and unclamp
the screw of tooth ring at this moment, rotating rotating sleeve 5 of this
oil pump in directions needed together with plunger. When plunger
rotating (overlooks) counterclockwise, oil supply increases, while plunger
rotating clockwise, oil supply reduces.
Section 4 Oil outlet valve
Oil outlet valve is installed on the fuel injection pump, it is an
automatic valve, when plunger is opened while pressing the oil , but as
plunger does not press the oil , it closes under the pressure function of oil
outlet valve spring and oil pipes. It is a pair of important matching parts,
its organization form has very great influencing for the oil supply
characteristic .The material object picture is as follows:
一、Function of oil outlet valve
Function of Oil outlet valve：
（1）Make inside cavity of barrel and high pressure pipelines to cut off
each other when it can not supply the oil , by preventing it from sucking
the fuel of the high pressure pipelines when plunger falls.
(2) Make the high-pressure pipeLines keep sure remnants pressure so
that the fuel pressure of pipelines can rise quickly while gushing out the
oil next time.
(3)When oil supply of the fuel injection pump is over, it can make
the oil pressure in the high-pressure pipelines drop rapidly, so as to
ensure that it is clear-cut to break the oil, dispel dripping the oil
phenomenon of fuel injector.
二、The installation location of oil outlet valve［Animation Demonstration］
The structure and operation principle of oil outlet valve
1. Constant volume type oil outlet valve
The most widely used valve is the constant volume type oil outlet
valve [Animation Demonstration ]. The conical surface of oil outlet valve
is sealing the surface of the valve. Its underpart has the cylindrically
unloading flange, the tail of the valve has cross sections, the reciprocating
motion in the direction bore of the valve seat.
The operation principle of this kind of oil outlet valve is as follows:
The cylindrically unloading flange on oil outlet valve has special
function, when the pressure of the fuel injection pump rises to exceed the
pressure of oil outlet valve spring and remaining pressure of oil pipes,oil
outlet valve is backed down, however,after it goes up some distance h, the
fuel could flow the high-pressure oil pipe, after the disconnected oil of
the fuel injection pump, under the function of the oil pressure in the
spring and high-pressure oil pipe, oil outlet valve falls some distance
h,then it goes back to valve seat. At this moment, the volume in the
high-pressure oil pipe increased 2dh/4. The fuel expanded in the oil pipe,
its pressure suddenly drops, enables gushing out the oil to stop
immediately, this can prevent the possibility of dripping the oil.
Volume 2πdh/4 is called the unloaded volume or reduced pressure
volume. The size of unloading volume has certain influence on course of
spraying of the fuel,the bigger to unload volume is, the smaller the
remnants pressure in the high-pressure oil pipe is, it will cause and the
initial injection time to lag behind in this way, therefore, it will make the
initial pointl of oil supply ti advance while unloading volume is larger,
the test is proved, it has greater influence for the oil supply, the unloading
volume of oil outlet valve is not changed for certain type fuel injection
pump, and the fuel injection pump of different types , unloading volume
of oil outlet valve is different.
Another kind of pattern of the constant volume type oil outlet valve is as
animation shows:
Its characteristic is that is sealed in the underpart conical surface,,
the volume of oil outlet valve is relatively small. It is made up of oil
outlet valve seat , oil outlet valve and spring parts ,etc.
Its working course is as follows: after plunger pressing oil , oil outlet
valve is opened from the seat surface,until the side bore of valve seat is
opened by the control oil edge of oil outlet valve,the fuel begins to flow
into the high-pressure oil pipe. After the oil supply is interrupted,oil outlet
valve begins to drop, when the side oil bore on the control oil edge of the
valve is totally sealed , oil return pipes are cut off, the function of
unloading of oil outlet valve begins, then until falling to the valve seat , it
is over to unload function, the unloading stroke is h.
The advantage of this kind of oil outlet valve is that the whole
package is apt to change, oil outlet valve is buffered and will not be
assaulted while taking a seat, so it is small to wear and tear, longe-lived.
This kind of oil outlet valve is applied to the P7 , P9 type and FM type the
strengthening fuel injection pump.
[Animation Demonstration ]It is another kind of oil outlet valve of
the underneath type of sealed conical surface. This kind of oil outlet valve
is in the course of taking a seat, after unloading flange enters leading
bores , some fuel that equals to unloading volume is gathered in
unloading flange underpart,now, it appears to slander by oil bore , throttle
function of oil bores slows down the impact speed and impact power of
oil outlet valve to seat surface,when oil outlet valve is totally closed,
plunger cavity fuel pressure only acts on the area that the average
diameter of sealed conical surface determines, this kind of structure has
improved opening the pressure and opening the speed of oil outlet valve.
Generally it is applied to the fuel injection pump of the medium-speed
diesel engine.
Constant pressure oil outlet valve
The structure of constant pressure oil outlet valve is shown as the
following picture. Hold another spherical constant pressure unloading
valve in oil outlet valve. When the fuel injection pump supplys the oil,
the whole oil outlet valve rises together. When the oil supply is over, after
oil outlet valve takes a seat, if the pressure in the high-pressure oil pipe
exceeds the pressure of opening of constant pressure valve, constant
pressure valve will be opened, the fuel flows back to plunger cavity, the
pressure in the high-pressure oil pipe drops, until the top pressure of oil
outlet valve is lower than the limiting pressure of constant pressure valve
spring, constant pressure valve is closed . If the twice or third pressure
wave exceeds the opening pressure of constant pressure valve, then
constant pressure valve is opened again,so that we dispel the further
reflection of the pressure wave,we can guarantee that the remnants
pressure of the high-pressure oil pipe is the definite value under various
kinds of situations. Therefore,this kind of constant pressure valve can
prevent two times from spraying and not spraying together within the
range of broad rotational speed and load ,it can prevent the cavitation at
the same time. The opening pressure of constant pressure valve is
generally within the range of 0.5- 1.0MPa.
Section 5 The fuel injector
The fuel injector is mounted on cylinder head, its function is to turn
the fuel fog into the superfine particle and gush out to the cylinder . The
requisition of the fuel injector atomized quality depends on combustion
chamber pattern mainly.
The fuel injector is made up of the fuel injector body on the top and
inject nozzle on the bottom, it can be divided into a opening type and
closing type according to structure of inject nozzle.
一、The opening fuel injector
Main characteristic of the opening fuel injector: inside cavity of fuel
injector always communicates with combustion chamber. Because it
doesn’t has the needle valve which closing the injection bore, so it is
called the opening fuel injector.
The structure of a kind of the opening fuel injector is shown as the
following picture:
The underpart of fuel injector body has injection bore, the needle
valve is intalled in it, the conical underpart surface of needle valve is
pressed tightly on seat surface of fuel injector body, there are axial bores
on the needle valve, the underpart has two bores becoming 90 degrees
each other, there is cannelure on the conical surface of the needle valve,
the cannelure plays a gushing out bores role. The fuel flows into the
cannelure through the high-pressure oil pipe from the fuel injection pump
to the axial bore, the fuel sprays the fog and turns into the superfine fuel
and presents flat fire fan-shaped and gushes out to the cylinder.
The advantage of opening type fuel injector is no moving parts that
accuratly cooperated, so it is simple structure. But its shortcoming is apt
to drip the oil, this is because when the oil supply begins, it is not set up
enough pressure yet in the high pressure pipelines, the fuel may flow into
the cylinder when being dripped. And at broken oil, dripping the oil
might happen too when oil pipe and fuel expand. So it is already seldom
used this kind of fuel injector on the modern diesel engine.
Classification of closing inject nozzle
二、Classification
of closing inject nozzle
Closing inject nozzle can be divided into needle type and axial
needle type. [Virtual Model]
Injection bore type inject nozzle [as animation shows ] is used in the
spraying type combustion chamber directly mainly, it is made up of
needle valve body and needle valve,injection bore number is l8, it can
be up to 10 at most, aperture 0.15-1.0mm. Injection bore numbers and
direction and is decided by the demand for quality and the fuel injector
arrangement in combustion chamber to spraying of combustion chamber
differently. Press spring on needle valve of inject nozzle, making needle
valve press on needle valve body seat surface closely , when the
high-pressure oil that the fuel injection pump sends acts on conical
surface, it could make needle valve lift and begin to spray .
Axial needle type inject nozzle [as animation shows ] is used in the
divided combustion chamber, namely in pre-combustion chamber and
swirl chamber. We can make axial needle head into different forms to
adapt to the demand for oil injection atomization of combustion chamber.
Axial needle head is made to two pieces of relative cutting toper, when
needle valve is lifted, the fuel is squirted through the annular interval
between injection bore and axial needle. Form the hollow conical shape
spray.
One kind of of axial needle type inject nozzle is called " throttle type
inject nozzle ".[as animation shows] Its axial needle head is relatively
large in length, the tip is made into the cone , making earlier stage spray
more intensive and form pre-spraying in advance, then the mainly a large
amount of spraying. We adopt throttle type inject nozzle, in a situation
that the low-speed and load are smaller , it can make the operation of the
diesel engine soft .
Long bore type inject nozzle[as animation shows], the direction of its
needle valve is far away from the hot district partly , so it can prevent
needle valve guidance district from blocking the phenomenon of glueing
because of being overheated . At present , we adopt this kind of inject
nozzle extensively in the high-speed strengthening diesel engine.
Mandatory cooling type inject nozzle [as animation shows], its
purpose is to reduce the hot load of inject nozzle, it can prevent glueing,
and lengthens service life , it is generally used in large-sized and
medium-sized strengthening diesel engine.
In the inject nozzle of the ship medium-sized and large-sized diesel
engine, some separate needle valve body from inject nozzle [as animation
shows], its design philosophy is to make needle valve far away from
combustion chamber、lighten hot load、improve service life, but it brings
about that the volume of pressure chamber of needle valve seat underpart
increases, this will not merely cause the dripping oil , and have very great
influence on the accumulating carbons outside and economy of diesel
engine. So some modern medium-sized diesel engines all tend to be
designed needle valve body and inject nozzle into an organic whole, this
reduces volume of the pressure chamber and improves economy of the
diesel engine greatly , for example it can make the specific fuel
consumption reduce 4-5g/ KW *h if we use 300 type new inject nozzles
as the following picture.
三、Typical fuel injector [Virtual Model]
1. the fuel injector of 12V150 type diesel engine
The structure of this kind of fuel injector[as animation shows], which
belongs to porous closing type fuel injector, it is made up of inject nozzle,
chink type filter matching parts, fuel injector body top rod , spring and
regular nut , the adjusting and pressing nut etc. Injection bore
numbersInjection bore diameterInjection bore angle=70.25140
degreeses.There is two rings trough on the surface of needle valve leading
cylinder, they play a sealing and lubricating role, awl angle 60 degrees of
needle valve, needle valve lift is 0.4-0.5mm, the needle valve opening
pressure is 20MPa. Its main characteristic is that have increased a
high-pressure chink type filter before inject nozzle. Its purpose is to
filtrate the impurity further, lighten the wearing and tearing of inject
nozzle matching parts and obstruction of injection bore, lengthen the
service life of inject nozzle.
Chink type oil filter , it is made up of sleeve and element. There are
40 oil inlet and outlet ditches altogether that the depth is 0.4mm 、length
is 23mm on the surface outside element of the cylinder, half of oil ditches
link the top、and half of oil ditches link the underpart among them, the
diameter interval between element and sleeve is reached 0.02- 0.04mm by
the apolegamy , it can strain the mechanical impurity above 0.02mm .
2.The fuel injector of 6135 type diesel engine
This fuel injector is long bore needle valve closing type fuel
injector[as animation shows], it is made up of fuel injector body and
inject nozzle. The adjusting pressure nut of fuel injector body top presses
the adjusting pressure spring through the spring top seat, this spring
pushes down needle valve through the seat under the spring and top rod.
There is oil passageway that communicates with high-pressure oil pipe by
centre bore, namely the fuel flows into inject nozzle through oil
passageway from then on.
This fuel injector is long bore needle valve closing type fuel injector,
inject nozzle body and inject nozzle are the couple grinding matching
parts. There are four injection bores of diameters 0.35mm on inject
nozzle head, distributing evenly, the spray angle as 150 degrees. Inject
nozzle top has flanges, presses it in the underpart of fuel injector body
with the nut. Inject nozzle and fuel injector body meet in the level,
ground carefully , in order to keep the oil seal. There is a locating stud
between the top level surface of inject nozzle and fuel injector body, it
guarantees that two oil passageways are identical, oil passageway links
the accumulating oil cavity directly. Long needle valve underpart has a
conical surface,which is located on needle valve seat of inject nozzle.
There are four above-mentioned injection bores on this valve seat. The
small cylinder on needle valve is inserted in the bore of top rod underpart ,
the spring tension on top rod compresses tightly needle valve on its valve
seat, and make injection bore close .
When the fuel injection pump presses the high-pressure fuel into the
accumulating oil cavity of inject nozzle underpart by pipelines joints and
chink type oil element, its oil pressure increases.Because of the fuel
pressure to the underpart conical surface of needle valve, it forms a axial
force, doing its most to make needle valve lift. When the fuel pressure
rises to the elasticity that can overcome adjusting pressure spring , needle
valve leaves valve seat promptly, the fuel gushes out the cylinder with the
high speed from four injection bores. When the fuel injection pump stops
supplyng the oil, the oil pressure drops in fuel injector, needle valve is
under the function of adjusting pressure spring, falls back to valve seat ,
the oil supply would stop immediately .
This opening pressure of fuel injector is 19MPa, this pressure is
decided by advance urgent strength of the spring, when there are
deviations , we can correct it with adjusting pressure screw .
3.The low inertia fuel injector[Virtual Model]
[as animation shows] This is used for low inertia fuel injector on
diesel engine of model PA6-280. Inject nozzle is divided into a cooling
type and non-cooling type, its neddle valve lift is 0.8mm , injection bore
parameter is 80.55140 degrees. If we use the light diesel oil ,we adopt
the non-cooling type inject nozzle , while burning the heavy oil , we use
cooling type inject nozzle. Opening pressure of neddle valve is 32.65MPa.
The characteristic of this kind of fuel injector is that adjusting pressure
spring is put close to inject nozzle underpart, top rod is very short, so the
quality and inertia of its moving parts is small. It has lightenned the
beating of the neddle valve to the seat and striking of top rod, making
neddle valve movement react to the oil pressure change sensitivly ,
especially when the neddle valve spray ends, the close performance has
been improved. To prevent cavitation of neddle valve seat surface,
prevent the gas from flowing backwards and leading to the fact inject
nozzle forms the glue , bad phenomenon of spraying etc. All have
obvious results on later stage when the card dies and may causes because
of the fact that neddle valve can not react sensitivly . Therefore, this kind
of low inertia fuel injector is used more and more on the diesel engine of
high-speed and high pressurized、high-power at present.
Pump-fuel injector
Pump-fuel injector puts the fuel injection pump and inject nozzle
together jointly and becomes a single part. It is installed the cylinder head
directly.
Because this kind of pump-fuel injector saves the high-pressure oil
pipe , and the volume of fuel between plunger and fuel injector is very
small, it can prevent the fuel from being compressed、the fluctuation
phenomenon of fuel and inflation of the high-pressure oil pipe,etc. The
adverse effect for the oil supply is reduced greatly, and it can produce the
pressure of spraying up to 100- 150MPa .
The main characteristic of pump-fuel injector is:
(1) It makes reality of fuel spray time accord with theory initially spray
time more precisely, it also makes the spray end time accord with the
theory spray end time at the same time.
(2) The dripping oil phenomenon doesn’t happen.
一、The structure of pump-fuel injector
It is shown as the pump-fuel injector that is applied to the high-speed
light-duty two stroke diesel engines, outside body 12 is made up of
overcoat nut 10 and barrel 25、inject nozzle 2,they are firmed closely
together, there are two injection bore 8 and 27 on barrel, there is annular
groove on plunger 24, both sides of groove are two hypotenuse a and c,
the gradient of the upward hypotenuse is larger than to the downward
hypotenuse. The annular groove communicates with underpart oil cavity
of barrel through radial bore b and axial bore d on plunger. Plunger top
has flanges, while stretching into the leading sleeve 16, plunger push rod
18 is installed inside the leading sleeve, the push rod is linked to with
leading sleeve 16 through pins 19. The leading sleeve utilizes spring 17 to
press the top, pins 15 are inserted in the vertical groove which the leading
sleeve 16,it can prevent its whereabouts while installing. Plunger top has
some levels , installing gear wheel 11 on it, gear wheel 11 clenches the
teeth with tooth rod 22.
There are six injection bore 1 of diameters 0.15mm on inject nozzle
2 ,it is equipped with non-return valve 4 within inject nozzle, pressing
it tightly with spring 3, on valve seat 5, there are three important function
in non-return valve 4 in fuel injector work:
(1) it is check valve between combustion chamber and the fuel injection
pump;
(2) its precisly control the beginning and the end of the oil supply,
enables gushing out the oil clear-cutly and agily ;
(3) it can guarantee atomization degree that the fuel is lighted
immediately at a low speed, because it is less than enough pressure and
doesn’t be opened.
Non-return valve 4 top is equipped with petal type level valve 6 and
valve seat 7. It is used in when the non-return valve can not be cooperated
closely (while dust particle is putting), it can prevent the fuel gas from
entering inside cavity of pump-fuel injector.Thin steel tube 28 of outside
plunger is used to prevent the overcoat nut inboard wall from the high
speed return fuel impacting.
Pump-fuel injector is installed in the cylinder head. Cam 1 makes the
plunger move downwards through roller tappet 2, top rod 3 , rocker arm
5 , plunger push rod 6. Plunger moves upward with the aid of the spring
tension.
The regulation of oil quantity to utilize is realized by rotating
plunger. It can make plunger rotate to move tooth rod 9. The small axle
7 links with tooth rod 9 through 8 levers, when rotating axle 7, it
can guarantee that pump-fuel injector tooth rod of every cylinder head
of diesel engine is moved at the same time .
二、Operation principle of the pump-fuek injector
1.The course of sucking oil[Animation Demonstration]
Fuel injection pump sucks out the fuel from the fuel tank, along the
oil pipe,through the pipe joints, metal element and oil passageway,the
fuel is sent into annular oil cavity. Some fuel flows back to the fuel tank
from here constantly by oil passageway and second element. Therefore,
the fuel circulates in annular oil cavity, it can make pump-fuel injector
cool and prevent piling up bubbles to among them .
2. The course of pressing oil[Animation Demonstration]
When plunger lies in the top position, the fuel flows into and is full of
underpart oil chamber in barrel from annular oil cavity through oil bore of
barrel, the annular groove and the centre bore of plunger,it is full of oil
chamber from the oil bore directly at the same time . As plunge moves
downward, oil bore of underpart plunger is covered by the end surface of
plunger, some fuel are pressed back from the above oil bore to annular oil
cavity.
3.The course of fuel injection[Animation Demonstration]
When the up hypotenuse on plunger hides oil bore on barrel, the fuel
begins to be gushed out the cylinder through the non-return valve by
inject nozzle. When plunger continues moving downward, until the down
hypotenuse of plunger begins to open down oil bore, the oil supply is over.
The fuel gets back to annular oil cavity from oil bore below at this
moment.
4.The regulation of oil supply[Animation Demonstration][Virtual
Model][Fork type Virtual Model]
When rotating plunger , it can make oil supply be changed
according with the change of the up hypotenuse of plunger to the oil bore
position on barrel. When the underpart of plunger down hypotenuse is
just facing toward the up oil bore, then oil supply is the biggest. If we
rotate plunger according to the shown direction of arrow point, then oil
supply is reduced. So, while rotating plunger , it not merely make oil
supply change, and fuel supply advance angle is alsochanged. With the
increase of oil supply, fuel injection advance angle increases. When
plunger rotates, the end time of oil supply is changed to some extent too,
but has little change, because the slope angle of the down hypotenuse of
plunger is relatively small. If vertical trough of plunger is just facing
toward up oil bore of barrel, it is oil supply interrupted position.
P-T type fuel injector
P-T type fuel injector[Virtual model of P-T part]
"Ｐ-T" is the abbreviation of the pressure (Pressure ) and the time
(time ) in English , it means regulating oil supply by the pressure-time
principle. This kind of fuel injector is that U.S.A. CUMMINS Company
designs more unique fuel injector. Its structure is as follows:
This fuel injector and closing type fuel injector are entirely different,
to be precise, it is a kind of combined opening type fuel injector. With
fuel injector nut, we tighten inject nozzle and barrel on fuel injector body.
Plunger and needle valve is made into an organic whole (it is called
plunger-needle valve). We clamp the protruding shoulder top and leading
sleeve together. The protruding sphere of push rod underpart cooperates
with concave sphere on plunger-needle valve, the return spring is
installed between fuel injector body and leading sleeve top bar, it is used
to keep close contact between plunger-needle valve and push rod、
between push rod and cam (or rocker arm head ).
Its operation principle is sketched as follows:
(1)sucking oil-returning oil: When plunger-needle valve upgoes, the
fuel that pressure has already been adjusted and flows into the oil pipes of
fuel injector from oil inlet bore A, through oil outlet bore B, the annular
groove and oil return bore c , d and oil return pipe of the needle
valve ,then gets back to the float case. Such fuel cycle helps cooling,
lubrication of fuel injector and plunger ,the getting rid of air. It still helps
to improve dependability of fuel injector and extension service life .
(2) oil measurement: Plunger-needle valve continues upgoing to open
measurement bore e, after the fuel flows into the pressure chamber, it
begins amount of oil course.
(3)fuel injection: it will close measurement bore when plunger-needle
valve moves downward, the fuel which enters inject nozzle head and is
supercharged is gushed out combustion chamber through 10 pieces of
aperture 0.2mm injection bore. Pressure of fuel injection is very high up
to 105MPa.
(4)the end of fuel injection-return oil: Plunger-needle valve continues
falling, when the conical surface of needle valve keeps in touch with the
conical surface of inject nozzle head, it is over to gush out the oil. At this
moment , it begins to return oil. The contact stress that the needle valve
takes a seat can be adjusted by promoting the organization of the push
rod .
(5)The overall animation demonstrating
Oil measurement function of fuel injector depends on three
factors ,such as the size of measurement bore, opening time of
measurement bore that fuel injection cam controls , oil inlet pressure of
fuel injector. For the diesel engine of certain type, the form of fuel
injection cam and size of measurement bore of fuel injector are certain,
like this, though opening angle of measurement bore countes with the
bent axle corner does not be changed , but opening time of measurement
bore countes with time, vary with the rotational speed of the engine ,
namely the rotational speed of engine raises and measurement time
shortens, amount of fuel injection is reduced. If amount of fuel injection
does not be changed, it can be improved oil inlet pressure of fuel injector
by P-T fuel pump, it can increase fuel consumption of measurement bore
to remedy oil inlet time and reduce the impact on amount of fuel injection.
Threrfore, fuel injection pressure of P-T fuel pump varys with the
variation of the load and rotational speed of the engine at the same time .
This is to utilize the principle of cybernetic loop oil supply of pressure、
time. Fuel from P-T fuel pump flows into the fuel injector through
measurement bore, probably 20% of the fuel is gushed out and entered
combustion chamber through measurement bore pressure chamber.
Remaining fuel enters oil return pipe through oil return oil measurement
bore.It is benefit to be changed while adjusting amount of fuel injection
that we make oil inlet measurement bore A to spiral shell form.
Section 6 The combustible gas mixture formation and combustion chamber pattern
一、The combustible gas mixture formation
The quality which forms combustible gas mixture with the air after
the fuel gushes out and enters the cylinder plays a decisive role to
combustion process. Because catching fire lag time is very short, the
forming of combustible gas mixture is finished within extremely short
time, in order to improve the quality of diesel engine combustible gas
mixture formation , we usually take the following measures:
1．The fuel which flows into the cylinder should be atomized well,
and has certain range, namely the oil particle is small and even , and is
full of the whole combustion chamber space. This can guarantee the fuel
of atomization and increase contact surface of the air of combustion
chamber, it can accelerate the fuel preheating, evaporation and oxidizing
before going off ,namely can shorten and catching fire lag period .
2. The form that the fuel sprays should be suitable for the form of
combustion chamber,in order to take shape on combustion chamber
space.
3. Cause the strong air vortex in combustion chamber, impel the fuel to
fully mix with the air before going off
The above-mentioned measures are realized through choosing
suitable combustion chamber pattern and gushing out the oil device .
二、Pattern of the combustion chamber
Because pattern of the combustion chamber is different in the diesel
engine, air mixture formation methods are different too ,they can roughly
be divided into: The air mixture formation, the oil film air mixture
formation and the compounding type air mixture formation. Combustion
chamber of the modern diesel engine can be divided into two big classes:
(1).direct injection combustion chamber: This kind of combustion
chamber is set up on the top of piston,it is a unified space. It can be
pointed the spray oil bunch cooperating with combustion chamber form
each other mainly , make the fuel and air mix evenly . Direct injection
combustion chamber can be divided such patterns as unifying type ,
semi-open , ball type oil film type and compounding type ,etc.
(2). divided combustion chamber: Combustion chamber is obviously
separated into two parts,one part is made up of the piston top surface and
cylinder head bottom surface; another part is in the cylinder head or the
cylinder block, the two link with one or several passways. The separately
type combustion chamber includes swirl chamber and pre-combustion
chamber mainly.
1. Unifying type combustion chamber [The picture demonstrating ]
Unifying type combustion chamber is formed by the unified volume
that cylinder head bottom surface , piston top surface and cylinder wall
form. Vortex movement is very faint in this kind of combustion chamber,
in order to make the fuel distributed to the whole combustion chamber
space as much as possible, piston is made to shallow concave generally,
make it cooperate well with oil bunches well, prevent the oil bunch from
keeping in touch with cylinder wall with combustion flame directly. this
kind of combustion chamber belongs to space air mixture formation. It
has the following characteristics:
(1)The form is simple, the structure is compact, heat dissipation area is
small, the heat loss is little, it is apt to start, specific fuel consumption of
the diesel engine is lower than the combustion chamber of other patterns,
so it is used more extensive.This kinds of combustion chamber is applied
to not only the large-sized, medium-sized, small-sized but also the
high-speed, medium-speed, low-speed diesel engines.
(2)In order to guarantee good atomized quality , we must adopt the higher
spraying pressure and porous fuel injector , the diameter of injection bore
is very small, so its processing and manufacturing relatively takes more
time.
(3)The highest burning pressure pz of the diesel engine and rising rate of
pressure are all relatively high, making the receiving strength of crank
connecting rod organization bigger.
(4) Change to the rotational speed of the diesel engine and fuel quality is
very sensitive . Because the rotational speed changes and the fuel quality
influences quality of spraying directly.
2. semi-open combustion chamber [The picture demonstrating ]
Semi-open combustion chamber is formed by two pieces of space: A
part is the deeper concave bore on the top of the piston, it is also the
narrow diameter of place of concave bore sometimes,it forms the piston
top combustion chamber , another part is the remaining space 2 of piston
top . The narrow passway is not separated obviously between two parts,
so is called semi-open type.
Semi-open combustion chamber has two respects function by the
spraying quality and the vortex when the air is pushed in the deep
concave bore of the piston top in the compressing course, it impels the
fuel and air to mix evenly.
Compare with the unifying type, semi-open combustion chamber
requisition for fuel system is relatively low, but still keeps the advantage
that is low specific fuel consumption, starting easily, making the work of
the diesel engine softer .
3. ball type oil film type combustion chamber
[The picture demonstrating ]
Ball type oil film type combustion chamber is a kind of pattern of
semi-open combustion chamber basically. But the working course is
different from half a separating type. Semi-open combustion chamber is
mainly that space atomization is mixed, but ball type oil film type
combustion chamber takes shape and mixes for the evaporation of the oil
film .
This pattern combustion chamber processes a deep spherical space
on the piston top . While it working, fuel injector sprays the fuel along the
air current direction and the cliff side of combustion chamber,under
entering vortex function strongly, makes the fuel stand cloth form the oil
film with very thin one storey , evaporates under lower temperature on
the wall of combustion chamber , reacts for the splitting decomposition
which controls the fuel. It is air mixture that oil gas in evaporation and air
mixed evenly. In the oil injection course, there is oil fog with superfine
small part dispersed out from the oil bunch, finishing catching fire
preparation at first in the blazing air, form the fire source , combustible
air mixture of the evaporation from the ball type room wall is lighted
by this fire source. Going on with burning, it produces a large number of
heat , forms the fire source , impels the oil film on the wall of combustion
chamber to evaporate , burn constantly.
The characteristic of ball type oil film type combustion chamber is:
the work is soft , it is with low noises to burn , arrange less smoke, the
performance index is good, and it can use many kinds of fuel . The
shortcoming is that the cold car to start is difficult, it is used in
small-scale high-speed diesel engines more.
4. the compounding type combustion chamber
[The picture demonstrating ]
The compounding type combustion chamber is one kind to lie
between ball type oil film and semi-open type combustion chamber
pattern. It has very good combination of space atomization and oil film
evaporation, realizing the mixing of the fuel and air.
The combustion chamber lies in the centre heart of piston, presents
the concave bore of " U " style of calligraphy. The oil injection direction
and the air vortex direction is vertically. There is a very little drift angle
which obeys the air current trend , it makes some fuel distributed for the
oil film along the cliff side of combustion chamber under vortex function;
Another part produces space atomization. The proportion of the two
relates to operating mode of the diesel engine. When the diesel engine is
higher in rotational speed, air current movements are strengthened, the oil
film formation increases, having the characteristics that the oil film is
burnt. While operating or starting at a low speed, the air current is low in
speed,it makes space atomization burn and increase , has the
characteristics of the space burning, thus improves the cold machine to
start performance . In addition, the compounding type combustion system
also can adapt to many kinds of fuel (for example the diesel oil ,
kerosene , petrol , heavy oil can all turn round steadily ), requirement of
fuel system is low grade characteristic.
5. Swirl combustion chamber[The picture demonstrating ]
Swirl type combustion chamber consists of two part swirl chamber
and main combustion chamber. Link to each other through one or several
passways between two parts. The direction of the passway and piston top
slope an angle, and it is tangent with swirl chamber . The volume of swirl
chamber accounts for 60 one 80% the compressing volume entirely. Fuel
injector is installed in swirl chamber, the fuel is sprayed along the vortex
direction. Swirl chamber is usually made into spherically, in the course of
compressing, the air in the cylinder is pressed in the vortex chamber by
the passway, produces strong organized rotation movements. When the
fuel gushes out and enters swirl chamber, stronger vortex was broken up
and taken shape evenly combustible gas mixture, and combustion
happens, it makes the gas pressure and temperature in swirl chamber rise.
While beginning the stroke of expanding, the unburned gas mixture in
swirl chamber and combustible gas mixture are mixed together, gushed
out the main combustion chamber by the passway, mix and burn with the
air in main combustion chamber further.
The characteristic of swirl type combustion chamber is:
(1) it does not have high expectations for fuel system, because it
relies on strong vortex function to take shape and mix air mixture mainly,
so does not need very high pressure of spraying .
(2) diesel engine works steadily. Because the initial combustion
process is going on in swirl chamber , it does not act on piston directly ,
makes the pressure rising rate of main combustion chamber relatively
small.
(3) it can't change sensitivly to the rotational speed of the diesel
engine. It can be strengthened because of the compressing vortex and
rising with the rotational speed, so can still guarantee better quality of
mixing in higher rotational speed, so swirl type combustion chamber is
suitable for the small-scale high speed diesel engine.
The shortcoming of swirl type combustion chamber is: Large in area
to heat dissipation, and swirl chamber keeps in touch with the cooling
water directly, it makes the scattered loss of heat strengthen ; Because
when the gas flows from vortex chamber to main combustion chamber,
throttle losses produced are relatively great, therefore it makes the cold
machine of diesel engine start the difficulty, the fuel consumption is
relatively higher.
6. pre-combustion chamber[The picture demonstrating ]
It is made up of two parts precombustion chamber that installed in
the cylinder main combustion chamber of piston top.There are one or
several bore passages communicating between the two parts. Fuel injector
is installed near precombustion chamber centre line. Pre-combustion
chamber is different from working course of swirl type combustion
chamber, the connection passway of precombustion chamber and inside
space are not tangent , so, the air current will not produce the vortex , but
the strong turbulence emerges , depends on turbulent function,makes
some fuel atomization mix. After some fuel catches fire to burn in
precombustion chamber at first , it makes the pressure and temperature in
precombustion chamber rise rapidly, while gushing out the air mixture
at a high speed mixing in precombustion chamber and entering main
combustion chamber, it causes the strong gas perturbation , makes most
fuel mix burning in main combustion chamber.
The volume of precombustion chamber is relatively small, generally
only accounts for 20% one 40% of total combustion chamber area. At the
same time, the passway area among main combustion chamber is
relatively small, so the difference of pressing between precombustion
chamber and main combustion chamber is relatively great, flow losses are
great too.
Precombustion chamber and swirl chamber,two kinds of combustion
chamber have similar characteristics: Because the passway between
precombustion chamber and main combustion chamber is very small in
area,it has strong throttle function, makes the pressure in main
combustion chamber rise slowly, maximum combustion pressure is
relatively low, the diesel engine works steadily; The requisition for fuel
system is relatively low, we can adopt the single bore axle needle type
fuel injector of simple structure, the requirement of oil injection pressure
is relatively low. The system fuel work is reliable ; The sensitiveness of
changing to the rotational speed of the diesel engine and fuel quality is
relatively small at the same time. The shortcoming of Pre-combustion
chamber is: The specific fuel consumption is high、difficulty starting.
Inject nozzle of precombustion chamber is easy to be damaged and
changed because of it works in high-temperature environment,.