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