Title of Invention

IMPROVED SMALL TURBOJET ENGINE

Abstract

ABSTRACT Pilotless aircrafts are remotely controlled with short flight duration. Low weight engine is a key requirement of these aircrafts to enable them to carry higher piyload and achieve as long range as possible. Closed type Lubricating systems, both pressure and scavenge pumps are deployed which add to the weight of the aircraft. The prior art in this field demonstrates that there is further scope to minimise the number of rotating components thereby design systems with less complexities and achieve overall reduction In weight of the aircraft. This invention relates to an improved small turbojet engine including novel oil mist lubrication, impingement starting system, fuel system, microprocessor based fuel control system together with appropriate fuel dispensing system for precision speed control, power generation unit and direct engine driven fuel pump and alternator for application in pilotless aircrafts, %

Full Text

This invention relates to an improved small turbojet engine including novel oil mist lubrication, impingement starting system, fuel control system and direct engine driven fuel pump and alternator for application in pilotless aircrafts. Background of the Invention Pilotless aircrafts are remotely controlled with short flight duration. Low weight is a key requirement of these aircraft to enable them to carry higher payload and achieve as long a range as possible. Starting system of a small turbojet engine in pilotless aircraft normally uses > electric motor which adds weight to the aircraft, > air starter requiring additional turbine which is complex to manufacture and adding to the weight of the aircraft, > jet fuel starter which are over designed and too expensive for this application. Lubricating systems in such engines use closed loop type wherein pressure and scavenge pumps are deployed which also add to the weight of the aircraft. US Patent 5782079 discloses a miniature liquid fuel turbojet engine wherein the improvements are directed to injection system and combustion chamber resulting in high combustion efficiency and satisfactory outlet temperature factor. This patent does not address issues related to lubrication and starting systems in such engines. US Patent 6290024 describes an improved oil mist generating system wherein air and oil are supplied to a mist generator where air and oil is combined to form oil mist. The system is characterised in that the oil is alternately provided from a main oil reservoir and an auxiliary oil reservoir each of which is provided with a mist generator. It also discloses an oil mist generator, which includes a heater manifold extending into an oil reservoir heating both air and oil prior to entry into a mist head in which the air and oil are combined to form an oil mist. These systems if used in pilotless aircraft would add to the weight of the aircraft due to the extra heater system, oil reservoir and mist generator. US Patent 6293263 deals with super charger having a drive portion and an atomiser for providing a lubricating oil/air mist to the supercharger. An oil /air mist inlet is formed in the gear case and oil/air mist channels are in communication with the oil/air mist inlet and the driven gear bearing races. Such a system is not applicable in pilotless aircraft system. There are too many rotating parts thereby enhancing the possibilities of system failure and increased weight. A few engines available in the market for applications in pilotless aircraft are given in Table-1. The thrust range varies from 272 kgf to 377 kgf and use closed loop pressure fed lubrication system. The alternators are driven by the engine through a gear system. The prior art in this field demonstrates that there is further scope to minimise the number of rotating components thereby design systems with less complexities and achieve overall reduction in weight of the aircraft. Summary of the Invention Accordingly an improved small turbojet engine has been designed that comprises the following features: a) An oil mist generator system providing mist lubrication for the bearing system where the mist is being formed by utilising the bleed air from engine compressor. b) An air impingement starting system providing air impingement on turbine blades through a nozzle to start the engine. c) A fuel pump and alternator capable of operating at engine speeds in the range of 21000 rpm to 32000 rpm. d) Microprocessor based fuel control system together with appropriate fuel dispensing system for precision speed control. Object of Invention a. Main Object of Present Invention is to provide power for the Pilotless Aircraft with an engine of minimised weight. b. Another object of present invention is to have oil mist generator system providing mist lubrication for the engine with reduced complexity and weight. c. Yet another object of present invention is to provide air impingement starting system on the turbine to start the engine. d. Another object of the present invention is to provide a fuel control system to achieve precision speed control. e. Yet another object of the present invention is to provide with directly engine driven alternator and fuel system. Statement of Invention An improved small turbojet engine for pilotless aircrafts of 350 to 400 kgf thrust class comprising air intake, compressor with bleed air, diffuser, annular straight flow combustion chamber, exhaust diffuser, jet pipe, propulsive nozzle, microprocessor based Digital Electronic Control Unit, alternator, a power generation unit, fuel pump and fuel control system, mist lubrication system, ignition system, air impingement starting system and the improved systems comprising of > Oil mist generator system providing mist lubrication for the bearing system comprising the oil tank (11), oil chamber (19), mist chamber (18), separator plate (23), mist tube (12), orifice tube (13), pressurized air supply (14), oil tube (24), banjo( 20) and oil filter (21).wherein the mist is formed by utilising the bleed air from engine compressor. > Air impingement starting system (31) wherein the air impingement on turbine rotor (32) is provided through a plurality of nozzles to start the engine. > Fuel pump and alternator (1) wherein their operation is at engine speeds in the range of 21000 rpm to 32000 rpm. > Microprocessor based fuel control system (1 & 8) together with appropriate fuel dispensing system for precision speed control. > Microprocessor based electronic control unit for starting, speed modulation in the specified range and shut down with a digital electronic control unit (DECU) by sending digital control signals to stepper motor to drive the fuel metering valve as per the fuel schedule embedded in DECU in digital form on a microcontroller chip. > Alternator driven directly by the engine wherein the power control unit of the alternator is mounted externally on the airframe. Preamble This improved small turbojet engine of 350 to 400 kgf thrust class is used for pilotless aircrafts and includes novel oil mist lubrication system, air impingement starting system, fuel control system and direct engine driven fuel pump and alternator. Detailed description of the invention Thus in accordance with this invention the improved small turbojet engine comprises air intake, compressor with bleed air, diffuser, combustion chamber, exhaust diffuser, jet pipe, propulsive nozzle, microprocessor based Digital Electronic Control Unit, alternator, oil mist lubrication system, ignition system, air impingement starting system etc. The invention with its advantages is now illustrated with non-limiting examples with the reference to the figures 1-5. Fig.1 represents the small engine of the present invention wherein, Part no. 1: the nose bullet houses an alternator and a fuel pump directly driven by engine shaft and also a microprocessor based electronic control unit and a power rectifier unit. Part no.2: air intake casing supports front bearing assembly on four struts providing passage for fuel lines, electrical control lines and lubricating oil mist. Part no.3: compressor assembly comprises four stages of integral bladed rotors, integral bladed stator casings and a thrust balancing disc and where bleed air tappings are taken from one of the compressor stator casings. Part no.4: diffuser assembly fabricated in aluminium alloy with contoured annular passage to diffuse compressor outlet air and guide the flow to the combustor. Part no.5: combustion chamber assembly is annular straight flow type with direct fuel injection through atomizers, contained within outer and inner casings. Flame initialisation is by high energy igniter. Part no.6: turbine assembly comprises precision cast integral rotor blades and stator blades of nickel base alloy. Turbine rotor is attached to drive shaft and the rear shaft extension is being supported on roller bearing housed inside the exhaust diffuser. Part no.7: exhaust diffuser consisting of inner and outer casings connected by three struts forming the annular passage for exhaust gases leading to the jet pipe. The inner casing supports the rear bearing and the outer casing is flanged to connect to the jet pipe. Part no.8: microprocessor based electronic control unit is for starting, speed modulation In the specified range and shut down. Digital electronic control unit (DECU) sends digital control signals to stepper motor to drive the fuel metering valve as per the fuel schedule embedded in DECU in digital form on a microcontroller chip. Part no.9: alternator driven directly by the engine. The power control unit of the alternator is mounted externally on the airframe. The lubrication system for bearings uses oil mist, generated with bleed air from compressor. Fig 2 shows the schematic diagram of the oil mist generator system. Referring to fig 2, the oil tank (part no.11) is divided into two chambers, namely an oil chamber (part no.19) and a mist chamber (part no.18) separated by a separator plate (part no.23). In the mist chamber two mist generators are assembled. Mist generator comprises a mist tube (part no. 12) and an orifice tube (part no. 13). The orifice tube (part no. 13) is positioned perpendicular to the supplied airflow and with the oil orifice axis along airflow direction. One end of the mist generator is connected to the pressurized air supply (part no. 14) to generate the mist. The orifice tubes (part no. 13) of mist generators are communicated to the oil chamber (part no. 19) through an oil tube (part no.24), a banjo(part no. 20) and an oil filter (part no.21). Pressurised air is supplied to the mist generator, which creates a venturi effect in the mist generator. Due to the venturi effect, oil is siphoned through the orifice tube (part no. 13). Further it mixes with the supplied air and forms the mist. The generated mist is driven by the drive air (part no. 17) to the bearings through the mist transfer tubes. Fig. 3 shows the arrangement of air impingement starting system. In the present invention, air impingement is exercised through a nozzle (part no.31) on to the existing turbine rotor (part no. 32), thereby avoiding any additional components and making the present invention simple. The engine is started by impinging air from high-pressure air bottles through a nozzle (part no. 31) on the turbine rotor (part no. 32). The engine reaches a speed of about 4500 to 6200 rpm. Within this engine speed, the fuel is ignited by the ignition system and the engine lights up. The engine continues to accelerate till idle speed. When the engine reaches idle speed the impingement air supply to the starting system is cut off. In an embodiment of present invention, plurality of nozzles may be used for air impingement starting system. In another embodiment centrifugal compressor may be used instead of axial compressor and diffuser. In another embodiment radial turbine may be used instead of axial turbine. In yet another embodiment, oil mist generator may use vortex passage for bleed air. Example 1 Performance Test of the Engine A test bed is designed and commissioned for testing the improved small turbojet engine. Compressed air from air bottles was used to start the engine during the tests. The engine started successfully and settled at idling speed. The engine was instrumented to monitor various performance parameters like engine speed, compressor exit pressure. Compressor exit temperature, Jet pipe pressure. Jet pipe temperature. Thrust, Fuel Flow etc and engine health monitoring parameters like Front Bearing Temperature (FBT), Rear Bearing Temperature (RBT), Vibration spectrum etc. Fig 4 presents the performance of the improved small turbojet engine in terms of thrust vs engine speed obtained during a number of tests. Example 2 Tests on Lubrication System In addition to the tests on the improved small turbojet engine, simulated tests were conducted on the mist lubrication system, on a test rig. Further the improved small turbojet engine was test flown on an aircraft. Rear Bearing Temperature (RBT) and Front Bearing Temperature (RBT) are monitored using thermocouples in all the tests. Fig 5 presents the trend of RBT and FBT with engine speed obtained during various tests. Both bearing temperatures are within maximum permissible temperature limit of the bearings (for RBT around 300°C; for FBT around 170°C). 8 The improved small turbojet engine described in this invention has several advantages over the prior art. They include: 1. An oil mist lubrication system, generating the mist using the bleed air from the compressor, makes it compact, lighter and less expensive compared to the conventional pressure pump/scavenge pump lubrication system and also avoids rotating parts. 2. Provision of air impingement starting system, by impinging the compressed air directly on the turbine blade, avoids inclusion of a separate turbine wheel and thereby reducing weight and cost. 3. Direct driven fuel pump and alternator coupled with axial flow compressor avoids additional gear system reducing the number of rotating components. 9 We claim 1. An improved small turbojet engine for pilotless aircrafts of 350 to 400 kgf thrust class comprising air intake, compressor with bleed air, diffuser, annular straight flow combustion chamber, exhaust diffuser, jet pipe, propulsive nozzle, microprocessor based Digital Electronic Control Unit, alternator, a power generation unit, fuel pump and fuel control system, mist lubrication system, ignition system, air impingement starting system and the improved systems comprising of > Oil mist generator system providing mist lubrication for the bearing system comprising the oil tank (11), oil chamber (19), mist chamber (18), separator plate (23), mist tube (12), orifice tube (13), pressurized air supply (14), oil tube (24), banjo( 20) and oil filter (21).wherein the mist is formed by utilising the bleed air from engine compressor. > Air impingement starting system (31) wherein the air impingement on turbine rotor (32) is provided through a plurality of nozzles to start the engine. > Fuel pump and alternator (1) wherein their operation is at engine speeds in the range of 21000 rpm to 32000 rpm. > Microprocessor based fuel control system (1 & 8) together with appropriate fuel dispensing system for precision speed control. > Microprocessor based electronic control unit for starting, speed modulation in the specified range and shut down with a digital electronic control unit (DECU) by sending digital control signals to stepper motor to drive the fuel metering valve as per the fuel schedule embedded in DECU in digital form on a microcontroller chip. > Alternator driven directly by the engine wherein the power control unit of the alternator is mounted externally on the airframe. 10 2. An improved small turbojet engine as claimed in claim 1 wherein the oil mist generator system consists of an oil tank (11), two chambers i.e. an oil chamber (19) and a mist chamber (18) separated by a separator plate (23) and two mist generators. 3. An improved small turbojet engine as claimed in claim 1 wherein the oil mist generator system comprises of a mist tube (12) and an orifice tube (13) and this orifice tube (13) is positioned perpendicular to the supplied airflow and with the oil orifice axis along airflow direction and one end of the mist generator is connected to the pressurized air supply (14) by utilising the bleed air from engine compressor to generate the mist and driven by the drive air system (17) to the bearings through the mist transfer tubes and the orifice tubes (13) of mist generators are communicated to the oil chamber (19) through an oil tube (24), a banjo (20) and an oil filter (21). 4. An improved small turbojet engine as claimed in claim 1 wherein the air impingement starting system comprises of high pressurised air system and nozzle and the air impingement is exercised through a plurality of nozzles (31) on to the existing turbine rotor ( 32) for starting of the engine, thereby avoiding any additional components and cuts off when engine reaches self sustaining speed. 5. An improved small turbojet engine as claimed in claim 1 wherein the engine compressor is a centrifugal compressor or an axial compressor and diffuser. 6. An improved small turbojet engine as claimed in claim 1 wherein the turbine is a radial turbine or an axial turbine. 7. An improved small turbojet engine as claimed in claim 1 wherein the mist generator uses vortex passage for bleed air. 11 8. An improved small turbojet engine substantially as herein described with reference to accompanying drawings. 12

Documents:

0846-mas-2002 abstract-duplicate.pdf

0846-mas-2002 abstract.pdf

0846-mas-2002 claims-duplicate.pdf

0846-mas-2002 claims.pdf

0846-mas-2002 correspondences others.pdf

0846-mas-2002 correspondences po.pdf

0846-mas-2002 description (complete)-duplicate.pdf

0846-mas-2002 description (complete).pdf

0846-mas-2002 drawings-duplicate.pdf

0846-mas-2002 drawings.pdf

0846-mas-2002 form-13.pdf

0846-mas-2002 form-19.pdf

0846-mas-2002 form-26.pdf

0846-mas-2002 form-3.pdf

0846-mas-2002 form-5.pdf

0846-mas-2002 pct.pdf