How Two Stroke Engines Work

How Two Stroke Engines Work


This 3D animated video explains how a two stroke engine works. We look at the two stroke engine’s main components, how it works, its applications, advantages and disadvantages. The animation clearly shows the cycle of the engine as it moves though the induction, compression, power and exhaust strokes. Coloured arrows are used to show the movement of the gasses through the engine.

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Introduction
Two stroke engines are of a simple and robust design. They are almost always petrol/gasoline fired engines. Two stroke engines are spark ignition type engines and are used primarily for small or very large applications.

The two stroke engine has found widespread use as it is relatively cheap and has a high power to weight ration compared to other prime movers.

Components shown in this video include the crankcase, crank webs, piston, con rod, injector, cylinder liner and spark plug.

Advantages
Simple design.
Robust and reliable.
Few components.
High power to weight ratio.

Disadvantages
Not very efficient compared to other prime movers.
Noisy/loud compared to four stroke engines.

This video lesson is part of our Diesel Engine Fundamentals course:

You can read more about two stroke engine in our technical encyclopaedia:

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35 Comments on "How Two Stroke Engines Work"


  1. so the “bang” part keep the crankshaft spinning? how does the crankshaft spin in the first place? sorry for my english not my fist language

    Reply

  2. This is the most learneable video i hawe ever seen of a 2stroke engines funcktion, Thenk you 🙂

    Reply

  3. Do you lose some air/fuel mixture in the upwards compression stroke? I'd say if you compress it but for a moment the exhaust port is opened you lose some compression and mixture.

    Reply

  4. I'm sure i missed something, but when the piston moves up again to compress the fuel air mixture, the exhaust canal is open for a small time until the piston closes that opening. Will you not lose a great deal of fuel and compression that way?

    Reply

  5. Great Video…Just to reinforce my understanding, if I have an engine that idles at 2,500 RPM is it safe to say that the piston completes 1 up/down stroke (crankshaft revolution) 2,500 times within a minute?

    Reply

  6. excuse me, just think what the application render to make that animation, thanks for the response.

    Reply

  7. I understand what makes the piston move downwards. But I don't understand what makes it go back up.

    Reply

  8. Does the spark causes an explosion with the combustible making the piston go up and down?

    Reply

  9. The exhaust port don't make since we're it's at. Because when the piston hose back up its going to push some of the fresh air and fuel mixure on its way up through the exhaust port .. there are no valves to stop it from going out through the exhaust port. Exhaust it's always open

    Reply

  10. I am now almost 62 and have owned more two stroke motorcycles over the years than four strokes. They're anathema to the powers that be, nowadays, so I'm compelled to be slowly dying of valve gap anxiety, solitude and yogurt.

    Reply

  11. Hmm not a good understanding at all the big marine engines are diesel and supercharged and you have not taken in to account the spanny on high powered bikes also a lot of the modern small marine are direct injection. You are also missing a reed or rotory port on the induction.

    Reply

  12. Explain what a reed valve is please. What a a pulse port for on atwo stroke? What is a rotary reed valve used for? How does a Rotary reed work and why do two stroke engines such as Snowmobiles and motorcycles use them if the use a carburetor?

    Reply

  13. Compression TDA to make perfect pure of fuel…
    If Vapore petrol was creat in other part…. what happen…?
    Its perfect combution…
    Please watching Channel Nurhendratmoko…
    On New Pistoon Engine Valveness…

    Reply

  14. What keeps the fuel air mixture from escaping through the exhaust port during the compression stroke?

    Is there engine oil in the crankcase?

    Reply

  15. change the title , " how a two stroke engine works with a 4 stroke piston , hahaha, i see the 3rd oil ring ,

    Reply

  16. Great video – thanks! May be worth mentioning that the fuel is pre-mixed with lubrication oil which means the lubrication is done within the mixture and thus no need for all the complicated lubrication systems the 4-strokes need 🙂

    Reply

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