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Presented By:
Bhojaraj.B.G
DEPARTMENT OF MECHANICAL ENGINEERING
G M INSTITUTE OF TECHNOLOGY
# 4, P B Road, Davangere “ 577 006
VISVESVARAYA TECHNOLOGICAL UNIVERSITY
BELGAUM “ 590 014
ABSTRACT
Two-stroke and four-stroke engines have ruled for over a hundred years. Australian farmer Malcolm beareâ„¢s ingenious six-stroke power plant has pots of potential waiting to be tapped, particularly for the booming motorcycle industry.
A new four stroke engine head design known as the Beare Head after its designer Malcolm Beare. The Beare Head uses a piston and ports very much like a two stroke engine to replace the over head valve system that is found in four stroke engines today. The four stroke block, pistons and crankshaft remain unaltered. This combination of two stroke and four stroke technology has given the engine its name “ the six stroke engine (2 + 4 = 6).
A number of prototype Beare Heads produced have been the subject of extensive testing and theoretical analysis. Key attributes of the Beare Head are: increased power, increased torque, fewer, lighter reciprocating parts, simpler manufacture.
The Pulse Fuel Injector and Nozzle have been tested. Unlike conventional fuel injectors, this technology uses compressed air to atomize liquid fuel and pre-mix it with air; this increases efficiency and reduces emissions in internal combustion engines.
The Pulse Fuel Injector and Nozzle again can be used together or separately and have wide applications, not o¬nly the automotive field but also in the area of gas turbines, aerospace and waste incineration.
1. INTRODUCTION
Malcolm Beare is 53 year old Australian wheat farmer is indeed an original thinker, in spite of a day job apparently so far removed from the world of mechanics. For the past 23 years, while working his 1300 hectare spread in the sun-drenched outback of South Australia, Malcolm has had plenty of time to reflect on various aspects of his alternative profession. The Beare Engine is a completely new development of the internal combustion engine.
Termed a six-stroke due to the radical hybridization of two- and four-stroke technology, the device achieves increased torque and power output, better fuel economy and cleaner burning with reduced emissions, longer service intervals, and considerably reduced tooling costs when compared with a conventional OHC four-stroke design.
A new four stroke engine head design known as the Beare Head after its designer Malcolm Beare. The Beare Head uses a piston and ports very much like a two stroke engine to replace the over head valve system that is found in four stroke engines today. The four stroke block, pistons and crankshaft remain unaltered. This combination of two stroke and four stroke technology has given the engine its name “ the six stroke engine (2 + 4 = 6).
The prototype six stroke engines already produced have been the subject of extensive testing and theoretical analysis. Key attributes of a six stroke engine include:
¢ Increased power
¢ Increased torque
¢ Fewer, lighter, reciprocating parts
¢ Simpler manufacture
2. THEORY
Actually retarding the upper piston drive has a positive outcome on power output and efficiency largely because it effectively increases compression ratio, reduces the rate of change in volume during the combustion period, opens the exhaust port later, increases the period of valve overlap thus utilizing the exhaust extraction effect and closes the intake port later. The negative effect of this is to increase the amount of energy input to the head, but this is more than compensated by the positive outcomes.
The Six stroke engine is fundamentally superior to the four strokes because the head is no longer parasitic but is a net contributor to - and an integral part of - the power generation within the engine. The Six strokes is thermodynamically more efficient because the change in volume of the power stroke is greater than the intake stroke, the compression stroke, and the exhaust stroke. The compression ratio can be increased because of the absence of hot spots and the rate of change in volume during the critical combustion period is less than in a four stroke. The absence of valves within the combustion chamber allows considerable design freedom.
The reasons for this high torque output are:
(1) The reed valves keep gas velocity high at low throttle openings and prevent spit back through the carburetor.
(2) There is a gain in mechanical efficiency because the cylinder head is returning power to the main crank, unlike a conventional four stroke which suffers parasitic losses from the valve train.
(3) The compression pressure is maintained at low throttle settings because of the stratification of the intake charge keeping the fuel mixture swirling on the outside next to the spark plugs and retaining some exhaust towards the centre. The cranking compression pressure was the same as the standard bike, at 135 PSI.
(4) The effective change in volume of the expansion stroke is actually larger than either two- or four-strokes, which means that more energy is extracted during the combustion process.
3. HOW IT WORKS
Below the cylinder head gasket, everything is conventional, so one advantage is that the Beare concept can be transplanted on to existing engines without any need for redesigning or retooling the bottom end. But the cylinder head and its poppet valves get thrown away. To replace the camshaft and valves, Beare has retained the cam drive belt and fitted an ultra short-stroke upper crankshaft complete with piston, which the belt drives at half engine speed just as it previously drove the cam. This piston drives up and down in a sleeve, past inlet exhaust ports set into the cylinder wall, very much like on a two-stroke: these are all exposed during both inlet and exhaust strokes.
Continuing the two-stroke analogy, two 35mm Mikuni CV crabs mounted on each cylinder feed mixture into it via a reed-valve block, thus preventing exhaust gasses from escaping through the inlet. At the other end of the upper crankshaft is a two-stroke type rotary disc-valve that regulates timing, cutting off the exhaust flow at the appropriate time to stop the gasses returning into the cylinder, thus creating sub-atmospheric pressure during the inlet cycle. This being it's only function, the rotary valve is lightly loaded, reducing lubrication and sealing problems. It does need close tolerances though, which led to warping of the stainless steel disc Malcolm used on his first six-stroke, based on a Honda XL125 farm bike. Replacing the disc with a cast-iron one (on a Mk2 XT500-based version), cured this problem at the expense of extra weight. The Ducati uses hardened anodized aluminum discs, which work well.
During the compression and expansion strokes, the upper piston seals off both ports, leaving the pressure contained between the two pistons, with the lower one a conventional flat-top three-ring design, while the conical upper one (so shaped to aid gas flow during both inlet and exhaust cycles by guiding it towards the ports) has two rings - one compression, one oil. In the combustion phase, twin spark plugs provide ignition via the stock Ducati CDI and a pair of Harley coils - one per cylinder - and not only does the engine run on pure petrol (no need to add oil, because all required surfaces are positively lubricated, in spite of the application of two-stroke technology), it's also happy on low octane unleaded fuel. Obviously there are no valve seats to suffer from lack of lead, and Malcolm says the compression ratio can be increased significantly from the Ducati motors 10.6:1 quite safely because of the lack of hotspots, without problems with detonation. So now the claimed advantages of all this start to come to light - allowing a higher compression while still happy with low octane unleaded make this an efficient and cleaner engine. There are no poppet valves to float or bend (OK, OK - I know this was once a Desmo, but this is a much more cost-effective way of achieving this than expensively machining a set of closing rockers for all the valves in a cylinder head, quite apart from the unwanted inertia such a system still entails)
In turn, this implies a far higher safe rev limit for the six-stroke - 28,000rpm in theory, given the half-engine speed operation of the upper crankshaft, and the fact that GP reed-valve two-strokes peak at 14,000rpm. But Malcolm Beare says the rev limit, as on such two-strokes, depends only on what the main (conventional) crankshaft is able to bear, and he's arbitrarily limited the Ducati-based 6S-V2 to 9,000rpm for that reason, at which point he says (according to computer predictions) 86bhp is delivered at the rear wheel - there aren't too many dynojet rigs out in the Australian outback! Comparisons are hard to make, because of the difficulty of determining the exact cubic capacity of the 6S-V2's six-stroke engine: what began as an elderly Pantah V-twin now has a total 744cc's of compression/expansion volume, and 602cc of inlet/exhaust volume, and instead of absorbing about 10% of engine power in driving the camshafts, the cam belts now deliver about 9% net power to the main crankshaft after combustion via the upper, conical porting piston (see, Desmo power!).
But if you figure that a '97 model Ducati 900SS delivers 73bhp at the rear wheel in stock form, that's quite an impressive claimed power increase.
But there are other, much more significant apparent spin-off benefits from the Beare design. First of these is fuel economy: Malcolm Beare claims his engine is 35% more economical at low revs/throttle openings than an equivalent conventional engine and 13% less thirsty at high rpm/full throttle, in spite of the doubled-up crabs. That should mean fewer hydrocarbon and CO2 emissions, because you're using less fuel to achieve the same performance. Next there's improved torque at lower revs - on both his Yamaha and Ducat-based prototypes Bearer discovered the six-stroke version produced the same torque as a four-stroke 1,000rpm lower down the scale, as well as producing exponentially more torque as revs rose. But in a commercial application, perhaps the most attractive benefit is the reduced number of moving parts, compared to a four-stroke design, so the six should be cheaper to make. Not as few as a two-stroke, but what you appear to be getting here is improved performance and torque, coupled with the inherent advantages of a four-stroke, on the cheap. Finally, as the upper two-stroke piston is driven at half engine speed, it should have twice the life of the lower four-stroke one. Sounds promising...
4. PRINCIPLES OF BEARE HEAD COMBUSTION CYCLE
The following is an simplified description of the combustion process of the Beare Head, and is designed for non-technical types. The images will give automotive engineers clues as to how the process is implemented.
1. INTAKE
The intake stroke happens when the piston is on its downward path with the intake valve open. This action creates suction, drawing atomized fuel, in this case gasoline mixed with air, into the combustion chamber. This is exactly the same action when liquid is drawn into a syringe.
2. COMPRESSION
The compression stroke happens as the piston begins its upward stroke with all the valves in the closed position. This compresses the air-fuel mixture causing it to become more volatile, or explosive.
3. IGNITION
The power stroke begins at a critical moment, just as the air-fuel mixture is at its most compressed. A supercharged voltage is delivered to the spark plugs from the ignition coil, at which point it ignites the fuel mixture. The valves in the engine are still closed during this period. Thus the explosion forces the piston down to turn the engine's crankshaft, delivering the power via the gearbox and clutch to the driving wheels.
4. EXHAUST
The final of the four strokes, as you have not doubt guessed, is the exhaust stroke. The piston is now on its second upward path, and the exhaust valves are now opening, allowing the spent gases to exit the engine via the exhaust pipes. At the top of this stroke the exhaust valves close, the intake valves open, and the whole process repeats - quite rapidly.
5. SPECIFICATION OF SIX STROKE ENGINE
PROTOTYPE 5 - DUCATI BASED
Engine Type Air-cooled opposed-piston rotary- & reed-valve 90° V-twin
Bore x stroke
86 x 57 lower, 60 x 25 upper
Capacity 616cc intake, 575cc compression corrected, 643cc expansion corrected, 592cc exhaust.
616cc intake, 756cc compression, 732cc expansion, 592 cc exhaust
Measurements taken with upper crankshaft 20° retarded
Corrected measurements taken after ports are closed.
Compression ratio 10.6 : 1 (approx)
Fueling
4 x 35mm Mikuni CV carburetors
Ignition
Dual ignition, Ducati CDI & two H-D 12 volt coils
Power
40 bhp at the rear wheel at 5000rpm as tested after Sir Alan Cathcart's test ride. (Computer predicts 86bhp @9000rpm, 41 ft/lb @ 6000rpm)
Valve timing
Intake open 20° BBDC 520° close 60° ABDC 240°
Duration 440° (this is not a mistake)
Maximum port area at 20° ATDC
Exhaust open 40° BBDC 500° close 60° ATDC 60°
Duration 280°
Maximum port area at TDC 0°
Overlap 260° (also not a mistake)
The reed valves control the beginning of intake according to engine demand.
Transmission
Clutch: wet multiplate
Gearbox: 5-speed
Final drive: 520 chain
Frame
Garden gate style 1" square tube space frame
Suspension
41mm FZR Yamaha forks, 50 x 25 RHS steel swing arm, twin Koni dampers
Brakes
Front: twin ÃƒË 300mm floating discs with 4-piston calipers
Rear: single ÃƒË 220mm disc with opposed piston caliper
Tyres
Front 120/70 VR17, Rear 160/60 VR17
Wheelbase
1400mm
Rake/Trail
98mm/23°
Weight
153kg dry
6. COMPARISON OF SIX-STROKE ENGINE WITH FOUR-STROKE ENGINE
1. In a six stroke engine the energy absorption is less because of slower acceleration of reciprocating parts The piston speed of the upper piston is about a quarter of the main piston; therefore its service life should be at least twice that of the main piston.
2. In the Beare design, per single cylinder, the number of parts is 15 compared to a four stroke of approx 40 to 50 parts. Also, to reduce manufacturing costs the head and block can be machined in o¬ne piece.
3. The bottom piston is a standard design and the Beare Head bolts directly o¬nto the engine block, replacing the overhead valves and standard head.
4. It reduces the weight and complexity of the engines head by as much as 50%. Instead of using energy to drive the head, the head actually develops energy for conversion to power back through the timing chains of an engine.
5. Torque is increased by 35% and efficiency increased by the same. This can be achieved by simply unbolting an existing head of a four-stroke engine and then bolting on a Beare Head.
6. Increased torque and power output,
7. Better fuel economy and cleaner burning longer service intervals and considerably reduced tooling costs when compared with a conventional OHC four-stroke design.
¢ Volume-angle diagrams for 4-stroke and 6-stroke engine
The intake begins at 0 degrees on the X-axis. The effect of the additional volume changes that the upper piston has on the volume of the engine is all positive from a thermodynamic point of view. If the engine were a normal 4 stroke the cylinder capacity would be 340cc. Of note - maximum volume at the end of the intake stroke occurs at 173 degrees instead of 180 degrees- the change in volume is 308cc which is less than a 4 stroke (340cc)- yet the total volume at the end of the intake stroke is 415cc as opposed to 375cc for a conventional stroke.
This means that the extra volume is best swept by gas velocities and not mechanical movement, and therefore mechanical input energy is less. Also, maximum volume is before bottom dead centre 173 deg. Consequently valve timing, if the same as a 4 stroke is more radical and is of longer duration in relation to engine volume and hence volumetric efficiency is considerably improved.
The change in volume during the compression stroke is slightly greater than a 4 stroke after the ports are closed. The expansion stroke is much greater than a 4 stroke; both from T.D.C. to B.D.C. and from T.D.C. till the exhaust port is open. It is possible to leave the opening of the exhaust port later than in a 4 stroke because maximum volume is not reached until after B.D.C.-548 deg. Instead of 540 deg. Hence the 6 stroke system is better from a thermodynamic point of view because more energy is extracted from the expansion process.
During the critical combustion period the rate of change in volume in the 6 stroke is less than a 4 stroke. Minimum volume is not reached until after T.D.C., at 361 deg. This is because of the phasing of the upper piston. It is retarded in reaching its T.D.C. until 20 deg. after T. D.C. (380). This is much better from a thermodynamic view in that combustion occurs at a more constant volume; hence ignition timing is not as critical as in a 4 stroke. There is room in the combustion chamber for up to 4 spark plugs and two direct injectors if needed.
¢ Pressure volume diagrams for 4-stroke and 6-stroke
¢ TORQUE ANGLE DIAGRAMS
¢ PHASE CHANGE
¢ COMPARISON CHART
7. GALLERY
DISC VALVE
The piston is half way up on the exhaust stroke. When the piston reaches TDC with the ports fully open, the disk will begin to cut off the exhaust. The valve runs clockwise.
CYLINDER HEAD FROM BELOW
CYLINDER HEAD “UPPER VIEW
UPPER CRANK
UPPER CRANK WITH PISTON
8. THERMODYNAMIC ADVANTAGES
The intake begins at 0 degrees on the X-axis. The effect of the additional volume changes that the upper piston has on the volume of the engine is all positive from a thermodynamic point of view. If the engine were a normal 4 stroke the cylinder capacity would be 340cc. Of note - maximum volume at the end of the intake stroke occurs at 173 degrees instead of 180 degrees- the change in volume is 308cc which is less than a 4 stroke (340cc)- yet the total volume at the end of the intake stroke is 415cc as opposed to 375cc for a conventional stroke.
This means that the extra volume is best swept by gas velocities and not mechanical movement, and therefore mechanical input energy is less. Also, maximum volume is before bottom dead centre 173 deg. Consequently valve timing, if the same as a 4 stroke is more radical and is of longer duration in relation to engine volume and hence volumetric efficiency is considerably improved.
The change in volume during the compression stroke is slightly greater than a 4 stroke after the ports are closed. The expansion stroke is much greater than a 4 stroke; both from T.D.C. to B.D.C. and from T.D.C. till the exhaust port is open. It is possible to leave the opening of the exhaust port later than in a 4 stroke because maximum volume is not reached until after B.D.C.-548 deg. Instead of 540 deg. Hence the 6 stroke system is better from a thermodynamic point of view because more energy is extracted from the expansion process.
During the critical combustion period the rate of change in volume in the 6 stroke is less than a 4 stroke. Minimum volume is not reached until after T.D.C., at 361 deg. This is because of the phasing of the upper piston. It is retarded in reaching its T.D.C. until 20 deg. after T. D.C. (380). This is much better from a thermodynamic view in that combustion occurs at a more constant volume; hence ignition timing is not as critical as in a 4 stroke. There is room in the combustion chamber for up to 4 spark plugs and two direct injectors if needed.
The change in volume during the exhaust stroke is less than a 4 stroke. This means that the negative pumping work is less than a 4 stroke. Extractive gas velocity is very important. Easily accomplished at T.D.C. with a fully open exhaust port.
The design with 4 intake ports fed by 2 reed blocks per cylinder allows the use of several different intake manifold types:
(1) 4 separate manifolds fed by 4 carburetors or injector bodies, of various length and diameters or all equal length and diameter.
(2) 2 separate manifolds bifurcated to each cylinder so that each has its own carburetor or injector body, with various lengths and diameters.
(3) 2 separate manifolds bifurcated to each cylinder in turn, so that each cylinder is fed by 2 carburetors in turn even though the system has a total of 2 carburetors or injectors, with various length and diameter runners..
(4) 3 intake manifolds, with 3 carburetors or injector bodies, 1 bifurcated to each cylinder with long small diameter runners, the other 2 with short large diameter runners.
The design can cope with various runner diameters and lengths because the reed valves allow any positive pressure pulses to pass through and cancel any negative ones, as well as providing good secondary atomization. Hence at low revs the long thin runners are in tune and at higher revs the shorter fatter ones take over with no need to shut down the long thin ones or visa versa as would be necessary with a normal 4 stroke. Swirl is in one direction at low revs and moves to tumble when the flows are in balance reverting to swirl in the other direction as the short fat ones predominate. A good spread of torque is achieved.
9. CONCLUSION
a. In a six stroke engine the energy absorption is less because of slower acceleration of reciprocating parts The piston speed of the upper piston is about a quarter of the main piston; therefore its service life should be at least twice that of the main piston.
b. In the Bearer design, per single cylinder, the number of parts is 15 compared to a four stroke of approx 40 to 50 parts. Also, to reduce manufacturing costs the head and block can be machined in o¬ne piece.
c. The bottom piston is a standard design and the Bearer Head bolts directly o¬nto the engine block, replacing the overhead valves and standard head.
d. It reduces the weight and complexity of the engines head by as much as 50%. Instead of using energy to drive the head, the head actually develops energy for conversion to power back through the timing chains of an engine.
e. Torque is increased by 35% and efficiency increased by the same. This can be achieved by simply unbolting an existing head of a four-stroke engine and then bolting on a Bearer Head.
f. Increased torque and power output.
g. Better fuel economy and cleaner burning Longer service intervals and considerably reduced tooling costs when compared with a conventional OHC four-stroke design
10. REFERENCES
1. autocarindia.com
2. sixstroke.com
3. dynobike.com
4. delphi.com
5. engineersedge.com
6. mooter.com
7. howstuffworks.com
8. Popular Mechanics Magazine
9. Auto car India Magazine
10. Applied Thermodynamics by Rajput
11. Automobile Engineering by Dr. Kripal singh
12. Automobile engineering by G.Nagula
13. Mechanical Engineering science by K.R.Gopalakrishna
14.
http://seminarsprojects.in
CONTENTS
1. INTRODUCTION¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦..1
2. THEORY¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦2
3. HOW IT WORKS¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦..3
4. PRINCIPLES OF BEARE HEAD COMBUSTION CYCLE¦¦¦6
5. SPECIFICATION OF SIX STROKE ENGINE¦¦¦¦¦¦¦¦10
6. COMPARISON OF SIX-STROKE ENGINE WITH FOUR- STROKE ENGINE¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.......12
7. GALLERY¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.. 20
8. THERMODYNAMIC ADVANTAGES¦¦¦¦¦¦¦¦¦¦...23
9. CONCLUSION¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦25
10. REFERENCES¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦..26