AU746173B2 - Two-stroke combustion engine - Google Patents

Description

AUSTIEA

Patents Act 1990 S COMPLETE SPECIFICATION a. a a a a a. a a a a.

15 Title Internal Patent Classification Application No.

Application Date Priority Data Number Date Applicant Inventor Two-stroke combustion engine F02B 033/22 F02B 019/02 PP6582 20.10.98 Dmitri Miroshnik Dmitri Miroshnik This invention concerns internal combustion engines.

The proposed engine uses the prolonged thermodynamical cycle. It allows to get more work on the expansion stroke. It also eliminates some shortcomings of the conventional internal combustion engines.

One of such shortcomings is time deficiency for the fuel combustion. This time deficiency occurs as a result of two main factors. The first of these factors is the kinematics of the crankconrod mechanism the conventional combustion engines use. One of this factor's characteristics is changing of overpiston volume during whole thermodynamical cycle including the period of fuel combustion ie the fuel combustion process occurs in the variable volume of the combustion chamber. The second factor is that the fuel combustion process occurs not instantly but takes some time and during this time the combustion chamber volume is significantly changed.

The combination of these two factors results in that the fuel S:combustion process starts at the end of the compression stroke and finishes in the middle of the expansion stroke ie the fuel combustion process is combined with the gas compression and expansion. This combination also leads to deflection of real thermodynamical cycle from theoretical cycle and results in engine power loss. Moreover, S"the fuel combustion during the expansion stroke causes the higher heat loss because a part of fuel combustion energy goes out from the cylinder through its walls.

The increase of engine speed leads to the increasing heat loss because with the increase of the engine speed the finishing of fuel combustion process more and more shifts to the bottom dead centre and the area of the cylinder walls increases.

The proposed engine eliminates the above shortcoming and it allows the engine power increase, improving the fuel economy and creating the conditions for engine forcing by the way of increase of its speed while retaining the high effectiveness of fuel combustion.

Figures 1,2,3,4,6 and 7 are the schematic diagrams of the different engine's embodiments. All these schematic diagrams have the common designations. The list of these designations is below.

1. Compressing cylinder 2. Inlet manifold 3. Adjustable flap 4. Inlet valve of the compressing cylinder 5. Piston of the compressing cylinder 6. Outlet valve of compressing cylinder 7. Channel or cold storage device S.8. Inlet valve of the combustion chamber 9. Combustion chamber 10. Inlet valve of the expanding cylinder 11. Fuel injector 12. Cover of the compressing cylinder 13. Expanding cylinder 14. Piston of the expanding cylinder 15. Outlet valve of the expanding cylinder 16. Power drainer 17. Conrod of the expanding cylinder 18. Crank of the expanding cylinder 19. Crankshaft 20. Crank of the compressing cylinder 21. Conrod of the compressing cylinder 22. Exhaust manifold 23. Starter-motor 24. Power supply 25. Gear wheel 26. Outlet valve of the combustion chamber ~;liLrlL1 ~.irk~ii~II 27. Channel 28. Cover of expanding cylinder 29. Cooling air or cooling water Clutch 31. Stop-valve 32. Stop-valve 33. Charging valve 34. Unstepped reduction gear Compressor 36. Relief valve 37. Outlet pipe 38. Channel 39. Gas turbine are the plotters of the proposed engine parameters.

The cycle of engine operation in Fig.1 is broadly as follows: The cylinder 1 on its downstroke sucks air through inlet manifold 2 where the adjustable flap 3 is installed. The inlet valve 4 of the cylinder 1 is opened, the piston 5 is driven downward and the cylinder 1 is filled up with air The inlet valve 4 closes at the bottom of the stroke when the piston 5 reaches bottom dead centre (BDC).

The outlet valve 6 is closed and the cylinder 1 is isolated from S"atmosphere air.

After the piston 5 passes BDC and starts to travel upward the air is compressed in the cylinder 1. The pressure and temperature of compressed air are increasing on the upstroke. The cylinder 1 is designed so that when the piston 5 is at the top dead centre (TDC) the clearance between piston 5 and its cover 12 of cylinder 1 practically equals zero.

The outlet valve 6 opens when the piston 5 has passed approximately the half of its working stroke. The compressed air is expelled through the opened valve 6 into channel 7 that connects the cylinder 1 with combustion chamber 9. Simultaneously with that the inlet valve 8 of the combustion chamber 9 opens. The compressed air fills up the volume of the combustion chamber 9 and the channel 7. The outlet valve 10 of the combustion chamber 9 is closed at this time. As the piston 5 travels upward to the TDC and when the valves 6 and 8 are opened and the valve 10 is closed the increase of the compressing air pressure takes place and reaches the designed value when the piston 5 is at TDC. The valves 6 and 8 close at this moment. The combustion chamber 9 is hermetically isolated from the cylinders 1 and 13 and then the atomised fuel is injected into the combustion chamber through the fuel injector 11.

S The air-fuel mixture is ignited by a spark or in other way. The air-fuel mixture combustion begins and it takes place inside the isolated volume of the combustion chamber. This volume is unchanged during the whole combustion process.

Atthis time the piston 5 of the cylinder 1 passes the TDC and begins to travel downward. The valve 4 opens and the atmosphere air fills up the cylinder 1 again as described above. The next cycle begins inside the cylinder 1.

The gas temperature and pressure increase and reach the S"maximum values during the combustion process. At this moment the valve 10 opens and hot gas speeds into the cylinder 13 from the combustion chamber 9. The piston 14 of the cylinder 13 is in its TDC and starts to travel downward at the moment of valve's opening. The hot gas fills up the overpiston volume and applies pressure on the piston 14 forcing it to move down. During the gas' expansion the useful work is done and can be used by the screw propeller 16 or by other devices.

The force of the expanding gas is transmitted to the device 16 through the piston 14, conrod 17, crank 18 and crankshaft 19. A I -fCFI~ II-- L II. part of useful work is used to rotate the crank 20 of the cylinder 1 and to compress the fresh air charge.

The gas expansion proceeds till the moment when the piston 14 reaches it's BDC. At this moment the inlet valve 10 dcloses. The piston 14 starts to travel upward and expels the exhaust gas from the cylinder 13 through the opened valve 15 into exhaust manifold 22 and then into atmosphere. The cylinder's 13 volume is practically cleaned from the exhaust gas when the piston 14 is in TDC and the cylinder 13 is ready to get a new portion of hot gas from the combustion chamber 9.

The distinctive feature of the proposed engine is that it's pistons and 14 reach its' TDC not simultaneously as it takes place in the patent 688442, but with some interval created by the crankshaft design. The piston 5 of the cylinder 1 reaches it's TDC first (Fig.

lb).This interval can be 40...120 degrees depending on the engine design and purposes.

The interval between the moments of reaching TDC creates the favourable conditions for organisation and realisation of fuel o combustion process.

Firstly, it allows the realisation of the fuel combustion to proceed o• with the constant and minimum combustion chamber volume. This reduces the power loss that the conventional internal combustion engines are suffering from. The reason of this power loss is deficit of gas pressure that is lower than theoretical value. It takes place in conventional engines because when the gas temperature is maximum the overpiston volume is significantly more than the volume of combustion chamber.

Secondly, the fact that the pistons of the proposed engine reach TDC not simultaneously allows the minimization of the heat loss through the combustion chamber walls. This heat loss decrease can be explained by the minimum surface area of combustion chamber Z;77 7 -L1 walls comparing with the conventional engines where the combustion chamber and the working cylinder volume are combined.

Thirdly, the time difference between reaching TDC by engine's pistons can be preset so that the interval is equal or more than the time required for the full fuel combustion. This feature of proposed engine gives the important advantages: the engine dependence from fuel combustion speed is practically disappears or significantly decreases because the full combustion finishes before reaching TDC by piston 14 at any combustion speed; there is no necessity to use the rich air-fuel mixture (c and therefore decreases the exhaust gas toxicity; oooo the effect of exhaust gas remaining in the combustion chamber is practically disappears or significantly decreases. It allows for the decrease of the air rate for blowing and cleaning of the combustion chamber; The volume of the channel 7 that connects the compressing cylinder 1 and the combustion chamber 9 is not included in the volume of combustion chamber 9 and thus affects the gas parameters inside the combustion chamber both before and after the fuel combustion. However the air pressure in the channel 7 increases every next cycle, reaches the designed value after several rotations and remains unchanged after that.

The starter-motor 23 drives the crankshaft up to speed powered by the power supply 24.

Normally the working volume of the cylinder 13 is bigger than volume of the cylinder 1 and it allows for getting a higher expansion ratio ie 7 v 6expansion &compression (1) It means that if maximum gas pressure of the proposed engine and conventional engine equals, the proposed engine's piston 14 receives more force from the gas pressure than the conventional engine's piston. In order to retain the desired level of reliability, the proposed engine cylinder's 13 volume is distributed between two cylinders in equal quantities. The pistons of these cylinders move in synchronism and each of them is set in motion by its own crankshaft. To make it adaptable to streamlined methods, the volume of the cylinder 1 is also distributed between two cylinders that have the equal volumes. The crankshafts 19 have the same radius of cranks and are made in accordance with the same ooo.

drawing so the crankshafts 19 are identical and thus interchangeable.

15 Fig. 2 is a schematic diagram of such an engine embodiment.

As can be seen in Fig.2 both cylinders 13 get the hot gas with high pressure from the same combustion chamber 9 and the gear wheels 25 that connect the crankshafts 19 synchronise the pistons' 5 and 14 motion.

20 One of the proposed engine's features is the transfer of the compressed air charge from the compressing cylinder into combustion chamber. During this transfer process the air charge moves via the channel 7 that connects the combustion chamber 9 and the compressing cylinder 1. It gives an opportunity to use the stage of charge transfer to reduce the temperature of air before the combustion chamber gets it. It is known that the air cooling increases charge density and weight thus increasing the engine power.

The proposed engine allows for a highly effective cooling of the compressed air charge before its combustion.

Fig.3 is a schematic diagram of such an engine embodiment.

This schematic diagram is a modification of the schematic diagram in Fig.l.

As it can be seen, a modification of the channel 7 is the difference between the engine embodiments in Fig.3 and in Fig.l.

The channel 7 in Fig.3 is the cold storage device and has a big volume. The outside surface of this channel is cooled by blown air 29 or is passed by cooling liquid 29. The volume of the cold storage device 7 is chosen considering the following: firstly, the bigger this volume the more surface area is cooled and the cooling is more effective.

secondly, the bigger this volume the lower the amplitude of air-pressure pulsation inside the cold storage device 7 as the air consumption has a pulsating character of changing when the engine 15 works.

thirdly, the bigger this volume the bigger the overall dimensions and weight of whole power unit.

The engines in Fig.3 and in Fig.1 operate with the following differences: the valve 6 opens when the air pressure in cylinder 1 is higher than that in the cold storage 7. It allows for avoiding of air pressure losses during the air transfer from the cylinder 1 into the cold storage device.

before the engine starts, the cold storage device 7 is filled up with compressed air from either an outside source of compressed air through the charging valve 33, or from the cylinder 1 that begins to function with the aid of the starter 23. During this filling process the clutch 30 is out of gear, the crank 18 of the cylinder 13 for expansion does not rotate. The stop-valve 31 is closed. It prevents the air escaping from the cold storage device 7, but inlet stop-valve 32 is opened thus allowing the cold storage device to be filled by the compressed air.

when the air pressure inside the cold storage device 7 reaches the designed value, the clutch 30 is in gear, the crank 18 starts to rotate, sets in motion the mechanism of gas distribution of the cylinder 13 and engine starts. The starter 23 switches off, the valve 31 opens. The relative angular position of cranks 18 and is irrelevant.

when the engine is turned off for a long time, the valves 31, 32 and 33 are gas-tightly closed, the cold storage device 7 is filled up and the air pressure in it remains the same as in the moment when the engine is stopped. It allows for the very fast and *0al o0 reliable engine start.

the cold storage device 7 can be filled from an outside source of the compressed air through the charging valve 33. During the filling process the outlet 31 and inlet 32 stop-valves are closed.

*0 9 9During the filling of the cold storage device 7 by the compressed air, the air temperature is more than 500K. The significant difference between the air temperature inside cold storage device 7 and coolant (air or liquid) that passes over the cold storage device 7 results in highly efficient cooling of the air charge at the time when it expels into combustion chamber. When degree of cooling 0 =0.8 and compression ratio 6=9.0 the charge temperature decrease results in At =328 C. It significantly increases the engine power and decreases the maximum gas temperature inside the combustion chamber 9.

The effect of air cooling before its combustion on the engine parameters is similar to the effect of supercharging of the conventional engines where the increase of air consumption is F' X~I~f;r~c ~r I achieved by the increase of the inlet air pressure before the air compression inside the cylinder.

Comparing the proposed engine (Fig.3) to the conventional engines with supercharging, the following important advantages of the proposed engine can be specified: when the specific powers are equal the proposed engine has the lesser specific fuel consumption matching of air consumption of a turbo-supercharger with the air consumption of the piston part of a conventional engine with supercharging is a very complicated process and it is optimal in a very narrow diapason of the operating conditions. In other operating conditions a turbo-supercharger has lower efficiency.

ooooThe matching of air consumption of the proposed engine comes oooo .by changing of theposition of the adjustable flap 3 in the inlet 15 manifold 2 and the position of the valve 33.

:The engine in Fig.3 can be used most effectively as a power unit on the big cargo vessels where the cooling of compressed air can be achieved with a high degree of cooling The cold storage device 7 has to be placed overboard under 20 the waterline for this purpose. It will save mechanical energy for cooling and increase the cooling degree. Moreover, the placement of cold storage device into overboard water (water temperature changes in narrow diapason) guarantees the stability of cooling degree and allows to control and adjust the engine parameters with high efficiency.

Fig.4 is a schematic diagram of the proposed engine embodiment that can be used as an engine-propeller power plant.

The difference between the schematic diagram in Fig.3 and in Fig.4 is the installation of the unstepped reduction gear 34 that is placed on the crankshaft 19. The crank 18 of the cylinder 13 rotates the

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inlet shaft of the unstepped reduction gear. The outlet shaft of the unstepped reduction gear rotates the crank 20 of the cylinder 1.

The installation of the unstepped reduction gear 34 allows the variable speed ratio of the cranks 18 and nlie n. Var It is known, the aircraft engine power decreases when the flight altitude increases. It is bound up with decrease of atmosphere pressure.

The aircraft engine in Fig.4 allows the climbing without power decrease.

The proposed engine and the conventional aircraft piston engine have the different high-altitude characteristics (Fig.5a). As a result, the flight performance criteria of the proposed engine such as altitude, speed, flight range rate of climb, bringing up to speed, 15 manoeuvrability are significantly better.

The engine in Fig.4 operates like the engine in Fig.3 with the "only difference. This difference is described below.

When the atmosphere pressure in the inlet pipe 2 is changing, the engine power has to be maintained on a certain level. In order to 20 achieve that, the air consumption in the combustion chamber 9 and in the cylinder 1 has to be maintained. It is attained by changing of crank 20 revolutions with the assistance of the unstepped reduction gear 34. The crank's 18 revolutions are not changing at this time.

The air consumption decreases when the altitude increases. It can be compensated by the increase of the crank's 20 revolutions.

is a comparing graphic illustration of design altitude performance of a conventional engine (TICE) and the proposed engine (MV).

i I As it can be seen in Fig.5a, a relative power curve of the proposed engine MV indicates more power excess than TICE has.

For instance, when the altitude H=3km, this excess is 30% and when it is more than Fig.5b is a plotter of gear ratio i=n201n18 against altitude H. As it can be seen, if the altitude is maximum the rotational speed of crank reaches the design value and i but when H=O then i =0.55.

The presence of the unstepped reduction gear 34 together with the ability to adjust the pressure inside the cold storage device 7 and also using the usual methods of adjustment allows the realisation of very flexible programs of adjustment of the proposed engine.

When the proposed engine is going to be used as an aircraft engine, the cold storage device 7 is placed overboard and the 15 atmosphere air 29 airflows it. It allows the saving of mechanical energy for cooling of compressed air.

The proposed engine can use the low compression pressure.

Fig.6 is a schematic diagram of the proposed engine embodiment with the low compression pressure. The atmosphere air 20 compression takes place in the compressor 35 but for engines on Fig.1,3,4 this process takes place in the cylinder. The compressor is installed on the crankshaft 19 that turns it.

The air, compressed in the compressor 35 goes into the cold storage device and then, after having been cooled, goes into the combustion chamber.

In other respects the engine (Fig.6) operates as it was described above. The distinctive feature of the engine (Fig.6) is the presence of a relief valve 36 in the combustion chamber 9 and the outlet pipe 37 that discharges the part of exhaust gas from the combustion chamber into atmosphere. The time of opening of the valve 36 and the time when this valve is opened can be chosen depending on the rN M m 14 specific design conditions. As a result of that, the design gas pressure can be set and the residual exhaust gas mixes with the fresh air charge and makes the new combustion mixture.

It is known that the presence of residual exhaust gas in the combustion mixture decreases the oxidation reaction speed and leads to the increase of the time of burn-out. The combustion of the conventional engines is not the independent stroke of the thermodynamical cycle, but it is combined with compression and expansion.

So the increase of the combustion time results in the power loss and it negatively affects on the fuel efficiency. So the conventional engine cylinders' clearing from the residual exhaust gas usually ,takes place by using of the cylinder scavenge. But it takes a part of the fresh air charge.

The disposable time for combustion of the proposed engine is approximately 2 times more than the time of the conventional engines. As a result, the residual exhaust gas can be used as a working medium thus decreasing the quantity of the fresh air charge in the combustion mixture. As a result the proposed engine consumes less air while achieving an equivalent maximum gas pressure.

The maximum value of the residual gas's part in the combustible mixture is determined experimentally. According to these experimental results the valve 36 timing specifies.

Fig.7 is a modification of the schematic diagram in Fig.6, that is a power forcing of the proposed engine.

In contrast to the engine in Fig.6 the exhaust gas of this engine is not exhausted into the atmosphere but goes through the exhaust manifold 22 and channel 38 into gas turbine 39. When this gas expands the useful work is done. This work is used by the power drainer 16 and compressor

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Claims (6)

1. An internal combustion engine, comprising: at least one cylinder for compression of the aircharge; at least one cylinder for expansion of hot gases; one combustion chamber that is arranged between both of said cylinders and connected by means of valve passageways; at least one crankshaft with the crank of cylinder for compression and the crank of cylinder for expansion wherein the cranks are displaced relatively each other in that way that the piston of cylinder for compression reaches its top dead centre earlier than the piston of cylinder for expansion and it can be equal up to 120 .e degrees of crank angle.

2. An internal combustion engine according to claim 1 wherein the swept volumes of the cylinder for expansion and the cylinder for compression are distributed between several cylinders for expansion and several cylinders for compression in the equal portions; the gas pressure force transmits onto two crankshafts that are arranged parallel to each other and are connected by means of synchronised 20 gearwheels; the combustion chamber takes the compressed air from all of the cylinders for compression and distributes the hot gases into all of the cylinders for expansion.

3. An internal combustion engine according to any one of preceding claims wherein between the cylinders for compression and the combustion chamber is installed a cold storage device for compressed air; the outside surfaces of this cold storage device are cooled by the air or liquid; the cold storage device is connected to the combustion chamber and the cylinders for compression by the sealed valve passageways; the cold storage device has also the charge- and stop-valves. Z;7 C. C

4. An internal combustion engine according to any preceding claims wherein unstepped or multistepped reduction gear box is installed on the crankshafts between the cranks of the cylinders for compression and the cranks of the cylinders for expansion; this reduction gear box provides the necessary rotary speed correlation between the cranks of cylinders for compression and the cranks of cylinders for expansion. 10

5. An internal combustion engine according to any one of preceding claims wherein the air compression takes place inside the screw compressor, or axial-flow compressor, or centrifugal compressor; the compressor is set in rotation from the engine's crankshafts and the compressed air goes into cold storage device.

6. An internal combustion engine according to any one of preceding claims wherein the exhaust gases from the cylinders for expansion goes into gas turbine that is connected with engine's crankshafts; gas turbine transfers the energy of exhaust gases expansion onto engine's crankshafts. Dmitri Miroshnik ,r