Fuel injection pumps in diesel engines
Only some of us have heard something about injectors and related elements. The magical way in which fuel passes from the fuel tank to injectors, for many remains a mystery.
The operation of diesel engines is largely based on supplying fuel and the right amount of air in the cylinders. Then, fuel-air mixture is compressed to high pressure and self-ignites. Thus generated energy puts the pistons in motion. Afterwards, it is transferred to the crankshaft, then to the gearbox and finally to the wheels. One should remember that the element responsible for delivering fuel is the supply pump as it transports fuel from the tank to the cylinders. Because of that, it is one of the most important components of the supply system.
Sectional pumps are the first pumps used for hydraulic fuel injection. Such pump consists of a set of fuel pumps (injection sections). Each section is related to one cylinder, but all are connected with a teeth bar. This last element rotates all the pistons along its longitudinal axis and controls fed fuel, thus controlling the power of the driving unit.
These pumps consist of such components as: fuel lines, pump cylinders, pistons, shut-off valves, high pressure hoses, fuel dose corrector, injectors and teeth bar.
Operation of sectional pumps
Sectional pumps can be divided into pumps with fixed start and variable end of injection, those with variable start and fixed end of injection and those variable start and variable end of injection.
They are easy to repair which is their main advantage, whereas the disadvantages are problems with compliance with standards of emission of harmful substances, waving engine speed, issues with adjusting fuel doses to individual pump sections, higher fuel consumption compared to other technologies and high production costs. One can see that sectional pumps have more cons than pros, which is why they are not used anymore.
Hydraulic fuel pump
A better and more reliable solution is the use of hydraulic fuel pumps in diesel engines. There are two types of these: in-line and rotary pumps. The second type is more common due to its small size, mass, lower production costs and modernity.
Hydraulic injection pump
In this type of pumps we can find in-line or serial arrangement of the pumping sections. These pumps are equipped with a separate pumping section, which consists of a cylinder and a piston rod. It is driven by a cam of the pump shaft, thanks to roller pusher. Another element of the system is the adjusting sleeve, mounted on the cylinder and connected to the piston foot.
A discharge valve and radial openings are located at the top of the cylinder. One of these holes connects the space with the supplying channel and the other one with the bleed channel. Fuel starts to be pumped when top edge of the piston covers the supplying opening. Pumping continues for the time when bleed opening is covered by controlling edge.
Rotary injection pump
Rotary injection pumps are used in low-pressure injection systems. Such solutions consist of the following elements: fuel supply lines, feed pump, housing, overpressure pump, rotor with cylinder and pistons, channel arrangement (inlet, distributor, outlet), high pressure lines for injectors. This type of pumps work because the driving plate is driven by the electric motor shaft. The rollers placed in notches of the plate, are pressed against the track. Fuel is between them and it is piled up in order to increase its pressure. Overflow valve protects against excessive pressure increase and it also creates fuel flow inside the pump. In addition, one uses starter device which changes injection timing.
The disadvantages of distributor pumps are failure to meet current combustion standards and fuel purity requirements, decreasing velocity at the end of dose which can lead to injector leakage, high material requirements and the need for surface treatment due to piston rod strikes to cam surface.
increased usage of fuel while starting the engine.
However, distribution pumps have more advantages than sectional pumps. One of them is more precise fuel dosage, another one – lower fuel consumption, there is also better operational stability, higher purity of exhaust gas, there are less components requiring precise machining. We can sum that up with relatively low price and small dimensions.
Most companies now use the Common Rail system. It is more efficient due to its better fuel dosage adjustment capability. Another plus of such system is that it complies with current emission standards. Common Rail is equipped with a high pressure pump. The piston fuel pump compresses it to very high pressure, it is pumped into the pressure reservoir (so-called rail), which is connected to the injectors.
Introduction of the Common Rail system required mastering of advanced manufacturing technology and appropriate control system. This is because high pressure pumps generate a pressure of about one thousand bars. At the same time, injectors feed fuel mist within a few milliseconds – this shows how precise specific components must be. Electronic controller calculates required injection rate per cycle in real-time and divides it into a few smaller parts so that the entire dose is not injected entirely in one moment.
The main advantage of this system is the possibility of being able to decide on injection dose freely. It is divided into several smaller doses, which results in higher engine efficiency. Combustion process runs smoothly, regulation of ignition timing and injection pressure is more precise. This means lowering noise and reduces harmful emissions. The disadvantages of this system are high production costs and high sensitivity to fuel quality. It is made in a precise manner and poor quality of fuel can lead to problems.