What is the static adjustment of the diesel engine and how is it carried out?
11 Apr '19, 05:54
Static adjustment is a setup procedure which carried out on a cold idle diesel engine.
Prior to performing the static adjustment, check the standards and tolerances for their deviations in the maker's manual.
Static adjustment includes the following operations:
1) checking and setting the height of the compression chamber in the cylinders;
2) determination of the opening and closing phases of valves;
3) installation of camshaft drive gears and gas distribution mechanism;
4) check and adjustment of thermal gaps;
5) checking and adjusting fuel equipment:
- check and adjust the start of fuel injection;
- check and set the "zero" fuel rack position;
- checking the uniformity of fuel supply to the cylinders and their alignment;
- check the nozzles for tightness and quality of atomization;
- installation and a preliminary check of the shaft speed governor;
- installation and adjustment of the air distributor.
The crucial stage of static adjustment is the selection of sets of precision pairs of high-pressure fuel pumps and injectors, adjustment and installation of them on diesel. The quality of injector nozzles and plunger-barrel pairs of high-pressure fuel pumps is primarily characterized by their hydraulic tightness. The latter is determined by the time of pressure drop within the limits specified by the standard.
It is recommended to install plunger-barrel pairs on diesel, in which the ratio of the maximum pressure drop to the minimum time does not exceed 1.3-1.4. This requirement must also be fulfilled for injector nozzles.
Effective flow sections of nozzles are characterized by the efflux of a certain dose of fuel at constant pressure (3-5 MPa). In a set of nozzles, it is advisable to ensure that the ratio of the maximum expiration time to the minimum is not more than 1.06.
It should be noted that with a complete replacement of high-quality manufactured nozzles and plunger-barrel pairs not only accelerates and improves the achievable quality of diesel adjustment but also provides real fuel economy.
From the experience, nozzles failures account for 95% of injector failures as they have especially low durability.
One of the important factors determining the quality and reliability of the nozzles are the deformations of its body at the time of assembly and installation of the nozzle. In particular, deformations lead to a breakdown of the tightness of the locking cone and to the freezing of the needle.
The high-pressure fuel pumps are checked for ease of movement of the rail in the extreme lower and upper plunger positions. Fuel rack jamming is not allowed. The cause of the seizure is often excessive tightening of the push-nuts securing the plunger bushings.
Zero flow ensures that all high-pressure pumps shut off simultaneously when the diesel control knob is set to the stop position. For a reliable stop of a diesel engine, the manual pump control drive should have some free play in the direction of decreasing feed, which makes it possible to turn off the pumps not at the zero position of the lever, but somewhat earlier. This ensures reliable stopping of the diesel after leveling the fuel intake during dynamic adjustment. To install a zero fuel supply, it is necessary to properly connect the plungers to the regulator rail.
Checking of the fuel injection start is usually made by noticing the beginning of the fuel movement in a transparent tube of small diameter, which is installed on the pump discharge connection and due to the small tube diameter (1-2 mm) quickly reacts to the beginning of the fuel supply when the diesel shaft is turned with opened indicator cranes).
The start of injection for all cylinders is regulated by means of a coupling connecting the high-pressure fuel pump to the diesel crankshaft. In individual cylinders, the start of injection can be changed using the pusher bolt of the high-pressure fuel pump. If the pusher bolt is screwed in, the angular interval between the beginning of the raising of the pusher and the beginning of the discharge increases (the feed advance angle decreases). If the pusher bolt is turned out, the angular interval between the beginning of the raising of the pusher and the beginning of the discharge is reduced (the feed advance angle increases). If the pusher's bolt is turned out very strongly, then with the arrival of the plunger at TDC it will hit the body of the discharge valve, as a result of which the pump will fail.
It must be borne in mind that changing the fuel advance timing with fine adjustment is permissible in strictly limited limits.
It is possible to measure the uniformity of cyclic fuel supply on an idle diesel engine as follows. A tube is installed on the pump fitting, the end of which is lowered into the tank. After removing air from the tube, several dozen full feeds are made. Measuring the amount of fuel in the tank, determine the size of one cycle supply. Repeating this operation on other pumps, assess the uniformity of cyclic fuel supply through the cylinders. Irregularity should not exceed 5%, and more strict alignment of innings is unjustified, since it does not guarantee the required unevenness of the actual cycle innings for a running diesel engine.
The final adjustment of the advance angle of fuel supply and cyclic fuel supply is made according to the results of measurements on a running diesel engine.
11 Apr '19, 06:18