Spektoruk. S.A
Kostanay
State University, Kazakhstan
Technical
service. The
power supply system of diesel engines
9% of
malfunctions of cars with diesel engines have power supply system. Typical
defects include: breach of impermeability and fuel leak, especially in high
pressure fuel line; air and especially fuel filters pollution; entering of oil
in tube; wear and misalignment of plunger pairs of high-pressure pump;
impermeability loss of the nozzles and the pressure decreasing of initial
needle lifting; wear outlets of injector, and their coking and clogging. These
malfunctions lead to start and supply change of fuel injection, uneven
operation of the fuel pump to the angle and quantity of supplied fuel,
deterioration of the atomization of fuel. What primarily causes an increase in
opacity of the exhaust gases and in minor degree leads to increasing of fuel
consumption and reducing engine power (3- 5%).
Control of power supply system
includes: check of system tightness and condition of fuel and air filters;
check of fuel pump; high-pressure pump and injectors. Leakage of the system is
under high pressure, is checked visually by dripping of fuel with working
engine.
Leakage from inlet part (from the
tank to transfer pump), leading to air leaks and malfunction of fuel pumping
equipment is checked by a special device. Part of the highway, which is under low pressure, can be checked for
leaks when engine is off by pressure test of manual fuel pump.
Condition
of dry air filters, installed on all of the latest car models, is checked by
vacuum behind filter using a water piezometer (should be less than 700 mm water
column).
Fuel filter condition can be checked
in the first approximation while idling engine work by pressure behind filter
part (allowed not less than 150 kPa), and more specifically by differential
pressure before and behind filter (20 kPa). Lower pressure also indicates
malfunction of transfer pump, which after a partition in a shop when tested on
a special stand should provide (at 1050 rev / min) not less than 50 kPa, the
pressure of not less than 400kPa and feeding at least 25 cm by 100 working
strokes (given the standards - for eight-cylinder engines MAZ and KamAZ).
Control of high-pressure pump and injectors on the vehicle is carried out in
excess of the engine regulations on smoke, and in aim to identify faults and
optimize the impact of technical maintenance and repair of the fuel equipment.
The most widely used method based on the analysis of changes in pressure,
attached using a special sensor that establishes at the nozzle of injector.
Diagnosing by this method is carried out by simplified analog devices with a
one built-in sensors and stroboscope (type K261), provides: a certain speed of
the crankshaft of the engine; setting of fuel injection timing; possibility of
verifying quality of speed controller, and an automatic clutch of fuel
injection timing, and pressure start of injection for each cylinder (the
interchange of the sensor). Less common are diesel-testers with oscilloscope
and simultaneous installation of sensors on all the nozzles because of
complexities of installing and removing sensors. In the absence of diagnostic tools for reducing opacity is necessary to
carry out maintenance work, mainly on injectors and high-pressure pump by their
removal and subsequent tests in a workshop.
The
nozzle is checked: for leaks at a pressure of 30 MPa, while pressure drop time
of 28 to 23 MPa should be not less than 8; at the beginning of recovery
(injection pressure), which shall be (16.5 ± 0.5) MPa for engines KamAZ for the
quality of the spray, which must be clear, mist and even the cross-section of
the cone, have a typical "metallic" sound. Pressure of
injection nozzle is adjusted by changing the thickness of shims mounted at the
spring or through the adjusting nut. The most difficult and responsible are the
cycle checking and adjustment of the high pressure pump to filing start, its
regularity and proper fuel supply carried out on special stands. Inaccuracy of
interval between the beginning of each fuel supply relative to the first
section does not exceed 20, and the unevenness at installation of rail in
position of maximum supply - not more than 5%. On the stand are governed
launcher and maximum cyclic fuel supply, as well as work fuel regulator (off
the fuel supply when the engine is stopped, the automatic fuel shut off in
fixing a maximum engine speed of the engine and start the frequency of the
automatic controller). Mounting of high pressure pump to the engine is carried
out using momentoskope - glass tube with an inner diameter of 1.5 - 2.0 mm
installed at the outlet choke 1st or previous order of pump section, at the
time of fuel appearance in which clutch are fixed that the angle is 16-19 to
VMT1- cylinder. Successful completion of
the works provides (with proper adjustment valves and a good engine
compression) minimum and maximum smoke opacity and maximum efficiency of the
diesel engine.
Serving
of HPFP (high pressure fuel pump)
It was found that the cause of
excessive smoke exhausted gas is insufficient accuracy of adjustment of high
pressure fuel pump at repair, and significant deviations in magnitude bandwidth
workers (installed on diesel) and fuel injectors. Consequently, there is a
particularly large unevenness at largest fuel supply cycle between the
individual cylinders of a diesel engine, which leads to an increase in specific
fuel consumption (fuel efficiency degradation). The main bit of errors in
adjustment of HPFP and nozzles on the motorless stand to make a nozzle are
caused by nozzles with high-pressure fuel pipes, to fill this gap in the
international practice of standardization used DTA (system control samples).
This system reduces errors in adjustment of fuel equipment. However, the use of
stand`s standards required to make adjustments to the values of cycle feeds of
high pressure fuel pumps with the completeness stand`s standards. In this
paper, the technique of adjusting pump and adjusting the parameters of the
table formed by adjusting the parameters of the injection pump. Only by
fine-fixed HPFP and regulator can achieve the best balance of power and fuel
consumption of a diesel engine in compliance with increasingly stringent
regulations for exhaust emission levels. Standard ISO sets the general
conditions for testing HPFP and characteristics of the test stand, showing
especially high demands on the rigidity and uniformity of the drive. Increasing
power consumption of HPFP due to increase of maximum pump pressure increases
the demands on a test bench. High power electric drive, a massive flywheel and
precise speed control ensures good stability test parameters.
Literature:
1. Shestopalov.S The device, service
and repair of cars. - Moscow, 2009
2. Car repair. National
characteristics of garage repair: V. Trifonov - St. Petersburg, Phoenix,
2008-416.
3. Repair of the car. Practical
course: Vladimir Trifonov - St. Petersburg, Phoenix, 2009-with 576p.