Basic Function Of Injection Valve - GF07.03-P-2001A
Engine139, 176, 177, 254, 256, 260, 264, 274, 279, 282
Example illustration of 6-cylinder spark-ignition engine (direct injection)
Overview
This document contains information on:
- General
- Function
- Fuel injection
- Injection valves with multi-hole nozzles
General
The injection valves inject the fuel into the respective cylinder (direct injection) or into the intake manifold (intake manifold injection).
The respective injected fuel quantity depends on the actuation duration of the corresponding injection valve.
The injection quantity is determined by additional factors:
- Opening and closing speed of nozzle needle.
- Needle lift height.
- Nozzle geometry.
- Fuel distributor pressure.
Function
Fuel injection
The injection valves switch very rapidly and can also inject the smallest fuel quantities.
Due to the high fuel pressure of approx. 130 to 250 bar, the outward opening nozzle produces a stable hollow-cone jet under all operating conditions, this is a basic requirement for an interruption-free stratified charge operation. The combustion engine control unit generates the control voltage of 140 to 210 V for the fuel injectors and actuates the fuel injectors with a ground signal. The stroke of the nozzle needle is, in this connection, approx. 35 μm. The piezo actuator module represents a capacitative load for the combustion engine control unit. When opening, a current of approx. 8 A flows for a few milliseconds. The combustion engine control unit reverses the polarity for opening and closing. The short switching times of the piezo injectors facilitate a multiple injection with short breaks during a combustion cycle.
Injection valves with multi-hole nozzles
Multi-hole injection valves are very similar to conventional fuel injectors (diesel engine) in terms of their design. The multi-hole nozzle enables very flexible types of jets, as the number and location of the injection jets can be adapted to the combustion chamber and the requirements of the combustion system. For example, an asymmetrical spray contour allows emission-critical areas in the combustion chamber to be left out in a targeted way, thereby preventing the open intake valves from being wetted during the injection as part of the intake stroke. A gap in the spray can also prevent the spark plug from being wetted with fuel. The injection orifices can vary depending on the insert. Variants usually have between 4 and 12 injection orifices. There is also the possibility of tilting the injection jets opposite the axis of the injection valve, which further increases the flexibility of the installation. Due to the design, there is always a dead volume between the valve seat and the injection orifice outlet. After the float needle is closed, the fuel that remains here evaporates into the combustion chamber. The residual fuel can cause carbonization on the nozzle, which may affect the distribution of the jet. The geometric design of the injection orifices can influence the spray distribution and mixture formation.
Injection valves with multi-hole nozzles are commonly used for direct injection.
Injection valves with C-nozzles are normally used for intake manifold injection.
| Component descriptions | Engine 176, 177, 256, 279 in model 223 | GF07.03-P-6120A | |
| Component description for fuel injectors | Engine 139, 177 in model 232 | GF07.03-P-6120F | |