In order for the four strokes to work properly, the action of the valve and fuel injection nozzle must be directly related to each of the four strokes of the piston. The intake valve, exhaust valve and fuel injection nozzle are pushed by the cam through the cam follower boom or tappet, vertebral rod, rocker arm and valve crosshead. The camshaft is driven by the crankshaft. In this way, the rotation of the crankshaft controls the action of the camshaft, and the camshaft controls the opening and closing sequence of the valves and the injection time (fuel supply).

進氣沖程

Intake stroke

在進氣沖程的終了，進氣門關閉，活塞開始上行而進入壓縮沖程。此時排氣門仍然保持關閉。在壓縮沖程的終了，燃燒室內的空氣由壓縮沖程開始時所占的容積，被活塞壓縮到一個很小的容積（根據發動機型號不同，其壓縮容積約為原來容積的1/14~1/16）。因此，壓縮比即為燃燒室內空氣量壓縮前和壓縮后體積之

At the end of the intake stroke, the intake valve closes and the piston begins to go up and enter the compression stroke. The exhaust valve remains closed at this time. At the end of the compression stroke, the air in the combustion chamber is compressed to a very small volume by the piston from the volume occupied at the beginning of the compression stroke (the compression volume is about 1 / 14 ~ 1 / 16 of the original volume according to the engine model). Therefore, the compression ratio is the sum of the volume of air in the combustion chamber before and after compression

空氣被壓縮到一個很小的空間后，使得空氣的溫度提高到足以使燃油著火。在壓縮沖程末期，以及作功沖程的開始階段，一小部分定量的燃油被噴入燃燒室。燃油被噴入燃燒室后，幾乎立即被其中的熱壓縮空氣所點燃。

After the air is compressed into a small space, the temperature of the air is raised enough to ignite the fuel. At the end of the compression stroke and at the beginning of the power stroke, a small amount of fuel is injected into the combustion chamber. After the fuel is injected into the combustion chamber, it is almost immediately ignited by the hot compressed air in it.

做功沖程

power stroke 

在做功沖程開始時，燃燒并膨脹著的氣體推動活塞向下運轉；進、排氣門全部關閉。由于更多的燃油噴入汽缸并燃燒，氣體溫度更高而更加膨脹，進一步推動活塞向下運動，這樣便增加曲軸旋轉的驅動力。

At the beginning of the power stroke, the burning and expanding gas pushes the piston downward; All inlet and exhaust valves are closed. As more fuel is injected into the cylinder and burned, the gas temperature is higher and expands, further pushing the piston downward, which increases the driving force of crankshaft rotation.

排氣沖程

Exhaust stroke

在排氣沖程中，進氣門關閉，排氣門打開，活塞向上運動。上行的活塞迫使燃燒室中燃燒過的廢氣通過打開的排氣口排到排氣歧管中。發動機的正常運轉取決于兩點。一首先是是壓縮以供點火；其次是將適量的燃油在適當的時間噴入氣缸。

During the exhaust stroke, the intake valve closes, the exhaust valve opens and the piston moves upward. The upward piston forces the burned exhaust gas in the combustion chamber to exhaust into the exhaust manifold through the open exhaust port. The normal operation of the engine depends on two points. First, compression for ignition; The second is to inject an appropriate amount of fuel into the cylinder at an appropriate time.

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