US20130312728A1

US20130312728A1 - Liquid Fuel Combustion System

Info

Publication number: US20130312728A1
Application number: US13/898,663
Authority: US
Inventors: Min-Hon Rei; Guan-Tyng Yeh; Yu-Ling Kao; Yu-Lin Chen
Original assignee: Green Hydrotec Corp
Current assignee: Green Hydrotec Corp
Priority date: 2012-05-25
Filing date: 2013-05-21
Publication date: 2013-11-28

Abstract

A liquid fuel combustion system is provided. The system comprises:

- a combustion stove, comprising a vaporization unit with a ring shape vaporization space, a burner assembly and a first pipeline;
- a liquid fuel storage tank, having a storage space;
- a second pipeline, having a third opening end open to the storage space and a fourth opening end open to the ring shape vaporization space; and
- a liquid fuel composition contained in the storage space, comprising a liquid fuel and an ignition promoter which provides a vapor pressure in the storage space,
  whereby the vapor pressure drives the liquid fuel composition to be delivered out the storage space through the second pipeline, vaporized in the ring shape vaporization space and then delivered by the first pipeline to the burner assembly.

Description

This application claims priority to Taiwan Patent Application No. 101210029 filed on May 25, 2012 and Taiwan Patent Application No. 102114174 filed on Apr. 22, 2013.

CROSS-REFERENCES TO RELATED APPLICATIONS

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a liquid fuel combustion system. Specifically, the present invention relates to a liquid fuel combustion system comprising easily ignitable liquid fuel composition.
2. Descriptions of the Related Art
In general, the heat source of a cooking stove is electricity or the combustion of either natural gas (hereinafter referred to as “NG”) or liquefied petroleum gas (hereinafter referred to as “LPG”). An electric cooking stove although is capable of providing a clean heat source without any CO₂emission, it has the shortcomings of low heat transfer rate and poor homogeneity of heat distribution. The NG or LPG fueled stove is a relatively popular choice for most people for its easy operation and relatively steady heating quality. NG is a convenient cooking fuel source for users located in the network of NG pipeline system. However, in many remote area or developing countries, it is too costly to have a NG supply network facility. As a result, in many countries, LPG becomes the most popular cooking fuel. But even LPG can be conveniently transported by storing LPG in a storage tank, it is not only expensive but also explosive when being leaked into air.
Because of LPG's high cost and potential explosion hazard, numerous attempts have been tried to develop a liquid fueled cooking stove such as a kerosene or methanol cooking stove. However, none of them can be operated as convenience as a LPG stove because of the following reasons. First, the liquid fuel cannot be conveniently delivered to the stove from its storage tank, and usually require an additional air pump or compressor or other driving force (e.g., hanging the storage tank at an elevation to provide enough gravitation force to force the fuel to flow to the stove). But the use of the air compressor/pump will put the liquid fuel in an explosive danger because of low explosion limit. For example, when using methanol as a liquid fuel, the air blended liquid fuel tends to explode if the methanol concentration in the air blended liquid fuel falls into the explosion limit of 4% to 65%. The second reason giving rise to the fail of the liquid fueled cooking stove is that, the flash point of liquid fuel (e.g., kerosene or methanol) is too high to be easily ignited. As a result, the liquid fuels cannot be ignited with an electronic igniter; they must be ignited using an “open flame” such as a flame torch or butane gun. Furthermore, a liquid fueled stove usually uses a fiber string to suck up the liquid fuel by capillary force to the burner section. In the case of kerosene stove, owing to its high flash point range (120° C. to 300° C.), the vaporization of kerosene is slow and difficult; this results in oily smell and smoke during burning. As to the methanol stove, the methanol flame during burning is unsteady and jumpy.
In this regard, the present invention provides a liquid fuel combustion system with high thermal efficiency, which requires no air pump or compressor to deliver the liquid fuel and comprises an easily ignitable liquid fuel composition that can be easily ignited using an electric igniter without the needs of open flame.

SUMMARY OF THE INVENTION

The primary objective of this invention is to provide a liquid fuel combustion system, comprising:

- a combustion stove, comprising:
  - a vaporization unit with a ring shape vaporization space;
  - a burner assembly, comprising a burning head, a first jet opening, and a burning tube connecting the burning head to the first jet opening, wherein the burning tube has at least one air opening; and
  - a first pipeline, having a first opening end open to the ring shape vaporization space and a second opening end open to the first jet opening;
- a liquid fuel storage tank, having a storage space;
- a second pipeline, having a third opening end open to the storage space and a fourth opening end open to the ring shape vaporization space; and
- a liquid fuel composition contained in the storage space, comprising:
  - a liquid fuel selected from the group consisting of C1-C4 alcohols, liquid hydrocarbons and combinations thereof; and
  - an ignition promoter, which is a high volatile hydrocarbon having a flash point lower than the liquid fuel and provides a vapor pressure in the storage space, wherein the amount of the ignition promoter is at least about 1 wt % based on the weight of the liquid fuel,
    whereby the vapor pressure composition drives the liquid fuel to be delivered out the storage space through the second pipeline, vaporized in the ring shape vaporization space and then delivered by the first pipeline to the burner assembly.

The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing one embodiment of the liquid fuel combustion system according to the present invention;

FIG. 2 is a schematic diagram showing one embodiment of the combustion stove of the liquid fuel combustion system according to the present invention;

FIG. 3 is a schematic diagram showing another one embodiment of the combustion stove of the liquid fuel combustion system according to the present invention;

FIG. 4 is a schematic diagram showing yet another one embodiment of the combustion stove of the liquid fuel combustion system according to the present invention;

FIG. 5A is a schematic diagram showing one embodiment of the burning head of the combustion stove;

FIG. 5B is a schematic diagram showing another one embodiment of the burning head of the combustion stove;

FIG. 5C is a schematic diagram showing yet another one embodiment of the burning head of the combustion stove;

FIG. 5D is a schematic diagram showing yet another one embodiment of the burning head of the combustion stove;

FIG. 6 is a schematic diagram showing one embodiment of the combustion stove comprising a plurality of burner assemblies;

FIG. 7 is a schematic diagram showing another one embodiment of the liquid fuel combustion system according to the present invention; and

FIG. 8 is a schematic diagram showing yet another one embodiment of the liquid fuel combustion system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, some embodiments of the present invention will be described in detail with reference to the appended drawings. However, without departing from the spirit of the present invention, the present invention may be embodied in various embodiments and should not be limited to the embodiments described in the specification and drawings. Furthermore, for clarity, the size of each element and each area may be exaggerated in the appended drawings and not depicted in its actual proportion. Unless it is additionally explained, the expressions “a,” “the,” or the like recited in the specification of the present invention (especially in the claims) should include both the singular and the plural forms.
Referring to FIG. 1, which shows an embodiment of the liquid fuel combustion system according to the present invention, the liquid fuel combustion system comprises:

- a combustion stove 1, comprising a vaporization unit 11 with a ring shape vaporization space 12, a burner assembly 13 and a first pipeline 14 connecting the vaporization unit 11 to the burner assembly 13;
- a liquid fuel storage tank 21 having a storage space 22;
- a second pipeline 23, having a third opening end 231 open to the storage space 22 and a fourth opening end 232 open to the ring shape vaporization space 12; and
- a liquid fuel composition (not shown) contained in the storage space 22.

According to the invention, the liquid fuel composition comprises a liquid fuel and an ignition promoter, wherein the ignition promoter is a high volatile hydrocarbon having a flash point lower than the liquid fuel and provides a vapor pressure in the storage space 22, whereby the vapor pressure drives the liquid fuel composition to be delivered out the storage space 22 through the second pipeline 23, vaporized in the ring shape vaporization space 12 and then delivered by the first pipeline 14 to the burner assembly 13 for combustion use.
Then referring to FIG. 2, which shows an embodiment of the combustion stove according to the present invention, the vaporization unit 11 is provided with a ring shape vaporization space 12, which provides a sufficient surface area for the liquid fuel delivered thereinto to be heated and vaporized. That is, the ring shape vaporization space 12 provides a buffering space for the vaporization of liquid fuel, smoothes the flow of the liquid fuel composition, and solves the flickering problem of flame. Besides, the vaporization unit 11 is disposed around and preferably above the burner assembly 13 to use the heat generated during the burning at the burner assembly 13 to vaporize the liquid fuel composition in the ring shape vaporization space 12.
According to the present invention, there is no special limitation on the appearance of the ring shape vaporization space 12. For example, the ring shape vaporization space 12 may be formed in a hollow disc shape (see FIG. 2) or a hollow bowl shape expanding up- and outward (see FIG. 3 or 4). In the hollow-disc-shaped vaporization space of FIG. 2, the ring shape vaporization space 12 has a thickness T₁and a planar width W₁; and in the hollow-bowl-shaped vaporization space of FIG. 3 or 4, the ring shape vaporization space 12 has a thickness T₂/T₃and a slope length L₁/L₂and an outward expanding tilt angle α₁/α₂. Generally, in the case of being formed in a hollow disc shape, the ring shape vaporization space 12 has a thickness of about 2 mm to about 8 mm, preferably about 3 mm to about 6 mm, and a planar width of about 10 mm to about 90 mm, preferably about 30 mm to about 50 mm; and in the case of being formed in a hollow bowl shape, the ring shape vaporization space 12 has a slope length of about 20 mm to about 60 mm, preferably about 30 mm to about 50 mm, a thickness of about 2 mm to about 8 mm, preferably about 3 mm to about 6 mm, and an outward expanding tilt angle of about 15 degree to about 40 degree, preferably about 20 degree to about 35 degree.
Again referring to FIG. 2, the burner assembly 13 comprises a burning head 131, a burning tube 132 and a first jet opening 133, wherein the burning tube 132 connects the burning head 131 to the first jet opening 133 and has at least one air opening 134. After being vaporized in the ring shape vaporization space 12 of the vaporization unit 11, the fuel flows through the first jet opening 133 of the burner assembly 13 to thereby reduce the pulse caused by the vaporization of the liquid fuel such that the fuel gas flow can be delivered stably and the flickering problem of flame can be solved. After passing through the first jet opening 133, the vaporized liquid fuel composition enters the burning tube 132. The burning tube 132 has at least one, preferably 2 to 6, air opening(s) 134 on the wall to suck air into the burning tube 132. The vaporized liquid fuel will mix with air in the burning tube 132, and then enters the scattering holes of burning head 131 to be ignited. The air opening 134 usually has an inner diameter of about 3 mm to about 6 mm. In some embodiments of the present invention, as shown in FIG. 2, there are four air openings 134 on the wall of the burning tube 132.
As shown in FIG. 4, the lower part of the vaporization unit 11 could be connected with an apron 121 to shade the possible splashing of liquid fuel composition. In the case where an apron 121 is applied to shade the possible splashing of the fuel, the outward tilting angle β of apron 121 should be ≦15 degree and the slope length L₃thereof should be well controlled so as to prevent the apron 121 from shading the air opening 134 and generating turbulent air flow. Generally, the slope length L₃of apron 121 is about 15 mm to about 35 mm, preferably about 25 mm to about 35 mm; and the angle β of apron 121 is about 5 degree to about 15 degree, preferably about 10 degree to about 15 degree. Preferably, the burning head 131 is disposed at the connection of the vaporization unit 11 and apron 121; and the distance between the apron 121 and burning head 131 is about 3 mm to about 10 mm, preferably about 5 mm to about 10 mm.
According to the present invention, there is no special limitation on the types of the burning head 131. Any burning head having scattering holes, such as a burning head with monocyclic holes (see FIG. 5A, the burning head is provided with holes 1311 as the scattering holes), hollow disc type burning head with multi-cyclic pores (see FIG. 5B and FIG. 5C, the burning head is provided with pores 1312 as the scattering holes), or plate type burning head (see FIG. 5D, the burning head is provided with pores 1312 as the scattering holes), may be adopted. Furthermore, according to the present invention, a catch-plate may be disposed beneath the burning head to catch the overflowing fuel.
As shown in FIG. 2, the first pipeline 14 of the combustion stove 1 has a first opening end 141 open to the ring shape vaporization space 12 and a second opening end 142 open to the first jet opening 133. Preferably, the combustion stove 1 further comprises a second jet opening 15 installed in the first pipeline 14. The second jet opening 15 is helpful to the fuel delivery. In this embodiment, the first pipeline 14 has a first inner diameter D1 at the section from the first opening end to the second jet opening and a second inner diameter D2 at the section from the second opening end to the second jet opening, and D1>D2. Through such design, the liquid fuel composition can be delivered stably for satisfactory combustion. In some embodiments of the present invention, D1 is more than 1 mm and not more than 8 mm and D2 is not less than 1 mm and not more than 5 mm.
According to the present invention, the number of the burner assembly can be chosen depending on users' needs. In the case where a plurality of burner assemblies is disposed, each burner assembly comprises a burning head, a burning tube and a first jet opening. For example, FIG. 6 shows an embodiment of a combustion stove having three burner assemblies, wherein the first pipeline has three second opening ends 1421, 1422 and 1423 individually open to one of the first jet openings 1331, 1332 and 1333 and a multi-direction manifold comprising three separate tubes 1431, 1432 and 1433.
It should be noted, there is no special limitations on the material of the vaporization unit, apron or relevant pipelines except that the material should have a good thermal conductivity. The examples of said material include aluminum, copper, brass and other copper alloys, and stainless steel.
In the liquid fuel combustion system of the invention, the ring shape vaporization space of the vaporization unit provides a relatively big space to facilitate the preheating and vaporization of the liquid. This arrangement can avoid generating a discontinuous plug flow, which occurs owing to the imperfect vaporization of liquid fuel and results in unstable flame and imperfect combustion. In addition, in the case where an apron is provided beneath the ring shape vaporization space, it makes flame more concentrate and facilitates the air suction. The improved air suction enhances the combustion-assisting effect and thus provides a relatively perfect combustion.
Regarding the liquid fuel storage tank of the liquid fuel combustion system of the invention, it is used to contain the liquid fuel composition. As shown in FIG. 2, the liquid fuel storage tank 21 may optionally comprise a feed opening 211 with a cover 213 for the supplement of the liquid fuel composition. The material of the liquid fuel storage tank 21 is not particularly limited. For example, the liquid fuel storage tank 21 may be made of a usual steel material. The fluid delivery system and kit disclosed in TW I314970 may be used as the liquid fuel storage tank of the liquid fuel combustion system of the invention, the contents of which are herein incorporated by reference in its entirety.
Regarding the second pipeline of the liquid fuel combustion system of the invention, it has a third opening end open to the storage space and a fourth opening end open to the ring shape vaporization space, whereby the liquid fuel contained in the storage space of the liquid fuel storage tank can be delivered to the ring shape vaporization space of the vaporization unit. The third opening end of the second pipeline may be installed within the storage space, e.g., at a position approaching the bottom of the storage space. For example, referring to FIG. 1, the third opening end 231 of the second pipeline 23 can be inserted into the storage space 22 from top to a position of about 1 cm or about 2 cm from the bottom. Of course the third opening end 231 of the second pipeline 23 can be inserted into the storage space 22 from the bottom as well. Furthermore, as shown in FIG. 1, the liquid fuel combustion system may further comprise a control element 24 installed on the second pipeline. For example, but not limited thereto, the control element 24 may be a flow control element, such as a needle valve, capable of opening the liquid fuel composition flow or adjusting the flow of liquid fuel, or just an on/off switch. In this case, the liquid fuel composition may be ignited with an electric igniter (not shown) around the burning head 131 after the control element 24 is opened. FIG. 7 shows another embodiments of the liquid fuel combustion system of the invention, where the control element 24 is an ignition switch with flow control function, it comprises an electric igniter 241 (such as a lighter flint) and a wire 242 connecting the electric igniter 241 to the control element 24. In this case, when the control element 24 is opened, the liquid fuel composition passes through the control element 24 and enters the combustion stove 1, and at the same time, the electric igniter 241 provides an electric arc to ignite the fuel coming out from the burning head 131. After igniting the fuel, the strength of the generated flame can be adjusted by the control element 24. The control element 24 here is commercially available. For example, it can be obtained by narrowing the diameter (e.g., to 0.08 mm to 1 mm) of gas outlet of gas stove sold in the market.
According to the present invention, the second pipeline 23 may further comprises a fifth opening end 233 being set below the air opening 134 and above a catch-plate 27 and equipped with an ignition unit 25, as shown in FIG. 8. Once the ignition unit 25 is started, the liquid fuel composition passes through the ignition unit 25 and enters the catch-plate 27, and meanwhile, the ignition unit 25 provides an electric arc to ignite the liquid fuel composition on the catch-plate 27. At this time, opening the control element 24 (a flow control element in this case) to make the liquid fuel composition enters the ring shape vaporization space 12, and the entered liquid fuel composition could be vaporized by absorbing the heat from the flame on the catch-plate 27. Usually, there will be a shutter 26 being disposed on the catch-plate 27 to concentrate the liquid fuel composition came from the ignition unit 25 to facilitate the ignition. The height of the shutter 26 should be controlled to prevent the shutter 26 from shading the air opening 134 and thus generating turbulent air flow. Similarly, the ignition unit 25 could be obtained from the gas stove sold in the market too.
Furthermore, in some embodiments of the present invention, the second pipeline 23 tilts downward to open to the ring shape vaporization space 12 as shown in FIG. 1. This is helpful in providing a relatively stable combustion.
According to the present invention, the storage space 22 contains a liquid fuel composition comprising a liquid fuel and an ignition promoter. The ignition promoter is a high volatile hydrocarbon having a flash point lower than the liquid fuel. “High volatile hydrocarbon” here means a hydrocarbon with a vapor pressure of about 15 kpa at standard state (20° C. and 1 atm). The ignition promoter makes the liquid fuel composition can be easily and quickly ignited. This allows the liquid fuel combustion system of the invention to use an electric igniter rather than open fire to ignite the liquid fuel composition and thus makes the system much safer. Specifically, it is known that the in the case of igniting a liquid fuel, the vapor concentration of the liquid fuel must be higher than its lower flammability limit (LFL) and the vapor must be heated to a temperature higher than its auto-ignition temperature. However, in general ambient temperature, it usually takes a long time to generate sufficient vapor concentration of liquid fuel; and thus, the ignition of liquid fuel usually takes a quite long time. For example, in the case of methanol, it takes about 30 sec to about 50 sec to generate sufficient vapor concentration to ignite methanol. The inventors found that the ignition promoter can significantly shorten the ignition time of liquid fuel. Without being bound to theory, it is believed that the ignition promoter slightly dissolves in the liquid fuel and forms a uniform liquid fuel composition; and after being delivered to the combustion stove, the dissolved ignition promoter can easily vaporized into vapor and reach its LFL. As a result, the liquid fuel composition can be quickly ignited without the needs of reaching the LFL of liquid fuel (e.g., methanol) itself.
Furthermore, since the ignition promoter is a high volatile hydrocarbon, it provides a vapor pressure in the storage space, whereby the vapor pressure drives the liquid fuel composition to be delivered to the burner assembly. Specifically, referring to FIG. 1 again, the vapor pressure of ignition promoter drives the liquid fuel composition to be delivered out the storage space 22 through the second pipeline 23, vaporized in the ring shape vaporization space 12 and then delivered by the first pipeline 14 to the burner assembly 13. Although we have known that the insoluble gas (such as air, nitrogen or hydrogen) can be installed into a liquid fuel storage tank to provide a driving pressure. The insoluble gas, however, is different from the ignition promoter in the present invention and cannot be partially solved into the liquid fuel to promote the ignition of liquid fuel. In the case of using the insoluble gas to provide a driving pressure, with the consumption of the liquid fuel, the fuel level in the storage tank is decreased, the volume over the liquid face is increased, and the driving pressure is thus decreased (P=nRT/V). In contrast, in the case of the liquid fuel composition according to the present invention, when the fuel level in the storage tank is decreased and the volume of the space over the liquid face is increased, the ignition promoter dissolved in the liquid fuel will be vaporized and the generated vapor thus maintains the pressure in the storage tank substantially constant.
In practical use of the liquid fuel combustion system of the invention, if the vaporization unit is not heated in advance, the liquid fuel composition in the vaporization unit and first pipeline is substantially in a form of a gas liquid mixture at the beginning. After the gas liquid mixture being delivered into the burning head and ignited, the liquid fuel composition in the ring shape vaporization space will start to be well vaporized through the heat provided by the combustion. Therefore, at the beginning, a small fraction of non-vaporized liquid fuel composition may be splashed from the air opening or burning head. To shade the possible splashing, the apron as described above may be disposed below the vaporization unit, whereby the splashed fuel will drop along the apron to the bottom of catch-plate to avoid potential risk.
According to the present invention, the liquid fuel is selected from the group consisting of C1-C4 alcohols, liquid hydrocarbons (e.g., C5-C12 hydrocarbons) and combinations thereof. For example, the liquid fuel may be methanol, ethanol, heptane, octane, cleaning naphtha, kerosene, diesel and the like. In some embodiments of the present invention, the liquid fuel is methanol or cleaning naphtha. As to the ignition promoter, it can be any high volatile hydrocarbons having a flash point lower than the liquid fuel. Generally, the solubility of the ignition promoter in the liquid fuel is preferably at least 1 wt % based on the weight of the liquid fuel. For example, the ignition promoter may be selected from the group consisting of liquefied petroleum gas (LPG), propane, butane, pentane, hexane, petroleum ether, dimethyl ether and mixtures thereof. Preferably, the ignition promoter is LPG (flash point: −60° C., standard state), butane (flash point: −60° C., standard state), or the combinations thereof. In some embodiment of the present invention, the ignition promoter is LPG. As to the amount of the ignition promoter, it depends on the species of ignition promoter, operating pressure, ambient temperature, and the like. For example, if the flash point of ignition promoter is relatively low or the ambient temperature is relatively high, a relatively small amount of ignition promoter is required; and if the ambient temperature is relatively low, the amount of ignition promoter should be increased. Of course the amount of ignition promoter should be sufficient to provide desired rapid ignition benefits, but it is also found that if the amount of ignition promoter is overhigh, it will not only increase the cost but also lead to an incomplete combustion. In view of this, according to the present invention, the amount of the ignition promoter is at least about 1 wt % and usually in an amount ranging from about 1 wt % to about 8 wt % based on the weight of the liquid fuel. In some embodiments of the present invention, the ignition promoter is in an amount ranging from about 4 wt % to about 8 wt % based on the weight of the liquid fuel.
Furthermore, since the flash point of the ignition promoter of the liquid fuel composition is lower than that of the liquid fuel, once the liquid fuel composition being delivered to the burning head, the vaporization speed of the liquid fuel is slower than that of the ignition promoter. As a result, the flame's strength may become unstable especially in a high ambient temperature. To solve this question, the inventor found that a material having a polarity between the liquid fuel and ignition promoter may be added into the liquid fuel composition as a stabilizer, which can stabilize the ignition promoter within the liquid fuel and stabilize the flame strength. Therefore, according to the present invention, the liquid fuel composition may further comprise a stabilizer. Without being bound to theory, it is believed that the stabilizer acts as an assistant or a bridge that facilitates the dissolution of ignition promoter in the liquid fuel and thus, can keep the ignition promoter from losing when the ambient temperature/pressure changes. For example, according to the check of the inventor, if 5 wt % (based on the weight of methanol) LPG is added into methanol, the gauge pressure of LPG vapor pressure is about 1.5 kg/cm²; and if a few amount of acetone is further added into the mixture of LPG and methanol, the gauge pressure of LPG vapor pressure is lowered to about 1.25 kg/cm². This manifests that acetone enhances the stability of LPG in methanol and the dissolution of LPG.
The stabilizer may be ketone(s), ether(s), a polymer with a molecular weight of less than about 5,000 Dalton, or combinations thereof. Specifically, the stabilizer may be selected from the group consisting of acetone, methyl ethyl ketone (MEK), dimethyl ether (DME), diethylene glycol (DEG), polyethylene glycol (PEG) with a molecular weight of less than about 5,000 Dalton, a polymer with a molecular weight of less than about 5,000 Dalton and having one or more hydrophilic functional group in its main chain (such as polyallyl alcohol), and combinations thereof. The hydrophilic functional group here is selected from the group consisting of an ether group, an ester group, an amino, a carboxyl (—COOH), a thiol (—SH) and combinations thereof. In some embodiments of the present invention, the stabilizer is acetone and/or MEK. Although the amount of the stabilizer should be sufficient to provide desired stabilizing, it is found that if the amount of stabilizer is overhigh, it may not only increase the cost but also affect the comburent effect. In view of this, according to the present invention, the amount of the stabilizer is in an amount of not higher than about 5 wt % based on the weight of the liquid fuel. Generally, the stabilizer is in an amount ranging from about 0.5 wt % to about 5 wt %, preferably from about 1 wt % to about 3 wt %. Besides, since the loss of ignition promoter in a low ambient temperature (e.g., in frigid zone) is relatively low, the amount of stabilizer can be reduced in this circumstance.
In addition to the ignition promoter and stabilizer, according to the present invention, the liquid fuel composition may further comprise a heat transfer promoter. It is known that the liquid fuel will be oxidized to water vapor and carbon dioxide after being ignited. When using the liquid fuel to heat a cooking pot, the gas flow (generated owing to the oxidization of liquid fuel) will form a thin layer at the bottom of the cooking pot (i.e., between the flame and the cooking pot). As a result, the higher the thermal conductivity of the thin layer, the better the thermal efficiency of the liquid fuel to the cooking pot. The inventor found that, the thermal efficiency of the liquid fuel can be improved by adding a heat transfer promoter to enhance the net thermal conductivity of the gas flow that forms the thin layer. The species of heat transfer promoter is not particularly limited but usually, it is soluble to the liquid fuel and easily to be vaporized, has a high thermal conductivity and barely remains on the cooking pot. In view of this, suitable heat transfer promoter may be a high thermal conductive material with a thermal conductivity of about 0.2 W/M-K to about 0.65 W/M-K and soluble to the liquid fuel. Preferably, the heat transfer promoter is selected from the group consisting of ethylene glycol, glycerol, ethylene diamine, water and combinations thereof. In some embodiments of the present invention, the heat transfer promoter is water.
To avoid the heat transfer promoter consuming too much heat released from the liquid fuel composition and thus lowering the thermal efficiency, the amount of the heat transfer promoter should be controlled. For example, in the case where the liquid fuel is methanol and the heat transfer promoter is water, water's vaporization heat (2,367 kJ/kg at 300 K) is almost thrice as high as methanol's vaporization heat (1,180 kJ/kg at 300 K), therefore we should avoid the vaporization of water consuming too much heat released by methanol and thus lowering the thermal efficiency. Therefore, the amount of the heat transfer promoter is usually from about 1 wt % to about 15 wt %, preferably from about 3 wt % to about 10 wt %, based on the weight of the liquid fuel. In the suggested amount, the heat transfer promoter can enhance the heat exchanger between the flame and the cooking pot while not consuming too much heat for its vaporization.
Moreover, the inventor also found that the ignition time of liquid fuel composition can be further shortened when using high thermal conductive liquid such as ethylene glycol, glycerol or water as the heat transfer promoter. Without being restricted by theories, it is believed that the solubility of ignition promoter is lowered in the presence of heat transfer promoter and the lower solubility facilitates the vaporization of ignition promoter after the liquid fuel composition being delivered to the burning head and thus shortens the ignition time.
Given the above, the liquid fuel combustion system has at least the following features: the system requires no air pump or compressor and thus is easy to carry; the liquid fuel composition can be easily ignited without the use of an open flame; and the designation of the combustion stove (the ring shape vaporization space, and the inner diameter of the first pipeline) makes the liquid fuel flow smooth and solves the flickering problem of flame.
Hereinafter, the present invention will be described in more detail with reference to the following Examples, but the scope of the present invention is not limited thereto.

EXAMPLES

According to the ratio indicated in Tables 1 to 6, the liquid fuel (methanol or cleaning naphtha) or the mixture of the liquid fuel and stabilizer and/or heat transfer promoter were loaded into the storage space of liquid fuel storage tank to provide liquid fuel compositions, and a predetermined amount of ignition promoter was then added into the storage space. The liquid fuel storage tank was then shaken to uniformly mix the components of liquid fuel composition. The pressure of the liquid fuel storage tank was measured and recorded in the tables.
Thereafter, the flow rate of liquid fluid composition was controlled in the range of about 10 g/min to about 20 g/min. An electric igniter was disposed adjacent to the burning head to provide an arc to ignite the liquid fuel composition. The required time period to ignite the liquid fuel composition while obtain a steady flame strength (ignition time θ) was measured and recorded in the tables respectively. After obtaining the steady flame strength, a cooking pot filled with water was disposed above the combustion stove of liquid fuel combustion system for heating.
The real combustion heat Qc (unit: kJ) provided for heating W kg water from initial temperature T₀° C. to 95° C. is calculated by the following equation:
Qc=F*ψ*ΔH
wherein, W=2; F is the flow rate of liquid fuel composition; ψ is the time required for raising the water temperature from T₀(initial temperature) to 95° C.; ΔH is the liquid fuel composition's combustion heat (unit: kJ/kg), and the combustion heat of the liquid fuel and ignition promoter are as follows:

LPG: 46,100

butane: 49,600

MEK: 33,890

cleaning naphtha: 44,940
methanol: 19,940
methanol with 4 wt % LPG dissolved therein: 20,980
methanol with 8 wt % LPG dissolved therein: 22,030
methanol with 4 wt % butane dissolved therein: 21,126
cleaning naphtha with 8 wt % LPG dissolved therein: 45,033
methanol with 2 wt % water and 4 wt % LPG dissolved therein: 20,560
methanol with 4 wt % water and 4 wt % LPG dissolved therein: 20,140
methanol with 8 wt % water and 4 wt % LPG dissolved therein: 19,300
methanol with 1 wt % MEK and 4 wt % LPG dissolved therein: 20,277
The theoretical combustion heat Qt (unit: kJ) required for heating W kg water from T₀° C. to 95° C. is calculated by the following equation:
Qt=Cp*(95−T ₀)*W
wherein, Cp=4.1868 kJ/kg·K; W is the weight of water (unit: kg); T₀is the initial temperature of water.
The relevant results were listed in the following Tables 1 to 7, wherein the thermal efficiency η=Qt/Qc.

TABLE 1

Influence of ignition promoter

methanol +	methanol +
4 wt % butane	4 wt % LPG	methanol

pressure (atm)	1.2	0.75	0.75
pressure source	butane	LPG	nitrogen
ignition time θ (sec)	4.5	5	>120, No flame
heating time ψ (sec)	391.8	401	459
power (kW)	3.48	3.28	3.13
thermal efficiency η (%)	47.4	47.7	44.8

Note
The liquid fuel was delivered by nitrogen.

TABLE 2

Influence of ignition promoter

	cleaning naphtha +
	8 wt % LPG	cleaning naphtha

pressure (atm)	1.6	1.6
pressure source	LPG	nitrogen
ignition time θ (sec)	1.2	3.1
heating time ψ (sec)	483	494
power (kW)	2.65	2.72
thermal efficiency η	43.8	42.7
(%)

Note
The liquid fuel was delivered by nitrogen.

TABLE 3

Influence of the amount of ignition promoter

	methanol +	methanol +
	4 wt % LPG	8 wt % LPG

pressure (atm)	0.75	0.95
pressure source	LPG	LPG
ignition time θ (sec)	5	6.5
heating time ψ (sec)	401.7	399.1
power (kW)	3.28	3.51
thermal efficiency η (%)	47.7	43.3

Note
The combustion was too heavy.

TABLE 4

Influence of heat transfer promoter

		methanol +
	methanol +	4 wt % LPG +
	4 wt % LPG	4 wt % water

pressure (atm)	1.25	1.55
pressure source	LPG	LPG
ignition time θ (sec)	1.81	1.75
heating time ψ (sec)	402	402
power (kW)	3.47	3.53
thermal efficiency η (%)	46.2	45.4

Note
The pressure in the liquid fuel storage tank was raised.

TABLE 5

Influence of the amount of heat transfer promoter

methanol +	methanol +	methanol +
4 wt % LPG +	4 wt % LPG +	4 wt % LPG +
2 wt % water	4 wt % water	8 wt % water

pressure (atm)	1.4	1.55	2.15
pressure source	LPG	LPG	LPG
ignition time θ	3.87	1.75	0.85
(sec)
heating time ψ	394	402	422
(sec)
power (kW)	3.60	3.53	3.30
thermal	46.5	47.3	50.3
efficiency η (%)

TABLE 6

Influence of stabilizer

		methanol +
	methanol +	4 wt % LPG +
	4 wt % LPG	1 wt % MEK

pressure (atm)	0.95	0.82
pressure source	LPG	LPG
ignition time θ	4.3	2.0
(sec)
heating time ψ	482	379
(sec)
power (kW)	3.62	4.24
thermal efficiency	35.8	38.02
η (%)

As shown in Tables 1 to 6, the ignition promoter is help to the ignition of liquid fuel (methanol/cleaning naphtha); the stabilizer can stabilize the ignition promoter and thus is helpful to obtain a smooth combustion (steady flame strength); and the heat transfer promoter can improve the thermal efficiency of liquid fuel.
Hereinafter, the effect of stabilizer (MEK) on the pressure of vapor LPG was measured and tabulated in the following Table 7.

TABLE 7

Influence of stabilizer on pressure

		methanol +
	methanol +	4 wt % LPG +
	4 wt % LPG	2 wt % MEK

time	pressure	fuel	pressure	fuel
(sec)	(kg/cm²)	consumption (g)	(kg/cm²)	consumption (g)

0	2.4	1	2.0	0
30	2	7.9	1.6	6.5
60	1.8	15.28	1.45	12.93
90	1.6	15.28	1.4	19.9
120	1.5	22.5	1.3	29
150	1.4	30.38	1.2	36.02
180	1.4	36.98	1.1	43.33
210	1.3	43.01	1.05	50.35
240	1.25	49.75	1	57.9
270	1.2	57.56	1	65.02
300	1.1	65.49	0.95	73
330	1.05	73.2	0.9	80.65
360	1	81.2	0.9	86.73
390	0.95	89.35	0.85	93.95
420	0.9	93.56	0.8	100.01

As shown in FIG. 7, the LPG pressure in the tank decreased with the consumption of methanol. However, in the case where 2 wt % stabilizer (MEK) was used, the decrease of pressure was lowered. This manifests that stabilizer is helpful to stabilize the pressure of ignition promoter. As a result, the ignition promoter can maintain a more concentration in methanol to help the consumption.
Furthermore, the solubility and pressure of LPL in methanol and MEK were measured to observe the effect of the stabilizer on stabilizing LPG vapor. The result was tabulated in the following Table 8.

TABLE 8

Solubility and pressure of LPG in methanol and MEK

	LPG/100 g		LPG/100 g
	methanol		MEK

pressure	solubility	pressure	solubility
kg/cm²	g/100 g	kg/cm²	g/100 g

1.61	0.91	1.68	1.47
2.62	2.76	2.2	2.84
3.19	3.83	2.89	4.88
3.68	4.77	3.53	6.86
4.55	6.44	3.9	7.93
5	7.35	4.45	9.55
		4.75	10.57
		5.02	11.3

As shown in FIG. 8, under the same pressure, the solubility of LPG in MEK is relatively high. This further manifests the stabilizing effect of MEK.
The liquid fuel compositions were prepared according to Table 9 and the ignition time of the liquid fuel compositions and the influence of different stabilizers are respectively measured and tabulated in Table 9.

TABLE 9

Effect of different stabilizers to the LPG in methanol

components		methanol +	methanol +	methanol +
(%)	methanol	MEK	DEG-100	PEG-500

methyl	96	95	95	95
LPG	4	4	4	4
MEK	0	1	0	0
DEG	0	0	1	0
PEG	0	0	0	1

Results

ignition time	2.5	2.0	1.8	1.8
(sec)
residue of the	none	none	none	none
combustion

pressure
variation in	discharged		discharged		discharged		discharged
the liquid fuel	percentage	pressure	percentage	pressure	percentage	pressure	percentage	pressure
storage tank	(%)	(atm)	(%)	(atm)	(%)	(atm)	(%)	(atm)

	0	0.95	0	0.82	0	0.81	0	0.8
	3	0.75	7	0.7	7	0.7	7	0.7
	7	0.7	13	0.65	13	0.65	17	0.7
	13	0.65	27	0.6	23	0.6	53	0.65
	47	0.62	47	0.6	33	0.55	90	0.6
	70	0.58	60	0.6	50	0.55	93	0.58
	90	0.5	77	0.58	86	0.5	100	0
	100	0	90	0.55	100	0
			97	0.53
			100	0

As shown in Table 9, the listed stabilizers all provide stabilizing effects (the decrease of pressure was lowered).
The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.

Claims

What is claimed is:

1. A liquid fuel combustion system, comprising:

a combustion stove, comprising:

a vaporization unit with a ring shape vaporization space;

a burner assembly, comprising a burning head, a first jet opening, and a burning tube connecting the burning head to the first jet opening, wherein the burning tube has at least one air opening; and

a first pipeline, having a first opening end open to the ring shape vaporization space and a second opening end open to the first jet opening;

a liquid fuel storage tank, having a storage space;

a second pipeline, having a third opening end open to the storage space and a fourth opening end open to the ring shape vaporization space; and

a liquid fuel composition contained in the storage space, comprising:

a liquid fuel selected from the group consisting of C1-C4 alcohols, liquid hydrocarbons and combinations thereof; and

an ignition promoter, which is a high volatile hydrocarbon having a flash point lower than the liquid fuel and provides a vapor pressure in the storage space, wherein the amount of the ignition promoter is at least about 1 wt % based on the weight of the liquid fuel,

whereby the vapor pressure drives the liquid fuel composition to be delivered out the storage space through the second pipeline, vaporized in the ring shape vaporization space and then delivered by the first pipeline to the burner assembly.

2. The system according to claim 1, wherein the ring shape vaporization space is formed in a hollow disc shape or a hollow bowl shape expanding up- and outward.

3. The system according to claim 1, wherein the combustion stove further comprises an apron connected to the lower part of the vaporization unit.

4. The system according to claim 1, wherein the combustion stove further comprises a second jet opening installed in the first pipeline.

5. The system according to claim 4, wherein the first pipeline has a first inner diameter D1 at the section from the first opening end to the second jet opening and a second inner diameter D2 at the section from the second opening end to the second jet opening, and D1>D2.

6. The system according to claim 5, wherein D1 is more than 1 mm and not more than 8 mm and D2 is not less than 1 mm and not more than 5 mm.

7. The system according to claim 1, wherein the inner diameter of the air opening ranges from about 3 mm to about 6 mm.

8. The system according to claim 1, wherein the combustion stove comprises a plurality of burner assemblies, and each of them comprises a burning head, a burning tube and a first jet opening; and the first pipeline has a plurality of second opening ends individually open to one of the first jet openings.

9. The system according to claim 8, wherein the first pipeline has a multi-direction manifold.

10. The system according to claim 1, wherein the third opening end is installed within the storage space.

11. The system according to claim 1, which further comprises a flow control element or an ignition switch with flow control function installed on the second pipeline.

12. The system according to claim 1, wherein the second pipeline further comprises a fifth opening end below the air opening and equipped with an ignition unit.

13. The system according to claim 1, wherein the second pipeline tilts downward to open to the ring shape vaporization space.

14. The system according to claim 1, wherein the ignition promoter is in an amount ranging from about 1 wt % to about 8 wt % based on the weight of the liquid fuel.

15. The system according to claim 1, wherein the ignition promoter is selected from the group consisting of liquefied petroleum gas (LPG), propane, butane, pentane, hexane, petroleum ether, dimethyl ether and mixtures thereof.

16. The system according to claim 1, wherein the liquid fuel composition further comprises:

a stabilizer being selected from the group consisting of ketone(s), ether(s), a polymer with a molecular weight of less than about 5,000 Dalton, and combinations thereof; and

a heat transfer promoter being soluble in the liquid fuel and having a thermal conductivity ranging from about 0.20 W/M-K to about 0.65 W/M-K,

wherein the stabilizer is in an amount of not higher than about 5 wt % and the heat transfer promoter is in an amount of not higher than about 15 wt %, based on the weight of the liquid fuel.

17. The system according to claim 16, wherein stabilizer is selected from the group consisting of acetone, methyl ethyl ketone (MEK), dimethyl ether (DME), diethylene glycol (DEG), polyethylene glycol (PEG) with a molecular weight of less than about 5,000 Dalton, a polymer with a molecular weight of less than about 5,000 Dalton and having one or more hydrophilic functional group in its main chain, and combinations thereof; and the heat transfer promoter is selected from the group consisting of ethylene glycol, glycerol, ethylene diamine, water and combinations thereof.

18. The system according to claim 17, wherein in the polymer with a molecular weight of less than about 5,000 Dalton and having one or more hydrophilic functional group in its main chain, the hydrophilic functional group is independently an ether group, an ester group, an amino, a carboxyl (—COOH), or a thiol (—SH).

19. The system according to claim 16, wherein the amount of the stabilizer is from about 0.5 wt % to about 5 wt % and the amount of the heat transfer promoter is from about 1 wt % to about 15 wt %, based on the weight of the liquid fuel.

20. The system according to claim 19, wherein the liquid fuel composition comprises about 4 wt % to about 6 wt % LPG as the ignition promoter, about 1 wt % to about 3 wt % methyl ethyl ketone as the stabilizer and about 3 wt % to about 10 wt % water as the heat transfer promoter, based on the weight of the liquid fuel; and the liquid fuel is methanol.