COMBUSTION OF LIQUID FUELS

Abstract: Liquid fuel is burned by feeding a mixture of a liquid fuel (such as petrol, diesel oil or fuel oil) together with liquid fuel which has been pre-gasified by rapid heating into a combustion zone. The combustion zone may be a furnace or internal combustion engine. The liquid fuel is gasified by contact with a hot body. An internal combustion engine comprises a heated chamber (26) having a heater (28), an air inlet (16) and a fuel inlet (20). The mixture of gasified fuel and air is then introduced into the inlet manifold (4) of the engine. Atomised liquid fuel and air is also inducted into the engine in conventional manner, such as via carburettor (8).

Description: COMBUSTION OF LIQUID FUELS Field of the Invention The invention relates to the combustion of liquid fuels, particularly fuels such as petrol or gasolene, diesel oil and fuel oil, in combustion processes such as spark ignition and compression ignition internal combustion engines, or furnaces. Background of the Invention Liquid fuels have for many years been the source of energy in internal combustion engines. The liquid fuel is inducted into the cylinder in the form of a mixture of atomised fuel droplets and air. One of the problems facing Automotive Engineers is that of ensuring even distribution of fuel within the air, and of ensuring complete combustion of the fuel within the cylinder. Incomplete combustion leads to poor fuel economy and increased pollutant exhaust emissions. However, liquid fuel has the advantage of being easily storable and having a high energy content per unit volume. It is also known to run internal combustion engines on gaseous fuels such as methane, propane, butane and hydrogen. Combustion processes tend to be improved and pollutant emissions are reduced. However, the handling and storage of compressed or liquified gases poses substantial difficulties and is hazardous. In fact, special pressurised storage vessels are required, which are generally bulky. Burners for furnaces have conventionally burnt many grades of gaseous and liquid fuels. In the case of heavy petroleum fractions, such as fuel oils, it has been normal practice to preheat these to reduce their viscosity prior to combustion. It is an object of the present invention to mitigate these disadvantages. Summary of the Invention The present invention provides an apparatus for burning a liquid fuel to produce heat or energy, which comprises: - a combustion zone for burning the fuel; - means for feeding fuel to the combustion zone; and - heating means for gasifying at least part of the fuel which is fed to the combustion zone, comprising a hot body heated to a temperature above the boiling point of the liquid fuel such that liquid fuel contacting the hot body is converted substantially instantaneously to the gas phase prior to being fed to the combustion zone. The present invention is applicable to the combustion of liquid fuel in furnaces and also to the combustion of liquid fuels in internal combustion engines. It is preferred that only a portion of the liquid fuel fed to the combustion zone is gasified, for example 20 to 70%, preferably 40 - 60%. In the case of an internal combustion engine, where only a portion of the liquid fuel is to be gasified, it is preferred that the gasified fuel be fed (preferably in admixture with air) into the inlet manifold of the engine. The remainder of the liquid fuel is fed in atomized form in conventional manner either as a mixture of air and fuel droplets via the carburettor into the inlet manifold or by direct fuel injection into the cylinder. In the case of a spark ignition engine, all the liquid fuel may be gasified, though for convenience in starting and speed control it is preferred to supply a part of the fuel in liquid form. In a diesel engine, a minimum quantity of diesel fuel in liquid form (usually less than 20%, preferably less than 15% of the total fuel) is fed through the injectors in order to provide a correctly timed induction and ignition of fuel. Preferably, the liquid fuel is gasified in a heated chamber provided with a heater which instantaneously converts the liquid to the gas phase. Preferably, the chamber is provided with an air inlet to allow passage of air therethrough in order to flush the gaseous fuel into the inlet manifold. In order to control the flow of air, a valve may be provided on the air inlet to the chamber. The heater in the heated chamber may be an electrical heater, or heating may be achieved by means of hot exhaust gas from the engine or by means of a liquified petroleum gas (LPG) burner. Clearly, more heat is required to gasify higher boiling hydrocarbons. For example, the heating means is generally heated to 110 - 130°C for petrol, 180 -220°C for kerosene, and 270-330°C for diesel oil. In the case of a furnace, liquid fuel may be fed to a proportion of the burners of the furnace, whilst pre-gasified liquid fuel is fed to the remaining burners. The liquid fuel and gasified fuel mix in the combustion zone and combustion is thereby improved. The entire fuel can be fed in gaseous form. In practice the gaseous fuel can also be mixed with the liquid fuel after atomisation thereof, so that the combination can be burnt in the combustion zone; or the liquid fuel and gasified fuel can be burnt in separate burners. Combustion is improved in all three methods. The invention also extends to a corresponding method of carrying out combustion. Description of Preferred Embodiment Embodiments of the present invention will now be described by way of example only with reference to Figure 1 which is a schematic diagram of an internal combustion engine wherein part of the liquid fuel is pre-gasified; and Figure 2 which shows an alternative way of feeding liquid fuel to the gasifier. The engine comprises an engine block 2 containing a plurality of cylinders and having an inlet manifold 4 and exhaust manifold 6. The engine operates according to a 4 stroke spark-ignition cycle and is provided with a conventional carburettor 8 having an air inlet 10 and a fuel feed line 12. The carburettor is mounted on the inlet manifold in the normal way. The modification according to the present invention comprises a chamber 14 having an air inlet 16 controlled by a valve 18 and a fuel inlet 20 provided at the top of the chamber. There is also an outlet 22 connected by a pipe 24 for feeding gasified fuel/air mixture into the inlet manifold 4. In the bottom of the chamber there is provided a cup 26 heated by means of an electrical heater 28 connected to the battery of the engine (not shown) . The apparatus is operated as follows. The engine is started using a starter motor (not shown) in the normal way with part of the fuel requirement of the engine passing to the carburettor and the other part passing through inlet 20 into the heated chamber 14 and thence into the inlet manifold as a gasified fuel/air mixture. The majority of the air requirements for the engine pass through inlet 10 and carburettor 8, though a minor flow of air passes through inlet 16 and heated chamber 14 to sweep the gasified fuel into the inlet manifold. The heated cup 26 is maintained at approximately 120°C by the electrical heater 28 though the precise temperature will depend upon the amount of fuel passing through the heated chamber. If necessary, the cup 26 may be thermostatically controlled to maintain a particular desired temperature which is sufficient to completely gasify the liquid fuel before it passes out of the chamber 14. Droplets of liquid fuel fall from inlet 20 into the heated cup 26 where they become substantially instantaneously converted to gas. The flow of air through air inlet 16 is controlled by valve 18 such as to efficiently transfer the gasified fuel into the inlet manifold with a minimum delay in order to avoid any acceleration lag. Valve 18 is manually adjusted or linked to the accelerator pedal to ensure automatic operation. The flow of liquid fuel into the heated chamber via inlet 20 is controlled by the reduced pressure in the inlet manifold 4. Once again, the air inlet valve 18 is operated so as to maintain the desired reduced pressure in the chamber 14 and thus adjust the liquid fuel flow into the heated chamber. Generally, the inlet 20 will be connected to a float chamber 30 in order to provide a flow of lv^ruid fuel controlled by a valve 34 to the heated chamb. 14. Alternatively, as shown in Figure 2, the liquid fuel can be introduced by means of positive displacement variable delivery pump 40. This feeds fuel directly into the chamber without the need for the float chamber or control valve. The ratio of atomised fuel passing into the inlet manifold from the carburettor 8 and the amount of gasified fuel passing into the inlet manifold from the heated chamber 14 is controlled by regulator 32 so as to maximise combustion efficiency and provide desired engine power and torque and exhaust emission characteristics. Example 1 A four-stroke spark-ignition carburettor petrol engine in a 15 Sri 3118 Peugeot 505 car was fitted with a fuel gasification apparatus as shown in Figure 1 which fed gasified fuel/air mixture into the inlet manifold. The vehicle was tested on a section of road with normal road traffic. The fuel consumption with the gasification apparatus disconnected was 6 kilometres per standard bottle of fuel. With the gasification apparatus connected, the fuel consumption improved to 10.4 kilometres per bottle of fuel. This represents an increase of 73.4% in distance travelled and a 42.3% saving in fuel consumed with the gasification device connected. There was also a noticeable improvement in acceleration performance. Example 2 An analogous test was carried out on an ISUZU diesel lorry, Model 350 No.40 Sri 7325. The mileage per standard bottle of fuel was as follows: 6 km per bottle - gasifier disconnected 10 km " " - «ι • connected This represents an additional mileage of 66.7% and a fuel saving of 40%.

Claims: CLAIMS 1. An apparatus for burning a liquid fuel to produce heat or energy, which comprises: - a combustion zone (2) for burning the fuel; - heating means (28) for gasifying at least part of the fuel which is fed to the combustion zone, comprising a hot body (26) heated to a temperature above the boiling point of the liquid fuel such that the liquid fuel contacting the hot body is converted substantially instantaneously to the gas phase prior to being fed to the combustion zone. 2. An apparatus according to claim 1 which is an internal combustion engine, provided with an inlet manifold (4) for inducting air into a cylinder constituting the combustion zone; which comprises a heated chamber (14) having an outlet (22) connected to said inlet manifold and having an air inlet (16) and a liquid fuel inlet (20) , and comprising a heating means to convert the liquid fuel to the gas phase. 3. An apparatus according to claim 2 wherein liquid fuel is drawn into the heated chamber by a partial vacuum existing in the inlet manifold during running of the engine. 4. An apparatus according to claim 2 wherein liquid fuel is fed into the heated chamber by positive displacement pump means. 5. An apparatus according to claim 2 wherein the air inlet is provided with a valve (18) which is variable to control the air flow into the heated chamber. 6. An apparatus according to claim 2 which further comprises means (34) for controlling the flow of liquid fuel to the liquid fuel inlet to the heated chamber. 7. An apparatus according to claim 2 wherein the heating means comprises a heated cup (26) for receiving liquid fuel and converting it to the gas phase. 8. An apparatus according to claim 2 wherein the heating means is selected from an electrical heater (28) ; a heat exchanger through which passes hot exhaust gas from the engine; or a liquified petroleum gas burner. 9. An apparatus according to claim 2 wherein from 20 to 70%, preferably 40 to 60% of the fuel fed to the engine is gasified in the heating means; the remainder of the fuel being inducted in liquid droplet form into the cylinder and not passing through the heated chamber. 10. An apparatus according to claim 1 which is a furnace. 11. A method of burning a liquid fuel to produce heat or energy, which comprises feeding gasified liquid fuel or a mixture of liquid fuel and gasified liquid fuel to the combustion zone; and burning the fuel in the combustion zone.

Inventors: KULASINGHE ARUMADURA NANDASENA, KULASINGHE, ARUMADURA, NANDASENA, SILVA
Applicants: HORNER MARTIN GRENVILLE, KULASINGHE ARUMADURA NANDASENA, HORNER, MARTIN, GRENVILLE, KULASINGHE, ARUMADURA, NANDASENA, SILVA
Application year: 1991
Main classification: F23K5
IPC codes: F02B3, F02M31, F23K5