INJECTION MOLDED NOZZLE AND INJECTOR COMPRISING THE INJECTION MOLDED NOZZLE

TECHNICAL BACKGROUND

The PTC-effect of ceramic material comprises a change of the specific electric resistivity p as a function of the temperature T. While in a certain temperature range the resistivity p is small with a rise of the temperature T, starting at the so-called Curie-temperature T _c , the resistivity p increases with a rise of temperature. In this second temperature range, the temperature coefficient, which is the relative change of the resistivity at a given temperature, can be in a range of 50%/K up to 100%/K.

SUMMARY

An injection molded nozzle is described, comprising a base body with a fluid channel connected to a fluid inlet and a fluid outlet. The base body comprises a ceramic material with a positive temperature coefficient of its ohmic resistance, henceforth termed "PTC ceramic". Upon application of a current, the base body is heated in a manner vaporizing a fluid receivable in the fluid channel. The fluid outlet is provided with a shape enabling ejection of the fluid as a vapour spray.

The nozzle is suited to directly vaporizing a fluid flowing through it, such as a chemically combustible fuel, so that the fuel can be released, in vaporous form, in or onto another medium. For example, the vaporized fuel may be ejected into a combustion chamber, where it is mixed with air to create a combustible mixture for the purpose of, for example, displacing a cylinder of an internal combustion engine. Fuels vaporizable by the nozzle particularly include ethanol. However, the PTC properties of the nozzle, that is,

the constitution of the PTC ceramic, can also be adjusted to vaporize other fuels such as gasoline or diesel.

Since the nozzle itself constitutes a part of a means to vaporize any fluid flowing through it, additional heating or vaporizing means, such as an additional heat exchanger in the form, for example, of wiring, piping or a heating rod need not be placed in contact with the fluid or into the nozzle itself. This greatly simplifies the construction, form and cost of the means to heat the fluid. Furthermore, as the nozzle itself constitutes a heating means for the fluid, its entire surface in contact with the fluid can be used as a heat exchanging means for the purpose of vaporising the fluid. This facilitates vaporizing the fluid in a particularly short amount of time.

The base body comprising the PTC-ceramic material has a self regulative property. If the temperature of the base body reaches a critical level, the resistance of the PTC ceramic also rises and thus reduces the electric current running through it. As a result, the PTC ceramic of the base body ceases to heat and is allowed to cool. Thus, no external regulation system is necessary.

According to one embodiment of the nozzle, its base body contains less that 10 parts per million (ppm) of metallic impurities. Metallic impurities are metallic materials that conflict with the desired heating properties of the PTC ceramic. Said desired properties include the ability to vaporize the fluid in the shortest amount of time possible.

It was found that one way to maintain the upper limit of 10 ppm of metallic impurities in a base body of the nozzle is to provide tools used for preparing the ceramic material of the nozzle's base body, such as a ceramic feedstock, with a hard coating preventing the abrasion of the tool into the ceramic material. A suitable coating was determined to include

Tungsten Carbide (WC) . The base body, itself molded out of the feedstock, thus contains less than 10 ppm of a metallic material contained on any surface of a tool contactable with the ceramic material.

Examples of tools used during the processing of the feedstock are mixing means such as a twin-roll mill. This may consist of two counter-rotating differential speed rollers with an adjustable nip that impose shear stresses on the material of the feedstock as it passes through the nip. Other tools include a single-screw or a twin-screw extruder as well as a ball mill or a blade-type mixer.

One embodiment of the nozzle comprises a base body with a ceramic material with a PTC ceramic having a Curie- temperature between -30 ⁰ C and 340 ⁰ C. In particular, a base body with a PTC ceramic having a resistivity at a temperature of 25 °C in the range of 3 ωcm to 30000 ωcm is preferred.

A base body comprising a PTC ceramic with the aforementioned properties relating to resistivity and Curie-temperature is suited to vaporising a fluid flowing through its fluid channel as rapidly as possible.

The base body of the nozzle preferably contains Barium Titanate (BaTiO ₃ ) , a Perowskite ceramic (ABO ₃ ) . In particular, according to one embodiment, the base body comprises the structure

Bai- _x - _y M _x D _y Ti ₁ - _a _ _b NMn _b O ₃

where x stands for a range between 0 and 0.5 and y, a and b each stand for a range between 0 and 0.01. In this structure M stands for a cation of the valency two, such as for example Ca, Sr or Pb, D stands for a donor of the valency three or four, for example Y, La or rare earth elements, and N stands

- A -

for a cation of the valency five or six, for example Nb or Sb.

According to one embodiment, the base body is preferably injection molded from a PTC-ceramic with the following composition :

ABO ₃ + SiO ₂

whereby A is one or more elements chosen from Ba, Ca, Sr, Y and B is one ore more element chosen from Ti, Mn and the part of Si is 0.5 to 4.5 mol, preferably 0.5 to 2.0 mol percent relating to the sum of both components.

The fluid outlet of the nozzle preferably is connected to a first section of the fluid channel and the fluid inlet to a second section of the fluid channel. The first section comprises a larger diameter than the second. At a given pressure at the fluid inlet, the flow rate of a fluid in the second section of the nozzle is higher than in the first section. The cross section of fluid channel can increase in steps or continually increase in the direction from the fluid inlet to the fluid outlet. Thus, the fluid channel may have a stepped or continuous conical shape.

The fluid outlet is preferably shaped as a funnel, enabling a particularly homogeneous ejection of the vaporized fluid as a conical spray.

A method for preparing a feedstock injection moldable into a nozzle is also proposed. The method comprises the preparation of a ceramic filler convertible by sintering to a PTC- ceramic. The ceramic filler is mixed with a matrix for binding the filler and the mixture comprising filler and matrix is processed into a granulate. During the preparation of the feedstock, tools contactable with the feedstock are used which have a low degree of abrasion such that a

feedstock comprising less than 10 ppm of impurities caused by abrasion is obtained. As previously mentioned, the tools may be provided with a hard coating that prevents said abrasion. The material of the PTC ceramic of the base body preferably corresponds to that of the ceramic filler of the feedstock.

As a result of the at least nearly absent impurities, when the feedstock is injection molded into its desired nozzle shape, its electrical properties such as low resistivity and / or slope of its resistance-temperature curve are maintained in the injection molded nozzle.

Additionally, an injector is proposed comprising an injection molded nozzle according to the embodiments described in this document, wherein a valve is provided preceding the fluid inlet of the nozzle such that it may control the passage of a fluid into the fluid channel of the nozzle.

According to an embodiment of the injector, a preheating element is provided preceding the valve, wherein the preheating element comprises a mold comprising a fluid channel, a fluid inlet and a fluid outlet. The mold further comprises a ceramic material with a positive temperature coefficient, whereby upon application of a current, the mold is heated such that a fluid passing through the fluid channel is preheatable.

The preheated fluid can then be passed via the valve to the injection molded nozzle, where it is rapidly vaporised and ejected via the fluid outlet of the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments are elaborated upon with the help of the following figures and examples.

Figure 1 is a schematic illustration of an injection molded nozzle,

Figure 2 is a perspective view of an injection molded nozzle with which a portion of its outer surface and outer electrode strips are shown.

Figure 3 is a perspective view of an injection molded nozzle depicting an inner part and a passivation layer of the nozzle .

Figure 4 is a perspective view of an injection molded nozzle depicting laminar protrusions on the inner side of the nozzle's base body.

Figure 5 is a cross sectional view of an injector comprising the injection molded nozzle.

DETAILED DESCRIPTION

Figure 1 shows an injection molded nozzle with a base body shaped as a stepped cone comprising a PTC ceramic. The conically shaped base body 2 comprises at least two sections 2a and 2b of differing cross section. The wider of the two sections 2a is connected to a fluid inlet 3 and the narrower of the two sections 2b to a fluid outlet 4. The two sections are preferably joined together by a sloped third section 2c of varying cross section. However, the two sections 2a and 2b can be joined together directly, whereby the transitional section 2c connecting the two section 2a and 2b with varying cross section is not necessary. The latter scenario is depicted by means of the dotted line in the figure.

The base body preferably contains Barium Titanate, in particular of a structure Bai- _x - _y M _x D _y Tii- _a - _b NMn _b θ3 as previously described. Preferably, the base body comprises a PTC ceramic having a Curie-temperature between -30 ⁰ C and 340 ⁰ C. In

particular, the base body may be adjusted to comprise a PTC ceramic having a resistivity at room temperature, in particular at 25 ⁰ C, in the range of 3 ωcm to 30000 ωcm.

More specifically, it is preferred that the PTC ceramic comprises BaCC>3, Tiθ2, Mn-containing solutions and Y-ion containing solutions, for example MnSO ₄ and YO3 _/ 2, and at least one out of the group of Siθ2, CaCC>3, SrCC>3, and Pb3θ ₄ . For example, out of these base materials, a ceramic material of a composition

( Bao , 329C)Cao , 0505 S r o , O 969 Pbo , 1306 ^ 0 , O O5 ) ( T l o , 5 O2Mno , 0007 ) Ol , 5045

can be provided. A base body of this ceramic material has a characteristic reference temperature T _b of 122°C and depending on the conditions during sintering, a resistivity range from 40 to 200 ωcm.

The material and electrical features of the base body described above are valid also for the embodiments described with the help of the following figures.

Subject to a voltage, the base body 2 is heated up such that a fluid flowing through it is correspondingly heated and vaporized. A suitable voltage is 13,5 V (12 V) or 24 V or a voltage in a range between the two, depending on the application of the nozzle. The corresponding current is given by the voltage and the resistance in dependence of the RT characteristic curve of the base body 2.

Figure 2 shows an injection molded nozzle 1 with a base body 2 in an essentially conical shape, the base body comprising a PTC ceramic. The wider end of the base body 2 is provided with a fluid inlet 3 and the narrower end of the base body with a fluid outlet 4. The fluid outlet 4 is funnel shaped with its wider opening showing out of the base body and its narrower opening pointing into the base body. The fluid

outlet and the fluid inlet are connected to each other by means of a fluid channel 5.

According to an embodiment of the nozzle, the base body is provided with electrodes 7 and 8 of mutually opposite polarity, each preferably comprising the shape of a strip extending longitudinally along the outer surface of the base body. The electrodes are arranged with a sufficient distance from each other to prevent electrical arcing. Alternatively, one electrode 8 of first polarity may be arranged on the inside surface of the base body, that is, along the fluid channel, and another electrode 7 of opposite polarity on the outside surface of the base body.

The electrodes preferably comprise at least one material chosen out of the group: Cr, Ni, Al, Ag. The electrodes can be thin film or thick film printed on the respective surfaces of the base body. They may alternatively be applied to the respective surfaces of the base body by means of galvanic deposition.

Figure 3 shows the injection molded nozzle 1 according to Figure 1, whereby it is shown how the fluid channel 5 comprises a first section 5a connected to the fluid inlet 3 and a second section 5b connected to the fluid outlet 4. At least at one point along the longitudinal axis of the nozzle the first section 5a has a wider diameter or cross section that at a point along the second section 5b of the fluid channel 5. Preferably, the first and second sections of the fluid channel 5 comprise constant or nearly constant cross sections .

The first and second sections 5a and 5b of the fluid channel can be connected to each other by means of a third section 5c. The third section has a narrowing diameter or cross section beginning at the first section 5a and ending at the second section 5b.

Notwithstanding the previously described geometries and shapes, the fluid channel may comprise a continuously decreasing cross section beginning at the fluid inlet 3 and ending at the beginning of the preferably funnel shaped fluid outlet 4.

According to one embodiment of the nozzle, the base body is provided with a passivation material comprising an insulative property by means of which a chemical reaction between the base body and a fluid receivable in the fluid channel, in particular a fuel, is preventable. The passivation material is preferably applied to the wall of the fluid channel as a layer 6, whose outer surface is shown in figure 3 by means of the dashed line. The passivation layer 6 contains a material particularly preventing a chemical reaction between ethanol, gasoline or diesel with the base body. To this end, glass was found to be a suitable passivation material contained in the passivation layer 6. In particular, it was found that a low melting glass or nano-composite lacquer is suitable. For example, the nano-composite lacquer can comprise one ore more of the following composites: Siθ2-polyacrylate-composite, Siθ2-polyether-composite, Siθ2-silicone-composite .

The feature of the passivation layer 6 is preferably combined with that of the strip shaped electrodes 7 and 8 according to the previous figure. The electrodes 7 and 8 can be burned into the base body already provided with the passivation layer 6, whereby the passivation layer melts away in the area where the electrode 8 on the inner surface of the base body is applied.

According to one embodiment of the nozzle, along the inner surface of the base body 2 being the wall of the fluid channel 5 and / or of the fluid inlet 3 and / or of the fluid outlet 4, at least one protrusion is provided. The protrusion serves to increase the surface area of the channel's wall

such that an increased heat exchange surface for vaporizing a fluid contained in the fluid channel is proffered.

According to one embodiment of the protrusion, it may be of laminar shape. A laminar shape is considered to be laminar to the extent that a fluid flowing by it does so in a largely laminar fashion. That is, the protrusion is shaped so as to minimise undue turbulence of the fluid.

According to one embodiment of the protrusion, it is shaped to give the vaporized fluid exiting from the nozzle a particular velocity differing in direction from the longitudinal axis of the nozzle and the direction given by the shape of the fluid outlet. Such a property may comprise a spin of the exiting vaporized fluid or a certain or an off- longitudinal axis spraying direction of the fluid. Thus, the spray exiting the nozzle may comprise a conical shape corresponding to the shape of the fluid outlet, wherein the conical shape may additionally not be rotationally invariant. The spray as a whole may be directed off of the longitudinal axis of the nozzle, thereby being injected into or onto another medium asymmetrically.

The protrusions described in this document may be provided in all sections of the inner surface of the nozzle, thereby including the fluid inlet and the fluid outlet. The protrusions may however be provided along the walls of the fluid channel and the fluid outlet only.

Figure 4 shows an embodiment according to which along the inner surface of the base body 2, along the fluid channel 5, a plurality of protrusions arranged parallel to each other are provided as twisted ribs. Complementing the ribs, a series of grooves 12a may be provided running parallel to them. The grooves may be seen as sections of the fluid channel's wall devoid of ribs or the grooves may actually be dug into the wall of the fluid channel in the sense that the

wall thickness of the base body is thinner in such sections that its average thickness along the longitudinal axis of the body. Such shapes are achievable by injection molding.

A series of ribs or grooves running parallel to each other increases the contact and heat exchange surface of the base body contactable with the fluid. In particular, the ribs or grooves may be arranged helically, that is, they may each run along the wall of fluid channel in a twisted shape. At the same time that such ribs and / or grooves enable the fluid to be vaporized more quickly, twisted ribs can impart a spin to the flowing fluid, such that when the vaporized fluid is ejected from the fluid outlet 3, the ejected spray will spin. A spinning spray of vaporised fluid will be ejected onto another medium, such as the interior of an internal combustion chamber, with a high degree of homogeneity. The spinning spray lends itself to more rapidly attaining a particularly homogenous fuel / air mixture in the combustion chamber .

A combination of the embodiments as specifically depicted by the figures 2 to 4 is possible. In this case, the injection molded nozzle 1 will comprise the base body 2 with electrodes 7 and 8, a passivation layer 6 along the wall of the fluid channel and along the inner all of fluid inlet 3 and the fluid outlet 4 and at least one protrusion 12 along the wall of the fluid channel.

The maximum cross section of the base body preferably lies in the range of 1.8 to 2.2 mm.

The maximum cross section of the fluid inlet 3 preferably lies in the range of 0.8 to 1.2 mm.

The maximum cross section of the fluid inlet 3 preferably lies in the range of 0.8 to 1.2 mm.

The maximum cross section of the fluid channel between the fluid inlet 3 and the fluid outlet 4 preferably lies in a range between 0.1 and 0.5 mm.

The length of the nozzle from the fluid inlet 3 to the fluid outlet 4 via the fluid channel 5 preferably ranges between 1 to 2 cm.

The electrodes 7 and 8, when formed as strips, preferably have maximum widths between 1.8 and 2.2 mm.

Figure 5 shows a cross section of an injector comprising an injection molded nozzle 1 according to the described embodiments and an injection molded preheating element 9. The preheating element 9 can be made of the same material in the same manner with the same geometric and / or topographic properties as any embodiment of the base body 2 of the nozzle 1. The preheating element however preferably does not comprise a funnel shaped fluid outlet but instead comprises a fluid outlet as a continuation of a fluid channel. By preheating a relatively cold fuel before it reaches the nozzle, a more efficiently combustible spray 11 ejected from the outlet 4 of the nozzle is obtained. The PTC-ceramic of the preheater 9 and the current applied are chosen such that the fuel is heated, but preferably not vaporised, before it enters the nozzle via the latter' s fluid inlet 3.

Arranged between the injection molded preheater 9 and the injection molded nozzle 1 is a valve 10. The valve may open in dependence of the temperature, and thus pressure, reached in the preheating element 9. The pretension of the valve may be adjusted on experimental basis depending on when the valve is shown to open at a given pressure level in the fluid channel of the preheating element 9. Preferably, the activation pressure for opening the valve 10 is at a level sufficient to discharge the fuel into the nozzle. The valve can comprise elastic means, such as a spring, that allow it

to snap open when the activation pressure is reached. The activation pressure for opening the valve and the corresponding valve pretension are adjusted to allow a flow rate through the nozzle at which the fuel still has time to be vaporised in the nozzle and ejected therefrom as a spray 11.