Operating Principle of Diesel Fuel Injection Pump

Fuel injection pump has three kinds of type such as inline type, distributor type, monocoque type. No matter what kind of products it is, the most important part is the pump. The quantity, pressure and time of fuel pump must be very precise and automatically adjust according to the load. Fuel injection pump is a sort of parts that requires fine and complex manufacturing process. Currently general diesel engine fuel injection pumps at home and abroad all are made by a few world professional factory.      

   

Operating Principle

To get to know working principle of pumps with case of in-line fuel injection pump. 

Power source is needed when operating fuel injection pumps. Cam disks at the lower parts of pumps are driven by crankshaft gears of engines. 

 

A plunger is the key component of a fuel injection pump. Taking medical injectors as a metaphor，then the removable plug is similar to the plunger and the cylinder can be called as a plunger sleeve. Assembling a spring inside of the cylinder on one side of plunger, therefore the other side will touch the camshaft. Plungers will move up and down inside of plunger sleeves each time the camshafts rotate for one round. This is the basic motion of fuel injection pump plunger.  

   

Plungers and plunger sleeves are very precise parts. There is a inclined slot on the body of plunger and a suction on the plunger sleeve. The suction is filled with diesel fuel. The diesel fuel flow into the plunger sleeve when the inclined slot of the plunger is on the suction. Thus, the plunger is pushed higher by the camshaft. When it reaches some certain height, the inclined slot will stagger away from the suction and the latter will be closed. In this situation, diesel fuel can not move any more while the plunger rising higher and pressing the diesel fuel. Once the pressure on the fuel reaches a certain range, then the one-way valve will be pushed open. Hence the fuel will flow through fuel injection nozzle and enter into cylinder combustion chamber.

 

One thing should notice is that, diesel engines are all equipped with inlet pipes and return oil pipes. It’s easy to understand the function of a inlet pipe, but what about the oil return pipe? That is because, there is only a part of diesel fuel enter into cylinder in spite of a certain amount of diesel fuel discharged by plungers. The rest is drained out from oil return hole. What’s more, the engine adjust the fuel injection quantity through the regulation of discharged fuel.

 

The plunger will move down after arriving at the topmost point. Then the inclined slot will meet again with the suction and diesel fuel will be sucked into the plunger sleeve. A new cycle begins. Each plunger system of the in-line injection pump correspond to one cylinder. In a in-line injection pump, there are four cylinders which require totally four plunger system. This make the products to be offered at big size. They are usually used in medium size or larger cars. For example, diesel engines of buses and trucks generally use in-line injection pumps. 

 

Fuel injection pumps used for diesel engines of cars and light vehicle are generally distributive type. They are featured with small sizes, light weight, less components and simple structures. This kind of pump uses one or two set(s) of plunger system to press diesel fuel and push them into fuel nozzles. 

 

There are two groups of plungers installed on the impeller. The plungers rotate together with impellers when driven by engines. The convex part of the cam ring presses the plunger and make it play a role of pump to send diesel fuel to oil hole in the middle of impeller. At this time, fuel diesel stay at the entrances of distributors and spray in sequence. 

 

Because the revolutions of two groups of plunger system(or one group of plunger system) are proportional to the increase of the number of cylinder, the injection pump is limited by the number of cylinder and maximum speed of revolution. 

 

With the development of diesel engine technology, now it’s popular with one kind of monomer type fuel injection pump (called monomer pump or pump nozzle). In fact, it combines above mentioned two types of injection pumps into one type. Each cylinder fuel injection is completed by their respective independent injection unit (monomer pump or pump nozzle).