The Bosch
common rail injector is the precise coupling of the diesel engine
system. The working condition of the injector directly affects the power,
economy and reliability of the diesel engine. From the working principle of the
injector, it is not difficult to see that the injector needs to have a certain
injection pressure, injection process and appropriate cone angle. In addition,
the injector should be able to quickly cut off the fuel supply when it needs to
stop the injection. No oil dripping.
In the working process of the injector,
there will be a variety of faults and phenomena, so what are the common
troubleshooting ideas and methods of the injector?
1. The Orifice is Blocked.
Because solid impurity particles are mixed
in the fuel, or carbon deposits are generated due to poor combustion, the
working time will be a little longer, and the injection hole will be semi
blocked. Once the injection hole is blocked, the fuel supply pressure of the
injection pump will rise with a knocking sound.
Prevention methods: on the one hand, the
fuel entering the injector shall be strictly filtered; on the other hand, the
combustion shall be improved to prevent the injection hole from being blocked
due to excessive carbon deposition.
2. Spray Nozzle Dripping
When the injector is
working, the sealing cone of the needle valve body will be frequently impacted
by the needle valve. In addition, the high-pressure fuel is continuously
injected from this place, the cone will gradually appear wear or spots, which
will cause the injector to drip oil. When the temperature of diesel engine is
low, the exhaust pipe emits white smoke, and when the temperature of diesel
engine rises, it becomes black smoke. The exhaust pipe will emit irregular
shooting sound. At this time, if the oil supply to the cylinder is stopped, the
smoke exhaust and firing sound will disappear.
Troubleshooting: remove the nozzle, check
whether the movement of the needle valve is flexible and whether the sealing of
the seat surface is good, and then carefully clean and research or replace the
new nozzle coupling.
3. Nozzle Corrosion and End Carbon
Deposition
The corrosion of spray nozzle is caused by
the cold corrosion caused by sulfide in exhaust gas. The corrosion of spray
nozzle is caused by the cold metal surface, so it is subject to chemical
corrosion. All nozzles found to be corroded shall be replaced.
Carbon deposition at the end of the nozzle
is easy to form when the diesel engine is running at idle speed or under low
load. When the load of the diesel engine increases, the carbon slag on the fuel
injector will be burned when the fuel is injected. The carbon deposition at the
end has a certain impact on fuel atomization and fuel distribution uniformity
during combustion, resulting in incomplete combustion, power reduction of
diesel engine, post combustion and various mechanical failures.
Troubleshooting: remove the nozzle and
remove the carbon deposit on the nozzle by mechanical or weak corrosion. It is
very important to remove the carbon deposit inside the spray hole, but the
sealing seat surface must be protected from damage. In order to prevent the steel
wire for cleaning from breaking in the hole, the steel wire must be installed
in the chuck, and the length of the steel wire exposed to the spray hole shall
not exceed 2 mm.
4. Needle Valve Stuck
The water or acid substance in the diesel
oil will rust the needle valve and get stuck. After the sealing cone of the
needle valve is damaged, the combustible gas in the cylinder will also rush
into the mating surface to form carbon deposits, which will cause the needle
valve to bite, and the injector will lose the injection effect, causing the
cylinder to stop working.
Troubleshooting: remove the fuel injector,
take out the fuel injector coupling, and use tools to pull out the needle
valve. If it is not easy to pull out, put the fuel injector coupling into the
diesel oil and heat it for about 20 minutes before taking it out. When taking
out the needle valve, the tail is padded with copper skin, and the tail is
clamped with pliers and pulled out while rotating. Pull it out and put it into
the cleaning solution for cleaning, and then refill it. If it is the invasion
of dirt, it will be flexible after cleaning. If it is due to the geometric
shape of the coupling parts that affects the flexibility, a small amount of
grinding paste should be added for light grinding, and cleaning should be
carried out after grinding.
5. Poor Atomization of Fuel
Injector
When the injection pressure is too low,
there is carbon deposit in the nozzle wear, the end face of the spring wear or
the spring force drops, it will cause the injector to open in advance, delay to
close, and form the phenomenon of poor atomization. The diesel engine power
drops, the exhaust gas emits black smoke, and the machine operation sound is
abnormal. In addition, because the diesel droplets with too large particle size
can’t be fully burned, they will flow into the oil pan along the cylinder wall,
which will increase the oil level, reduce the viscosity and worsen the
lubrication, and may also cause the accident of tile burning and cylinder
pulling. At this time, the fuel injector shall be disassembled for cleaning,
maintenance and re commissioning.
6. Broken Spring
In addition to the permanent deformation
caused by the decrease of the rigidity of the pressure regulating spring of the
injector, the fracture of the spring is also frequent, which has become one of
the weak links of the injector. It is mainly caused by the poor fatigue
strength of spring steel under high temperature, high load and high frequency working
conditions.
Solution: improve the fatigue strength,
select high-quality heat and fatigue resistant materials, and carry out surface
treatment and shot peening to enhance the fatigue strength. In order to make
the pressure regulating spring work safely and reliably, reduce the dynamic
load of the spring, the fuel injector can be designed as the spring can be
immersed in the diesel oil in the fuel injector body. So that when the fuel
injector is working, the working ring of the spring can produce hydraulic
“buffer” and some lubrication effects, so as to prevent the spring from
breaking due to the formation of pitting surface on the contact surface.
7. The End Face of Needle Valve Body is
Worn.
The end face of the needle valve body is
impacted by the frequent reciprocating motion of the needle valve, which will
gradually form a pit over a long period of time, thus increasing the lift of
the needle valve and affecting the normal operation of the injector. The needle
valve body can be clamped on the grinder to grind the end surface, and then the
fine grinding paste can be used to grind the glass plate.
8. The Guide Surface of Needle Valve and
Needle Valve Hole is Worn.
The frequent reciprocating movement of the
needle valve in the needle valve hole, together with the invasion of impurities
in diesel oil, will make the guide surface of the needle valve hole wear
gradually, so the gap increases or there are scratch marks, resulting in the
increase of the internal leakage of the injector, the decrease of the pressure,
the decrease of the injection quantity, the delay of the injection time, and
the difficulty of starting the diesel engine. When the injection time is
delayed too much, the diesel engine can’t even run. At this time, the needle
valve coupling should be replaced.
9. The Joint Hole Between the Injector
and the Cylinder Head Ieaks and leaks Oil.
When the fuel
injector is installed in the cylinder head, the carbon deposit in the
installation hole shall be carefully removed, and the copper gasket must be
flat and shall not be replaced by asbestos plate or other materials to prevent
poor heat dissipation or failure to play a sealing role. If the copper washer
is made by ourselves, it must be processed with red copper according to the
specified thickness to ensure that the distance between the injector and the
cylinder head plane meets the technical requirements. In addition, when the
pressure plate of the fuel injector is installed firmly, unilateral bias shall
be avoided, and it shall be tightened evenly according to the specified torque,
otherwise the head of the fuel injector will suffer from gas leakage and oil
channeling due to deformation and deflection.
10. The Fuel Injector Return Pipe is
Damaged.
When the wear of needle valve couple is
serious or the fit between needle valve body and injector shell is not tight
enough, the return oil quantity of injector increases obviously, some of which
can reach 0.1-0.3kg/h. If the oil return pipe is damaged or leaked, the oil
return will be lost, resulting in waste. Therefore, the oil return pipe must be
intact and sealed so that the oil can flow into the oil tank smoothly. If the
return pipe is connected to the diesel filter, a check valve shall be set at
its terminal to prevent the diesel in the filter from flowing back into the
injector.
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