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The relationship between the two and four stroke of marine YAMAHA engine
Dec 21, 2017

What is the difference between the two stroke and four stroke engines of the yamaha engine?

1、Working principle of two stroke engine?

     The piston moves from the lower stop point to the top stop. It will complete the intake and compression working process, which belongs to the first stroke of the piston reciprocating movement. The piston moves from the top stop to the stop point. It will complete the working process of the combustion expansion (work) and exhaust. It is the second stroke of the reciprocating motion of the piston. When the piston moves from the top stop point to the top stop point and closes the air vent and exhaust port, the exhaust and gas exchange process terminates, and the fresh combustible mixture in the cylinder will start initially compressed. At the same time as the piston moves upward, crankcase below the piston volume increases, the pressure in the crankcase decreased when the vacuum degree of vacuum, the crankcase degree reaches a certain level, the reed valve automatically opens, the mixture is drawn into the carburetor atomization in the crankcase. When the piston continues to move upwards, the spark plug emits an electric spark and ignites the compressed combustible mixture when it is going to close to the stop point. At this time, the burning gas expands rapidly, causing the temperature and pressure of the combustion chamber to rise sharply, forcing the piston to move downward, and the piston works by connecting rod and crankshaft. When the piston moves from the top stop point to the downward stop point, the pressure inside the crankcase will increase as the volume decreases, and the reed valve will turn off automatically. At this point, the combustible mixture entering the crankcase will start to be pre compressed. When the piston goes down to the exhaust port, the exhaust gas is discharged into the atmosphere through the vent, exhaust pipe, and muffler. When the piston continues downward to the opening of the gas exchange, the fresh combustible mixture pre compressed in the crankcase is entered into the cylinder through the air inlet, and the exhaust gas in the cylinder is further discharged. This process is called scavenging process. So the engine finished a working cycle.

2、Working principle of four stroke engine?

    First stroke intake stroke: when the piston has a certain crank angle before the top stop point, the inlet valve opens, and the combustible mixture is inhaled. When the piston moves from the top stop point to the downward stop point, the exhaust valve closes at a specified crankshaft angle at the top stop point, and at the same time, the volume of the cylinder on the piston increases, causing the cylinder to form vacuity, and the flammable mixture continues to breathe through the intake valve. When the piston goes to the lower stop point, the intake valve is closed when a specified crank angle is turned. At this time, the intake work process is finished.

    The second stroke compression stroke: the piston moves from the bottom dead center to the top stop point. When the intake process ends, the intake valve and the exhaust valve are all closed, so the combustible mixture in the cylinder is compressed.

    The third stroke combustion expansion works as a power stroke. When compression stroke is made, when the piston comes up to a certain crank angle before reaching the top stop point, spark between the spark plug electrodes will ignite the compressed combustible mixture. The combustion of the combustible mixture increases the temperature and pressure in the cylinder, and the piston moves under the high pressure and high pressure, and then moves from the top stop point to the downward stop point, and it works with the connecting rod to drive the crankshaft to rotate.

    The fourth stroke exhaust stroke: when the crankshaft angle is before a piston goes to the bottom stop, the exhaust valve opens, and the exhaust gas starts to exhaust through the exhaust valve when the combustion expansion stroke. The crankshaft continues to rotate and moves the piston from the lower stop point to the top stop. Exhaust gas out of the cylinder. This exhausting process is until a specified crankshaft angle after the piston line is first stop, and the exhaust valve is terminated when it is closed.

Advantages and disadvantages of two stroke engines


* 1 times per rotation, so the rotation is smooth.

* not need air door, spare parts, so the maintenance is convenient and cheap.

* the inertia force produced by the reciprocating movement is small. Small vibration and low noise.

* in comparison with the four stroke engine, the speed is simultaneously high in power.

* it has a double explosive force compared to the four stroke. Therefore, under the same volume, if the average effective pressure is the same, the power is 2 times (1.7).


* the intake exhausting process is short, so the loss of fuel is great.

* there is an air inlet on one side of the cylinder wall, and the piston ring is easy to wear in contact with the cylinder. This paper provided by Qingdao Aolong rubber boat!

* because the vent is on the cylinder, it is easy to overheat.

* slow and unstable.

* lube oil is much more consumed.

The advantages and disadvantages of the four stroke engine


The process of air intake, compression, expansion (explosion) and exhaust is carried out individually, so the work is reliable and efficient, and the stability is good. The speed range of low speed to high speed is large (500 ~ 1000rpm).

* there is no gas flow loss and low fuel consumption rate as there is no two stroke engine.

* it runs smoothly at low speed and is lubricated by the lubrication system. It is not easy to overheat.

* the intake process, the time of the compression process, the volume efficiency and the average effective pressure are high.

* the heat load is smaller than the two stroke engine. Do not worry about the problem of deformation and ablation. Large capacity, can be designed as a high power engine.


* valve gas distribution mechanism is complex, many parts and difficult maintenance

* mechanical noise

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