COMPLATE AFTER PROVISIONAL
LEFT ON 5 MAR 2007

FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
THE PATENTS RULES, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
AN INTERNAL COMBUSTION ENGINE HAVING DUAL FUEL SUPPLY

INVENTOR
Names
Nationality Address

Mohanavelu Parthiban and Barve Shripad Madhav
both Indian Nationals
Bajaj Auto Limited, Akurdi, Pune 411035, Maharashtra, India

APPLICANTS

Name
Nationality
Address

Bajaj Auto Limited
Indian Company
Akurdi, Pune 411035, Maharashtra, India

PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:-

This invention relates to an internal combustion engine having a dual fuel supply.
Two and three wheel motor vehicles are an important mode of transport used for commuting in and around cities. Such vehicles have engines operating on the two and four stroke cycle, employing petrol as a fuel. As environmental laws become more stringent, emissions from such vehicles are required to reduce. One way of achieving lower emissions is to use a gaseous fuel such as LPG (Liquefied Petroleum Gas) or CNG (Compressed Natural Gas). Further, use of such gaseous fuels provides economic benefit since they are currently of lower cost than liquid fuels such as petrol.
It may be desirable for such a gas fuelled vehicle to include a "back up" fuel supply system to avoid a situation where the gaseous fuel may become exhausted at a location where there is no refueling station in the near vicinity, yet there may be relatively ready availability of liquid fuels, especially petrol. Petrol is therefore conveniently used as the back-up fuel supply.
Under cold starting conditions, and perhaps other conditions, an engine operating on gaseous fuel may only start with difficulty. Various methods have been tried to improve the starting ability of such an engine. Such methods include heating of gaseous fuel at the time of starting and fuel enrichment. US Patent No. 4285700 discloses a system wherein fuel enrichment is achieved during starting and wide open throttle condition. European Patent No. 331732 discloses use of a control valve operable during starting depending on the engine temperature. JP 58206841 discloses sensing of air intake temperature and engine temperature to determine use of additional fuel supply. JP 11324749 discloses a

system of starting the engine in petrol mode and switching over to gaseous mode. Such systems involve complicated circuitry and expensive components which add cost and maintenance requirements.
It is the object of the present invention to provide an engine with a dual fuel supply which addresses the problem of starting, particularly under cold conditions.
With this object in view, the present invention provides an internal combustion engine comprising:
a) a liquid fuel supply including a choke and carburetor for supplying a
liquid fuel-air mixture to the engine in a liquid fuel mode; and
b) a gaseous fuel supply including a mixer for mixing gaseous fuel and air for delivery to the engine in a gaseous fuel mode; and
c) an air intake duct
wherein said gaseous fuel supply is connected, for delivering gaseous fuel, to said air intake duct on an engine side of said mixer at a point having higher vacuum pressure, than at said mixer, for inducing gaseous fuel into said air intake duct. This delivery point is preferably downstream of a throttle for the engine.
Gaseous fuel and liquid fuel may be introduced to the air intake duct or inlet manifold at a
common entry point. For example, gaseous fuel and liquid fuel may be introduced to a
choke which may have a common fuel supply duct through which either gaseous fuel or
liquid fuel may be introduced to the choke chamber, or cylinder, for forming an enriched
fuel-air mixture to assist with starting depending on whether gaseous fuel mode or liquid
fuel mode is selected by the engine operator. In addition, where gaseous fuel mode is

selected, a gaseous fuel-air mixture may continue to be delivered to the engine by the mixer.
The choke may be actuated by an operating means that is common for both liquid fuel supply and gaseous fuel supply modes.
The choke may comprise a cylinder with a piston movable within the cylinder and connected to an actuating means operable by the engine operator, a fuel inlet duct, an air inlet duct and an air outlet duct. At one end of travel for the piston, the fuel inlet duct is closed such that fuel is not delivered to the cylinder. Under this condition, the engine operator starts the engine without enrichment, a carburetor of the engine operating in a conventional fashion. The carburetor also operates in conventional fashion under other engine running conditions: idle and off-idle.
The choke is most likely to be operated on cold starting of the engine where fuel vapourises less readily making starting difficult. Under such conditions, the engine operator or driver may actuate the choke. The choke may be actuated by cable means connected to a knob operable by the driver.
When operating in gaseous fuel mode, air may be introduced to the choke through at least
one duct, for example, the fuel inlet duct, which has previously carried liquid fuel, for
example petrol or gaseous fuel. Liquid fuel may be introduced to the choke through a duct
which has previously carried air such as the air inlet or air outlet duct. In either case, such
provision at the choke allows better control over air-fuel ratio control. The duct(s), in this
case, have diameter and flow area selected for air-fuel ratio control, for example to form

an air-fuel mixture having air-fuel ratio maintained within acceptable limits for combustion or to be readily ignitable whether or not petrol or gaseous fuel is used. In particular, the diameter and flow area of the air inlet duct may be selected with air-fuel ratio control in view.
Conveniently, the gaseous fuel is LPG or CNG or another available gaseous fuel. The gaseous fuel may be the primary fuel supply to the engine. The liquid fuel is conveniently petrol fuel used as a secondary or back up fuel supply for the engine. Petrol may thus be used as a backup fuel only with the benefits of lower environmental and operating costs. The gaseous fuel supply includes a gaseous fuel supply tank, a regulator, power valve and mixer in conventional manner. In accordance with the invention, however, a connecting duct connects the gaseous fuel supply to the fuel supply duct in the choke. The connecting duct may take the form of an extension from a gas supply passage supplying gaseous fuel from the gaseous fuel supply tank to the mixer. When the engine is operated in liquid fuel or petrol mode, with the gaseous fuel supply cut-off, air may be introduced through the duct or extension to lean out the petrol-air mixture to avoid rich misfire or other combustion problems. The extension and/or air inlet duct to the choke may be of diameter(s) and flow area(s) selected to achieve air-fuel ratio control, for example being optimized to induce only such quantity of air as to form an air-fuel mixture having a readily ignitable air-fuel ratio. Alternatively, a valve - such as a selectively operable solenoid valve - may be included to close the extension from air ingress when required; for example, when a driver changes a selector switch to petrol mode.
In a further aspect of the invention, there is provided a method of operating a carbureted
engine having a choke, a liquid fuel supply and a gaseous fuel supply comprising a mixer

for mixing gaseous fuel and air for delivery to the engine through an air intake duct wherein gaseous fuel is delivered to the air intake duct on an engine side of the mixer at a point having higher vacuum pressure, than at the mixer, for inducing gaseous fuel into the air intake duct.
In a still further aspect of the invention, which may be combined with the above described method of operating a carbureted engine, there is provided a method of controlling air fuel ratio in a carbureted engine having a choke provided with liquid fuel duct(s) for carrying liquid fuel during a liquid fuel mode and air duct(s), a liquid fuel supply and a gaseous fuel supply comprising, when the engine is operated in a gaseous fuel mode, delivering air to the choke through a liquid fuel duct for leaning a gaseous fuel — air mixture to be delivered to the engine.
The method aspects are conveniently implemented on starting of the engine, particularly under cold conditions.
The engine and method of the present invention enable fuel enrichment on cold starting making an engine easier to start.
The engine of the present invention may be more completely understood from the following description of a preferred embodiment thereof made with reference to the accompanying drawings in which:
Figure 1 is a part sectional schematic view of prior art engine having a carbureted petrol
mono-fuel supply system and viewed in the direction of the engine;
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Figure 2 is a schematic layout of a prior art engine having a carbureted dual fuel supply system, when operated in petrol fuel mode;
Figure 3 is a sectional schematic view of a prior art engine having a carbureted dual fuel supply system, when operated in gaseous fuel mode;
Figure 4 is a schematic layout of an engine having a carbureted dual fuel supply in accordance with one embodiment of the present invention, when operated in petrol fuel mode;
Figure 5 is a schematic layout of the engine of Figure 4 when operated in gaseous fuel mode;
Figure 6 is a part sectional schematic view of the engine of Figures 4 and 5;
Figure 7 is a detail sectional view of the choke of the engine of Figures 4 to 6 showing air and gas flows in gaseous fuel mode; and
Figure 8 is a detail sectional view of the choke of the engine of Figures 4 to 6 showing air and petrol flows in petrol fuel mode.
Figure 9 A is a typical sectional view of float chamber of a carburettor when engine runs on petrol fuel mode,
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Figure 9B is a typical sectional view of float chamber of a carburettor when engine runs on gaseous fuel mode,
Referring now to Figure 1, there is shown a carbureted motorcycle engine 100 operated on petrol fuel in accordance with the prior art. The mono-fuel engine 100 includes an enrichening circuit, to assist with fuelling at starting including a choke 10 having a cylindrical body 1. Body 1 has a choke piston 3 located within its chamber having the form of a cylindrical bore 2. Choke piston 3 is actuated by the motorcycle rider, for example, on cold starting of the engine 100, to enrich the fuel mixture to be delivered to the engine 100. Actuation of the choke 10 may be achieved by the rider pulling a choke knob, connected to the choke piston 3 by a cable (not shown).
Cylindrical bore 2 is provided with air inlets 4 and 5 and petrol supply duct 6. Mixing of air and fuel takes place within cylindrical bore 2 and a rich air fuel mixture is discharged to the engine through port 7. When the choke piston 3 is at the lowermost point 2a of cylindrical bore 2, petrol supply duct 6 and the air inlets 4 and 5 are closed and the carburetor 11 operates normally, mixing air and fuel in correct proportion for operation of the engine.
Under cold starting conditions, the rider operates the choke knob or control, actuating the choke 10 by moving choke piston 3 upward within the cylindrical bore 2 of choke 10. On such upward movement of choke piston 3, petrol supply duct 6 and air inlet ducts 4 and 5 open, delivering air and petrol to cylindrical bore 2 to form an enriched air fuel mixture for delivery to the engine 100 to facilitate starting.
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Figures 2 and 3 are schematic layouts of a prior art engine 116 operating with a dual fuel supply. The gaseous fuel is LPG and the liquid fuel is petrol fuel. In this illustration, LPG is the primary fuel and petrol fuel is a secondary fuel or "back up" to be employed if LPG fuel runs low and it is not easy to refill. The LPG fuel supply circuit is of conventional type including a regulator 13, a power valve 14 and a mixer 12 for mixing gas and air to form a combustible fuel mixture for delivery to the motorcycle engine 116. A manifold vacuum sensing pipe 121 connects the manifold 17 and regulator 13. Mixer 12 receives LPG fuel from gaseous fuel tank 23 through regulator 13 and power valve 14. Carburetor 11 receives petrol fuel, during petrol mode, from a petrol tank 21 through petrol solenoid 15. An inlet of the carburetor 11 is connected to mixer 12 and an outlet of the carburetor 11 is connected to engine 116 through inlet manifold 17. Mixer 12 and carburetor 11 receive air supply from an outlet of air filter 19 through an air intake duct 18. The mixer 12 provides a gaseous fuel-air mixture for operation of engine 116 when in the LPG fuel mode, as schematically shown in Figure 3. Dual fuel supply systems of the illustrated kind are known in the art and operated in conventional manner. However, difficulty in starting engine 116 in gas mode may be experienced under cold conditions.
Figures 4 to 9 show the engine 117 of the invention. Engine 117 has a dual fuel supply as
well. Again, a carburetor 111 having a throttle 122 and fuel delivery point 123 is
included to receive petrol, during petrol mode, from petrol tank 21 through petrol solenoid
15. However, in contrast to engine 116, mixer 112 is not the sole source of a gaseous
fuel-air mixture for operation of the engine, particularly on starting, which may be the
cause of difficulty in cold conditions. In engine 117, gaseous fuel (LPG) is delivered to
air intake duct 118 and choke 101 at a point on the engine side of mixer 112 having higher
vacuum pressure than at the mixer 112. This results in better gaseous fuel (LPG)


induction into the air intake duct 118 and better starting performance, particularly under cold starting conditions. Specifically, and in contrast to the prior art described above, gaseous fuel is introduced directly to the enrichening circuit of engine 117 and more specifically the choke 101 of that enrichening circuit. This choke 101 is connected to the gaseous fuel supply by an extension 120 which joins a gas supply duct 130 from the LPG tank to mixer 112 upstream of the mixer 112.
Extension 120 is also connected to the same duct 106 through which petrol would be introduced to choke 101 in petrol mode. This common fuel supply duct 106 enables supply of LPG fuel or petrol fuel dependent on the operating mode.
When the engine is started in LPG gas mode, the same choke control as used for petrol is actuated. Such actuation causes the choke piston 3 to open the common fuel supply duct 120 to admit gaseous fuel with air also being admitted to the choke 101 through air inlet ducts 4 and 5 and the lower portion of petrol supply duct 106 to form an enriched LPG-air mixture facilitating starting of the engine 117, especially under cold conditions. This operating mode is schematically illustrated in Figures 5 and 7. In this condition, supply of petrol does not take place since a selector switch (not shown) is in off condition that cuts off petrol supply to carburetor 111.
In one embodiment, shown schematically in Figure 8, air is introduced through extension 120 and through common fuel supply duct 106, in addition to air through air inlet ducts 4 and 5 when engine 117 is operated in petrol mode. The diameters and flow areas of air passage 4 and extension 120 are selected to achieve air-fuel ratio control, being optimized
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to introduce only such quantity of air that maintains a readily ignitable air fuel ratio for starting of the engine 117.
Figure 9A describes supply condition of fuel in petrol fuel mode. Float chamber (45) is fixed to carburettor body (51) in which petrol level (46) is maintained. When the engine runs on petrol due to suction at venturi (not shown) and atmospheric pressure at breather (48), petrol is supplied to the engine through the pilot jet (49) or main jet (50) or starter jet (6) or combination thereof. As the petrol level (46) lowers, petrol is led in the float chamber by opening passage (47) with the help of float (not shown) & float pin (not shown). During starting, air above petrol level (46) is sucked through passage (5) along with petrol through passage (6) to enrich the air fuel mixture.
Figure 9B describes condition of float chamber in gaseous fuel mode. Carburettor float chamber (45) fixed to the carburettor body (51) is filled with air because of breather (48). When the engine runs on gaseous fuel due to suction, gaseous fuel and air mixture is supplied to the engine. In this condition, air passes through the pilot jet (49) or main jet (50) or starter jet (6) or combination thereof. During starting, air in float chamber is sucked through passage (5) & passage (6) to the starting circuit.
Modifications and variations to the engine of the present invention may be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed within the scope of the present invention. For example, the invention is not limited by the specific nature of the gaseous fuel or the type of vehicle, particularly two or three wheeler, in which the dual fuel supply system is employed.
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WE CLAIM:
1. An internal combustion engine comprising:
a) a liquid fuel supply including a choke and carburetor for supplying a liquid-fuel air mixture to the engine in a liquid fuel mode; and
b) a gaseous fuel supply including a mixer for mixing gaseous fuel and air for delivery to the engine in a gaseous fuel mode; and
c) an air intake duct
wherein said gaseous fuel supply is connected for delivering gaseous fuel to said air intake duct on an engine side of said mixer at a delivery point having higher vacuum pressure, than at said mixer, for inducing gaseous fuel into said air intake duct.
2. The engine of claim 1 wherein said delivery point is downstream of a throttle for the engine.
3. The engine of claim 1 or claim 2 wherein gaseous fuel and liquid fuel are introduced to the air intake duct at a common entry point.
4. The engine of claim 3 comprising a choke having a common fuel supply duct through which gaseous fuel or liquid fuel are introduced to a choke for forming an enriched fuel-air mixture depending on whether gaseous fuel mode or liquid fuel mode is selected by an engine operator.
5. The engine of claim 4 wherein, when gaseous fuel mode is selected, a gaseous
fuel-air mixture continues to be delivered to the engine by the mixer.
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6. The engine of claim 4 or 5 wherein the choke is actuated by an operating means that is common for both liquid fuel supply and gaseous fuel supply modes.
7. The engine of any one of claims 4 to 6 wherein the choke comprises a cylinder with a piston movable within the cylinder and connected to an actuating means operable by the engine operator, a fuel inlet duct, an air inlet duct and an air outlet duct.
8. The engine of claim 7 wherein the fuel inlet duct is closed at one end of travel for the piston such that fuel is not delivered to the choke cylinder.
9. The engine of claim 7 or 8 wherein the fuel inlet duct allows air to be introduced to the choke for air-fuel ratio control.
10. The engine of any one of claims 7 to 9 wherein the air inlet or air outlet duct allows fuel to be introduced to the choke for air-fuel ratio control.
11. The engine of claim 10 wherein diameter and flow area of a duct carrying air or fuel is selected to achieve air-fuel ratio control.
12. The engine of claim 11 wherein diameter and flow area of the air inlet duct is selected to induce such quantity of air as to form an air-fuel mixture having a readily ignitable air-fuel ratio.
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13. The engine of any one of claims 7 to 12 wherein the actuating means is a cable means connected to a knob operable by the engine operator.
14. The engine of any one of the preceding claims wherein gaseous fuel is the primary fuel supply to the engine and the liquid fuel is used as a secondary or back up fuel supply for the engine.
15. The engine of claim 14 wherein said gaseous fuel supply includes a gaseous fuel supply tank, a regulator, power valve and mixer and a connecting duct connecting the gaseous fuel supply tank to a fuel supply duct of the choke.
16. The engine of claim 15 wherein said connecting duct is an extension from a gas supply passage supplying gaseous fuel from the gaseous fuel supply tank to the mixer.
17. The engine of claim 16 wherein said extension allows air to be introduced to lean out the air-fuel mixture during liquid fuel mode.
18. The engine of claim 17 wherein diameter and flow area of the extension is selected to achieve air-fuel ratio control.
19. The engine of claim 18 wherein diameter and flow area of the extension is selected to induce such quantity of air as to form a readily ignitable air-fuel mixture.
20. The engine of any one of claims 16 to 19 including a selectively operable solenoid
valve to close the extension from air ingress when required.
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21. A method of operating a carbureted engine having a choke, a liquid fuel supply and
a gaseous fuel supply comprising a mixer for mixing gaseous fuel and air for delivery to
the engine through an air intake duct wherein gaseous fuel is delivered to the air intake
duct on an engine side of the mixer at a point having higher vacuum pressure, than at said
mixer, for inducing gaseous fuel into the air intake duct.
22. A method of controlling air fuel ratio in a carbureted engine having a choke provided with liquid fuel duct(s) for carrying liquid fuel during a liquid fuel mode and air duct(s), a liquid fuel supply and a gaseous fuel supply comprising, when the engine is operated in a gaseous fuel mode, delivering air to the choke through a liquid fuel duct for leaning a gaseous fuel - air mixture to be delivered to the engine.
23. The method of claim 21 or 22 wherein the method is implemented on starting of the engine.
24. The method of claim 21 wherein the choke is provided with liquid fuel duct(s) for carrying liquid fuel during a liquid fuel operating mode and air duct(s) comprising, when the engine is operated in a gaseous fuel mode, delivering air through a liquid fuel duct for leaning a gaseous fuel - air mixture to be delivered to said engine.
25. The engine substantially as hereinbefore described with reference to Figures 4 to 9.