Why are Injectors Often Easy to Break? Just Take off and You'll Know!

From: http://www.sinocmpinjector.com

The fuel injector is the most precise component in an electronically controlled diesel engine. Its role is to spray up to 160 MPa of fuel into the cylinder for combustion. For a diesel engine rating at 1900 revolutions, there are 16 injection processes per second on average, and each injection process is divided into 3-5 small injections such as pre-injection and main injection harsh.

Dismantling Bosch Injector, Exploring Cause of Damage
Injectors have extremely strict requirements for the cleanliness of fuel. Water or impurities above 5 microns can cause damage. Poor quality filters are difficult to intercept the impurities and water in the fuel, causing damage to many of excavator owner's injectors. What the inside of the damaged injector looks like may not be seen by many friends. Today I'll disassembling an injector that has been severely worn, let us check it out.

This is an electronically controlled fuel injector from Bosch in Germany. At present, most of the fuel systems of domestic electronically controlled diesel engines apply this company's products. It's worth a lot, and each one costs more than $150. For a six-cylinder engine, if you replace it all, you will lose about $900.

First remove the solenoid valve on the top of the injector. The role of the solenoid valve is to control the fuel injection. Let the fuel be injected into the cylinder at the correct flow rate and at the correct time.

This part is the valve assembly in the injector. It is one of the most easily worn parts inside the injector.

The two parts in the plate are valve stems. For comparison, we have specially found a new valve stem for comparison. It's a worn valve stem on the left and  a brand new one on the right.

Zooming on the lens, it can be seen from the comparison that the left valve stem has been severely worn, which is almost fatal to the injector.









Needle valve is worn Nozzle becomes larger

Let's look at the bonnet again. The pit on the bonnet is also one of the parts that are prone to wear. There will be a steel ball in the pit. The solenoid valve controls the fuel injection through it. After the inside of the pit is worn, the amount of oil returned to the injector will increase due to the tight closing of the steel ball, which will cause the needle valve to close tightly.

These dimples are very small, and in order to capture the details, I used a Canon Budweiser macro lens. Even so, it is still difficult to see clearly, which is enough to show how precise the machining of the parts inside the injector.

This part is the injector nozzle, and the fuel is injected into the cylinder from its head. In the entire injector, its working environment is the worst because it directly faces the extreme working environment of high temperature and high pressure in the cylinder.

The tip of the needle valve of the nozzle plays a role of sealing the fuel. When fuel injection is not needed, it must be leak-proof. It can be clearly seen from the photo that the tip of the needle valve of this nozzle has been severely worn, and it is likely to cause the injector to drip oil when working. Drip oil from the injector can cause the piston to overheat locally and even cause the piston to perforate.

Finally, let's look at the orifices of the injector nozzles. They are used to inject fuel into the cylinder. They are so small in diameter that they are almost invisible to the naked eye. The diameter of the hole is directly related to the injection amount per unit time. If the fuel contains particulate impurities, it will cause irreparable wear to the injection hole. Over time, the diameter of the nozzle will become larger and larger. As a result of the larger nozzle holes, the amount of oil supplied increases, causing torque to exceed the limit, black smoke, and high fuel consumption.

Obviously, the nozzle hole on the left is significantly larger than the brand new hole on the right. In other words, the nozzle on the left has been severely worn and can no longer be used.

Not damage, no greedy.
The fuel injector is a very precise whole. If any one of the points is out of order, its performance will be greatly reduced. Black smoke, insufficient power, high fuel consumption, and even difficult start-ups will be followed by a series of failures. To repair them, only a very large cost of money and time can be paid.

However, you don't have to worry too much. As long as you insist on using genuine filters and adding high-quality oil, the actual life of the injector is very long, and it can even reach the same life as the entire vehicle.

How to Extend the life Span of the Injector

From:http://www.sinocmpinjector.com

The function of the injector is to spray the fuel into finer mist droplets, and according to the requirements of the form of the combustion chamber, the fuel is dispersed in the combustion chamber and mixed with the compressed air to combust. The quality of the injector's work quality has a great impact on the performance of the diesel engine, so in the use of the diesel engine, we must pay attention to the use and maintenance of the injector.


1 Structural characteristics of the injector

The fuel injector is mainly composed of fuel injector body, needle valve coupler, ejector rod, fuel injector spring, tight cap and pressure regulating screw. The high-pressure fuel sent from the injection pump enters the annular cavity of the injector body and the needle valve coupling. When the pressure reaches 11. 77 MPa (ZS4S1 injector), the needle valve is lifted against the pressure of the spring. At this time, a certain amount of fuel is sprayed into the vortex chamber through a spray hole. After the fuel is injected, the pressure drops, and the needle valve blocks the injection hole again under the action of the spring force. The fuel leaked from the gap between the plunger surface of the needle valve assembly rises from the inside of the casing through the pipe joint bolt and the oil return pipe, and part of it is used as the glow plug winter cold start oil, and most of it flows back to the fuel tank.

2 Inspection and disassembly of injector

When the engine suffers from insufficient power or black smoke, the first thing to think about is whether the injector is not working properly. At this time, the injector can be removed from the engine and tested on the injector test bench. 11. Press the handle of the hand oil pump evenly at a speed of 10 times per minute to check the injection pressure and dripping. At 77 MPa, injection starts. Before this time, there must be no leakage in the fuel injection nozzle. A small amount of moisture is allowed in the injection hole, but there must be no oil dripping. If the oil dripping phenomenon indicates that the conical surface is not well sealed, the fuel injection nozzle should be cleaned or the sealed conical surface should be ground. If the injection pressure does not meet the requirements, you can loosen the protective cap to adjust, and increase the injection pressure by screwing in the pressure regulating screw, otherwise the injection pressure decreases.

When the fuel injection pressure meets the requirements, the hand oil pump handle can be pressed at a speed of 60 to 70 times per minute. Observe the spray condition. The oil mist should be fine and uniform, and there should be no splash of oil droplets visible to the naked eye. The cone angle of the mist beam direction is about 4 °. The fuel should be cut off promptly and the sound is crisp. If it does not meet the requirements, it should be dismantled.

When the injector needs to be disassembled and inspected, the disassembled injector should be cleaned in clean kerosene or diesel oil. Rough and fine wash containers should be separated. Needle valve pairs should be placed in pairs and not messy. The dirt can only be scraped off with wood or copper, and then wiped with a soft cloth. Cotton yarn is prohibited. The cleaned needle valve should have good sliding properties. After wetting the needle valve coupler with light diesel, withdraw the needle valve from the valve body by 1/3 and tilt the needle valve body by 45 °. Under the action, it should fall slowly without jamming. If the conical surface of the needle valve and seat is poorly sealed, it can be ground with a 500 # green chromium oxide fine grinding paste. The ground needle valve parts should be carefully cleaned.

Before assembly, all parts should be carefully cleaned. When assembling the fuel injection nozzle, the pressure regulating spring should be in a relaxed state. When tightening the injector fastening nut, be sure to apply proper force. For a needle valve body with a large outer diameter of 17 mm, the torque should be 58.8 to 78.4 N · m; for a large outer diameter of 22 mm, the torque should be 78.4 to 98 N · m. When replacing the fuel injection nozzle, be sure to pay attention to the model. It should not be mistaken for the same size and can be used. For example, the ZS15S15 injector and the ZS4S1 can be swapped, but not replaced. After the fuel injector is reinstalled, the test adjustment must be performed again on the test bench.

3 Precautions during use

(1) Pay attention to the quality of the product when purchasing the injector needle valve assembly. If the quality of the needle valve assembly is too poor, the needle valve assembly is not tightly sealed, and the diesel leaks. When the cylinder is compressed and doing work, the diesel fuel on the surface of the nozzle will burn, which will cause the needle valve to become stuck.

(2) The fitting accuracy of the injector needle valve assembly is extremely high, and the injection hole diameter is very small. Therefore, clean diesel oil of a prescribed brand must be selected in strict accordance with seasonal changes. During storage and filling, pay attention to cleanliness. Do not mix impurities into the fuel. Before use, it must be precipitated and filtered before being added to the fuel tank. The diesel filter should be maintained on time, and the sedimentary oil in the filter and the fuel tank is often discharged to prevent the intrusion of dust and dirt and aggravate the wear of the needle valve coupler.

(3) Clean the anti-rust oil for the newly replaced needle valve coupler. The new fuel injector fittings should be cooked in diesel at 70 ～ 80 ℃ for 10 minutes, and then the needle valve should be pulled back and forth in the valve body in clean diesel to thoroughly clean the anti-rust oil. If you only wash without boiling, you will not be able to completely clean the rust preventive oil in the injector parts, and it is easy to cause the needle valve to deposit carbon, cement or even get stuck during work. In addition, when cleaning the needle valve coupling, do not touch it with other hard objects to prevent scratching the needle valve guide surface.

(4) Be careful not to overheat the diesel engine when using it. When the temperature of the diesel engine is too high, the fuel injection nozzle will be deformed by heat and work abnormally. Carbon deposits in the injection holes and the shaft needle will easily cause the needle valve to overheat and die.

(5) Check the fuel injection pressure. Modern diesel engines require different fuel injection pressures due to different combustion chamber structures. The fuel injection pressure of 295 diesel engines is 11. 77 MPa, the fuel injection pressure of the injector is too high or too low to harm the diesel engine. In the initial stage of use of the injector, due to the wear of the parts and the elasticity of the pressure spring, the injection pressure of the injector changes greatly. Excessive fuel injection pressure will increase the amount of dripping and cause carbon deposits. It will also cause the needle valve to get stuck in the closed position of the needle valve body, causing individual cylinders to malfunction or not work. The fuel injection pressure is too high, and the fuel atomization is finer, but the fuel injection distance is too large, causing part of the fuel to be injected into the combustion chamber wall, which is poorly mixed with the air, so that it cannot be completely burned, and also makes the cylinder knock when the diesel engine is running. The fuel injection pressure is too low, the fuel is poorly atomized, the oil mist particles become coarse, and the range is shortened. It cannot penetrate the entire combustion chamber, making the fuel and air poorly mixed, resulting in incomplete combustion of the fuel, exhaust smoke, and increased carbon deposits in the cylinder. Diesel engines are not easy to start. Therefore, in use, the fuel injection pressure and atomization quality of the injector should be checked and adjusted in time. If necessary, it should be adjusted on the injector tester to make the fuel injection pressure and atomization cone angle meet the requirements of the original machine.

Composition, Working Process, Application and Installation of Diesel Fuel Injectors

From: http://www.sinocmpinjector.com

The fuel injector is one of the precision components of the diesel engine. Its function is to inject the high-pressure fuel supplied by the fuel injection pump directly into the combustion chamber in the form of a mist and reasonably distribute it to form a combustible mixture. The correct use and maintenance of the fuel injector has a great impact on the dynamic performance and economic performance of the diesel engine, especially for the diesel engine used in winter, the use of the fuel injector is even higher. Let ’s talk about how to use and maintain the injector with 195 diesel engine as an example.

1 Understand the composition and working process of the injector
The injectors for medium and small power diesel engines are closed injectors. When the closed fuel injector is not injecting fuel, the fuel injection hole is closed by a spring-tightened needle valve, which separates the combustion chamber from the fuel chamber of the fuel injector. Only when the diesel pressure in the oil chamber overcomes the spring force of the injector spring can the needle valve be opened and the diesel can be injected. The injector consists of a needle valve, a needle valve body, an injector body, an injector spring, an injector pressure adjustment screw, a tappet, a protective cap, and a tight cap (nut).

The needle valve and needle valve body are precision parts that have undergone optional research and development. 0.0015 ~0. 0025 mm. After the needle valve sealing cone surface is ground with the needle valve body, a sealing ring line is formed, and its width is not greater than 3 mm. The pressure adjusting (tightening) screw is used to adjust the pressing force of the spring, thereby adjusting the injection pressure of the injector.

Fuel injection pressure of injector: 480G, 485Q is 13. 2 ± 5 MPa, 290QN is 13. 7 MPa, 390Q is 11. 76 MPa, 195 is 17. 2 ± 0. 5 MPa. During work, the pressure regulating screw (wire) is locked by the protective cap. The diameter of the injection hole on the end face of the needle valve body is 1 ~3 mm, and the head of the needle valve is inserted into the injection hole of the needle valve body, between them, with 0.01 ~ 0. 02 mm circular gap. When the needle valve is opened, diesel is sprayed from the annular gap.

2 Notes for use
(1) Use diesel engines reasonably and select diesel according to the season. The precision of the injector needle valve coupler is extremely high, and the injection hole diameter is very small. Therefore, the clean diesel oil of the specified brand must be selected in strict accordance with the seasonal changes, otherwise the injector will not work properly.

(2) Ensure that the working temperature of the diesel engine is normal. To ensure this, it is necessary to calibrate the fuel supply time and the gas distribution phase, and to ensure that the diesel engine is not overloaded for a long time. In addition, it is necessary to ensure that the technical status of the cooling system is normal and the water temperature is appropriate (maintained between 80 ° C and 90 ° C). When repairing the diesel engine, carefully remove the carbon deposits around the combustion chamber, intake and exhaust valves, pistons, cylinder liners, exhaust pipes and fuel nozzles, and decide to repair or replace them according to their technical status. Otherwise, excessive carbon deposits in the above areas will cause poor heat dissipation of the engine, poor exhaust, and excessive local temperature, which will burn the injector nozzles.

(3) Before using the new injector, the rust-proof oil must be removed. The new injector parts are coated with rust preventive oil. Because the anti-rust oil has a large viscosity, it is not easy to be dissolved by diesel oil at normal temperature. If it is directly installed and used without cleaning, it will affect the atomization performance of the fuel injection, and the needle valve is easily stuck.

(4) When starting the diesel engine in winter, do not supply oil when the pressure reducing lever is in the preheating position. When the diesel engine is working and the black smoke continues to be interrupted, it is necessary to find out the nozzles with poor spraying in time. The injectors for single-cylinder diesel engines can only be checked on the injector tester. The "cylinder" method determines which cylinder the fault is in.

(5) Pay attention to removing carbon deposits. Because diesel and air are burned in the cylinder, some diesel will not burn completely and form carbon deposits, which directly affects the diesel engine's heat dissipation. When the injector is used for 1 to 2 months, it should be removed, cleaned in diesel oil, and the carbon deposits on the outside of the compression nut and needle valve body should be scraped off with an old saw blade. In addition, use a thin steel wire brush to clean the carbon deposits around the injection holes and the needles, and remove the carbon deposits from the copper gasket under the tight cap of the injector and the impurities and carbon deposits in the cylinder head seat holes.

3 Technical points of injector installation
Matters needing attention in the installation of fuel injectors:
(1) Check all parts of fuel injectors thoroughly.

(2) Check if the step of the nozzle's fastening nut has a slip angle. If there is a slip angle on the step, the compression nut will not work, causing the needle valve to become stuck and unable to move. Therefore, when changing to a new fuel injection nozzle, the condition of the pressure cap must be checked. The pressure cap that has been used for a long time must be replaced. When installing the pressure cap, the tightening torque should be appropriate, which is generally 60 to 80 N · m. Do not use excessive force, otherwise the injector will be easily damaged. When you continue to use the old pressure cap, you must carefully remove the carbon deposits in its inner cavity, otherwise, it will easily deform the injection nozzle body, resulting in inflexible needle valve movement and affecting the spray quality.

(3) For injectors that have been used for a long time, the needle valve lift is increased due to the long-term impact wear of the nozzle needle tail valve shoulder on the end face of the injector body (the normal value is 0. 35 ~ 0.45 mm) and affect the fuel injection. At this time, grinding can be used to eliminate wear marks. When grinding, the contact surface of the injector body is ground on the flat glass with a fine grinding paste, and the center line of the injector body should be perpendicular to the plane of the flat glass. In addition, check the small steel ball in the lower end of the ejector. If it is lost, reinstall a steel ball with a diameter of 1 mm. At the same time, when assembling the fuel injector, the pressure regulating spring should be relaxed to a free state, so as not to press the needle valve in advance before the fuel injector is installed, so that the incorrect installation will affect the work.

(4) During assembly, the injector cap tightly presses the upper end surface of the needle valve body and the lower end surface of the injector body through the support shoulder. The end of the needle valve is in the shape of an inverted cone pin. The inverted cone pin is inserted into the injection hole of the needle valve body to form an inverted cone annular gap. When the needle valve is raised for injection, a positive cone mist shape can be formed. Oil bundles, greatly improving spray quality.

(5) During installation, in order to align the oil inlet of the injector with the high-pressure oil pipe nut joint, the high-pressure oil pipe nut joint and the oil inlet of the injector should be bolted together, and then evenly tighten the spray 2 to 3 times Fix the oiler bolts and tighten the high-pressure oil pipe nut joint.

(6) The gasket of the fuel injector must not be missed. The purpose of the sealing gasket is not only to prevent air leakage, but also to provide a sealing function. At the same time, it is also to ensure that the injector has an optimal position, so that the diesel engine can obtain the best economy and power. If the sealing gasket is not installed properly, the joint between the injector and the injector seat hole will not seal properly and cause air leakage. If there is air leakage, the injector should be removed to check whether the gasket is not installed. Do not blindly tighten the injector nut. If there is no gasket or gasket in the seat hole due to long-term use, it should be replaced or replaced. A qualified seal. Seal ring specifications have strict requirements. If the gasket is too thick or too thin, it will destroy the optimal working position and performance of the injector.

Introduction of Short-term Precise Control Function (CVO) of High-pressure Injector

From: http://www.sinocmpinjector.com
CVO Function to Start the Engine

With the increasing shortage of energy in various countries, major OEMs have chosen to increase system injection pressure as one of the technical solutions to improve GDI engine emissions. High rail pressure can fully atomize the fuel, and with proper airflow movement, the quality of the mixture can be greatly improved. A more homogeneous mixture can make the combustion process more complete and thorough, and the emissions will be reduced. In addition, advanced fuel injection strategies are more inclined to use multiple injections at large loads and some special conditions (such as catalyst heating), and also use the highest system injection pressure at part load. These technological trends require that injectors work more in the small pulse width area.

Picture 1. Needle valve lift curve in the small
 pulse width area of the injector

However, for all high-pressure injectors of the solenoid valve type, the injection accuracy with a small pulse width is difficult to guarantee. This is mainly because when the pulse width is small, the needle valve is not fully opened, and the fuel injection amount is very sensitive to the lift of the needle valve. Small          changes in lift may cause large changes in the fuel injection amount. Figure 1 is the actual needle valve lift curve of a certain batch of high-pressure solenoid valve injectors (same model) working in a small pulse width region. It can be seen from the figure that under the same excitation pulse width, There is also a significant deviation in the needle valve movement of batch injectors, and these differences will inevitably result in different injection quantities.

Picture 2. CVO control effect

CVO Improves Injection Accuracy of Injectors

In order to improve the injection precision of the small pulse width area of the high-pressure injector, Bosch has developed the short-term precise control function of the injector. For a certain injector, the fuel injection quantity corresponds to the needle valve lift curve. The CVO function is to control the fuel injection quantity by adjusting the needle valve lift to the target position. The correspondence between the fuel injection amount and the needle valve lift was obtained from the CVO system test bench. Figure 2 shows the comparison effect with and without CVO (CVO3 is applicable to the 350bar system). It can be seen from the figure that the CVO function can significantly improve the injection accuracy of the injector in the small pulse width area (ballistic area, transition area), Improved injection accuracy for large pulse width areas.

Impact of CVO on Engine Performance

For engines that have integrated the CVO function, because the injection accuracy can be guaranteed, the calibration strategy does not need to deliberately avoid small pulse width areas, which provides the possibility for the implementation of a more effective calibration idea. The following figure shows the comparison results of the emissions of an engine with or without CVO.

Picture 3. Comparison of the presence and absence of
CVO emissions for an engine under different operating
conditions

As can be seen from Figure 3, for the engine, without changing the calibration strategy, due to the reliable fuel injection accuracy, the injection dispersion of each cylinder under the heating condition of the catalyst becomes smaller, and the combustion stability is significantly enhanced. The PN and HC emissions have dropped significantly. Under partial load conditions, the original two injections at 120 bar can now achieve three injections at 200 bar. The fuel atomization is more complete and the wet wall effect is reduced. Under the premise of ensuring the same gaseous emissions, PN emissions are effectively reduced. Under certain WLTC acceleration conditions, the CVO function can ensure the accuracy of each injection of multiple injections, the wet wall effect is reduced, and PN and HC are reduced to a certain extent.

Although the above shows that engine emissions with integrated CVO function will be improved, the CVO function itself is not a function for emissions. The development of CVO is only to improve the injection accuracy. The improvement of injection accuracy can make more effective and advanced calibration Strategies and ideas were realized, which in turn led to improvements in emissions. CVO escorts development of gasoline engine technology.

With stricter regulations on emissions intensity in various countries, CVO has become the main technical method for GDI gasoline engines equipped with 350bar systems to solve the problem of fuel injection accuracy. Facing more stringent regulatory requirements in the future, the next-generation GDI gasoline engine is likely to develop in the direction of higher system pressure, more frequent, and more complex fuel injection strategies. In this technology trend, CVO functions will become increasingly important.

Picture 4. Schematic diagram of the
CVO system test bench

In order to better serve foreign customers, United Electronics has established a CVO system test bench (a schematic diagram of the bench structure is shown in Figure 4). This test bench is a reliable tool for obtaining the true characteristics of the injector and the basic calibration data of the CVO. Must go through. With the use of the test bench, United Electronics has now built a comprehensive CVO working capability including systems and software and hardware, which will greatly improve the efficiency of foreign project testing and save development time and costs.