JPH05200328A - Fuel injector nozzle - Google Patents

Abstract

PURPOSE:To obtain a high pressure fuel injector nozzle for internal combustion engine excellent in wear resistance and having long life by making a nozzle ejector part of a ceramic and providing the injector nozzle with a specific dimensional aperture. CONSTITUTION:In the high pressure fuel injector for internal combustion engine having the injector of <=0.2mm aperture and used at >=150kg/mm<2> injection pressure, at least the nozzle injector 13 part is formed from ceramic. In this case, the ceramic constituting the nozzle injector 13 is a silicon nitride base ceramic having >=99% theoretical density ratio and is a composite ceramic of silicon nitride and silicon carbide and the ratio of silicon carbide is <=40vol.%. And the silicon nitride-silicon carbide composite ceramic constituting the nozzle injector 13 is made of a Si-C-N amorphous powder synthesized by vapor phase reaction of hexamethyl-disilazane with ammonia. Or a zirconia base ceramic having >=99% theoretical density ratio is also used as the ceramic constituting the nozzle injector.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fuel injection nozzle,
In particular, it relates to a fuel injection nozzle made of ceramics having excellent heat resistance and wear resistance.

[0002]

2. Description of the Related Art Diesel engines are currently said to have the highest thermal efficiency among prime movers, but their exhaust gas countermeasures have been taken up as an important issue from the viewpoint of environmental protection these days. There is. That is, various countermeasures against the generation of soot (particulate) and NO _x , such as a purifying device including a catalytic action, are being studied. In it, it has been shown that rapid mixing of fuel and air increases burning rates and significantly reduces soot generation.

High-pressure fuel injection is effective for rapid mixing, and is reported, for example, in "ACE Technical Papers No. 1" (published in March 1991, New Combustion Systems Laboratory Co., Ltd.). As described above, a high-pressure injection system of 280 kg / cm ² has been prototyped and is under consideration.

Generally, when the injection pressure exceeds 150 kg / cm ² , it is found that the fuel in the fuel spray becomes fine particles and the mixing of the fuel and air is improved, and the combustion chamber and the injection nozzle suitable for the injection device are further improved. NO _x
It was confirmed that the emission of soot can be significantly reduced without increasing the emission of. It has also been confirmed that this injection nozzle preferably has a small diameter of 0.2 mm or less.

However, when fuel is injected at a high injection pressure with a nozzle having such a small diameter injection hole, the conventional metal nozzle suffers significant wear of the injection hole, and the injection state deviates from an appropriate injection state in a relatively short time. On the contrary, there is a problem that the amount of discharged soot increases.

Accordingly, it is an object of the present invention to provide a high pressure fuel injection nozzle for an internal combustion engine which is excellent in wear resistance and has a long life.

[0007]

[Means for Solving the Problems] In view of the above purpose, 0.2 mm
As a result of various studies on a high-pressure fuel injection nozzle for an internal combustion engine having an injection hole with a diameter smaller than or equal to the diameter and an ejection pressure of 150 kg / cm ² or more, the inventors have found that in order to reduce the wear amount, at least the nozzle It has been found that the injection hole portion may be made of ceramic rather than metal.

When a ceramic injection hole portion is used, the amount of wear of the injection hole due to the high-pressure injection flow of fuel per unit time is inversely proportional to the square root of the product of fracture toughness and hardness of the material, and ) V = k / √ (Kc · H) (1) (In the formula, V represents the wear amount per unit time, Kc represents the fracture toughness of ceramics, H represents the hardness of ceramics,
k indicates a constant. ). In addition to these physical properties, it also depends greatly on the state of the fine structure, and it is known that the finer the structure (crystal grains), the higher the abrasion resistance. From these facts, as the material of the injection hole of the ceramic nozzle, one having high fracture toughness and hardness and a fine microstructure may be selected. Therefore, if silicon nitride ceramics or zirconia ceramics is used, I found something good. The present invention has been completed based on these findings.

That is, the high-pressure fuel injection nozzle for an internal combustion engine of the present invention has injection holes with a diameter of 0.2 mm or less,
It is used with an injection pressure of mm ² or more, and is characterized in that at least the nozzle injection hole portion is made of ceramics.

By using a silicon nitride ceramics having a theoretical density ratio of 99% or more or a zirconia ceramics having a theoretical density ratio of 99% or more as the ceramics forming the nozzle injection holes, it is possible to further improve wear resistance and long life. It can be a high-pressure fuel injection nozzle.

The present invention will be described in detail below. In the fuel injection nozzle of the present invention, at least the nozzle injection hole is made of ceramics. As this ceramic, one having high fracture toughness and high hardness is preferable as described above, and it is particularly preferable to use silicon nitride ceramics or zirconia ceramics. The theoretical density ratio of ceramics is preferably 99% or more. If the theoretical density ratio is less than 99%, pores are likely to exist, particles are likely to drop off from the pores, wear is likely to occur, and the nozzle life cannot be extended.

The silicon nitride ceramics are not limited to those composed of silicon nitride and a sintering aid, but may be composite ceramics containing silicon carbide or the like. Silicon nitride / silicon carbide composite ceramics are particularly preferable in terms of hardness.

The content ratio of silicon carbide in the silicon nitride / silicon carbide composite ceramics is 10 in total of silicon nitride and silicon carbide.
0% by volume is preferably 40% by volume or less,
It is preferably from 15 to 35% by volume. The content rate of silicon carbide is
If it exceeds 40% by volume, the hardness is improved, but the fracture toughness is reduced, and as a result, the wear resistance is reduced, which is not preferable.

As a method of dispersing and compounding silicon carbide particles in silicon nitride particles, in addition to a method of simply mixing the respective powders, Si-C-N amorphous synthesized by a gas phase reaction of hexamethyldisilazane and ammonia. It is possible to use a method in which powder is used and nano-sized silicon carbide particles are dispersed in silicon nitride particles serving as a matrix during firing.

The silicon nitride forming the matrix is preferably silicon nitride having high toughness and high strength in which so-called needle crystals are grown, and silicon nitride powder is added to oxide-based sintering aids such as alumina, yttria and magnesia. Is added.

The blending amount of the sintering aid varies depending on the kind of the sintering aid to be used, but is about 5 to 25% by weight with the total of silicon nitride and the sintering aid being 100% by weight.

The zirconia used in the zirconia-based ceramics includes those containing yttria or the like as a stabilizer in an amount of about 3 mol% or less. As zirconia-based ceramics, for the purpose of improving hardness,
A composite of alumina is preferable.

The proportion of alumina to be dispersed and composited is preferably 80% by volume or less, and more preferably 20 to 70% by volume, with the total amount of zirconia and alumina being 100% by volume. When the content of alumina exceeds 80% by volume, the hardness is improved, but the fracture toughness is reduced, and as a result, the wear resistance is reduced, which is not preferable. Further, in the case of an alumina dispersion system, when the compounding amount is large, the structure becomes coarse, that is, the average particle size becomes 2 μm or more, and alumina is
Due to the anisotropy of the coefficient of thermal expansion, if relatively large crystal grains are present, the crystal grains will easily fall off, which will reduce wear resistance more than the fracture toughness.

In the case of zirconia-based ceramics,
An oxide-based sintering aid such as magnesia can be added.

An example of the fuel injection nozzle of the present invention is shown in FIG. This nozzle 1 is a tubular body made entirely of ceramics, and this tubular body is composed of a tubular portion 11 (inner diameter a) and a tapered tip portion 12 whose diameter is gradually reduced. Injection holes 13 are formed. The diameter b is 0.2 mm or less, but the inner diameter a may be about 1 to 3 mm. The nozzle 1 of the present invention is preferably one in which the entire nozzle is made of ceramics as in the present embodiment, but the present invention is not limited to this, and at least the injection hole portion may be made of ceramics, for example, the tip. It is also possible that only the portion 12 is made of ceramic and is joined to a tubular member such as a metal.

[0021]

As described above, the fuel injection nozzle of the present invention is
Since at least the injection hole part is made of ceramics, it has a long life when used as a high-pressure fuel nozzle for internal combustion engines such as diesel engines with injection pressure of 150 kg / cm ² or more even with small diameter injection holes of 0.2 mm or less. As a result, it is possible to provide an engine system in which exhaust soot is reduced as much as possible.

[0022]

The present invention will be described in more detail with reference to the following specific examples.

Example 1 and Comparative Example 1 82.5% by weight of α-silicon nitride having an average particle size of 0.4 μm and an average particle size of
15% by weight of 0.4 μm yttria and 2.5% by weight of alumina with an average particle size of 0.3 μm were sufficiently mixed, and the obtained mixed powder was sintered at 1780 ° C. for 2 hours to give an outer diameter of 8 mmφ and a length of
A 20-mm dense (theoretical density ratio 99.5%) silicon nitride sintered body was prepared, and the inner diameter (a) of 2 m as shown in Fig. 1 was produced from this sintered body.
A nozzle with m and a tip hole diameter (b) of 0.15 mm was produced by ultrasonic processing.

The silicon nitride ceramic nozzle thus obtained was installed in an ultrahigh pressure injection device, and a single cylinder, naturally aspirated engine with a displacement of 2 liters (bore 135 mm × stroke 140 mm) was used to rotate at 5000 rpm. , Pressure 250MPa 12
After running for 0 hours, wear resistance was evaluated. as a result,
The diameter of the tip injection hole is 0.176 mm, and the wear amount is 0.026 mm.
Met.

For comparison, the same wear resistance was evaluated using a nozzle of the same shape made of high-speed steel, and the tip injection hole diameter was 0.334 mm, and the wear amount was
It was significantly worn down to 0.184 mm.

Examples 2 to 6 Various silicon nitride mixed powders containing the sintering aids (yttria and alumina) prepared in Example 1 and β-silicon carbide having an average particle size of 0.3 mm are shown in Table 1. A dense ceramic nozzle was produced in the same manner as in Example 1 from the powders mixed in the ratio.

Each of the obtained nozzles was subjected to the same abrasion resistance evaluation test as in Example 1. The results are shown in Table 1 together with the theoretical density ratio of ceramics.

The distal injection port of the first table silicon nitride ⁽¹⁾ silicon carbide theoretical density ratio 120hr after the operation No. (volume%) (volume%) (%) diameter (mm) wear amount (mm) Example 2 95 5 99.6 0.178 0.028 Example 3 85 15 99.4 0.170 0.020 Example 4 75 25 99.3 0.163 0.013 Example 5 65 35 35 99.4 0.165 0.015 Example 6 55 45 98.5 0.218 0.068 Note) (1): Sintering used in Example 1 Auxiliary material.

As is clear from Table 1, Examples 2 to 6
The silicon nitride / silicon carbide composite ceramics fuel injection nozzle of No. 1 had less wear than the nozzle of Comparative Example 1 made of high-speed steel described above. Particularly, the nozzles of Examples 2 to 5 in which the blending amount of silicon carbide was 40% by volume or less had a very small amount of wear.

Example 7 A silicon nitride / silicon carbide sintered body (silicon carbide 25% by volume, theoretical density ratio) using Si--C--N amorphous powder as a raw material synthesized by a gas phase reaction of hexamethyldisilazane and ammonia. 99.3%), a dense ceramic nozzle was produced in the same manner as in Example 1.

The silicon nitride / silicon carbide composite ceramics nozzle thus obtained was subjected to the same abrasion resistance evaluation test as in Example 1, and after 120 hours of operation, the diameter of the tip injection hole was 0.169 mm. The amount of wear was 0.019 mm.

Examples 8 to 13 Zirconia containing 3 mol% of yttria and having an average particle size of 0.3 μm, and high-purity alumina having an average particle size of 0.3 μm were used as the second material.
Dense ceramic nozzles were produced in the same manner as in Example 1 from the powders mixed in the proportions shown in the table. The theoretical density ratios of the ceramics constituting the obtained nozzles were all 99.0% or more.

The same abrasion resistance evaluation test as in Example 1 was conducted for each nozzle. The results are shown in Table 2 together with the average particle size of ceramics.

The distal injection port of the second table of zirconia alumina average particle diameter 120hr after the operation No. (volume%) (volume%) ([mu] m) diameter (mm) wear amount (mm) Example 8 90 10 0.6 0.188 0.033 embodiment Example 9 80 20 0.8 0.179 0.029 Example 10 70 30 0.8 0.180 0.030 Example 11 50 50 1.1 0.185 0.035 Example 12 30 70 1.6 0.184 0.034 Example 13 10 90 2.4 0.233 0.083

As is apparent from Table 2, Examples 8 to 13
The zirconia / alumina composite ceramics fuel injection nozzle of No. 2 had less wear than the high-speed steel nozzle (Comparative Example 1). In particular, when the content of alumina was 80% by volume or less (Examples 8 to 12), the amount of wear was remarkably small.

[0036]

As described in detail above, since the fuel injection nozzle of the present invention has at least its injection hole made of ceramics, it has a small injection hole with a diameter of 0.2 mm or less.
When used as a high-pressure fuel nozzle for an internal combustion engine such as a diesel engine used at an injection pressure of cm ² or more, it has a long life. In particular, if a silicon nitride ceramics or zirconia ceramics having a high fracture toughness and hardness and a fine crystal structure is used as the above ceramics, it is possible to obtain a long-life nozzle having better wear resistance. ..

The fuel injection nozzle of the present invention as described above is suitable for an internal combustion engine, particularly a diesel engine, in which exhaust soot is reduced as much as possible.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a fuel injection nozzle of the present invention.

[Explanation of symbols]

 1 ... Fuel injection nozzle 11 ... Cylindrical part 12 ... Tip part 13 ... Injection hole

Claims (6)

[Claims] 1. An injection hole having a diameter of 0.2 mm or less, 150 kg
A high-pressure fuel injection nozzle for an internal combustion engine, which is used at an injection pressure of / mm ² or more, wherein at least the nozzle injection hole portion is made of ceramics. 2. The fuel injection nozzle according to claim 1, wherein the ceramic forming the nozzle injection hole is silicon nitride ceramics having a theoretical density ratio of 99% or more. 3. The fuel injection nozzle according to claim 2, wherein the silicon nitride ceramics forming the nozzle injection hole is a composite ceramic of silicon nitride and silicon carbide,
A fuel injection nozzle characterized in that the proportion of the silicon carbide is 40% by volume or less. 4. The fuel injection nozzle according to claim 3, wherein the silicon nitride / silicon carbide composite ceramic forming the nozzle injection hole is synthesized by a gas phase reaction of hexamethyldisilazane and ammonia. -N is a fuel injection nozzle obtained from amorphous powder. 5. The fuel injection nozzle according to claim 1, wherein the ceramic forming the nozzle injection hole is a zirconia-based ceramic having a theoretical density ratio of 99% or more. 6. The fuel injection nozzle according to claim 5, wherein the zirconia-based ceramics is zirconia / alumina composite ceramics, and the ratio of the alumina is
80% by volume or less, the crystal grain size of the ceramic is 2 μm
A fuel injection nozzle characterized in that: