OIL FREE GAS COMPRESSOR

Abstract: An oil free gas compressor utilizes a pair of compressor units driven by the exhaust gases of an internal combustion engine. A four-cylinder internal combustion engine (1) has a pair of exhaust branches (4' and 4'') each of which is connected to two different cylinders of the engine (1). The gases in the branches (4' and 4'') are applied to respective gas turbines (3' and 3'') which are individually coupled to a pair of serially connected compressors (5' and 5'') provided with an interstage cooler (6). The resultant compressed air can be used for servicing a grounded jet aircraft by supplying air for ventilation or for engine starting.

Description: DESCRIPTION OIL-FREE GAS COMPRESSOR TECHNICAL FIELD The present invention concerns a new compact gas compressor unit of high efficiency and output. It is one object of the present invention to provide an efficient compact gas compressor unit adapted to deliver oil-free compressed gas, e.g. air. Oil-free compressed gas is required for various purposes such as the cooling of sensitive electronic systems where it is important that the cooling gas should be absolutely clean as impurities might adversely affect the electric properties of the system; or in the chemical and food industries in cases where a gas atmosphere of a high degree of purity is required. BACKGROUND ART Conventionally oil-free compressed gases, e.g. air, are supplied by means of mechanically driven oil-free piston or turbo-type compressors. A piston-type oil-free compressor requires a rather sophisticated insulation betwen the oil lubricated pistons and the oil-free gas compressor space and this renders the entire unit bulky and expensive. Alternatively, oil-less, dry-lubricated pistons are sometimes used but this enforces slow piston speeds which results in big and heavy machinery operating at low speed ranges. Mechanically driven turbo-type compressors deliver basically oil-free gas. However, with a standard-speed prime mover, such a compressor requires O PI complicated and heavy speed-multiplying transmissions and gears to achieve the necessary high rotational speed, so that these units again are bulky and expensive. It is thus one object of the present invention to provide a compact and efficient gas compression unit capable of delivering oil-free gas and in which the design compression ratio can be selected at will according to the requirements. A further object of the present invention concerns jet starting auxiliary equipment. For servicing a jet aircraft towards take-off the following systems are, inter alia, required: a. power supply for the electric system of the aircraft; b. an air supply for ventilation of the aircraft; c. injection of compressed air into the engine for start. In known equipment the compressed air injector is a separate unit requiring its own engine and compressor. Such an arrangement is wasteful and it is thus a further object of the present invention to provide auxiliary equipment for the injection of compressed air into an aircraft jet engine for start, which can be coupled with either of the power supply and ventilation installation. DISCLOSURE OF INVENTION With these objects in view the invention provides a gas compressor assembly comprising in combination: (a) a volumetric internal combustion engine having means for dividing the exhast gases into at least two parallel streams, and further having a corresponding number of exhaust gas delivery means; and (b) a multi-stage compressor unit the number of whose stages corresponds to the number of said exhaust gas delivery means with each stage being linked to one of said exhaust gas delivery means, each stage comprising a gas turbine as prime mover adapted for actuation by exhaust gases from said engine, and a turbocompressor coupled thereto. In a compressor assembly according to the invention the turbocompressors are operated by the exhaust gases of the volumetric internal combustion engine and in consequence no engine oil can pass into the turbocompressors and the compressor gas delivered by the latter is oil-free. The compressor assembly according to the invention may be used for the compression of air and the delivered oil-free compressed air is suitable for cooling electronic equipment, for use in various sensitive chemical and food industries and also for the starting of a jet engine. Where a unit according to the invention is used for the starting of a jet engine the volumetric internal combustion engine thereof, having two or more exhaust gas delivery means as specified, will at the same time also serve for powering either or both of the power supply and ventilation installations. Thus in this particular aspect of the invention it is possible to link an auxiliary, gas operated turbocompressor unit to an existing power supply and/or ventilation installation. The invention thus also provides for use in a gas compressor assembly as specified, a multi-stage compressor unit each of whose stages is adapted to be linked to exhaust delivery means of an internal combustion engine and each comprising a gas turbine as prime mover and a turbocompressor coupled thereto. fURE-4( / _ OMPI The term "volumetric internal combustion engine" used herein denotes any sort of internal combustion engine in which a piston is displaced by internal combustion engines, diesel type internal combustion engines as well as rotary, Wankel type internal combustion engines. As a rule the compression ratio of each compression stage in an assembly according to the invention is at least 2:1. The overall compression ratio rises exponentially with the number of stages. For example, where a compressor unit in an assembly according to the invention comprises two stages each having a compression ratio of 2: 1, the overall compression ratio will be 4:1, where the number of 2:1 compression stages is 3, the overall ratio will be 8:1, etc. It is thus easily understood that in accordance ' with the invention, the overall design compression ratio can be selected at will by selection of the design compression ratio of each stage and the provision of a desired number of stages. If desired, cooling arrangements may be provided between stages. However, there may be cases where cooling is not desired. For example, where the oil-free compressed air is used in the chemical or food industry it may be required that in addition to being oil-free the gas, e.g. air, should also be sterile. The desired sterilization is then simply achieved by allowing the air to heat up through all compression stages. Where the compression in each stage is 2:1 the gas is heated in each stage by about 100 degrees Centigrade so that in a unit comprising two such stages without interstage cooling, the compressed gas is delivered at a temperature of about 200 degrees Centigrade which is sufficient for sterilization. The operation of a turbocompressor having a gas turbine as prime mover by a means of exhaust gases from an associated internal combustion engine is known per se , e.g. from so-called superchargers in which the compressed air delivered by the turbocompressor is injected into the engine. There are also known so-called Schwitzer Turboconveyors (trade mark) in which the exhaust gases from a diesel engine are used to actuate a gas turbine driven turbocompressor and the compressed air delivered by the latter is used for conveying, e .g . for discharging a liquid or free-flowing bulk material from a container tank. However, none of these known devices comprises an arrangement by which the exhaust gases from the combyustion engine are separated into two or more parallel, flows and a corresponding number of turbocompressor stages is provided, each being actuated by one of said exhaust streams. Nor has it ever been suggested to use such an arrangement for the production of oil-free gases, e.g. air. Thus, the present invention for the first time provides a compact assembly of the kind specified comprising two or more compression stages and a corresponding number of parallel exhaust streams from the engine, each actuating one of said stages. BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated, by way of example only, in the accompanying drawings in which: Fig. 1 is a diagrammatic illustration of one embodiment of the invention; Fig. 2 is a diagrammatic illustration of a similar embodiment as in Fig I comprising in addition a super-charger for the engine; and Fig. 3 is a diagrammatic illustration of yet another embodiment, again similar to that of Fig. 1, comprising a multi-stage turbo-supercharger. BEST MODE FOR CARRYING OUT THE INVENTION he embod iment of Fig . 1 comprises a four-cylinder internal combustion engine 1 having two exhaust gas collectors 2' and 2" each linked to two out of the four cylinders of engine 1. Two gas turbines 3' and 3" are linked to the associated exhaust gas collectors through pipes 4* , 4" respectively. Gas turbine 3* is coupled to and serves as prime mover for a turbocompressor 5' and likewise turbine 3" is coupled to and serves as prime mover for a second turbocompressor 5". Compressors 5 * , 5" are connected in series with interposition of a cooler 6 and couplings 7' and 7". The compressors 3', 3" and turbines 5', 5" are parts of a two-stage compressor unit 3" , 5 M constit ting the first and 3 * , 5' the second compression stage. Air intake is through pipe 8 fitted with a filter unit 9 and compressed air delivery is through pipe 10. The expanded exhaust gases from gas turbine 3' are discharged through exhaust pipe 11* fitted with a silencer 12' and likewise the expanded exhaust gases from gas turbine 3" and discharged through exhaust pipe 11" fitted with a silencer 12 M . The combustion engine 1 comprises an air intake arrangement 13 and manifold 14 for the delivery of air into each of the engine cylinders. The engine further comprises a shaft 15 which, if desired, may be coupled to a driven unit. For example, where the arrangement according to Fig. 1 is used as jet starting auxiliary equipment for the injection of compressed air into the jet engine of an aircraft during start, engine 1 may be common to this equipment and to an electric power IT ^ supply; and/or ventilation equipment and in such a case shaft 15 will be coupled to a generator and/or a fan. The embodiment of Fig. 2 is essentially similar to that of Fig. 1 and similar parts are indicated by the same numeral. It comprises in addition a supercharging arrangement for engine 1 comprising a supercharger 16 coupled with the shaft 15 of engine 1 through a clutch 17 and fitted with an air intake 18 and an air delivery pipe 19 connected to the air intake manifold 14. The operation of the embodiment of Fig. 1 and 2 is as follows. When engine 1 operates pressurized exhaust gases are delivered to collectors 2* and 2" and from there into the gas turbines 3* and 3" which thereby operate the turbo charges 5' and 5". Air is sucked in through filter 9 and pipe 8 and is subjected to a first stage compression stage in the sub-unit 3", 5". The compressed air from this sub-unit is delivered through the cooler δ into the second sub-unit 3', 5' where it is subjected to the second stage compression. The so-compressed air is delivered through auxiliary pipes 10. The expanded exhaust gases from the two stages are discharged through exhaust pipes 11', 11" and the silencers 12' and 12", respectively. In the installation of Fig. 1 air from the atmosphere is sucked into engine 1 through intake 13 whereas in the arrangement of Fig. 2 the atmospheric air arriving through intake 18 is subjected to compression in supercharger 16. The installation of Fig. 3 is again basically similar to that of Fig. 1 and again similar components are designated by the same numerals. In addition this installation comprises a multi-stage turbo-supercharger arrangement comprising a first gas turbine 21' located between exhaust pipe 4 • and gas turbine 3 • and linked to the latter through a pipe 22'; and a second auxiliary gas turbine 21" located between exhaust pipe 4" and gas turbine 3" and linked to the latter through a pipe 22". Associated with the auxiliary turbines 21* and 21" are turbocompressors 23* and 23" respectively, fitted respectively with air intakes 24' and 24" and linked to manifold 14 of engine 1 through, respectively, delivery pipes 25* and 25". In operation the compressed exhaust gases form engine 1 are first injected into auxiliary gas turbines 21' and 21" where they are partly expanded and the so partly expanded exhaust gases are then delivered into gas turbines 3* and 3" whereupon the operation is as before. The auxiliary turbine 21' and 21 • ' operate the turbocompressor 23* and 23'- which deliver compressed air through pipes 25' and 25 ' ' into manifold 14 from where it is injected into the various cylinders of the combustion engine 1. It is thus seen that each of units 21 ' ■ , 23' and 21 ' ' , 23 ' * acts as supercharger the two superchargers being connected in parallel to engine 1 which is tantamount to one single compression stage. For the rest the embodiment of Fig. 3 operates as those of Figs. 1 and 2.

Claims: CLAI S 1. A gas compressor assembly comprising in combination: a) a volumetric internal combustion engine having means for dividing the exhaust gases into at least two branches,- and further having a corresponding number of exhaust gas delivery means; b) a primary compressor unit associated with each of said exhaust gas delivery means, each unit comprising a gas turbine as prime mover responsive to exhaust gases from said engine for driving a turbocompressor; c) means connecting the output of one of the turbocompressors to the inlet of the other; and d) means connected to the outlet of said other t rbocompressor for injecting the air compressed thereby into an environment other than the air intake manifold of said engine. 2. An assembly according to claim 1 including an interstage cooler located between the turbocompressors. 3. An assembly according to claim 1 serving as jet starting auxiliary equipment by being adapted to inject the compressed air into the jet engine of an aircraft. 4. An assembly according to claim 1 wherein said engine is supercharged by a supercharger mechanically driven by said engine. 5. An assembly according to claim 1 including an auxiliary compressor unit associated with each of the primary compressor units, the gas turbine of each auxiliary unit being driven by the exhaust of the gas turbine of the primary compressor unit with which the auxiliary compressor unit is associated, and the output of the turbocompressor of each auxiliary unit being coupled to the air intake manifold of said engine. 6. A method for supplying jet aircraft with compressed oil-free air utilizing an internal combustion engine comprising the steps of: a) dividing the exhaust gases of the engine into at least two branches; b) using the exhaust gases in each branch to drive separate gas turbines that operate in parallel and which. in turn drive separate air compressors that are coupled in series; and c) supplying the output of the compressors to service a grounded jet aircraft. 7. A method according to claim 6 for supplying ventilation air to the aircraft comprising the step of supplying the output of the compressors to the ventilation intake of the aircraft. 8. A method according to claim 6 for supplying motive power to start a jet engine comprising the step of supplying the output of the compressors to the starting air intake of the engine. 9. A method for sterilizing air by utilizing the assembly of claim 1 wherein the temperature of the air at the outlet of said other turbocompressor is elevated by compression of the air by the turbocompressors to a level that sterilizes the air.

Inventors: ORIAN I
Applicants: ORMAT SYSTEMS INC
Application year: 1979
Main classification: F02C7
IPC codes: F02B37, F02C6, F04D17, F04D25, F04D29