Petrol injectors

Genesis and application.

The fuel supply of petrol engines has undergone considerable evolution over recent decades. Since the early days of this type of engine, engineers have sought to improve the efficiency of their power supply in order to achieve greater efficiency, power and reduced fuel consumption. From simple carburettors to mechanical and electronic injection systems to advanced direct injection technologies, each solution has had its unique advantages and disadvantages. Today's direct injection (GDI) technologies represent the pinnacle of precision and efficiency, although developments in this field are still ongoing, striving for even greater efficiency and eco-friendliness. Advanced injection systems are able to better control the combustion process, leading to significantly lower emissions. As a result, cars are more environmentally friendly and meet stricter emission standards. 

A landmark in the development of fuel injection technology was the introduction of fuel injection systems in the 1960s, when Bosch unveiled the D-Jetronic, the first electronic fuel injection system that allowed more precise fuel metering through the use of sensors and an electronic controller. In the following decades, the technology was gradually refined, and the 1980s saw more advanced systems such as L-Jetronic, which was the first to use an air mass flow meter. 

Systems with only one central injector replacing the carburettor (hence the name single-point injection) were on the market, but their place was relatively quickly taken by systems in which fuel is supplied to each cylinder via a separate injector (so-called multi-point injection). The need for precise engine control and reduced fuel consumption resulted in the development of sequential injector control, i.e. the individual opening and closing of each injector. This was followed by the development of series-produced petrol direct injection systems, which further reduced fuel consumption and contributed to lower exhaust emissions.

Construction and principle of operation.

The injection system of a petrol engine consists of several basic components:

1. Fuel tank
2. Fuel pump
3. Fuel filter
4. High pressure pump (in direct injection systems)
5. Fuel pressure control valve
6. Fuel rail
7. Fuel pressure and temperature sensor(s)
8. Fuel injectors
9. Electronic engine controller and a range of sensors and actuators 

The petrol injector contains the following components:

1. Injector housing
2. Control valve (solenoid or piezo element)
3. Needle
4. Nozzle
5. Inlet filter and seals

The petrol injectors are the final link in the injection system and are responsible for accurately supplying the correct dose of fuel to the engine cylinders. Fuel sucked from the tank is pumped under pressure into the system and then purified by passing through a filter. In indirect injection systems, the fuel goes into a reservoir and from there to the injectors. In direct injection systems, there is a pump between the fuel filter and the accumulator (rail) that generates high fuel pressure. The fuel is injected when the injector is opened, which is done by energising the actuator, which is usually the coil. In some solutions, especially in direct injection systems, piezo injectors are present. The process starts with the engine's electronic control unit (ECU), which decides on the amount of fuel to be injected into the engine on the basis of signals from various sensors (such as the mass air flow sensor, crankshaft position sensor, engine temperature sensor, etc.). The ECU sends an electrical pulse to the coil of the injector solenoid, which generates an electromagnetic field. The magnetic field attracts the core of the electromagnet, which is connected to the needle (needle valve). The magnetic force overcomes the resistance of the spring, which normally holds the firing pin in the closed position, and lifts it, opening the injector. When the needle is raised, the flow path for the fuel opens. Fuel under high pressure flows through the injector nozzle and is sprayed into the combustion chamber or intake manifold. The injector nozzle is designed to create a fine mist of fuel for better mixing with air and more efficient combustion. When the electrical pulse sent by the ECU ends, the current stops flowing through the solenoid. The magnetic field disappears and a spring returns the needle to the closed position. In this way, the injector closes, interrupting the flow of fuel.

The main task of the injector is to deliver a properly measured dose of fuel to the engine cylinder. The fuel portion must be accurately atomised to ensure proper evaporation, mixing with air and combustion. To achieve this, the injector must be precisely and quickly controlled and supplied with fuel at a sufficiently high pressure. 

Remanufacturing process.

Unfortunately, petrol injectors are not remanufacturable in the full sense of the word. This is mainly due to their design - most of them cannot be taken apart without irreparable damage, so access to the components is impossible. For this reason, there are no remanufacturing procedures and manufacturers do not supply spare parts.

In the case of most petrol injectors, therefore, we can only talk about cleaning them and checking the dosage and spray quality of the fuel.

The injectors removed from the engine are subjected to an initial visual assessment. At this stage, the external condition of the injectors is checked and any visible damage is looked for. The injectors are placed in an ultrasonic bath, which effectively removes accumulated dirt and deposits. The process uses ultrasonic waves to generate microscopic bubbles, which implode to strip contaminants from the surface of the injector. The injector test benches we use are also equipped with a backwash function to remove sediment and deposits from inside the injector.

After cleaning, the injectors are tested on special test benches that simulate the operating conditions in the engine. Here, leakage, fuel dosage and fuel atomisation quality are checked. Tests are carried out at various pressures to ensure that the injector is operating correctly throughout its operating range.

If the injector is not damaged or worn mechanically and is electrically efficient, its cleaning will bring satisfactory results and will allow it to be used for a long time.

Causes and types of damage.

The most common symptoms of damaged petrol injectors are:

1. Uneven engine running
2. Loss of engine performance
3. Increased fuel consumption
4. Misfire
5. Check engine light on

The most common causes of petrol injector failure:

1. Contamination, poor fuel quality
2. Sediment accumulation
3. Overheating
4. Mechanical wear
5. Problems with eclectic components