FORM-2
THE PATENT ACT,1970
(39 OF 1970)
AND
THE PATENT RULES, 2003
(As Amended)
COMPLETE SPECIFICATION (See section 10;rule 13)
"A DEVICE WHICH PROVIDES BETTER MIXING OF AIR AND FUEL MIXTURE FOR COMBUSTION"

A DEVICE WHICH PROVIDES BETTER MIXING OF AIR AND FUEL MIXTURE FOR COMBUSTION
FIELD OF THE INVENTION
The present invention relates to a device that provides better mixing of air and fuel mixture for combustion, for example, in the case of LPG used in domestic cooking stove. The present invention particularly relates to energy efficient devices that increase performance of domestic LPG cooking stove.
BACKGROUND OF THE INVENTION
In the current scenario, there is tremendous demand for fossil fuels. These fossil fuels are depleting at a rapid rate. Therefore, efforts need to be made to conserve it. In order to meet the impending fuel crisis, an extensive research is being carried out in the areas of fuel conservation and alternative fuels. Liquefied Petroleum Gas (LPG) is the most convenient and clean fuel for domestic use and is very popular these days. LPG is an exceptional energy source due to its origin, relative advantages, and applications.
The LPG stove manufacturing industry is about 50 years old and is mainly concentrated in the small-scale sector and also LPG as a cooking fuel is very economical and clean. For domestic application of cooking, many LPG stove manufacturers are supplying BIS certified LPG stoves in Indian market. BIS standard IS4246:2002 for domestic gas stoves specifies minimum thermal efficiency of 68%.
In LPG cooking stove, there are various features such as primary air entrainment, burner port orientation and size of ports, design of heat reflector and pan support, and gap between burner top and vessel bottom base, which play an important role in its thermal efficiency. Presently available LPG burners have primary air entrainment mechanism that has incorrect placement of LPG nozzle, which results in inappropriate amount of primary air entering into the mixing tube along with LPG. Also, currently available burner tops have non optimized port orientation, port area, size of ports, and their inclination angle. Further, the improper heat reflector in present cooking stove causes higher heat losses. All these aspects finally result in lower thermal efficiency.

In order to improve the thermal efficiency, minimalistic changes have to be incorporated so that an Indian customer doesn’t feel any economic burden. The mixing tube is one of the important components of the stove setup. By changing the mixing tube alone from the existing cooking gas stove there should be an improvement in thermal efficiency. Mixing tube mixes the air and the fuel before it is fed to the burner top. Therefore, there is a long felt need to optimize the mixing tube so that the thermal efficiency is enhanced by controlling the combustion process.
SUMMARY OF THE INVENTION
It is intended that all such features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. The following summary is provided to facilitate an understanding of some of the innovative features unique to the disclosed embodiment and is not intended to be a full description. A full appreciation of the various aspects of the embodiments disclosed herein can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
The mixing tube disclosed here addresses an optimized mixing tube with an enhanced thermal efficiency via a controlled combustion process. The mixing tube disclosed here for a LPG stove comprises a cylindrical tube and a cup, where the cylindrical tube comprises an inlet opening, one or more slots, and a venturi that are positioned in series to each other. The inlet opening is positioned at a distal end of the cylindrical tube to house a nozzle, where the inlet opening ensures smooth entering of partial amount of primary air and the nozzle injects fuel into the cylindrical tube. The slots are positioned on a circumferential surface of the cylindrical tube for the primary air entrainment. The venturi is in fluid communication with the inlet opening, the slots, and the nozzle within the cylindrical tube, where the venturi optimizes the pressure gradient of the primary air and the fuel received from the inlet opening, the slots, and the nozzle.
The cup comprises an annular channel that is in fluid communication and positioned in series with the cylindrical tube. The annular channel comprises a triangular wedge section attached to a wall of the annular channel and is positioned in line with flow of

the air-fuel mixture from the cylindrical tube. The triangular wedge section smoothens the flow of the turbulent air-fuel mixture and reduces back-pressure on the flow of the air-fuel mixture. A burner top is positioned over the cup to receive the air-fuel mixture from the annular channel for combustion. In an embodiment, the venturi comprises a converging section to increase velocity of the air-fuel mixture that is received from the inlet opening and the slots.
In an embodiment, the venturi comprises a throat section in fluid communication with the converging section to receive the high velocity air-fuel mixture. The throat section lowers pressure of the air-fuel mixture and transfers the low-pressure air-fuel mixture towards a diverging section of the venturi in fluid communication with the throat section. In an embodiment, the diverging section increases the pressure of the air-fuel mixture that is received from the throat section, and the high-pressure air-fuel mixture is transferred to a straight mixing zone.
In an embodiment, the mixing zone is positioned in series with the venturi and in fluid communication with the venturi within the cylindrical tube. Mixed primary air and fuel is introduced in the mixing zone and the air-fuel mixture is transferred to the annular channel of the cup. In an embodiment, the mixing tube comprises at least two of the slots that are positioned on the circumferential surface of the cylindrical tube, wherein each slot is positioned radially opposing to each other for the primary air entrainment.
In other words, the mixing tube disclosed here provides better mixing of air and fuel mixture for combustion of LPG fuel improves the efficiency of domestic LPG cooking stove by 2±0.5 %. The mixing tube provides sufficient primary air entrainment that results in a better mixture of LPG and air for combustion. The venturi effect controls pressure gradient in mixing tube and ensures well-ordered movement of LPG-air mixture. A triangular wedge section is provided in cup of the mixing tube to smoothen the flow and reduce back-pressure to the flow of the air fuel mixture. Hence, the mixing tube disclosed here is topologically modified, where the mixing of fuel and air is enhanced with even distribution of fuel gas mixture at all ports of the burner top.
BRIEF DESCRIPTION OF DRAWINGS

The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
Figure 1 shows an exploded view of a general apparatus for combustion of LPG fuel.
Figure 2 is an isometric view that describes general construction of the mixing tube, according to an exemplary embodiment.
Figure 3A is a top view of a mixing tube, according to an exemplary embodiment.
Figure 3B is the sectional side view of the mixing tube shown in Figure 3A, according to an exemplary embodiment.
DESCRIPTION OF THE INVENTION
The present invention is directed to provide an apparatus for combustion of LPG fuel for application in domestic usage having high thermal efficiency. In addition to this, another aim is to develop a cooking stove with a potential for LPG savings and better performance. The above aims have been achieved through modified design of the mixing tube based experimental and numerical methods that has an improved combustion of LPG fuel and capture of the heat losses.
The foregoing advantages as well as the particular construction of the mixing tube will become more noticeable and understandable from the following detail description thereof when read in conjunction with the accompanying drawings.
In the general working of a LPG stove, the LPG enters through a nozzle into a mixing tube where air entrainment happens because of pressure gradient. The LPG-air mixture comes out from the ports of burner top and combustion takes place. The heat reflector design controls the secondary air for combustion. The mixing tube of the LPG cooking stove, which is known in the prior art comprises of a tube for receiving the gas, where

the gas is mixed with ambient air to form a combustible mixture. In view of the above, the present invention discloses a mixing tube for the LPG Stove, which has a better mixing capability, which is simple in operation, and is cost effective. The mixing tube disclosed here provides better mixing of air and fuel mixture for combustion of LPG that results in an increase in thermal efficiency and gas savings for the application in domestic usage. Ideally, premixed combustion of air and fuel generates the highest efficiency in any burner and the same concept is applicable for a domestic cooking gas stove.
Figure 1 shows the exploded view of a general apparatus 100 for combustion of LPG fuel, according to an exemplary embodiment. The nozzle holder 102 is machined and fitted to the primary tube 104. Gaseous fuel at line pressure is accelerated into the nozzles 106, and is expelled as jets into the mixing tube 108. At the throat 110 of the mixing tube 108, the air from the atmosphere (primary air) is inducted into the mixing tube 108 due to the negative pressure in the throat 110 and propagates further. The amount of air that is aspirated depends on the opening area of the throat 110, nozzle gas flow rate (or gas exit velocity). The gas being injected from the nozzle 106 accelerates the inducted primary air and mixing of gas and air takes place. Due to the design of the nozzle 106, the gas expands in width as per the spray pattern. The gas and air mixture fills the throat 110 with a relatively high velocity mixture at a slight negative pressure relative to the atmospheric pressure. This high velocity mixture is then decelerated in mixing tube 108 that comprises a cylindrical tube 112 attached to the cup 114, resulting in the increase in the static pressure.
The straight cylindrical tube 112 of the mixing tube 108 discharges into the diffuser cap (not shown) which comprises a cap with the profile for the air-gas mixture flow. The gas at the discharge of the cup 114 is at a slight positive pressure and then the air-gas mixture flows into the burner top 116. The burner top 116 is a solid end cap having multiple ports on the circumferential surface. The ports are of pre-determined diameter and placed at defined pitch. Since, the LPG stove is used for cooking purposes at home, a drip tray 118 is provided to collect the spilled substance from any cooking pan that is positioned over the pan support 126. The legs 120 are provided at 4 corners of the burner body 122 to provide the support to the burner body 122 and to provide space for

cleaning. Two knobs 124 are provided on the burner body 122 whose position can be adjusted from ‘Sim to full’ enabling the user to control the gas flow rate as per the cooking requirement.
Figure 2 is the isometric view that describes general construction of the mixing tube 200, according to an exemplary embodiment. In order to address this combustion efficiency, the mixing tube 200 is proposed herein to improve the overall thermal efficiency of the LPG stove. As disclosed here, the mixing tube 200 comprises a cylindrical tube 202 and a cup 204, where the cylindrical tube 202 comprises a converging inlet opening 206, one or more slots 208, and a venturi 210 that are positioned in series to each other. The mixing tube 200 further comprises a mixing zone 212 that is positioned in series after the combination of the inlet opening 206, the slots 208, and the venturi 210.
The mixing tube 200 also comprises an attachment portion 214 that is configured to be fastened to a burner top via a nut and a bolt, so that the air-fuel mixture is transferred to the ports of the burner top during combustion. The mixing tube 200 provides better mixing of air and fuel mixture for combustion of LPG fuel and improves the thermal efficiency of domestic LPG cooking stove. In other words, the mixing tube 200 disclosed here provides sufficient primary air entrainment and LPG gas fuel that results in a better mixture of LPG and air for combustion. The venturi effect caused by the venturi 210 controls pressure gradient in mixing tube 200 and ensures trouble free and well-ordered movement of LPG-air mixture.
Figures 3A and 3B show a top view and a sectional side view respectively of the mixing tube 200, according to an exemplary embodiment. The mixing tube 200 comprises the cylindrical tube 202 and the cup 204, where the cylindrical tube 202 comprises a converging inlet opening 206, the slots 208a and 208b, and the venturi 210 that are positioned in series to each other. The inlet opening 206 is positioned at a distal end of the cylindrical tube 202 to house a nozzle 216, where the inlet opening 206 ensures smooth entering of partial amount of primary air and the nozzle 216 injects fuel into the cylindrical tube 202. The slots 208a and 208b are positioned on a circumferential surface of the cylindrical tube 202 for the primary air entrainment. In an embodiment,

the mixing tube 200 comprises at least two of the slots 208a and 208b that are positioned on the circumferential surface of the cylindrical tube 202, where each slot 208a or 208b is positioned radially opposing to each other for the primary air entrainment. The venturi 210 is in fluid communication with the inlet opening 206, the slots 208a and 208b, and the nozzle 216 within the cylindrical tube 202, where the venturi 210 optimizes the pressure gradient of the primary air and the fuel received from the inlet opening 206, the slots 208a and 208b, and the nozzle 216.
The cup 204 comprises an annular channel 220 that is in fluid communication and positioned in series with the cylindrical tube 202. The annular channel 220 comprises a triangular wedge section 222 attached to a wall 224 of the annular channel 220 and is positioned in line with flow of the air-fuel mixture from the cylindrical tube 202. The triangular wedge section 222 smoothens the flow of the turbulent air-fuel mixture and reduces back-pressure on the flow of the air-fuel mixture. A burner top is positioned over the cup 204 to receive the air-fuel mixture from the annular channel 220 for combustion. In an embodiment, the venturi 210 comprises a converging section 226 to increase velocity of the air-fuel mixture that is received from the inlet opening 206 and the slots 208.
In an embodiment, the venturi 210 comprises a throat section 228 in fluid communication with the converging section 226 to receive the high velocity air-fuel mixture. The throat section 228 lowers pressure of the air-fuel mixture and transfers the low-pressure air-fuel mixture towards a diverging section 230 of the venturi 210 in fluid communication with the throat section 228. The diverging section 230 increases the pressure of the air-fuel mixture that is received from the throat section 228, and the high-pressure air-fuel mixture is transferred to the straight mixing zone 212. The mixing zone 212 is positioned in series with the venturi 210 and is in fluid communication with the venturi 210 within the cylindrical tube 202. The mixed primary air and fuel is introduced in to the mixing zone 212 and the air-fuel mixture is transferred to the annular channel 220 of the cup 204. This air furl mixture is transferred to the ports of the burner top that is positioned above the cup 204 to complete the combustion process.

In a first embodiment, a first type of the mixing tube 200 comprises a LPG flow rate of 61 to 65 LPH, corresponding vessel number 4, and BIS standard IS:4246, wherein the first type of the mixing tube 200 comprises:
The inlet opening 206 with a length in a range between 6.5 mm to 12.5 mm and an angle of convergence within a range between of 67 to 73 degrees;
The cylindrical tube 202 with a length within a range between 99 mm and 105 mm102 mm, and a diameter within a range between 19 mm and 25 mm;
Each slot 208 with a length within a range between 19 mm and 25 mm, and a width within a range between 9 mm and 15 mm;
The venturi 210 with a length within a range between 31. 35 mm and 37. 35 mm, and the venturi further comprising:
The converging section 226 with a length within a range between 10.5 mm
and 16.5 mm,
The throat section 228 with a length within a range between 4 mm and 10
mm and diameter within a range between 12.7 mm and 18.7 mm, and
The diverging section 230 with a length within a range between 10.85 mm
and 16.85 mm;
The mixing zone 212 with a length within a range between 28 mm and 34 mm, and a diameter within a range between 19 mm and 25 mm; and
The cup 204 with an outer diameter within a range between 59.50 mm and 65.50 mm and an inner diameter within a range between 30.35 mm and 36.35 mm.
In a second embodiment, a second type of the mixing tube 200 comprises a LPG flow rate of 71 to 75 LPH, corresponding vessel number 5, and BIS standard IS:4246, wherein the second type of the mixing tube 200 comprises:
The inlet opening 206 with a length within a range between 7.7 mm and 13. 7 mm and an angle of convergence within a range between 67 degrees and 73 degrees;
The cylindrical tube 202 with a length within a range between 103 mm and 109 mm and a diameter within a range between 20 mm and 26 mm;
Each slot 208 with a length within a range between 21.3 mm and 27.3 mm and a width within a range between 11 mm and 17 mm;
The venturi 210 with a length within a range between 32 mm and 38 mm, and the venturi further comprising:

The converging section 226 with a length within a range between 11 mm and 17 mm,
The throat section 228 with a length within a range between 3.5 mm and 9.5 mm and diameter within a range between 13.7 mm and 19.7 mm, and
The diverging section 230 with a length within a range between 11 mm and 17 mm;
The mixing zone 212 with a length within a range between 29 mm and 35 mm and a diameter within a range between 20.3 mm and 26.3 mm; and
The cup 204 with an outer diameter within a range between 70.4 mm and 76.4 mm and an inner diameter within a range between 35.5 mm and 41.5 mm.
Thermal efficiency testing of LPG cooking stove that incorporates the disclosed mixing tube 200, was carried out in a laboratory that uses fully automated testing. The mixing tube 200 was found to provide higher thermal efficiency as compared to mixing tubes available in market. When the mixing tube 200 is used to replace an existing mixing tube, it provides an increased thermal efficiency of 2 ±0.5 %.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore, contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined.

We Claim:
1. A mixing tube for a LPG stove comprising:
a cylindrical tube and a cup, wherein the cylindrical tube comprises an inlet opening, one or more slots, and a venturi that are positioned in series to each other;
the inlet opening positioned at a distal end of the cylindrical tube to house a nozzle, wherein the inlet opening ensures smooth entering of partial amount of primary air and the nozzle injects fuel into the cylindrical tube;
the slots positioned on a circumferential surface of the cylindrical tube, wherein the slots are positioned for the primary air entrainment;
the venturi in fluid communication with the inlet opening, the slots, and the nozzle within the cylindrical tube, wherein the venturi optimizes the pressure gradient of the primary air and the fuel received from the inlet opening, the slots, and the nozzle; and
the cup comprising an annular channel that is in fluid communication and positioned in series with the cylindrical tube, wherein the annular channel comprises a triangular wedge section attached to a wall of the annular channel and is positioned in line with flow of the air-fuel mixture from the cylindrical tube, wherein the triangular wedge section smoothens the flow of the turbulent air-fuel mixture and reduces back-pressure on the flow of the air-fuel mixture, and wherein a burner top is positioned over the cup to receive the air-fuel mixture from the annular channel for combustion.
2. The mixing tube as claimed in claim 1, wherein the venturi comprises a converging section to increase velocity of the air-fuel mixture that is received from the inlet opening and the slots.
3. The mixing tube as claimed in claim 2, wherein the venturi comprises a throat section in fluid communication with the converging section to receive the high velocity air-fuel mixture, wherein the throat section lowers pressure of the air-fuel mixture and transfers the low pressure air-fuel mixture towards a diverging section of the venturi in fluid communication with the throat section.

4. The mixing tube as claimed in claim 3, wherein the diverging section increases the pressure of the air-fuel mixture that is received from the throat section, and wherein the high-pressure air-fuel mixture is transferred to a straight mixing zone.
5. The mixing tube as claimed in claim 4, wherein the mixing zone is positioned in series with the venturi and in fluid communication with the venturi within the cylindrical tube, wherein mixed primary air and fuel is introduced in the mixing zone and the air-fuel mixture is transferred to the annular channel of the cup.
6. The mixing tube as claimed in claim 1, comprises at least two of the slots that are positioned on the circumferential surface of the cylindrical tube, wherein each slot is positioned radially opposing to each other for the primary air entrainment.
7. The mixing tube as claimed in claim 1, wherein a first type of the mixing tube comprises a LPG flow rate of 61 to 65 LPH, corresponding vessel number 4, and BIS standard IS:4246, wherein the first type of the mixing tube comprises:
the inlet opening with a length in a range between 6.5 mm to 12.5 mm and an angle of convergence within a range between of 67 to 73 degrees;
the cylindrical tube with a length within a range between 99 mm and 105 mm, and a diameter within a range between 19 mm and 25 mm;
each slot with a length within a range between 19 mm and 25 mm, and a width within a range between 9 mm and 15 mm;
the venturi with a length within a range between 31. 35 mm and 37. 35 mm, and the venturi further comprising:
the converging section with a length within a range between 10.5 mm and 16.5 mm,
the throat section with a length within a range between 4 mm and 10 mm and diameter within a range between 12.7 mm and 18.7 mm, and
the diverging section with a length within a range between 10.85 mm and 16.85 mm;
the mixing zone with a length within a range between 28 mm and 34 mm, and a diameter within a range between 19 mm and 25 mm; and

the cup with an outer diameter within a range between 59.50 mm and 65.50 mm and an inner diameter within a range between 30.35 mm and 36.35 mm.
8. The mixing tube as claimed in claim 1, wherein a second type of the mixing tube comprises a LPG flow rate of 71 to 75 LPH, corresponding vessel number 5, and BIS standard IS:4246, wherein the second type of the mixing tube comprises:
the inlet opening with a length within a range between 7.7 mm and 13. 7 mm and an angle of convergence within a range between 67 degrees and 73 degrees;
the cylindrical tube with a length within a range between 103 mm and 109 mm and a diameter within a range between 20 mm and 26 mm;
each slot with a length within a range between 21.3 mm and 27.3 mm and a width within a range between 11 mm and 17 mm;
the venturi with a length within a range between 32 mm and 38 mm, and the venturi further comprising:
the converging section with a length within a range between 11 mm and 17 mm, the throat section with a length within a range between 3.5 mm and 9.5 mm and diameter within a range between 13.7 mm and 19.7 mm, and
the diverging section with a length within a range between 11 mm and 17 mm;
the mixing zone with a length within a range between 29 mm and 35 mm and a diameter within a range between 20.3 mm and 26.3 mm; and
the cup with an outer diameter within a range between 70.4 mm and 76.4 mm and an inner diameter within a range between 35.5 mm and 41.5 mm.