What is a 2-stroke engine and a 4-stroke engine?

Question

Which one of these cause more pollution?

Answer 1

Short answer is that 2 stroke causes more pollution

2 stroke engine runs on a mix of oil and gas

4 stroke engine runs on gas, and requires oil to be added separately.

Answer 2

Namsaev nows his stuff i agree with him

Answer 3

2-stroke engines, mostly found in small motorcycles, only requires 2 strokes to complete intake, compression, combustion and exhaust. Intake accurs simultaneusly with exhaust with the intake pressure pushing the exhaust gases out. 2-stroke engines are not very fuel efficient and can emit heavy pollutants of burnt, unburnt fuel and oil.

4-stroke on the other hand performs each step sequentially. 4 stroke engines can be more fuel efficient and less polluting.

Answer 4

4-Stroke

1. The fuel intake valve is open. The piston descends, sucking in the fuel-air mixture.

2. The intake valve closes. The piston rises, compressing the fuel mixture.

3. The spark plug fires, igniting the mixture and driving the piston downwards.

4. At the bottom of the stroke, the exhaust valve opens. The piston then moves upwards, expelling the exhaust gases.

2-Stroke

1. The spark plug fires at the top of the stroke, with it's fuel-air mixture, driving the piston downwards. While going down energy is supplied to the crankshaft, and after that much of the exhaust is expelled.

2. The fuel mixture is sucked in, the piston rises, compressing the mixture.

The 2-stroke is simpler, lighter, but causes much more pollution.

Answer 5

A 2 stroke fires the fuel everytime the piston goes down once and comes up once(hence 1+1=2 stroke).A 4 stroke fires the fuel every time the piston goes down once(fired fuel or pressure stroke),up once(pushing exhaust out),down once(sucking fuel in),up once(compressing fuel to be fired).Hence 1+1+1+1=4 stroke.

Answer 6

2 stroke engine cause too much pollutiion.

Answer 7

the 2stroke engine has just an intake and exhaust valve and is much simpler the 4 stroke has the intake and exhaust  but it also has 2 more valves per piston but they are about the same ,the 2 stoke is simpler

Answer 8

A four stroke has four seperate cycles or strokes in this sequence, intake, compression, power, and exhaust. Each cylinder only fires every other revolution.

A two stroke engine only has two strokes. Intake is combined with compression and power is combined with exhaust. Each cylinder  fires every revolution.

Two strokes are much messier as they tend to let more unburned fuel out the exhaust pipe. They have more power generally per cubic inch displacement than a four stroke engine.

Answer 9

Read Scot P's answer for the technical part.

In general, because of its lightness, simplicity and because it is much more powerful than a 4-stroke engine, 2-strokes are mainly used for special purposes where these things are important... dirtbikes, small mopeds, karts, gardening tools, etc.

The exhaust of 2-strokes is a bit more polluting, but not as bad as most people think, at least today. They just conclude that they must be very polluting because with two-strokes the smoke is often visible, and with four-strokes it's mostly not.

The main point is that, as I said, 2-strokes are mostly used in areas with special requirements, like racing, which is why they are much less in numbers than 4-strokes. Compared to the millions and millions of 4-stroke cars, 4-stroke motorcycles, diesel trucks and industrial air pollution, they have hardly any weight at all and are falsely punished for being what they are

Answer 10

4-stroke becuase it burns more gas and makes more smoke,when you start it up. but some 2-strokes make a lot of smoke when you start them up.

Answer 11

Can never remember which one is which. One is like a "normal engine" like in a car that just uses gasoline. The other is like in a chainsaw that requires an oil and gas mixture. If you have ever seen the exhaust that comes out of one of those power tool I would say that causes more polution.

Answer 12

There's 2 types of pollution.

- Local smog, like what festers in L.A.  This is a result of fuel not burning properly in the engine.  2-stroke engines are REALLY REALLY BAD for this type.

- Carbon dioxide, which affects the whole planet.  2-stroke engines are about average for this.

One eco-thing you can do is use B100 biodiesel (100% biodiesel) where you would use 2-cycle oil.  So if you're running 40:1, use 40 parts gasoline to 1 part B100 biodiesel.

There are diesel 2-stroke engines that aren't so bad, that's because they have normal engine lubrication and don't use an oil/gas mix.  GM bus engines and GM/EMD locomotives use this technology, it works nice.

What's a 2-stroke engine?  The piston moves up and down in the cylinder every time the crankshaft turns.  In a 4-stroke engine, each cylinder firing takes 4 moves or 2 crankshaft turns:

Intake (down) pulls air/fuel into the cylinder.

Compression (up) compresses the air/fuel for ignition.

Power (down) sparks and burns the air/fuel for power.

Exhaust (up) pushes exhaust out of the cylinder.

In a 2-stroke engine you have 3 cycles:

Compression (up) compresses the air/fuel for ignition.

Power (down) sparks and burns the air/fuel for power.

Scavenging (near the bottom) which is intake and exhaust at the same time.  Ports open, the exhaust is let out, and intake air/fuel is pushed in.  Some exhaust stays in the cylinder and some unburnt air/fuel is pushed through into the exhaust.  It's a mess.

Answer 13

A 2-stroke engine uses gasoline that is mixed with 2-cycle engine oil...Dirtbikes, Weed eaters, small boats.

A 4-stroke engine uses only regular gasoline, no oil mixed. Cars/trucks, motorcycles,  lawnmowers, fourwheelers...

If you take the same amount of exhaust from a 2cycle and same amount from a 4stroke engine...the 2 cycle engine exhaust is more polluted, however, 2 cycle engines are smaller and produce less quantity of exhaust in general than most 4stroke engines.  4 stroke engines make up the majority of engines people use.

Answer 14

2 strokes combine intake and compression cycles into a single stroke, and combine exhaust and power cycles into the second stroke. This leads to more power per revolution, but also more waste, as much of the exhaust remains unburned as it's being ejected from the cylinder.