Bosch Common Rail Injectors Work Introduction
- Last Updated 12月 29, 2020
Bosch has been a pioneer in making hi-end engine components. The Bosch common rail injectors are one such complicated system that is heavily used in modern CRDi diesel vehicles.
Since CRDi already has a common rail to regulate fuel pressure, the injectors just inject fuel when instructed by the ECU. However, given the accuracy of a CRDi, the job of a common rail injector gets complicated.
So in this article, we will discuss the working of the bosch injector system and look at the reasons common rail injectors fail.
How do bosch injectors work?
A common rail injection (CRI) system is a highly accurate fuel injection system with the ability to inject 5 times per stroke. Meaning a CRI can inject fuel five times in one engine stroke at different intervals.
To attain such accuracy the injection system is controlled by ECU (Engine control unit). The ECU depending on the engine load regulates the fuel supply to produce the required amount of power. You can read the working of the CRDi engine here.
A diesel engine uses direct injection meaning it directly injects fuel into the combustion chamber. In modern-day diesel engines, it is an injector’s job to inject fuel not only inaccurate amounts but at a pressure where fuel is properly atomized. Better the atomization better the combustion.
To achieve high-level atomization, fuel is pressurized by a high-pressure fuel pump ( 100-200 Mpa bar) and sent to the common rail. The common rail is connected to all the injection systems and supplies high-pressure fuel. Hence they are called common rail injectors.
Depending on the Bosch injector type, it can either use solenoid or piezo control for fuel injection.
Working of Bosch Solenoid type injector:
The solenoid-type injectors are the most common CRI injectors. In such injectors, an electromagnet is used to control the solenoid which controls the injector needle.
Upon the signal from the ECU, an electromagnet is activated which sucks up the armature. This also pulls the check balls with it. The check ball controls the opening/closing of the A-throttle. The fuel is injected both on the top and bottom of the injector.
The fuel at the bottom is atomized and sprayed in the chamber. But the fuel at the top does something interesting. As the check ball goes up, it opens a small cavity for high-pressure fuel to flood in. The cavity is connected with an exit called the fuel return line.
The faster the fuel gets in, the faster it gets out, creating a low-pressure area above the piston connected to the injection nozzle. The low pressure at the top and high pressure at the bottom pushes the piston up hence opening the injector nozzle needle. As the nozzle opens, the high-pressure fuel is let out of a very tiny opening, which ends up atomizing the fuel.
Which main components consist of the bosch injector? 
Bosch injectors are made of several small components. You start with the injector body that houses everything from the solenoid to the piston and the nozzle. In the injector body, you have the solenoid coil assembly containing the valve body. The Valve body houses the check ball, which allows the formation of low pressure above A throttle.
Below the valve body is the control piston that is connected to the injector nozzle needle.
- Injector Body
- Injector nozzle
- Solenoid coil assembly
- Valve body
- Solenoid Armature
- Control Chamber
- Control Piston
- Nozzle needle
How to repair the common rail injector?
Common rail injectors are hard to repair as they need high-level equipment. It all starts with disassembling the injectors, finding and replacing the problem component, and re-assembling it.
Remember that disassembling the injector requires special tools. Which are also necessary for assembling it. The injector also needs advanced machinery to perform any testing, and its repair is not something that can be done at home.
Disassembling Common rail injector:
- You start by removing the solenoid cap and then the solenoid itself. Remember to remove the valve ball and seat.
- Then you remove the nozzle tight cap and the injector nozzle.
- Carefully remove the guide sleeve along with intermediate shim and dowel pins. This will allow you to remove the nozzle spring and its adjusting shim.
- Now unscrew the valve assembly and remove the injector valve. The injector needle will also come out right along.
- Then remove the ring and support ring of the needle.
Why did your Diesel Common Rail Injectors Fail?
Common rail injectors can fail due to multiple reasons. However, most failed injectors have some common symptoms. These reasons are:
Failed Solenoid Valve: The Solenoid valve is what is responsible for the injector working. Only when the valve opens, the fuel comes in. Without which the injector would not inject. This can be caused due to the melting of the electromagnetic coil. Higher voltage can cause the coil to fail, making the whole injector useless.
Corroded or Worn out injector parts: Injectors can also fail due to corrosion or getting worn out because of overuse.
While injectors are made to last the lifetime of a vehicle (150,000 miles), they can wear out earlier. Heavier engine load requires the injector to work more causing it to wear out early. Corrosion can also happen due to the bad quality of fuel or water insertion inside the injectors.
Loose high-pressure connector: The high-pressure connector that connects the fuel supply to the injector can get loose and cause a leak. This leak would also result in pressure loss which will significantly reduce the atomization level. Hence resulting in poor combustion.
External damage: If the injectors are reassembled or installed incorrectly, they can take physical damage reducing their working capacity. Over tightening or lose fit can affect their performance heavily.
