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Technology Info >> Four type of Diesel fuel injection system

1.       In-line fuel injection pump system

The volume is large, each cylinder corresponds to one sub-pump, and the sub-pump is connected with the corresponding cylinder through a high-pressure oil pipe, and the injector uses the pressure of the diesel itself to passively inject oil. The system mostly uses mechanical centrifugal governor, which has good reliability but poor precision. The driver controls the preload of the governor spring through the throttle, and the centrifugal force generated by the flyweight centrifugal block and the spring force are mutually restricted to maintain dynamic balance. The spring force moves the oil quantity control mechanism in the direction of increasing the oil supply amount, and the fuel supply amount increases to accelerate the diesel engine, and the centrifugal force of the governor flyweight centrifugal block also increases, and the centrifugal force causes the oil quantity control mechanism to move in the direction of oil reduction. Restricting the increase of the rotational speed, the throttle position corresponds to the preloading force of the speed regulating spring, and the spring preloading force corresponds to the rotational speed, thereby achieving the purpose of controlling the rotational speed. Once the governor fails or the oil quantity control mechanism is stuck or disconnected, it is easy to cause the diesel engine to "fly". The smoke is darker when accelerating, and the fuel utilization rate and exhaust emission standards are lower. The injection pressure is 17~19 MPa, which is not conducive to the full atomization combustion of diesel.

2.       Distributor (rotary) fuel injection pump system

   The same as the in-line type, the plunger type fuel injection pump and the mechanical centrifugal governor are used, the injector is connected with the fuel injection pump, and the injector is passive injection; The difference is that the distribution pump reduces the number of plunger pumps (only one plunger/element), and the high-pressure diesel is sent to the injectors of each cylinder through the distribution rotor in the order of operation of each cylinder. The high-pressure fuel pipe must be installed according to the installation. The direction of rotation of the distribution rotor is connected to the working sequence of each cylinder. The reduction in the number of distribution pumps reduces the size of the fuel injection pump itself, resulting in a more compact structure and lower costs. The increase in drive speed results in a higher injection pressure. The distribution pump drive speed can reach 3 times the crankshaft speed. Under the premise of the same degree of sealing of the plunger, the higher the driving speed of the fuel injection pump, the higher the injection pressure, and the injection pump pressure of the distribution pump can reach 60~80 MPa. The high pressure injection facilitates the more complete atomization of the diesel fuel and reduces the smoke.

3.       PT fuel supply system

   This is a Cummins patent. The injector is an active fuel injection. The low-pressure diesel fuels in the injector through the rocker arm to press the plungers in the injectors to generate high pressure. The injector is also a plunger pump, and P and T respectively act on the injector. The pressure of the oil cup metering hole and the opening time of the metering hole.

4.       Electronic control system/ Common rail fuel injection pump system

   There are two major categories of electronically controlled governor systems and electronically controlled injector systems. The electronically controlled governor system is to change the mechanical centrifugal governor of the inline pump and the distribution pump to the electronically controlled governor. This type of diesel engine utilizes various sensors. After the control unit processes the feedback signal of the speed sensor, the control signal is applied to the electromagnetic actuator, and the electromagnetic force is used to control the fueling or oil reduction. The pump body is exactly the same as the mechanical centrifugal type. The electronic control system can achieve intelligent control of fuel injection rate. The electric control in-line pump system is also equipped with a "flying" protection device.

The electronically controlled injector system can be also divided into an electronically controlled pump nozzle system and an electronically controlled common rail system.

The electric control pump nozzle system is an improved type based on the PT fuel supply system. The solenoid valve is opened and closed to control the amount of oil entering the oil cup, and the governor is removed. The pumping mode is still the rocker arm plunger, the same as the PT fueling system. The electronically controlled common rail system has a fuel rail installed on the cylinder head. The fuel rail is a long tubular sealed container, and each cylinder injector is mounted on the container to jointly use the fuel rail, the so-called common rail. The fuel pump uses a one-way valve to continuously pump diesel into the common rail to generate high pressure, similar to the air reservoir of the brake system. The pressure sensor feeds back the pressure value in the common rail to the control unit and regulates the pressure in the common rail by controlling the proper opening of the solenoid valve. The pressure in the common rail is the injection pressure of the injector, which can reach 100~120 MPa. The oil pressure is produced in a completely different way than the plunger pump. The fuel supply timing is controlled by the opening timing of the injector solenoid valve, and the fuel injection amount is controlled by the continuous opening time of the solenoid valve, so the system requires neither an advancer nor a governor. The normal operation of the system requires that the injector solenoid valve must be able to open and close quickly and reliably on time, and can withstand long-term high frequency opening and closing conditions. The electronically controlled diesel engine has better power and fuel economy, and the smokeless color is black when accelerating, but the cost of the electronic control device is relatively high.

 

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