Nozzle pump: structure and principle of operation

Pump-nozzle is an injection system, designed to supply the fuel mixture in diesel engines. The use of such system gives an opportunity to increase engine power, reduce fuel consumption and toxicity, noise level.

In this type of injection system a single central device, the injection pump, is responsible for fuel supply and distribution. Each cylinder is equipped with its own injector.

The system is driven by the camshaft, which is fitted with special cams that act on the pump injector via the rocker arm to make it work. If this system as well as others are faulty, consider contacting an auto recycling company. It will most likely be more profitable than wasting money, time, and nerves on repairs:

How the nozzle pump system is constructed

The pump-injector system consists of such elements as: plunger, shut-off piston, pilot and check valves, spray needle.

The plunger is designed to create working pressure inside the nozzle. The plunger’s forward movement is provided by the cams of the camshaft, and the return movement is provided by the spring.

The main function of the pilot valve is fuel injection, and more specifically injection control. Two types of valves can be used in such systems – electromagnetic and piezoelectric.

The valve based on the piezoelectric element is more advanced due to its high response time. The main design element of the pilot valve is its needle.

The atomizer spring is necessary to ensure that the atomizer needle fits securely in the seat. The spring force is supplemented by the fuel pressure force, all accomplished by a shutoff piston mounted on one side of the spring and a check valve mounted on the opposite side of the spring.

The atomizer needle ensures direct injection of diesel fuel into the engine combustion chamber.

The nozzle valves are controlled by the engine control unit, which controls the operation of the nozzle valve on the basis of the sensor data.

How the pump injector system works

Efficient reception and distribution of fuel in the pump-injector system takes place in three stages – pre-injection, main injection and supplementary injection.


The pre-injection stage is designed to ensure smooth combustion of the fuel during the main injection stage. The main injection stage, in turn, ensures a smooth supply of fuel mixture in all operating modes of the engine. 

So, at the preliminary stage of fuel supply the pump injector works according to the following scheme. The cam of the camshaft transmits mechanical force to the rocker arm, which lowers the plunger down.

The fuel mixture begins to flow through the channels located in the injector housing. Then the valve closes, temporarily stopping the fuel supply. This creates a high pressure of TC, reaching 13 MPa.

At this level of pressure the needle, overcoming the force exerted on it by the spring, performs pre-injection of the combustible mixture.

The pre-injection stage is completed by opening the inlet valve. The fuel enters the line, at the same time its working pressure is reduced. At this stage one or two injections of FC can be made, depending on the mode of operation of the diesel.

Main injection

The start of the main injection phase is followed by the subsequent lowering of the plunger. After the valve is closed, the FC pressure continues to build up and reaches 30 MPa. At this pressure, the needle is lifted and the main injection occurs.

The high pressure provides significant fuel compression, as a result of which more fuel enters the combustion chamber. The largest amount of combustible mixture is injected at the maximum possible pressure of 220 MPa, thus achieving maximum engine power.

The end of the main injection stage is similar to the previous stage after the inlet valve is opened. This is accompanied by a drop in fuel pressure and lowering of the spray needle.

Supplementary injection

The final stage is supplementary injection, which is used to clean the particulate filter of soot, soot and contaminants. The supplementary fuel injection is performed by lowering the plunger in the same pattern as the main injection. At this stage, as a rule, two injections of diesel fuel are carried out.

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