Injection nozzle (diesel engine)
The injection valve in the diesel engine is known as the injection nozzle . Another name is injector .
construction
Injection nozzles consist of the nozzle body and the nozzle needle. Both are made of high quality steel and lapped . The tolerances are between 0.002 and 0.003 mm. Because of these narrow tolerances, the individual parts are not interchangeable. Rather, all manufactured individual parts are measured separately and the individual parts that fit together with the tightest residual tolerance are paired.
function
In simple systems, the nozzle needle is pressed into the seat by one or two compression springs on the nozzle holder. The fuel pressure creates a vertical lifting force. If this is greater than the spring force, the needle is pushed up and fuel is injected. If the pressure drops, the nozzle closes (again). The nozzle opening pressures are between 115 and 300 bar, depending on the manufacturer. The maximum injection pressure can, however, be up to 2,700 bar, depending on the system and engine load / speed.
In modern injectors of the common rail system, the nozzle needles are operated by a servomechanism. As a result, the nozzles open at high (for example 2,500 bar (Volvo V60)) and low pressures (200 bar) only when the injector is activated, i.e. regardless of the pressure applied.
Types
Hole nozzle
This type is only used in direct injection engines.
A distinction is made between seat hole nozzles and blind hole nozzles.
In the case of the seat hole nozzle, the nozzle holes are closed directly by the valve member (nozzle needle).
In the case of the blind hole nozzle, there is a residual volume below the nozzle seat in which a residual fuel remains that was not injected through the nozzle holes, which can result in increased emissions of unburned hydrocarbons (HC) in the exhaust gas and a higher tendency of the nozzle to coke. However, more favorable flow conditions can be achieved through a mixing volume upstream of the nozzle holes. In order to keep the unwanted residual volume as low as possible, there are also mini blind hole nozzles in which the dead volume is kept as low as possible by "filling up".
The nozzle body has several spray holes. Depending on the engine, the number is between 5 (cars) and 14 (large diesel engines, e.g. for ships or power plants). The hole diameter varies between 0.15 mm (cars) and 0.4 mm (trucks). The number, angle and size of the injection holes, as well as the flow conditions at the nozzle holes influence the injection jet and its atomization (spray pattern), which, in coordination with the injection quantity, injection pressure, pressure curve, combustion chamber geometry, charge movement, compression pressure and temperature, affect the combustion quality during combustion of the Determine diesel fuel.
The modern injection valves (injectors) have either a magnetic coil or, increasingly, a piezo actuator as an active element , with the piezo control enabling up to five multiple injections in one combustion cycle due to faster reaction times. In the case of multiple injections, the pressure increase (smoother combustion process) can be influenced by appropriate pre-injection and thus the acoustic comfort situation can be improved. Furthermore, there is the possibility of regenerative soot filter cleaning by post-injection, whereby the unburned fuel is used to post-burn the soot collected in the filter.
Pump nozzle
In the pump-nozzle system , the single piston pump is combined with the injection nozzle. This reduces the disruptive influences of the fuel pressure lines on the system. The control of the pump element used to be done mechanically, today the injection duration is controlled by a piezo or magnetic valve. When open, these valves connect the pressure channel and return. This causes the pressure to collapse and the injection nozzle to close. However, the injection pressure cannot be regulated. The high, sudden load on the camshaft drive is a disadvantage.
Spigot nozzle
The spigot nozzles are used in engines with a prechamber or swirl chamber and have a much lower opening pressure of 80 to 145 bar . In this design, the only injection hole is closed by a pin when it is closed. As a result, there is no remaining volume and the injection jet can be changed by the shape of the pin. Possible are e.g. B. Pre-injection or pressure-dependent change in the jet shape. During the development of the pin, the soot deposit that always occurs is taken into account, which means that new nozzles that do not yet have the soot deposit may burn less cleanly until the deposit has formed.
Problem cases
Injection nozzles can coke, especially when using vegetable oils as fuel. The result is poorer nebulization, poorer combustion and thus poorer exhaust gas values. This can lead to the fact that the engine control unit does not start the engine . This is then the self-protection of the engine from unregulated combustion processes. It is then essential to clean the nozzle or the injector. This coking process can be delayed or avoided by suitable coordination of the nozzle hole geometry. High temperatures or short-distance operation are considered to be a contributing factor to coking of the injection nozzles. Most of the coking is directly related to the sooting of the exhaust gas recirculation in a diesel engine.
literature
- Max Bohner, Richard Fischer, Rolf Gscheidle: Expertise in automotive technology. 27th edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 2001, ISBN 3-8085-2067-1
- Richard van Basshuysen, Fred Schäfer: Handbook Internal Combustion Engine Basics, Components, Systems, Perspectives. 3rd edition, Friedrich Vieweg & Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden, 2005, ISBN 3-528-23933-6
Web links
- Youtube: Test of an injection nozzle
- focus.de of June 10, 2013, Risk with Diesel Engines: Particle Filter Time Bomb , accessed on November 17, 2019.
Individual evidence
- ↑ https://www.heise.de/autos/artikel/Vorstellung-BMW-2er-Active-Tourer-und-Gran-Tourer-Facelift-3937445.html from January 10, 2018, accessed on November 19, 2019.