JPH0988740A - Fuel gasification device and heater for fuel gasification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve fuel consumption and to purify exhaust gas by shifting the maximum evaporation rate point of fuel droplets on a heating surface to the high temperature side, and raising set temperature on the heating surface to promote gasification of fuel. SOLUTION: A heater 6 for fuel gasification is arranged in an injection area of an injection nozzle 5a of a fuel injector 5 in the inside of an intake manifold 4 connected to a combustion chamber 2 of an gasoline engine 1 through a suction valve 3. The heater 6 is heated by an electrified heating member and it is furnished with a heating body 10 on which a ceramic coated layer 9 is formed by flame coating zirconia (ZrO2 ) on an upper surface of a metallic plate 7 as a base material. Surface temperature with fuel droplets attached on a surface of the ceramic coated layer 9 heated at 300 deg.C by being injected from the injection nozzle 5a is devised to be maintained at lower temperature than temperature at which gasoline locally causes a Leyden frost phenomenon, as the ceramic coated layer 9 is made of zirconia of a low thermal conduction rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vaporizer and a fuel vaporization heater for heating fuel droplets injected from a fuel injector to accelerate the vaporization thereof before being sent to a combustion chamber.

[0002]

2. Description of the Related Art In order to improve fuel efficiency of a gasoline engine and to purify exhaust gas, it is preferable that almost complete combustion be realized in a combustion chamber. For that purpose, it is desirable that the fuel sent to the combustion chamber be sufficiently atomized (atomized) or vaporized.

For example, Japanese Patent Laid-Open No. 5-26130 discloses a fuel injector with a heater capable of preheating fuel before injection so that fuel such as gasoline injected from the fuel injector can be atomized efficiently. Is disclosed.

Further, in JP-A-49-120023, the heating surface (made of metal) forming the bottom of the fuel vaporizer is heated by utilizing the residual heat of the exhaust gas, and the atomization is completed in the vaporizer. There is disclosed a fuel vaporization device that realizes complete vaporization (including atomization) of fuel by vaporizing unburned fuel with heat of a heating surface. In this fuel vaporizer, the heating surface temperature is set to a temperature at which the fuel is in a nucleate boiling state. Nucleate boiling refers to a boiling state in which a large number of bubbles are generated in a droplet and vaporization proceeds not only from the droplet surface but also from inside the droplet.The nucleate boiling state increases the evaporation rate of fuel. The fuel can be vaporized in a short time. Further, Japanese Patent Laid-Open Publication No. Sho 49-120023 discloses a device having an electric heater on the heating surface in addition to this structure.

Further, when the intake manifold is provided with an injection nozzle, a heater is provided so as to arrange the heating surface in the injection area, and fuel droplets which have not been sufficiently atomized (atomised) by spraying are provided. There is also a fuel vaporization device that promotes the vaporization of the fuel by adhering it on the heating surface.

[0006]

FIG. 8 is a graph showing the relationship between the heating surface temperature and the fuel evaporation rate. As can be seen from the evaporation rate curve L in the same figure, vaporization proceeds from the droplet surface of the fuel (natural convection region) while the heating surface temperature is relatively low, and the temperature rises to exceed the saturation temperature of the fuel and When bubbles start to be generated in the droplets and the temperature further rises, the number of the bubbles increases and a so-called nucleate boiling state occurs, resulting in an extremely high evaporation rate. Then, the evaporation rate of the fuel reaches a maximum at a temperature called a maximum evaporation rate point. When the temperature of the heating surface becomes higher than the nucleate boiling region, the contact area between the heating surface and the droplet decreases due to the increased bubbles, and it becomes difficult to transfer heat from the heating surface to the droplet, so that the evaporation rate of the droplet gradually increases. Falls (transition boiling range). Then, when the contact area becomes extremely small, the droplet finally floats from the heating surface (Leidenfrost phenomenon) and enters a film boiling state (film boiling region).

As the bubbles grow larger, it becomes more difficult for heat to be transferred from the heating surface to the droplets, so that the evaporation rate significantly decreases. Therefore, there is a maximum evaporation rate point at which the evaporation rate of the droplet becomes maximum, and the evaporation rate cannot be improved even if the heating surface temperature is higher than the temperature at which nucleate boiling of the fuel droplet occurs. There was a limit to what we could do.

This is also mentioned in JP-A-49-120023, and due to the Leidenfrost phenomenon,
It is said that if the heater temperature is raised too high, it has the opposite effect. In other words, the occurrence of the Leidenfrost phenomenon has been a major cause of being unable to raise the evaporation rate further (more than in the nucleate boiling state). As shown in FIG. 8, if the heating surface temperature is further increased in the film boiling region, the evaporation rate becomes higher than that in the nucleate boiling state. However, at such a high temperature, the filling rate of the air-fuel mixture becomes high. It will drop significantly.

By the way, in the conventional device, even if the fuel is injected, the fuel may not be vaporized at the intake timing timing and some of the fuel droplets may remain on the heating surface as it is, and the injected fuel may remain until the next combustion timing. Not all had been supplied to the combustion chamber. Then, in order to supply the required amount of fuel to the combustion chamber, the amount of fuel injected from the fuel injector is adjusted to a large amount in consideration of the amount of fuel that is not completely vaporized on the heating surface. Therefore, there is a problem that the fuel injection amount per time increases and the fuel efficiency deteriorates.

Further, if the temperature of the heating surface fluctuates with time or the temperature varies on the heating surface, the temperature may change from the high temperature side of the transition boiling region to the temperature corresponding to the film boiling region. In this case, the non-atomized droplets that have floated from the heating surface due to the Leidenfrost phenomenon are supplied to the combustion chamber together with the intake air. Since the droplets that have not been atomized and are not yet a cause of unburned fuel, HC, etc., it is possible to improve fuel efficiency and purify exhaust gas by supplying such droplets to the combustion chamber. There was a problem that it did not exist.

The present invention has been made to solve the above problems, and an object thereof is to set the heating surface temperature to a higher temperature by shifting the maximum evaporation rate point of fuel droplets to a higher temperature side. A fuel vaporization device and a heater for vaporizing fuel, which are capable of promoting the vaporization of fuel, thereby improving fuel efficiency and cleaning exhaust gas.

[0012]

In order to solve the above problems, in the invention according to claim 1, a heating surface is provided in the injection region of the injection nozzle of the fuel injection device in the fuel supply passage connected to the combustion chamber of the gasoline engine. What is claimed is: 1. A fuel vaporization device comprising: a heating element to be arranged; and a heat supply means for heating the heating element so that the heating surface has a set temperature, wherein the heating element is a metal or a ceramic having a high thermal conductivity. And a ceramic coating layer made of low thermal conductivity ceramic coated on the surface of the substrate so as to form the heating surface.

According to a second aspect of the invention, the ceramic coating layer is made of zirconia. In the invention according to claim 3, the thickness of the ceramic coating layer is 100 to 500 µ.
m.

According to the fourth aspect of the present invention, the surface of the ceramic coating layer is provided with an uneven portion having a diameter of 10 to 50 μm. In the invention according to claim 5, an uneven portion having a diameter of 10 to 50 μm is formed on the surface of the ceramic coating layer, and the set temperature of the heating surface is set in the range of 140 ° C. to 440 ° C.

In the sixth aspect of the invention, the set temperature of the heating surface is set within the range of 220 ° C to 370 ° C.
In the invention according to claim 7, the fuel supply passage includes an intake manifold connected to the combustion chamber, and a vaporization chamber connected to the intake manifold and provided with the injection nozzle, and the heating body is provided in the vaporization chamber. The heating surface is provided so as to be arranged in the spray area of the spray nozzle.

In the invention described in claim 8, the above-mentioned claim 1
A heater for vaporizing fuel is provided with the heating element according to claim 7. Therefore, according to the first aspect of the present invention, the heating surface of the heating body is heated to the set temperature by the heat from the heat supply means in the fuel supply passage connected to the combustion chamber of the gasoline engine. Of the fuel injected from the injection nozzle of the fuel injection device, the fuel that has not been atomized (atomized) becomes droplets and adheres to the heating surface. This set temperature is generally set higher than the maximum evaporation rate point on the metal surface of the fuel. The fuel droplets attached to the heating surface are heated and evaporated by the heat transferred from the surface of the ceramic coating layer. At the moment when the fuel droplets are attached, the interface temperature with the droplets drops sharply, and heat is conducted from the surroundings to the interface where the temperature drops so as to eliminate this temperature gradient.
However, since the ceramic coating layer is made of a ceramic having a low thermal conductivity, its heat transfer speed is relatively slow, and the heat transfer speed of heat transferred from its interface portion to the droplets before the temperature gradient is fully recovered. An equilibrium state is reached in the meantime, and the interface temperature is maintained at a temperature at which the Leidenfrost phenomenon does not occur during droplet evaporation. For this reason, even if the liquid droplets are heated on the heating surface at a high set temperature at which the Leidenfrost phenomenon occurs at the initial stage of attachment, the evaporation proceeds while rapidly maintaining the nucleate boiling. As a result, the evaporation rate of the fuel droplets on the heating surface is increased, so that the vaporization rate of the fuel can be improved.

According to the second aspect of the present invention, the ceramic coating layer is formed of zirconia, which has a relatively low thermal conductivity among ceramics, so that the ceramic coating layer has a relatively large size in the vicinity of the interface with the droplets attached to the heating surface. It is possible to form a temperature gradient, and it is possible to shift the maximum evaporation rate point to a high temperature at the set temperature of the heating surface without causing a situation in which the liquid droplets cause film boiling. Then, the evaporation rate is reduced by the amount that the set temperature can be set high.

According to the third aspect of the present invention, when the thickness of the ceramic coating layer is less than 100 μm, it is difficult to form an appropriate temperature gradient in the vicinity of the interface due to the influence of heat from the base material at a preset temperature. As compared with the conventional metal heating surface, it is difficult to set the set temperature so high that it becomes difficult to reduce the evaporation rate of the droplets. Therefore, the thickness of the ceramic coating layer should be 100 μm or more in order to form an appropriate temperature gradient in the vicinity of the interface with the droplet in order to reduce the evaporation rate of the droplet. In addition, the thickness of the ceramic coating layer is 500μ
If m is exceeded, it takes time to recover the heating surface to the set temperature after vaporizing the droplets, and the heating surface is not recovered to the set temperature by the next fuel injection timing. In this case, each time the fuel droplet is ejected, the interface temperature of the heating surface after the droplet adheres continues to decrease, and the evaporation rate decreases. Therefore, in order to maintain a high evaporation rate of droplets, the thickness of the ceramic coating layer is preferably 500 μm or less.

According to the fourth aspect of the invention, the fine irregularities having a diameter of 10 to 50 μm formed on the surface of the ceramic coating layer serve as nuclei of bubbles in the droplets attached to the surface, and the droplets A large number of bubbles are generated for the temperature therein, and the surface area of the droplets is effectively increased to increase the evaporation rate.
Further, since a large contact area between the droplet and the heating surface is ensured by the large number of fine irregularities, the amount of heat transferred from the heating surface to the droplet per unit time is increased, and the evaporation rate is further increased correspondingly. .

According to the invention described in claim 5, 1 is formed on the surface.
According to the heating surface coated with the ceramic coating layer made of zirconia on which the irregularities corresponding to the diameter of 0 to 50 μm are formed,
By setting the set temperature within the range of 140 ° C. to 440 ° C. by the action of claim 2 and the action of claim 4, it is possible to increase the evaporation rate of the droplets higher than the maximum evaporation rate by the metal heating surface. Become.

According to the invention described in claim 6, 1 is formed on the surface.
According to the heating surface coated with the ceramic coating layer made of zirconia on which the irregularities corresponding to the diameter of 0 to 50 μm are formed,
By setting the set temperature within the range of 220 ° C. to 370 ° C. by the action of claim 2 and the action of claim 4, the evaporation rate of the droplets is increased by about 50% with respect to the maximum evaporation rate by the metal heating surface. It becomes possible.

According to the invention as set forth in claim 7, even if the intake chamber connected to the combustion chamber is provided with the vaporizing chamber for sending only the vaporized fuel in advance, the heating element provided in the vaporizing chamber Vaporization is promoted by covering the heating surface arranged in the injection area of the injection nozzle with the ceramic coating layer. Therefore, almost the same amount of vaporized fuel as the fuel injected from the injection nozzle is supplied to the combustion chamber through the intake manifold during the combustion cycle. It is not necessary to adjust the fuel injection amount too much in consideration of the generation of unvaporized fuel.

According to the invention of claim 8, claim 1
~ The effect according to any one of claims 7 is obtained.

[0024]

DETAILED DESCRIPTION OF THE INVENTION A fuel vaporizer embodying the present invention will be described below with reference to FIGS. As shown in FIG. 1, an intake valve 3 is provided in a combustion chamber 2 of a gasoline engine 1.
An intake manifold 4 serving as a fuel supply passage is connected to and disposed via the. A fuel injector 5 as a fuel injection device is provided in the intake manifold 4 upstream of the intake valve 3 by a predetermined distance in a state in which a nozzle 5a of the fuel injector 5 projects into the intake manifold 4. The heater 6 for fuel vaporization, which constitutes the fuel vaporizer, is arranged in the intake manifold 4 at a position corresponding to the injection direction of the fuel injector 5.

As shown in FIG. 2, the heater 6 comprises a metal plate 7 made of SUS (stainless steel) as a base material, and a zirconia (ZrO ₂ ) known as a ceramic having a low thermal conductivity via a binder 8 on an upper surface of the metal plate 7. Ceramic coating layer 9
The heating element 10 is formed by covering the heating element 10 and the heating element 10 disposed on the back surface side of the heating element 10 and constituting the heat supply means.

The energizing heat generating member 11 is connected to the battery power source 12 via the temperature control circuit 13. A temperature sensor 14 for contacting the side surface of the metal plate 7 and detecting the temperature thereof is connected to the temperature control circuit 13, and the energization heat generating member 11 is connected by the temperature control circuit 13 based on a detection signal from the temperature sensor 14. Current value flowing through the surface of the ceramic coating layer 9 is controlled to a predetermined temperature (about 30
It is designed to be kept at 0 ° C.

The ceramic coating layer 9 is made of zirconia (Zr
O ₂ ) is formed by thermal spraying by a thermal spraying method (for example, plasma spraying method). The layer thickness Tz of the ceramic coating layer 9 is in the range of 100 to 500 μm. Further, for the purpose of increasing the binding force of zirconia (ZrO ₂ ) to the surface of the metal plate 7 made of SUS, the ceramic coating layer 9 is interposed via the binding material 8.
Is covered. In the present embodiment, the binding material 8 is a nickel-chromium-aluminum-cobalt-yttria composite body (manufactured by Daiichi Meteco Ltd .; 461NS or 365-365).
2) is used. In addition, zirconia (ZrO ₂ ) having a relatively coarse particle size (manufactured by Daiichi Meteco Ltd .; 201
BNS or 204).

The ceramic coating layer 9 is formed on the entire surface of the metal plate 7, and the surface area of the ceramic coating layer 9 (that is, the sprayed area) is such that the irradiation area of the fuel injected from the injection nozzle 5a is on that surface. It is set to fit all.

The surface roughness of the ceramic coating layer 9 is
It is in the range of about 10 to 50 μm. This is because when the ceramic coating layer 9 is formed by the thermal spraying method, minute irregularities having a diameter according to the particle size of the thermal spraying powder are formed on the surface thereof. Therefore, in the present embodiment, a relatively coarse zirconia powder is used. Because it is used as a thermal spraying powder, minute irregularities having a diameter of about 10 to 50 μm are formed on the surface. Since the droplet diameter of the fuel injected from the injection nozzle 5a of the fuel injector 5 is on the order of several hundreds of μm, the minute irregularities are sufficiently smaller than the droplet diameter. Incidentally, in the present embodiment, zirconia (ZrO ₂ ) is used as the low thermal conductivity ceramic,
The coating layer can also be formed of other ceramic materials known as low thermal conductivity ceramics.

Next, the operation of the fuel vaporizer will be described. When the ignition key is turned on and the engine 1 is driven, the temperature control circuit 13 energizes the energizing heat generating member 11 to heat the heating body 10, and at the same time, fuel injection from the injection nozzle 5a of the fuel injector 5 is started. . The heating surface temperature quickly reaches 300 ° C. and is maintained at that temperature. The energization of the energization heat generating member 11 is continued, and the heating surface temperature is maintained at 300 ° C. while the engine 1 is being driven.

The fuel injected from the injection nozzle 5a is atomized. At this time, the droplets F that have not been sufficiently atomized adhere to the heating surface S of the heater 6 with the force of ejection. In particular, since the fuel is not easily atomized in the center of the injection area, most of the fuel adheres to the heating surface S as droplets F. At least all the droplets F having a diameter larger than the critical droplet diameter that can contribute to complete combustion adhere to the heating surface S.

Before the attachment of the droplets, the surface temperature of the ceramic coating layer 9 is kept at 300 ° C. Since the ceramic coating layer 9 is a very thin film having a layer thickness Tz of 100 to 500 μm, if the heating surface temperature reaches the set temperature of 300 ° C., the inside of the layer has a uniform temperature of 300 ° C. . Fuel droplets F attached to the surface of the ceramic coating layer 9
Is vaporized by being heated by the heat transmitted from its interface.

That is, as shown in FIG. 3, the droplet F attached to the surface (hereinafter referred to as a heating surface) S of the ceramic coating layer 9 passes through the contact interface P between the droplet F and the ceramic coating layer 9. And is boiled and vaporized by the heat transmitted from the ceramic coating layer 9 side.

First, when the droplet F adheres to the heating surface S, it comes into contact with the low temperature droplet, and subsequently, the liquid locally evaporates on the contact surface and heat is rapidly removed from the ceramic coating layer 9. As a result, the surface temperature Ta of the ceramic coating layer 9 whose temperature Ta was 300 ° C. immediately before the deposition of the droplet F instantaneously drops to the temperature Tb. afterwards,
By supplying heat to the low-temperature portion that has cooled to the temperature Tb from around it, a large temperature gradient that is instantaneously generated becomes small.

Here, the material of the ceramic coating layer 9 is
Is low thermal conductivity zirconia (ZrO ₂) Consists of
The amount of heat supplied to the low temperature part from the surroundings per unit time
However, compared to materials with high thermal conductivity such as metal
Pretty small. On the other hand, the interface from the heating surface side to the droplet F side
Since there is heat outflow due to heat transfer through P, this heat flow
Output and inflow of heat due to heat conduction to the low temperature area near the interface
An equilibrium state is reached in the interim. And high heat transfer of metal etc.
A large temperature gradient was created in the beginning compared to that of a material with conductivity.
Before the composition is fully recovered, the interface temperature becomes the initial temperature.
At a temperature Tc that is considerably lower than the temperature Ta (= 300 ° C)
The equilibrium state is reached, and the equilibrium state is maintained
move on.

If the material forming the heating surface S is a material having high thermal conductivity such as metal, the temperature gradient is not so great and the interface temperature Tc remains approximately 300.degree. However, since it is a ceramic, especially zirconia (ZrO ₂ ) which is a material having a relatively small thermal conductivity, the ceramic coating layer 9 has a very surface layer region near the contact interface P as shown in FIG. , Interface temperature Tc to temperature Ta (= 300
A region R (region surrounded by a chain double-dashed line) showing a large continuous temperature gradient up to (° C.) is formed. The shaded area in the figure is the temperature Ta (= 300 ° C.) temperature region during vaporization of the droplets.

That is, even if the droplet F is heated to 300 ° C. until just before the droplet F adheres, the temperature Tc of the interface P is 300 ° C. while the droplet F adheres and the droplet F continues to evaporate. Held well below. This temperature Tc is near the maximum evaporation rate point.

If the interface temperature Tc is suppressed to near the maximum evaporation rate point on the metal heating surface, the droplet F nucleate-boils on the heating surface S and vaporizes in a short time. As described above, the droplet F does not vaporize sufficiently and does not remain on the heating surface. In addition, the heating surface temperature is higher than the Leidenfrost point TL, which is said to cause the Leidenfrost phenomenon in the case of the conventional metal heating surface, by about 100 ° C., but the Leidenfrost phenomenon occurs when the ceramic coating layer is provided. Since it does not exist, the situation in which the non-atomized droplets F having a diameter larger than the critical droplet diameter are sucked into the combustion chamber 2 as they are does not occur. In this way, only the atomized or vaporized fuel that can contribute to complete combustion is supplied to the combustion chamber 2, and complete combustion is realized. Moreover, since all of the injected fuel is supplied to the combustion chamber 2 in the combustion cycle, it is not necessary to adjust the injection amount too much in consideration of the unvaporized amount, and it is possible to improve fuel efficiency. Further, since the droplets F having a diameter larger than the critical droplet diameter are not supplied to the combustion chamber 2, incomplete combustion is avoided and the exhaust gas is also cleaned.

Here, the layer thickness Tz of the ceramic coating layer 9 is 100 to 500 μm, and the layer thickness Tz is 100 μm.
Since the above is ensured, an appropriate temperature gradient is formed in the temperature gradient region R without being affected by the base metal (SUS). As a result, the heating surface temperature Ta can be set to a sufficiently high temperature, and the evaporation rate of the droplet F can be increased accordingly. Further, since the layer thickness Tz is suppressed to 500 μm or less,
It is possible to reliably recover the heating surface temperature Ta after vaporizing the droplets to the set temperature 300 ° C. by the next fuel injection timing. Therefore, the surface temperature of the ceramic coating layer 9 is 30
It is possible to avoid a situation in which the next fuel injection is performed before the temperature is recovered to 0 ° C., and this is repeated, the interface temperature Tc becomes lower than the temperature in the nucleate boiling region, and the evaporation rate cannot be improved. If such a situation cannot be avoided, a part of the fuel will remain on the heating surface, making it impossible to improve fuel efficiency. Although the heating surface temperature is 300 ° C., which is higher than that of the conventional device, the required amount of intake air is sufficiently secured because the reduction due to thermal expansion of intake air does not occur so much.

Next, the ceramic coating layer 9 has a maximum evaporation rate point.
Of experimental results showing that it contributes to the shift of the
It is shown in FIG. Aluminum (Al), SUS (stainless steel
Steel) and SUS as a base material, and fine zirco on the surface
Near (ZrO₂), Coarse zirconia (ZrO₂),fine
Alumina (Al₂O_Three), Coarse alumina (Al
₂O _Three) Sprayed to form each coating layer
6 types of solid surface samples were used as heating surfaces. FIG.
Is the initial heating surface temperature Ta for each solid surface sample.
Life of gasoline droplets dripping on the heated surface
Is a graph from the experimental results showing (between).

After the heating surface temperature Ta reached a steady state by the thermocouple, 2.85 μl of gasoline attached to the needle-shaped tip portion was vibrated and dropped on the heating surface S with a microsyringe. Evaporation time is measured using a high-speed video camera and is 1se
c. The above measurement was visually performed with a stopwatch.

As can be seen from the graph of FIG. 4, metal (A
The maximum evaporation rate point of the heated surface of (1, SUS) is around 210 ° C., and the evaporation time is longer at a temperature exceeding this point. From this, it can be seen that in the conventional device in which the heating surface of the heater is made of metal, when the temperature of the heating surface exceeds about 210 ° C., the life of the droplets is shortened by returning.

On the other hand, according to the heating surface coated with ceramics, the life (evaporation time) is kept short even when the maximum evaporation rate point of the metal heating surface exceeds about 210 ° C. Especially ZrO ₂
Has a relatively short life in a wide temperature range exceeding about 210 ° C., which is the maximum evaporation rate point of the metal heating surface.

For fine zirconia (ZrO ₂ ), about 21
It can be seen that the life (evaporation time) in the temperature range of 0 ° C to about 390 ° C can be made slightly shorter than the shortest life of metal (about 300 msec.) (At the temperature of about 310 ° C, the shortest life of about 24).
0 msec.). Further, it is understood that the life (evaporation time) of coarse zirconia (ZrO ₂ ) can be made shorter than the shortest life (about 300 msec.) Of metal in the temperature range of about 140 ° C. to about 460 ° C. 220 ° C for particularly coarse zirconia
In the temperature range of about 370 ° C. to about 370 ° C., the service life is about 200 msec., Which means that the service life of gasoline droplets can be about 2/3 of the service life of the metal heating surface.

Further, the life of zirconia is kept short in a wide temperature range. This means that the Leidenfrost phenomenon does not occur even if the heating surface temperature fluctuates somewhat and shifts to the high temperature side, for example. On the other hand, in the case of the metal heating surface (Al), the droplet life is remarkably increased in the heating surface temperature range of 210 to 220 ° C., and even if the heating surface temperature is set to the maximum evaporation rate point (about 210 ° C.), it slightly increases. As a result of the rise in temperature, the life of the liquid droplets becomes longer, and the liquid droplet fuel that is not smaller than the critical liquid droplet diameter and is not atomized is supplied to the combustion chamber 2. The maximum evaporation rate point of zirconia is difficult to grasp from this graph, but it is estimated to be around 300 ° C. The coarse zirconia is the same as that used for the thermal spray material of the ceramic coating layer 9 of the present embodiment.

One of the reasons why the coarse zirconia has the effect of shortening the life of the liquid droplet is that fine irregularities having a diameter of about 10 to 50 μm are formed on the surface of the ceramic coating layer 9 formed by thermal spraying. Can be mentioned. This is because the fine irregularities serve as nuclei for bubbles generated at the time of boiling to promote the generation of bubbles from a low temperature region, and the increase of the droplet surface area due to the large number of bubbles formed inside thereof promotes vaporization. Also,
Since there are a large number of irregularities having a reasonably fine diameter on the heating surface, a large contact area between the droplet and the heating surface can be secured, and the amount of heat transferred from the heating surface to the droplet per unit time can be increased. It can also be increased. From these factors, it is estimated that the coarse zirconia has the shortest droplet life of each sample in all measured temperature ranges.

In this way, the heating surface S is covered with the ceramic coating layer 9
By forming it by coating with, the evaporation rate of gasoline droplets is about 1.5 as compared with the conventional heater having a metal heating surface.
If it can be doubled, it becomes possible to vaporize almost all of the fuel droplets F attached to the heating surface S during the intake timing. As a result, in the combustion chamber 2, only the fuel atomized to be smaller than the critical droplet diameter is supplied to achieve complete combustion, and it is not necessary to adjust the fuel injection amount from the injection nozzle 5a too much. It is possible to improve the exhaust gas and purify the exhaust gas.

As described in the prior art, in order to secure the required amount of fuel to be supplied without sufficiently vaporizing the liquid droplets on the heating surface at the intake timing, the injection amount from the injection nozzle is set to be large so that the fuel consumption is poor. Is avoided. Further, even if the heating surface temperature fluctuates over time or the heating surface has unevenness in temperature, as seen from the graph of FIG. 4, the effect of shortening the droplet life is recognized in a wide temperature range. Even if there are variations, the Leidenfrost phenomenon does not occur and the evaporation rate does not decrease. As a result, as described in the related art, since the liquid droplets floating up due to the Leidenfrost phenomenon before being vaporized are not supplied to the combustion chamber together with the intake air, they are supplied to the combustion chamber like the conventional device. It is possible to prevent incomplete combustion from being caused by the large droplets having a critical droplet diameter which has been left and to remain as carbon in the combustion chamber or exhaust HC and the like as a part of incomplete combustion gas.

As described in detail above, according to the heater 6 of this embodiment, the effects listed below can be obtained. (A) By covering the heating surface S of the heater 6 with the ceramic coating layer 9 having low thermal conductivity, the maximum evaporation rate point of the fuel droplets F can be practically shifted to the high temperature side.
Therefore, even if the heating surface temperature Ta is 300 ° C., the fuel droplets F do not cause the Leidenfrost phenomenon, and the fuel droplets F injected onto the heating surface S during the intake timing timing.
Almost all of can be vaporized. As a result, unvaporized fuel does not remain on the heating surface S, and fuel droplets that have not been atomized are not supplied to the combustion chamber 2. Therefore, it is possible to improve fuel efficiency and clean exhaust gas. Can be planned.

(B) Since the material of the ceramic coating layer 9 is zirconia (ZrO ₂ ), the set temperature can be set sufficiently high by increasing the shift amount of the maximum evaporation rate point to the high temperature side. The life (evaporation time) of the fuel droplets F on the heating surface S can be shortened to sufficiently increase the vaporization rate.

(C) The layer thickness Tz of the ceramic coating layer 9 is 1
Since the range is from 0.00 to 500 μm, an appropriate temperature gradient region R is formed near the interface to form the heating surface temperature (set temperature) Ta.
Can be set to a sufficiently high value, and rapid temperature recovery of the heating surface temperature to the set temperature can be realized.

(D) Coarse zirconia was used as the thermal spraying raw material powder to form 1 on the surface (heating surface S) of the ceramic coating layer 9.
Since a large number of fine uneven portions having a diameter of 0 to 50 μm are formed, the fine uneven portions serve as nuclei for bubbles to generate a large number of bubbles and increase the droplet surface area. The contact area between the droplet F and the heating surface is increased, and the amount of heat transfer from the heating surface to the droplet per unit time can be increased. As a result, it is possible to increase the evaporation rate of the droplets and improve the vaporization rate. Further, since the effect of shortening the life of droplets is recognized in a wide temperature range by using the thermal spray coating layer made of coarse zirconia, even if the set temperature (heating surface temperature Ta) varies to some high temperature side, the Leidenfrost phenomenon does not occur and the critical temperature is not reached. Fuel droplets F having a diameter larger than the droplet diameter are used in the combustion chamber 2
It is possible to avoid the situation of being sent to.

(E) The heating surface temperature Ta (set temperature) is set to 22.
Since the temperature is set to 300 ° C., which is within the temperature range of 0 to 370 ° C., the life (evaporation time) of the gasoline droplet F can be shortened to about 2/3 of the shortest life on the metal heating surface.

The present invention is not limited to the above embodiment, but may be configured as follows, for example, without departing from the spirit of the invention. (1) As shown in FIG. 5, a ceramic coating layer 9 made of zirconia (ZrO ₂ ) is formed on the upper surface of an electric heating member 21 made of metal such as SUS (stainless steel) via a binder 8.
May be formed, and the electric heating member may also serve as the base material. According to this structure, the structure of the heater 6 is simple, and the ceramic coating layer 9 is almost directly bonded to the electric heating member 21 via only the bonding material 8. Therefore, the temperature response of the heating surface S can be improved. Can be good.

(2) As shown in FIG. 6, zirconia (Zr) is formed on the upper surface of the electric heating member 22 made of PTC ceramic.
The ceramic coating layer 9 made of O ₂ ) may be directly formed. In this case, if the Curie temperature of the PTC ceramic 22 is set in the range of 140 ° C. to 440 ° C., the life of the gasoline droplets F can be made shorter than that of the metal heating surface, and in particular, the Curie temperature of 220 ° C. to 370 ° C. By setting the range, the life of the gasoline droplet F can be about 2/3 of the maximum life on the metal heating surface. Therefore, it is particularly desirable to set the Curie temperature in the range of 220 ° C to 370 ° C. According to this configuration, in addition to the configuration of (1) above, temperature control is not required, and the temperature control circuit 13, the temperature sensor 14, and the like can be eliminated.

(3) As shown in FIG. 7, the present invention is applied to a fuel supply device 24 provided with a vaporization chamber 23 for previously vaporizing the fuel before sending it to the combustion chamber 2 through the intake manifold 4. Good. The injection nozzle 5a of the fuel injector 5 connected to the fuel tank 25 that stores the gasoline G projects into the vaporization chamber 23.
The heater 6 is arranged on the bottom surface in the vaporization chamber 23 in which a is directed. The heater 6 is formed by energizing an electric heating member 26 made of PTC ceramic with a ceramic coating layer 9 made of zirconia (ZrO ₂ ). Electric heating member 2
6 has its Curie temperature set to about 300 ° C,
Heat is generated by the current from the battery power supply 12. The vaporization chamber 23 is connected to the intake manifold 4 via a pipe 27, and the supply amount of vaporized fuel from the vaporization chamber 23 to the intake manifold 4 side is controlled by opening / closing control of an electromagnetic valve 28 provided in the pipe 27. . According to this configuration, almost all of the fuel injected from the injection nozzle 5a to the heating surface S at a predetermined timing can be vaporized by the timing when the electromagnetic valve 28 opens, and the vaporized fuel required for the combustion chamber 2 can be obtained. It is not necessary to set the injection amount of the injection nozzle 5a to be large in order to secure it, so that the consumption amount of combustion can be reduced. Further, it is possible to always secure a constant concentration of vaporized fuel according to the injection amount.

(4) The set temperature of the heater 6 in FIG.
The temperature is not limited to C and may be set to another temperature in the range of 220 to 370C. Also with this configuration, the evaporation rate of the gasoline droplets can be made about 1.5 times the maximum evaporation rate on the metal heating surface. Also, set the temperature to 140
The temperature may be in the range of up to 440 ° C. According to this structure, the evaporation rate of the gasoline droplets can be made higher than the maximum evaporation rate of the metal heating surface.

(5) In the heater 6 of FIG. 2, the PTC ceramic is used in place of the electric heating member 11 to heat the metal plate 7, and the temperature control circuit 13 and the temperature sensor 14 are used.
May be deleted.

(6) The material of the ceramic coating layer 9 may be other ceramics having a low thermal conductivity other than zirconia (ZrO ₂ ). For example, zircon may be used. Further, zirconia may be partially stabilized zirconia or stabilized zirconia.

(7) The method for forming the ceramic coating layer 9 is not limited to the thermal spraying method. For example, the ceramic coating layer 9 may be formed by a reactive ion plating method, an activated reactive vapor deposition method (ARE method), a hollow cathode discharge method (HCD method), or the like.

(8) A thin plate of zirconia obtained by sintering may be bonded onto a base material by a method such as brazing to form the ceramic coating layer 9. (9) The heat supply unit is not limited to the configuration in which the electric heating member is used as the heat source. For example, the heating body 10 may be heated by using the residual heat of the exhaust gas. JP-A-49-12
A ceramic coating layer of, for example, zirconia may be formed on the heating plate of the fuel vaporizer disclosed in Japanese Patent Publication No. 0023 to improve the fuel evaporation rate. Alternatively, the heating body 10 may be heated by utilizing the residual heat of the exhaust gas, and when the temperature is lower than the set temperature, the heat may be replenished by the energizing heat generating member.

(10) Instead of a metal such as the metal plate 7 as the material of the base material, a ceramic having a high thermal conductivity may be used. For example, SiC, Si ₃ N ₄ or the like may be used. (11) The fuel is not limited to gasoline, and the present invention may be applied to a gasoline engine that uses other liquid fuel such as methanol.

The invention grasped from the above-mentioned embodiment and not described in the scope of the claims will be described below together with the effect thereof. (A) In any one of claims 1 to 7, the ceramic coating layer is formed by a thermal spraying method. By appropriately selecting the particle size of the thermal spray raw material powder,
It is possible to easily form a ceramic coating layer having a fine uneven portion of 50 μm.

(B) In any one of claims 1 to 7, the heat supply means includes an electric heating member made of PTC ceramic. According to this configuration, it is not necessary to control the temperature.

(C) In (b), the Curie point of the PTC ceramic is in the range of 220 ° C to 370 ° C. According to this configuration, the heating surface temperature is 220 ° C. to 37 ° C.
The temperature can be set to 0 ° C., and the life of the droplet can be about 2/3 of the shortest life on the metal heating surface within this wide temperature range.

[0066]

As described in detail above, according to the invention described in claim 1, the heating surface of the heating element is formed by coating a base material having a high thermal conductivity with a ceramic coating layer made of a ceramic having a low thermal conductivity. Since the set temperature can be set higher than the maximum evaporation rate point of the metal heating surface, the vaporization rate of the fuel injected on the heating surface can be increased. As a result, more fuel injected from the injection nozzle can be supplied to the combustion chamber in the combustion cycle as vaporized fuel, and fuel consumption can be improved. Further, even if the heating surface is set higher than the maximum evaporation rate point of the metal heating surface, it is possible to prevent the fuel droplets from causing the Leidenfrost phenomenon, and the fuel is not supplied as droplets to the combustion chamber. , HC, etc. are less likely to be generated, and the exhaust gas can be cleaned. Further, it is possible to improve the low temperature startability in winter and the like.

According to the second aspect of the invention, since the ceramic coating layer is made of zirconia, which has particularly low thermal conductivity among ceramics, the set temperature of the heating surface is set sufficiently higher than the maximum evaporation rate point of the metal heating surface. In addition, the vaporization rate of the fuel can be further increased in a wide temperature range.
According to the invention described in claim 3, since the thickness of the ceramic coating layer is in the range of 100 to 500 μm, the set temperature can be set appropriately higher than the maximum evaporation rate point of the metal heating surface, and the temperature of the heating surface is recovered. Therefore, the fuel vaporization rate can be effectively improved.

According to the invention described in claim 4, the surface of the ceramic coating layer is formed so as to have fine irregularities corresponding to a diameter of 10 to 50 μm, and bubbles are generated by the fine irregularities serving as a nucleus of bubble generation. In addition to increasing the number of droplets and increasing the surface area of the droplets, the minute irregularities increased the contact area between the droplets and the heating surface to increase the amount of heat transfer per unit time, further increasing the vaporization rate of fuel droplets. Can be increased.

According to the invention of claim 5, the surface of the ceramic coating layer made of zirconia is formed so as to have fine irregularities corresponding to a diameter of 10 to 50 μm, and the preset temperature of the heating surface is 140 ° C. Since it is set within the range of 440 ° C., the evaporation rate of the fuel droplets can be made higher than the maximum evaporation rate when the metal heating surface is used.

According to the invention of claim 6, claim 5
In particular, by limiting the set temperature in the range of 220 ° C. to 370 ° C. in the invention, the evaporation rate of droplets can be increased by about 50% with respect to the maximum evaporation rate when the metal heating surface is used.

According to the seventh aspect of the invention, even if the intake chamber connected to the combustion chamber is provided with the vaporizing chamber so as to send only the vaporized fuel, the heating element provided in the vaporizing chamber Since the vaporization of the fuel injected to the heating surface is promoted and the amount of injection that is set to a large amount in consideration of the non-vaporized portion is unnecessary or small, the fuel consumption can be reduced.

According to the invention of claim 8, claim 1
-The effect as described in any one of Claim 7 is acquired.

[Brief description of drawings]

FIG. 1 is a partial side sectional view of a gasoline engine including a heater.

FIG. 2 is a schematic side sectional view of a fuel vaporizer.

FIG. 3 is a schematic cross-sectional view for explaining a vaporization mechanism of fuel droplets.

FIG. 4 is a graph showing droplet life with respect to a heating surface temperature.

FIG. 5 is a schematic side sectional view of a fuel vaporizer of another example.

6 is a schematic side sectional view of another example of a fuel vaporizer different from FIG.

FIG. 7 is a schematic side sectional view of a fuel supply device of another example.

FIG. 8 is a graph of an evaporation rate curve.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gasoline engine, 2 ... Combustion chamber, 4 ... Intake manifold as fuel supply passage, 5 ... Fuel injector as fuel injection device, 5a ... Injection nozzle, 6
... A heater as a fuel vaporization heater while constituting a fuel vaporizer, 7 ... A metal plate as a base material, 9 ... Ceramic coating layer, 10 ... Heating body 11, 21, 22 ... Members, 12 ... Battery power source constituting heat supply means, 13 ... Similarly temperature control circuit, 14 ... Similarly temperature sensor, 23 ... Vaporization chamber as fuel supply passage,
S ... Heating surface, Tz ... Layer thickness.

Claims (8)

[Claims] 1. A heating body having a heating surface arranged in an injection area of an injection nozzle of a fuel injection device in a fuel supply passage connected to a combustion chamber of a gasoline engine, and the heating body so that the heating surface has a set temperature. A fuel vaporizer comprising a heat supply means for heating, wherein the heating body is a base made of metal or ceramic having high thermal conductivity, and a coating is formed on the surface of the base to form the heating surface. Vaporization device including a ceramic coating layer made of the ceramic having low thermal conductivity. 2. The fuel vaporizer according to claim 1, wherein the ceramic coating layer is made of zirconia. 3. The thickness of the ceramic coating layer is 100 to
The fuel vaporization device according to claim 1 or 2, which has a range of 500 μm. 4. The surface of the ceramic coating layer has 10 to 10
The fuel vaporizer according to any one of claims 1 to 3, wherein an uneven portion having a diameter of 50 µm is formed. 5. The surface of the ceramic coating layer is 10 to 10.
The fuel vaporizer according to claim 2, wherein an uneven portion having a diameter of 50 μm is formed, and the set temperature of the heating surface is set within a range of 140 ° C. to 440 ° C. 4. 6. The set temperature of the heating surface is 220 ° C. to 37 ° C.
The fuel vaporizer according to claim 5, which is set within a range of 0 ° C. 7. The fuel supply passage comprises an intake manifold connected to the combustion chamber, and a vaporization chamber connected to the intake manifold and provided with the injection nozzle, wherein the heating element is provided in the vaporization chamber. The fuel vaporizer according to any one of claims 1 to 6, which is provided so as to dispose the heating surface in an injection area. 8. A fuel vaporization heater comprising the heating element according to any one of claims 1 to 7.