Two-stroke and four-stroke car engines
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2 stroke fires every time the piston goes up. There are no valves for intake or exhaust, just ports. 4 stroke fires, next time it comes up it exhausts, on the down it intakes, and fires when it goes back up.
To add to the other comment; two stroke, very light weight and almost twice the power for the same sized four stroke engine. Two stroke is heavily polluting for two reasons, the ports let unburned fuel escape and the engine also burns oil that also escapes through the port.
2 stroke cars are almost non existent now. I’d say 99.9% are 4 stroke. There was a 2 stroke car called the Trabant from ~~the USSR block countries~~ East Germany a long while ago.
Within a car engine you have a tube, called a cylinder, filled with a moving metal plate called a piston. The cylinder/piston is the power generating part of the engine.
In concept, there are 4 steps to a piston producing power.
1) You need to fill the cylinder with a mixture of air and gasoline.
2) You need to squeeze the air and fuel down to a very tight space.
3) You ignite the fuel/air mixture creating pressure, this pressure becomes a force that pushes on the piston and ultimate that’s how the engine gets power.
4) You need to eject the fumes/smoke out of the cylinder and repeat back to step 1.
Logically these steps take time, so engines don’t *constantly* produce power, it’s only on step 3 that you get power. So a single cylinder engine would operate like – nothing.nothing.POWER.nothing. That’s a pretty rough ride. So engines will have multiple cylinders off-timed from each other. Imagine a 4 cylinder engine, you could have one cylinder firing while the other 3 are at different stages. Great!
Except 4 cylinders are big, heavy, and expensive – that’s ok in a car or truck, by lousy in a backpack mounted leaf blower, or a cheap mass produced lawnmower at Home Depot.
So you can combine the 4 steps above so that they overlap. You can fill the cylinder with air/fuel as you squeeze into a tight space, one step, and then you can ignite it while you eject it, second step. This doubles the rate that power is produced, so you can use half the engine (weight/cost/size) for the same output.
The number of steps I described are referred to as “Strokes”.
The trade off: a 2-stroke engine is smaller, cheaper, simpler, lighter, but more polluting and less fuel efficient. That’s why they are generally used only in applications where weight, size, and cost are prioritized over the environment and fuel costs. For example, lawnmowers, leaf blowers, maybe gocarts and dirtbikes, small cheap stuff.
4 stroke engines are bigger, more complicated, more expensive, but more efficient and less polluting. So you’ll see them in applications where the engine is a long term purchase, where size or weight is less of a concern, laws might be in place to regulate minimum efficiency or pollution control standards for example cars, generators, boat motors, etc.
A piston engine has to accomplish four tasks during its “cycle”:
1. Suck in fresh air and fuel
2. Compress the fuel and air
3. Burn the fuel and air to create power
4. Get rid of the exhaust gas
A four stroke engine performs each of these actions in a separate motion, so the piston goes up and down twice (up-down-up-down) per combustion cycle.
A two stroke engine combines the four tasks in one cycle (up-down). This means the four steps overlap instead of each having their own stroke. This is really bad for efficiency and pollution, but it makes the engine design simpler and you get more power, since the engine has a power stroke every cycle instead of every two cycles. Two stroke engines were historically used in applications where light weight and low cost was important. As four stroke engines (and electric motors) have become less expensive, and pollution regulations have gotten stricter, two stroke engines have mostly died out.
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