What is the HPF in a diesel engine, how it works, in what varieties is it available?
Any car engine is a complex mechanism, which is composed of a number of important units. If you take diesel engines, the important place in their design is occupied by fuel pumps.
What is a fuel pump
It is easy to understand what is the fuel injection pump in the car. Under this abbreviation is meant a high-pressure fuel pump. It is located in the diesel engine, although, it can also be found in some gasoline engines. This unit is responsible for supplying the fuel mixture under high pressure. Exactly in this is the basis of functioning of any diesel engine.
Next, we will have to consider the principle of operation of this part, its structure and existing varieties. And also we will study the reasons for installing a high pressure TH on gasoline engines.
How does the diesel engine high pressure pump work?
The work of the diesel engine is complex and multistage. An important, even the main role is played by the high pressure pumping mechanism. Many people will be interested to study an HPF working principle, and we are going to do it now.
The fuel mass under pressure goes to the injectors. This process should not occur randomly, but at a certain moment. It is controlled by an automatic system. The task of the high pressure fuel system is to create the necessary pressure. Due to the complete combustion of the fuel in the cylinders, the user gets the maximum engine power.
The design and the operating principle of the HPV is designed to ensure a working pressure of 150 MPa or more. This is a very high indicator. To achieve it, the pump must meet a number of requirements. For example, the material for the manufacture of this part must be extra strong and reliable. Manufacturers use a special aluminum alloy AL9.
The design of the pump includes a plunger pair. This is a cylinder with a small diameter and a rod of the appropriate size. For these parts, a special steel grade is used, which is designed for high working loads (25X5MA). Very high demands are placed on these parts.
The speed of the crankshaft determines the amount of diesel sent to the feed and the torque at which this occurs. By depressing the accelerator pedal the load is increased and the engine receives the right amount of fuel. If the pump system is in good condition and works without interruptions, the engine will run smoothly and evenly.
The design of the diesel engine HPF may differ depending on the type of mechanism. There are 4 main varieties of pumps that are installed on diesel units.
Types of high pressure pumps for diesel fuel supply
On different engines, which differ in modification and generation, different fuel pumps can be installed. In total, there are four varieties of high-pressure fuel pump that are used in diesel engines.
These devices are distinguished by the presence of an individual plunger pair for each cylinder. They are concentrated in a single body, and the fuel is supplied through separate channels. The principle of operation of such a unit is as follows:
- The plunger is driven by the rotation of the camshaft, which is equipped with a drive coming from the engine crankshaft;
- the pusher makes the plunger move on the sleeve;
- at a given pressure, the exhaust valve opens, causing the fuel mixture to flow into the working cylinder;
- the timing and amount of fuel can be controlled mechanically or electronically.
In-line pumping systems have proven their worth. They are reliable and hardy. Nowadays, such devices are used on larger vehicles. For passenger cars, other mechanisms are chosen.
Distributive injection pump of the engine
Here there are only a few plungers, which are responsible for regulating the fuel pressure. A distribution head and channels are used to supply the fuel mixture. Such mechanisms are loved by motorists because of a number of important advantages:
- small dimensions and reduced weight allow them to be used in the design of passenger cars without problems;
- the fuel supply is always uniform.
Low working life is one of the disadvantages, the reason of it is increased load on the plunger pair.
Trunk fuel pumps
Almost all modern cars with diesel engines, which are equipped with accumulator system of Common Rail fuel supply, are equipped with these mechanisms. This mechanism is distinguished by the fuel supply directly to the fuel rail, which acts as an accumulating reservoir.
The construction is designed in such a way that the injection and injection processes are separated. As a result the processes become more controllable. Most often the manufacturers install models with 1-3 plunger pairs, which are driven by springs or a compressed gas mixture. Models with hydraulics are not uncommon.
Such mechanisms are the most modern. But for their work it is necessary to use high quality fuel. Otherwise the quality of their work and durability will decrease.
Diesel engine booster pump
The booster pump system performs two processes at once:
- In the preparatory stage, the fuel is cleaned through filters that remove solid elements from its composition.
- The operating phase consists in transferring the cleaned fuel onward through the system.
During the low-pressure pump operation, the diesel is fed in a slightly higher volume. Due to the work of the booster pump, the pressure is normalized at moments of high load on the engine.
Why is the fuel injection pump installed on the gasoline engine?
Previously, such mechanisms could only be found on diesel engines. When injector gasoline units appeared, there was a need to install such parts on such mechanisms as well. In injection engines, the fuel is pumped to the injectors under high pressure. This is not the only function of the HPF on the gasoline engine, although it is the main one. These devices are responsible for some other important functions:
- regulating the amount of fuel mass that goes into the supply;
- controlling when fuel should be injected into each cylinder.
Such systems are not installed on other types of gasoline engines.
Such systems, even though they are made of durable material with strict adherence to high requirements regarding safety and reliability, still need regular maintenance and control. Only the well-coordinated work of this mechanism will provide trouble-free operation of your car even after a long downtime and in severe frosts. Believe me, it is better to periodically check the condition of the pump and the power unit as a whole, than to try in vain to start the car.
My Dear Diesel: Why the Diesel Engines Break Down and How They Are Repaired
Since the final residence of diesel engines in passenger cars, not only the owners, but also craftsmen with a little apprehension looked at this “miracle of technology. Yes, the gain on fuel and traction is obvious – but what happens if the engine breaks down? The peculiarity of all heavy fuel engines without exception is the precision of the assembly of the most critical parts, as well as the value of the working pressure – of course, if we are talking about modern engines. Looking at the normo-hours in the service, concerning the repair and maintenance of fuel equipment, everyone will involuntarily ask: “Is the game worth the candle?”. Yes and no.
On the one hand you get an incredibly productive engine with great traction and reduced consumption, on the other hand you have to pay more attention to the fuel quality, more frequent change of the fuel filter and quite large expenses in case of need for repair or replacement of system elements. But if the first point of the scale is more important, and you are the owner of the automobile “on diesel” with Common Rail system, then it is necessary to look how elements of this system are repaired. Today we will find out how the repair of the fuel injection system is performed.
Briefly about the device
Common Rail: this word combination is on everyone’s ears, and many even know what it is. Simply speaking, it’s nothing but a system of diesel fuel injection from the common rail directly into the engine cylinder under very high pressure (1,600 – 1,800 bar). Some may say: but the diesel fuel has long been injected directly, what is the peculiarity? The answer lies on the surface, in the name itself: it’s a “single line”.
Before the advent of Common Rail, diesel fuel under pressure created by the HPP (high pressure fuel pump) was sent directly to the nozzle, through which it was injected into the cylinder. In the new system, the pump pressurizes the fuel in the fuel rail, which itself is an accumulator – and from the ramp fuel through the pipes is fed to the injectors.
Thanks to this scheme, it turns out that all injectors have at their disposal fuel at the same pressure at any time and in any quantity – and this pressure is quite high. It is necessary for a better atomization and, therefore, mixing of the fuel with the air, and thus for a more complete combustion. These are all links in a chain that leads to improved engine efficiency.
Why couldn’t a common fuel ramp be dispensed with? To answer yourself this question, try inflating a balloon to its maximum size in one sitting. If you’re a whale, you can do it without a problem. If you’re a human, you’ll either have to try really hard or just take a few breaths and exhales. So here: the system is fed by a small high-pressure pump with low friction losses, but with the ability to pump 1600 bar into a tube called a fuel ramp.
The next element in the circuit is the injectors. In modern engines, they can be electromagnetic or piezoelectric. The latter, by the way, are the last word in diesel engineering.
To complete the schematic picture of Common Rail we can add that the fuel from the ramp goes to the injectors, but is not blocked in the ramp, and is taken away through the drainage channel. In fact, the fuel in the system is constantly circulating, but as soon as the signal “comes” to the solenoid valve, it “opens” the injector, and the fuel is sprayed into the cylinder. By the way, it is about the device and operation of injectors we will talk about in the next article.
The structure of the injector
Structurally, pumps can be rotary or, as in our case, plunger pumps. Since the plunger pump came into our field of vision, and at the moment it is more common, we will consider various variations of this design.
The principle of operation is very simple: the spring-loaded plunger moves inside the cup, collecting and pushing out the diesel fuel from the cavity above it. The plunger is moved by means of a camshaft. Often there are three plungers installed in the body. The cavity above the plunger has one-way valves for inlet and outlet. In general, the pump is designed almost like a heart.
If we refer to the details, we can distinguish three types of HPF.
The first is a “bare” pump: the fuel is pumped by a separate pump mounted in the tank. The second one is an HPF with a pressure regulator. And finally, the third – where both booster pump and pressure regulator are installed, which discharges the fuel under overpressure into the “return” in case of need.
There are also slight differences in the design of the plungers. For demonstration purposes, we disassembled and repaired an HPF with a plunger that moves in a cup, which can be removed from the body and replaced as an assembly. However, there are also designs in which the housing itself acts as a cup. Basically, there is nothing more to say about the mechanics here – it is the simplest.
What can break?
The first and almost the only enemy of all the parts of the diesel fuel system is water. The fuel injection pump with its precision adjustment of the plunger-stage pair and valves is not an exception here. Remember the article about the diesel filter sump with water drain valve? Well, if you do not watch the water in the sump, then at one moment your car will lose traction “at low revs”, or may be in the whole rpm range – as luck would have it. However, it is fair to say, that often quality of our diesel leaves much to be desired, therefore even if to pour out water from sediment tank daily, but to fill up at suspicious stations – the result will be the same.
One more point, which should be allocated in the beginning: in any case it is impossible to let the fuel injection pump work “dry” – in other words, it is necessary to exclude the engine start without pumping the fuel system. The fuel injection pump is lubricated by fuel, and operation without lubrication “sentences” it in a matter of minutes.
Any breakdown of the fuel injection pump is somehow connected with corrosion or ingress of foreign particles on the working surfaces. Exactly it can become the reason of the jammed plunger or one-side valves. The breakdowns can also include wear of the shaft bushings in the front cover of the HPF housing. It’s not uncommon for the shaft packing to be worn. But the bushings and oil seal are nothing compared to corrosion.
Of course, not all possible breakages are mentioned in the previous paragraph. For example, the O-rings of the body or flange covers can also break (depending on the design) – but that usually only happens during disassembly. The pressure regulator can fail – both its electrical and mechanical part. That is the end of the list of potential failures.
But there are no questions about the fuel pump, as there is simply nothing to break. It is an usual external gear pump – the same as the oil pump in Zhiguli.
In any service that respects itself and the client before getting into the “iron”, perform computer diagnostics of the engine and its systems. Thanks to it you can localize the breakdown – or rather, roughly understand who was the culprit of improper operation of the engine. Finally convinced that it is HPF, it is directed to a repair shop.
Here first of all the pump is installed on a special diagnostic stand and all necessary pipes are connected. Having selected in the menu the required set of letters and numbers by the part number the diagnosis process is started. The most convenient thing here is that the work of the test bench is based on the system of prompts. By running the set diagnostic program, the technician sees the test results in real time and draws conclusions based on them.