Construction of Hole Type Fuel Injector for Diesel Generator Set Part 2

This article continues to introduce the working principle and structure of the hole type fuel injector for diesel generator users.

High pressure fuel enters the annular groove at the upper end of the needle valve body through the oil passage in the filter element and injector body from the inlet pipe joint. This groove is connected to the annular space at the lower part of the needle valve body through two inclined holes. The high-pressure diesel flowing through the lower cavity exerts an upward axial thrust on the conical surface of the needle valve. When this force overcomes the frictional force between the pressure regulating spring and the needle valve body (which is very small), the needle valve moves upward and opens the injection hole [as shown in Figure 5-2 (b)]. Therefore, high-pressure fuel is sprayed into the combustion chamber from the injection hole at the lower end of the needle valve body. The lift of the needle valve is limited by the lower end face of the injector body, which is beneficial for quickly cutting off fuel. When the fuel injection pump stops supplying fuel, due to the sharp drop in oil pressure in the high-pressure fuel pipe, the needle valve quickly closes the injection hole and stops supplying fuel under the action of the pressure regulating spring.

During the operation of the fuel injector, a small amount of fuel will leak out from the gap between the needle valve and the needle valve body. This part of the fuel can lubricate the needle valve and rise along the gap around the tappet, entering the return pipe through the hole on the return pipe bolt 1 and flowing back into the fuel tank. To prevent small debris from blocking the spray hole, a slotted filter element is installed on the high-pressure oil pipe joint.

The fuel injector is fixed in the injector seat hole on the cylinder head with two fixing screws and sealed with a copper cone to prevent air leakage. During installation, the head of the fuel injector should protrude a certain distance from the plane of the cylinder block (specific regulations apply to various machines). For this purpose, shims can be added between the copper cone and the fuel injector, or the copper cone can be replaced to adjust. 

The domestically produced 135 series diesel engines all use orifice injectors. Its characteristics are: small nozzle diameter, good atomization quality, but high precision requirements, which brings certain difficulties to small hole processing, and the nozzle is easily blocked by carbon deposits during use.

The pressure regulating spring installed on the upper part of the fuel injector body presses the needle valve tightly against the sealing cone surface of the needle valve body through the tappet, causing the injection hole to close. Only when the oil pressure rises enough to overcome the elastic force of the pressure regulating spring, can the needle valve rise and start fuel injection. The injection pressure at the beginning of injection depends on the elasticity of the pressure regulating spring, which can be adjusted with a pressure regulating screw.

Dingbo Power was founded in 1974 and is one of the earliest manufacturers of generators and diesel generator sets in China. If you want get more information, please feel free to send email to sales@dieselgeneratortech.com we will pay highly attention on your question.