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.