Spray nozzle

A fuel injector, the injection valve is known in the diesel engine. Their other name is injector.

Construction

Injection nozzles consist of the nozzle body and the nozzle needle. Both are made from high quality steel and lapped. The tolerances from 0.002 to 0.003mm. Because of this tight tolerances, the items are not interchangeable. Rather, all manufactured components will be measured separately and combined the dimensionally matching with the closest residue tolerance items to each other.

Function

In simple systems, the nozzle needle is pressed by one or two compression springs of the nozzle holder in the seat. With the fuel pressure creates a lift force acting vertically. If it is greater than the spring force, the needle is pushed up and fuel is injected. If the pressure drops, closes the nozzle ( again). The nozzle opening pressures are dependent on the manufacturer bar 115-300. However, the maximum injection pressure can be bar at up to 2500 depending on the system and engine load / speed.

In modern injectors of the common rail system, the nozzle needles are operated by a servo mechanism. This open the nozzle at high (up to 2500 bar ) and low pressures (200 bar) only in case of control of the injector, ie irrespective of the pressure.

Types

Hole nozzle

This type is used exclusively with direct injection engines.

A distinction is made between the seat hole nozzles and blind hole nozzles.

The valve cone orifice nozzle holes directly from the valve member ( jet needle ) are closed.

In the blind-hole nozzle under the nozzle seat is a residual volume in which a residual fuel remains that has not been injected through the nozzle holes, resulting in increased emissions of unburned hydrocarbons (HC) in the exhaust gas may result. However, one can achieve through a nozzle holes upstream mixing volume favorable flow conditions. In order to keep the unwanted residual volume as low as possible, there are also mini blind hole nozzles in which one keeps as low as possible " top up " the dead volume.

The nozzle body includes a plurality of injection holes. Depending on the engine, the number between 5 (PKW) to 14 ( large diesel engine, eg for ships and power plants ). The hole diameter varies between 0.15 mm (cars ) and 0.4 mm ( truck). The injection hole number, angle and size, as well as the flow conditions at the nozzle holes affect the injection jet and its atomization ( spray pattern ) that the in coordination with the injection quantity, injection pressure, pressure gradient, combustion chamber geometry, charge movement, compression pressure and temperature combustion quality in the combustion diesel fuel determined.

Modern injection valves ( injectors) as an active element having either a solenoid or a piezoelectric actuator in an increasing trend, the piezo driving possible by faster reaction times up to five multiple injections in a combustion cycle. When multiple injections can affect the pressure rise ( smoother combustion process ) and thus improve the acoustic comfort situation through appropriate pilot. There is also the possibility of the regenerative soot filter purification by injection, the unburned fuel to the combustion of the soot collected in the filter is used.

Pump nozzle

In the pump-nozzle system, the single -plunger pump is combined with the injector. This reduces the disturbing influence of fuel pressure lines to the system. The control of the pump element was used to mechanically, nowadays, the injection period is controlled by a piezoelectric or solenoid valve. These valves connect to state pressure channel and return open. Characterized the pressure collapses, and the injection nozzle closes. However, the injection pressure is not controlled. A disadvantage is the high, sudden load on the camshaft drive.

Pintle

The pintle nozzles are used on engines with pre-or vortex chamber and have a much lower opening pressure of 80 to 145 bar. In this design, the only injection hole is sealed in the closed position by a pin. Thus, there is no remaining volume, and the injection jet may be changed by the shape of the pin. Such possibilities include pre- or pressure-dependent change in the beam shape. In the development of the Journal of always generated Rußbelag is factored in, which means that new nozzles that do not yet have the Rußbelag, possibly burn unclean until the surface has formed.

Problem cases

Injectors can coking, particularly in the use of vegetable oils as a fuel. This results in poorer atomization, a poorer combustion and thus lower exhaust emissions. This may be so pronounced that the engine control unit does not execute the boot process. This is the self-protection of the engine against uncontrolled combustion processes. Cleaning of the nozzle or the injector is then absolutely necessary. By suitable adjustment of the nozzle hole geometry of these coking can be delayed or even avoided. As a contributing factor of coking of the injectors are high temperatures. Most coking is the sooting of EGR in a diesel engine directly related.