In view of the rapid development of new, high- performance engines and fuel-injection systems with sophisticated functionality (e.g. multiple injection phases), continuous development of the nozzle is a necessity. In addition, there are number of aspects of nozzle design which offer scope for innovation and further im- provement of diesel engine performance in the future. The most important aims are: minimizing untreated emissions in order to
reduce or even eliminate the expense of costly exhaust-gas treatment equipment that also presents difficulties with regard to waste disposal (e.g. soot filters) minimizing fuel consumption optimizing engine noise.
There various different areas on which atten- tion can be focused in the future development of the nozzle (Figure 1) and a corresponding variety of development tools (Figure 2). New materials are also constantly being developed which offer improvements in durability. The use of multiple injection phases also has con- sequences for the design of the nozzle.
If different types of fuel (e.g. designer fuels) are used, this also affects nozzle design because of the differences in viscosity or flow charac- teristics. Such changes will in some cases also demand new production processes such as laser drilling for the injection orifices.
116 Nozzles Future development of the nozzle
Tribology Pressure-wave resistance Dead volume Injection- pattern shaping Flow tolerance Orifice - diameter - leading-edge contour - shape - surface - variability Long-term stability Seat geometry Body heat resistance Detrimental volume Blind hole
Main points of focus of nozzle development
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N M K1 86 1E3D flow simulation (a) Transparent nozzle
Mechanical jet examination
Optical jet examination (b) Transparent engine
Test engine
a b
Development tools for nozzles
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N M K1 862ENozzles High-precision technology 117
1 Nozzle body sealing face 2 Nozzle-needle guide clearance 3 Injection orifice High-precision technology
The image associated with diesel engines in many people’s minds is more one of heavy- duty machinery than high-precision engineering. But modern diesel fuel-injection systems are made up of components that are manufactured to the highest degrees of accuracy and required to withstand enormous stresses.
The nozzle is the interface between the fuel- injection system and the engine. It has to open and close precisely and reliably for the entire life of the engine. When it is closed, it must not leak. This would increase fuel con- sumption, adversely affect exhaust-gas emis- sions and might even cause engine damage.
To ensure that the nozzles seal reliably at the high pressures generated in modern fuel-injection systems such as the VR (VP44), CR, UPS and UIS designs (up to 2,050 bar), they have to be specially designed and very precisely manufactured. By way of illustration, here are some examples:
To ensure that the sealing face of the nozzle body (1) provides a reliable seal, its has a dimensional tolerance of 0.001 mm (1 µm). That means it must be accurate to within approximately 4,000 metal atom layers!
The nozzle-needle guide clearance (2) is 0.002...0.004 mm (2...4 µm). The dimensional tolerances are similarly less than 0.001 mm (1 µm).
The injection orifices (3) in the nozzles are cre- ated by an electro-erosion machining process. This process erodes the metal by vaporization caused by the high temperature generated by the spark discharge between an electrode and the workpiece. Using high-precision elec- trodes and accurately configured parameters, extremely precise injection orifices with diame- ters of 0.12 mm can be produced. This means that the smallest injection orifice diameter is only twice the thickness of a human hair (0.06 mm). In order to obtain better injection characteristics, the leading edges of the
nozzle injection orifices are rounded off by special abrasive fluids (hydro-erosion machining).
The minute tolerances demand the use of highly specialized and ultra-accurate measuring equipment such as
optical 3-D coordinate measuring machine for measuring the injection orifices, or laser interferometers for checking the
smoothness of the nozzle sealing faces.
The manufacture of diesel fuel-injection com- ponents is thus “high-volume, high-technology”.
1 2 3 A matter of high-precision
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N M K1 7 09-2YA nozzle holder combines with the matching nozzle to form the nozzle-and-holder assem- bly. There is a nozzle-and-holder assembly fitted in the cylinder head for each engine cylinder (Figure 1). These components form an important part of the fuel-injection system and help to shape engine performance, ex- haust emissions and noise characteristics. In order that they are able to perform their func- tion properly, they must be designed to suit the engine in which they are used.
The nozzle (4) in the nozzle holder sprays fuel into the diesel-engine combustion chamber (6). The nozzle holder contains the following essential components:
valve spring(s) (9)
which act(s) against the nozzle needle so as to close the nozzle;
nozzle-retaining nut (8)
which retains and centers the nozzle; filter (11)
for keeping dirt out of the nozzle;
connections for the fuel supply and return lines which are linked via the pressure channel (10).
Depending on design, the nozzle holder may also contain seals and spacers. Standardized dimensions and combinations provide the required degree of adaptability combined with the minimum of component diversity.
118 Nozzle holders
Nozzle holders
Fig. 1 11 Fuel supply 12 Holder body 13 Fuel return 14 Nozzle 15 Sealing gasket 16 Combustion chamber of diesel engine 17 Cylinder head 18 Nozzle-retaining nut 19 Valve spring 10 Pressure channel 11 FilterK B A L Z 105 S V XX…
K B C D Nozzle holder L No letter V No letterLong nozzle collar = Short nozzle collar
Test holder = Standard nozzle holder
P S
Nozzle (collar dia. 14.3 mm) Nozzle (collar dia.17 mm)
Length (mm)
Z No letter
Two inlet passages = One inlet passage A
E
N
Spring at bottom
Nozzle-holder dia. 17 mm (Type P nozzle), dia. 25 mm (Type S nozzle)
Spring at bottom
Nozzle-holder dia. 21 mm (Type P and S nozzle) Spring at bottom
Nozzle-holder dia. 17/21 mm (Type P nozzle) Attached by flange or clamp
External thread on nozzle-retaining nut Sleeve nut
Ser. no.
Specimen:last 7 digits of the
drawing number Bosch type designation codes for nozzle holders
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S M K1 83 1E 4 5 6 2 3 10 1 11 9 8 7Schematic diagram of a nozzle-and-holder assembly on a direct-injection engine 1
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U M K1 7 1 9-1YThe design of the nozzle holder for direct-in- jection (DI) and indirect-injection (IDI) en- gines is basically the same. But since modern diesel engines are almost exclusively direct- injection, the nozzle-and-holder assemblies illustrated here are mainly for DI engines. The descriptions, however, can be applied to IDI nozzles as well, but bearing in mind that the latter use pintle nozzles rather than the hole-type nozzles found in DI engines. Nozzle holders can be combined with a range of nozzles. In addition, depending on the required injection pattern, there is a choice of
standard nozzle holder (single-spring nozzle holder) or
two-spring nozzle holder (not for unit pump systems).
A variation of those designs is the stepped holder which is particularly suited to situa- tions where space is limited.
Depending on the fuel-injection system in which they are used, nozzle holders may or may not be fitted with needle-motion sensors.
The needle-motion sensor signals the precise start of injection to the engine control unit.
Nozzle holders may be attached to the cylinder block by flanges, clamps, sleeve nuts or external threads. The fuel-line connection is in the center or at the side.
The fuel that leaks past the nozzle needle acts as lubrication. In many nozzle-holder designs, it is returned to the fuel tank by a fuel-return line.
Some nozzle holders function without fuel leakage – i.e. without a fuel-return line. The fuel in the spring chamber has a damp- ing effect on the needle stroke at high injec- tion volumes and engine speeds so that a similar injection pattern to that of a two- spring nozzle holder is generated.
In the common-rail and unit-injector high- pressure fuel-injection systems, the nozzle is integral with the injector, so that a nozzle- and-holder assembly is unnecessary.
For large-scale engines with a per-cylinder output of more than 75 kW, there are appli- cation-specific fuel-injector assemblies which may also be cooled.
Nozzle holders 119
a b c d e f g h i j
2 cm
Examples of nozzle-and-holder assemblies
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