Contents
Automobile’s electrification issues need to be addressed in order to decrease dependency on fossil fuel and comply with future emission policies. However, pure-electric automobiles still contain numerous drawbacks. Therefore, the hybrid automobiles are the best transfer option. The hyper-expansion cycle engine (Atkinson or Miller) is ideal for hybrid automobiles.
In contrast to conventional gasoline engines, over-expansion engines can achieve higher expansion ratios, resulting in higher thermal efficiency while maintaining the standard effective compression ratio to stop knocking problems. Therefore, Toyota hybrid vehicles all operated using the Atkinson cycle.
What is an Atkinson Cycle?
TheAtkinson cycle發動機是A.type of IC engine. AnAtkinson cycleis mainly designed to improve the4-stroke gasoline engine’sefficiency by one particularimprovement. In simple words, thethis cycle發明是為了利用循環的發電部分，同時最小化吸入衝程期間的燃料消耗。
In1882, anengineerJames Atkinsoninvented theAtkinson cycle.
雖然four basic phases的奧托周期still exist, Atkinson launched a new timing order for the suction valve shutting during the compression stroke. Leaving the suction valve open a little longer efficiently reduces engine displacement during the suction process but maintains the maximum expansion ratio during combustion or the expansion stroke. This makes the engine to extract maximum energy from the ignited air-fuel mixture before leaving the mixture to the chamber.
Atkinson Cycle Working
一個Atkinson cycleworks in the same way as an奧托周期作品。但是，它是一種修改的奧托循環形式。一個Atkinson cycleworks in the following way:
- Adiabatic compression（壓縮衝程）：首先，活塞幫助發動機從外部吸入空氣燃料混合物進入氣缸。之後，活塞向上移動（從BDC到TDC）以壓縮空氣燃料混合物。在活塞的這種向上運動（從1至2）期間，它通過壓縮它來增加混合物的溫度和壓力。然而，在該過程中，空氣燃料混合物的焓保持恒定，而體積減小（如下圖所示）。
- Isochoric compression(ignition phase): As the piston and compressed air-fuel mixture reaches at point 2, an external heat source provides heat to the compressed mixture. Due to this ignition, the air-fuel mixture’s enthalpy and pressure increase. However, no changes occur in the volume during this phase. This phase is the same as the isochoric compression phase of the Otto cycle. During this process, the piston moves more and compresses the mixture without changing its volume.
- 絕熱擴張(power stroke) – After the ignition process, the power stroke starts. In this stage, the gas (combusted air-fuel mixture) perform work on the piston and moves it from TDC to BDC. Due to the piston’s downward motion, the gas expands, and the piston’s downward motion rotates the曲軸, which further rotates the flywheel. In this process, the gas volume increases while pressure reduces. This process is known as Isentropic because there is no change in the enthalpy.
- Isobaric exhaust (exhaust stroke): The objective of the latest Atkinson cycle is to permit the pressure inside the cylinder equal to atmospheric pressure at the expansion stroke’s end to be. In this cycle, the decompression doesn’t occur in the cylinder like the Otto cycle. After this exhaust stroke, the piston moves toward TDC from BDC, and the whole cycle repeats.
For a better understanding, watch the following video:
Read Also:Working of Otto Cycle
Types of Atkinson Cycle Engine
The Atkinson cycle engine has the following major types:
1）Atkinson“差動引擎”
Firstly, theAtkinson cycle是實施的1882.
先進的版本相比,這個循環佤邦s implemented as an opposed piston engine (the Atkinson differential engine). In such case, a single曲軸was linked with two opposing pistons via a non-linear連杆.
For the half revolution, one piston remains uniform while the other piston approaches it and returns. While, in the next half revolution, the second piston goes in uniform condition, but the first piston approaches it and returns.
Therefore, for each revolution, one piston of the Atkinson differential engine delivered the compression and power strokes while the other piston delivered the exhaust and suction strokes.
閱讀更多：Different types of Internal Combustion (IC) Engines
2) Atkinson “Cycle Engine”
In 1887, Atkinson invented another engine that was called as “cycle engine.” It had a cam, poppet valves, and an eccentric arm to generate four strokes of the piston for each turn of the曲軸. The Atkinson cycle of this engine had a shorter suction stroke and compression stroke than the power stroke and discharge stroke.
The “cycle engines” were manufactured and sold by UK engine manufacturers for many years. Atkinson was also given production permission to other companies.
3) Atkinson “Utilite Engine”
Atkinson was designed 3rdengine that was known as the “Utilite Engine.” The 2nengine (Cycle” engine) of Atkinson’s was effectual, but it had a linkage that was very hard to balance for quick working. Therefore, Atkinson felt that he should perform modifications to make his cycle more suitable as higher-speed engines.
After improvements in the previous model, Atkinson designed a new model that was “Utilite Engine.” In this new design, he had eliminated the連杆and created a more balanced, more traditional engine that could run at a speed of approximately 600 rpm and generate power at every revolution. His “Cycle engine” had a proportionally longer expansion stroke and a shorter compression stroke.
的操作Utilite engineis very similar to that of a standard 2-stroke, except that the exhaust port is in the center of the stroke.
In this design, a cam functioned valve (which doesn’t open until the piston approaches the stroke end) in the power stroke to stop backflow of the pressure as the piston passes through the discharge valve. This discharge valve opens when the piston reaches near the bottom of the stroke.
When the piston returns for a compressed stroke, the exhaust valve remains open, and fresh air fills the combustion chamber and expels exhaust gases until the discharge port is enclosed with the piston.
As the discharge or exhaust port closes, the piston starts to pressurize the remaining air in the combustion chamber.
一個小的fuel pump在壓縮過程中注入燃料。點火源是其他阿特金森發動機的熱水管。該施工提供了一個帶有長電源和短壓縮筆觸的2行程發動機。
Read Also:Working of Rankine Cycle
Why do we need to reduce the compression ratio for the Atkinson cycle?
In the奧托周期, after the combustion process, the force exerted on the piston during the power stroke increases so that when the piston reaches BDC, the exhaust valve opens, and useless heat discharges from the combustion chamber.
Therefore, this cycle uses to reduce the compression ratio for more expansion during the expansion stroke so that the entire force generated due to the combustion process can be used on the piston before the piston reaches BDC.
This means that the Atkinson cycle always has a lower/equivalent performance than the Otto cycle. However, the Otto cycle has lower thermal efficiency than the Atkinson cycle.
Efficiency of the Atkinson Cycle
The efficiency of the Atkinson cycle can be calculated by the below-given formula:
In the above equation, the work done by the system is calculated as:
W = Work done by the system = QS- 問：R
In the above equation:
QR= Heat rejected by the system
QS= Heat added to the system
Expansion Ratio (e) = V4’/V3
和
Compression Ratio (r) = V1/V2
對於等式壓縮過程（1至2）：
For the Isochoric compression process (2 to 3):
絕熱擴張(3 to 4):
After putting the values of the T4, T2, T3in the Efficiency formula. After putting these values, the final efficiency formula will be:
阿特金森循環效應的優點
- The conventional engines of the cars run in the partial load range. The use of the butterfly valve is particularly convenient and flexible to regulate fresh air into the cylinder. Though, the butterfly valve creates a large negative pressure in the inlet manifold, which leads to a significant loss of air at the inlet valve. If you can control the throttling damages, you can save 15% to 20% on fuel consumption. TheAtkinson Cycle Effecthas been shown to be a valuable way of improving fuel economy at part load by controlling engine load and reducing pumping losses.
- This cycle is suitable for hybrid vehicles as the electric motor compensates for the loss of power at low speed.
- 奧托循環的壓縮比小於阿特金森循環的膨脹比。因此，阿特金森發動機效率更高。
Disadvantages of Atkinson Cycle
- The Atkinson cycle engine consumes less fuel but also generates less power.
- This cycle has a lower compression ratio.
阿爾金森周期與奧托周期之間的差異
| Atkinson Cycle | 奧托周期 |
|---|---|
| 一個Atkinson cycle has higher efficiency than the奧托周期. | 一個奧托周期is less efficient. |
| It consumes less fuel; therefore, it generates low power. | This engine has high power because it has a high compression ratio. |
| This engine consumes low fuel. | It consumes high fuel. |
| It has a higher expansion ratio than the compression ratio of the Otto cycle. | The奧托周期具有比Atkinson循環的壓縮比更高的壓縮比。 |
FAQ Section
為什麼Atkinson循環更高效？
The Atkinson cycle ismore efficient因為它具有比壓縮比大的膨脹比。它延遲了吸入閥的關閉，直到活塞在壓縮行程中完成20％至30％的上行程序。
What is the biggest engine in the world?
Wärtsilä RT-flex96Cis the biggest engine in the world. The Wärtsilä RT-flex 96C is a turbocharged 2-stroke piston diesel engine that was developed to drive large container boats.
What cars use the Atkinson cycle?
以下汽車使用Atkinson發動機：
- 馬自達致敬電氣/汞水手/福特逃生
- Chrysler Pacifica插件混合模型小型貨車
- Ford C-Max plug-in hybrid and hybrid model
- Chevrolet Volt