PowerPoint PresentationStroke 1: Fuel-air mixture introduced into
cylinder through intake valve
Stroke 2: Fuel-air mixture compressed
Stroke 3: Combustion (roughly constant volume) occurs and product
gases expand doing work
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Atkinson Cycle
The Atkinson-cycle engine is a type of internal combustion engine
invented by James Atkinson in 1882.
Due to the unique crankshaft design of the Atkinson, the expansion
ratio may differ from the compression ratio. By adjusting the
linkage to allow a power stroke that is longer than the compression
stroke, the engine can achieve greater efficiency than with the
Otto cycle engine.
The exhaust expansion stroke was 1.78 times longer than the intake
stroke.
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Atkinson Cycle
While Atkinson's original design is no more than an historical
curiosity, many modern engines use unconventional valve timing to
produce the effect of a shorter compression stroke/longer power
stroke, thus realizing the fuel economy improvements the Atkinson
cycle can provide.
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Atkinson Cycle
The goal of the modern Atkinson cycle is to allow the pressure in
the combustion chamber at the end of the power stroke to be equal
to atmospheric pressure; when this occurs, all the available energy
has been obtained from the combustion process. For any given
portion of air, the greater expansion ratio allows more energy to
be converted from heat to useful mechanical energy meaning the
engine is more efficient.
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Atkinson Cycle
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Reduces pumping losses in the engine.
Reduces the amount of fuel-air to be compressed, resulting in
greater fuel efficiency
Allows the expansion stroke to be longer than the compression
stroke, improving thermal efficiency
Original Cam Profile
1 mm additional curve
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2) Welding the marking area
Welding
Grind the welding area using the hand grinder to get 1mm thickness
addition.
Results
a) Specific Fuel Consumption (sfc) Versus Load at 3000 rpm
Brake Thermal Efficiency (b) versus load at 3000 rpm
Nilai BTE sepatutnya lebih rendah. Tak mungkin BTE enjin petrol
boleh tinggi hingga 40%. Kesilapan ini berlaku akibat kesalahan
mengukur kadar penggunaan bahan api.
Apa yang penting yang ingin ditunjukkan dalam graf ini adalah
perbezaan BTE antara sebelum dan selepas menggunakan teknologi
Atkinson Cycle.
Project Conclusion
The objective of this project was successfully achieve
The improvement given by Atkinson Cycle in range of 20% to 33% for
specific fuel consumption and 5% to 13% for brake thermal
efficiency compare to the Original engine.
Note: Significant reduction on fuel consumption is due to reduction
of fuel actually combust. Some amount of fuel are drawn back to
intake manifold due to longer intake valve opening.
Offset Crankshaft and other Friction Reductions
When the reduction of friction loss is deemed worthwhile,
relatively simple design changes make it possible. We used
the rubbing of the piston against the cylinder walls as an example
of friction loss above. This particular source of loss is
most severe during the combustion stroke when the hot gasses push
down on the piston. The connecting rod that links the piston
to the crankshaft makes an angle with the axis of the piston so
that as the piston pushes down it is itself pushed to one side,
hard against the cylinder wall. By simply moving the
crankshaft a bit to one side, the connecting rod can be made more
upright during the combustion stroke so that the force of the
piston against the cylinder wall is smaller and hence friction is
reduced. Both the Prius and Insight engines use offset
crankshafts. The Prius engine is also limited by the computer
to a lower than normal maximum spin rate of 4500 r.p.m. This
reduces the peak stress on engine components, making it possible to
make them smaller and lighter, resulting in less friction
loss.
Offset Crankshaft and other Friction Reductions
Elimination of Enrichment