Most air pollution from internal combustion engines is caused by unburned fuel in exhaust gas from the engine. It is well known that while fuel in the vapour phase combusts in an internal combustion engine, fuel in the liquid phase does not combust completely, and this causes the pollution. It is therefore advantageous to introduce fuel into the combustion chamber of an internal combustion engine as a gas, i. e. in the vapour phase. Another advantage of introducing fuel into an internal combustion engine in a vapour phase is that the combustion of virtually all of the fuel leads to greater efficiency of the engine.

In the past, many devices for the vaporisation of fuel, prior to introducing the fuel in an internal combustion engine, have been proposed. However, the practical implementation of many such devices has been retarded by the change in composition of the fuel (e. g. petroleum fuel) during the use of such devices. In devices that rely on vaporising petroleum in a fuel tank, for example, the low boiling point fractions of fuel evaporate, leaving an increasing amount of higher boiling point fractions behind in the tank.

Similarly, many fuel vaporising devices rely on the dripping back of higher boiling point fractions of non-vaporised fuel to a float chamber. This also leads to a change in the composition of the fuel. Other devices for the vaporisation of fuel rely on heated air, for vaporising the fuel. However, air is a poor conductor of heat and fuel particles travelling in an air current do not absorb heat from the heated air readily.

It is an object of this invention to provide a new and improved device for the vaporisation of fuel, especially for internal combustion engines.

SUMMARY OF THE INVENTION According to a first aspect of the invention there is provided a device for vaporising a liquid, typically a liquid fuel, the device including a vaporisation chamber having an inlet for introducing the liquid into the chamber and an outlet for removing the liquid in a vapour phase from the chamber; heating means for heating an internal vaporisation surface of the chamber; and impingement means for causing the liquid introduced into the chamber to impinge with the heated vaporisation surface in the chamber.

Advantageously, the impingement means is a centrifugal force. The centrifugal force may be caused by a vortex of gas within the vaporisation chamber.

Advantageously, the vaporisation surface is roughened.

Preferably, the vaporisation chamber is defined by a cylindrical side wall, typically a tubular side wall, having first and second ends which are closed, with the inner surface of the side wall providing the vaporisation surface.

Advantageously, it is the side wall of the chamber that is heated by the heating means.

Conveniently, the inlet extends through the side wall of the vaporisation chamber and is defined by an inlet pipe which is oriented tangentially relative to the side wall.

The outlet is typically defined by an outlet pipe which extends into the vaporisation chamber, through the first closed end thereof, and which is oriented in parallel with a longitudinal axis of the tubular side wall.

According to a preferred embodiment of the invention there is provided a cyclone device for vaporising a liquid, typically a liquid fuel, the cyclone device including: a vaporisation chamber, the chamber including a cylindrical, preferably a tubular, an inner vaporisation side wall having a first end which is closed and a second end which is also closed ; an inlet pipe extending through the side wall of the vaporisation chamber, the inlet pipe being oriented tangentially relative to the side wall of the vaporisation chamber; an outlet pipe extending into the vaporisation chamber through the first end thereof and being oriented parallel relative to a longitudinal axis of the side wall ; and heating means for heating the side wall of the vaporisation chamber.

Advantageously, the inner vaporisation side wall is roughened.

Advantageously, the heating means is arranged to heat the side wall of the vaporisation chamber to a temperature which is greater than the boiling point of the liquid.

The heating means may be an electrical heater such as a band heater or an induction heater that heats the side wall of the vaporisation chamber, but is preferably provided by a jacket that surrounds the side wall and is heated by a hot gas, typically an exhaust gas from an internal combustion engine.

According to a second aspect of the invention there is provided a method of vaporising a liquid, typically a liquid fuel, in a cyclone device including a vaporisation chamber defined by a tubular inner vaporisation side wall, an inlet into the chamber, and an outlet out of the chamber, the method including the steps of entraining droplets of the liquid in an air stream entering the chamber, forcing the air stream into the chamber through the inlet and out of the outlet, and thereby causing a vortex therein so that the liquid droplets are forced to impinge with the inner vaporisation side wall of the chamber by a centrifugal force caused by the vortex, and heating the inner vaporisation side wall to a temperature greater than the boiling point of the liquid, so that the liquid droplets vaporise on the side wall and leave the chamber, via the outlet, in the vapour phase.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a fuel vaporisation device of the invention; Figure 2 is a cross-sectional view of the device shown in Figure 1 on the line 2-2; and Figure 3 is pictorial view of the device shown in Figures 1 and 2 attached to an internal combustion engine.

DESCRIPTION OF EMBODIMENTS This invention relates to a device for vaporising a liquid fuel, typically a composite hydrocarbon fuel such as petroleum or diesel or an alcohol such as methanol. The device is designed primarily for the vaporisation of fuel for an internal combustion engine, but may be used in any situation when it is necessary to obtain the vaporisation of a liquid.

In this embodiment of the invention the fuel vaporisation device is designed to be situated between the intake manifold of an internal combustion engine and a fuel supply source. The fuel supply source may be a carburetor, a fuel injection system, or any system that delivers fuel.

Referring to Figures 1 and 2, the fuel vaporisation device 10 includes a vaporisation chamber 12 which is defined by a tubular side wall 14 which is closed at a first end thereof by a plate 16 and at a second end thereof by a plate 18. The second plate 18 is depicted as being planar, but may be conical in shape. An inlet pipe 20 extends through the side wall 14 to form an inlet 22 into the chamber 12. It will be noted that the inlet pipe 20 is oriented tangentially relative to the side wall 14. An outlet pipe 24 extends through the first closed end 16 into the vaporisation chamber 12, forming an outlet 26 from the vaporisation chamber 12. It will be noted that the outlet pipe 24 is oriented parallel with a longitudinal axis A of the side wall 14. It will also be noted that the outlet pipe 24 is located centrally within the vaporisation chamber 12. The vaporisation chamber 12 is, for all intents and purposes, a cyclone device. Thus, the outlet pipe 24 should be one third of the diameter of the diameter of the vaporisation chamber 12. Also, the height of the outlet pipe 24 above the closed end 18 of the chamber 12 should be equal to the radius2/diameter of the outlet pipe 24.

The vaporisation chamber 12 is surrounded by heating means in the form of a heating jacket 28 which is arranged to heat the side wall 14, and also the end plates 16 and 18 thereof. The heating jacket 28 is provided with two gas inlets 32 and 34 and a gas outlet 30. Of course, there may only be one gas inlet or there may be more than two gas inlets and there may also be more than one gas outlet.

The vaporisation chamber 12 and jacket 28 may be made of any material that can withstand high temperatures and conduct heat. Typical materials include brass, copper, stainless steel and aluminium.

Referring to Figures 1 and 3, in use, the fuel vaporisation device 10 may be connected to the cylinder head 37 of a four cylinder internal combustion engine 38. The device 10 has four hot gas inlets 32,33,34 and 35 which extend into the heating jacket 28 and which are connected to exhaust pipes 40 and 42 from the engine 38. Hot exhaust gas from the engine 38 passes from the exhaust pipes 40 and 42 into the heating jacket 28 through the inlets 32,33,34 and 35, and out through the exhaust gas outlet 30. The hot exhaust gas heats the side wall 14 and end plates 16 and 18 of the vaporisation chamber 12 to a temperature above the boiling point of the fuel, in the case of petroleum fuel, to a minimum temperature of 204°C, thus heating the inner surface of the side wall 14 which becomes a vaporisation surface. The inlet pipe 20 of the device 10 is connected to an air intake and a source of fuei, in the form of a carburetor 46. The outlet pipe 24 of the vaporisation chamber 12 is connected to an inlet manifold 44 of the engine 38. When the internal combustion engine 38 is operated, the suction of the inlet manifold 44 sucks air containing entrained fuel droplets (indicated by stippling) from the carburetor 46 via the inlet pipe 20, through the inlet 22, into the vaporisation chamber 12 and out through the outlet pipe 24. The air 36 that is sucked into the vaporisation chamber 12 forms a vortex within the vaporisation chamber 12, which in turn places a centrifugal force on the fuel droplets. The fuel droplets, which are heavier than the air, are caused to move outwardly and impinge with the inner side wall 14 of the vaporisation chamber 12. The side wall 14 is heated by the exhaust gases from the engine 38, thus heating the inner surface of the side wall 14 which becomes an inner vaporisation surface. The intimate contact between the fuel droplets and inner heated vaporisation side wall 14 causes vaporisation of the fuel droplets. The vaporised fuel droplets, which are lighter than the air and thus minimally subjected to the centrifugal force within the vaporisation chamber 12, are sucked into the outlet pipe 24 with the air 36, and exit from the vaporisation chamber in the vapour phase.

From the outlet pipe 24, the vaporised fuel/air mixture passes through the manifold 44 and then enters the cylinder head 37 of the internal combustion engine 38.

According to a preferred embodiment of the invention, the inner heated side wall 14 on which the fuel droplets vaporise is roughened. The surface may be roughened to a profile depth of about 20 microns by shot blasting or chemically etching the surface. Alternatively, the roughened inner surface may be formed by a composite inorganic coating, or a sodium silicate coating. The roughened surface provides a greater surface for the vaporisation of the fuel, to ensure better vaporisation of the liquid.

As mentioned above, the fuel vaporisation device above may be used for a variety of fuels. It is however important that the side wall 14 of the vaporisation chamber 12 is heated to a temperature above the boiling point of the fuel. In the case where the fuel is petroleum, the side wall 14 should be heated above 204°C, preferably about 210°C. In the case where the fuel is diesel, the vaporisation chamber 12 should be heated to above 270°C preferably about 300°C.

In addition to the advantage of providing vaporised fuel to an internal combustion engine, the device is sufficiently small to be fitted to combustion engines in motor vehicles with transverse engines, and can be oriented vertically, horizontally within the engine compartment. Also, because there are no moving parts, the device is not subject to mechanical wear. Furthermore, due to the size of the vaporisation chamber 12, and the brief period of time that the fuel remains within the chamber, there is little chance of explosion, even if the temperature within the vaporisation chamber exceeds the boiling temperature of the higher boiling fuel fractions.

Example 1 A first prototype of the abovementioned fuel vaporisation device will now be described with reference to Figures 1 and 2.

The tubular side wall 14 has a length of 147 mm and a diameter of 92 mm, and is made from brass plate, having a thickness of 1mm. The inlet pipe 20 has a diameter of 30mm and is made from steel, with a 1mm thickness.

The outlet pipe 24 is located 7mm above the second plate 18 of the vaporisation chamber 12, is made from steel, and has a thickness of 1mm.

Instead of being surrounded by a heating jacket 28 which is heated by exhaust gases, in this example, the heating jacket is an electric band heater. A glass observation port is affixed at the second plate end 18.

The device 10 was connected via the inlet pipe 20 to the outlet pipe of the carburetor of an internal combustion engine. The outlet pipe 24 was attached to a vacuum device and a vacuum was applied. On application of the vacuum a substantial amount of liquid fuel was observed through the observation port spiraling about the outlet pipe 24. The same experiment was carried out, after the side wall 14 had been heated by the electric band heater to a temperature of 210°C. The liquid fuel from the carburetor was vaporised and no liquid was observed through the observation port.

EXAMPLE 2 A second prototype of the abovementioned fuel vaporisation device will now be described with reference to Figures 1 and 2.

The tubular wall 14 has a length of 120mm and a diameter of 90mm, and is made from copper, having a thickness of 0,5mm. The inlet pipe 20 has a diameter of 30mm and is made from stainless steel, with a 2mm thickness.

The outlet pipe 24 is located 7mm above the second plate 18 of the vaporisation chamber 12, and is made from stainless steel, and has a thickness of 2mm. The device 10 is surrounded by a heating jacket 28 which has a diameter of 130mm. Four exhaust gas inlet pipes which have a diameter of 30mm and which are made from steel extend into the heating jacket 28. The exhaust gas inlet pipes are to be connected, to the exhaust ports of an internal combustion engine for supplying heated exhaust gas into the heating jacket 28. An exhaust gas outlet pipe 30 from the heating jacket 28 is made from steel, and with a diameter of 50mm, for attachment to the exhaust outlet system.