2-stroke engines? dead? i dont think soJun 15 '01 Write an essay on this topic.
Popular Products in Sport and Outdoor
The Bottom Line 2-stroke is simple but effective, but why, and whats the fuss about them all about?
Being a keen boat user myself, and being a boat designer and builder i often have to look at different power options for boats. sometimes just for designs i have made, and sometimes for personal use. Those of you who own or are thinking of owning a boat will have to make the same decisions, when it comes to power. Outboard engines are a great piece of enginering i think, and its amazing how much power can be produced from such a small lump. But what makes this power? what is the advantages and disadvantages of different engines? well there are loads of designs out there, all claiming different things so i am going to try and shed some light on the subject for those of you who dont really know their outboards. there is 2 main types of outboard engine, 2 stroke and 4 stroke, each a different engine in its own. We all know what a 4 stroke engine is, thats the type of engine you find in your average car or van. But few know of the 2 stroke engine. The 2 stroke engine completes its 'power cycle' in 2 strokes of the piston, or 1 revolution of the crankshaft. The design of this engine is much more lightweight and less complex than that of the 4 stroke due to the fact it doesnt need valves, springs, camshafts etc, as it uses a system commonly known as 'ports'. Ports are located in the wall of the cylinder at specific places. Ports are used for the intake and exhaust. The exhaust is on one side of the cylinder, and the intake the other. Each port is opened and closed by the movement of the cylinder. This process means that both sides of the piston are used for different tasks. Because of this system it means 1 stroke can do the job of 2 strokes in a 4stroke engine. You still with me?. So there is 2 strokes, the up stroke is the intake and compression stroke. As the piston moves up one side compresses the fuel/air mixture, while the other side sucks in the mixture ready for the next stroke. The fuel is taken in via a 1-way valve known as a 'reed valve'. The second stroke is the power and exhaust stroke. The compressed fuel is ignited and the explosion forces the piston down giving the engine its driving force. At the same time, the exhaust ports are opened and the exhaust escapes the cylinder. This process of the exhaust leaving while the fuel mixture enters is known as 'scavenging'. make sense? thats the basic operation process of a 2 stroke engine. so if they are so simple and light weight, why are they not liked as much as the 4 stroke engine? well, there is mixed opinions on this: The 2 stroke produces more power than a 4 stroke, from experience a 30HP 2 stroke is more powerful than a 40HP 4-stroke, but that is only a personal experience point of view. But because of the fact the intake and exhaust is done together, they tend to be less economical due to the fact that fuel can escape through the exhaust ports. Although not a problem in itself, it does mean that fuel is wasted. Also, the lubrication system on a 2 stroke is different to that of a 4 stroke. 4-strokes use a seperate lubrication system. Basically oil is pumped around the engine over the moving parts which lubricates them, where as a 2 stroke lubricates itself during the cycle. Oil is mixed with the fuel and during the fuels path to the cylinder it is fed over the crankshaft etc lubricating it as it passes, then the oil is burnt with the fuel. This system has advantages and disadvantages. It means that there is no need to change oil, filters, etc, also it means the moving parts get a fresh coat of oil each pass. But becuase of the burning of oil, it is more polluting and that is the big reason 2-strokes are not liked, they produce more pollution and are generally not as clean as a 4-stroke. You can usually tell which type an engine is by the colour of the exhaust, a 2-stroke will pump out blue smoke, and usually quite a bit of it, where as a 4-stroke doesnt, (unless it has a problem). So basically a 2-stroke produces more power than a 4stroke, but is not as clean and economical. So it becomes a balancing act between power and economy. Those who want power and simplicity, and are not to worried about economy would probably do better with a 2-stroke, where as if economy and clean running is your thing then 4-stroke it the way forward. The choice is yours. Hope this has helped explain the main difference between the 2 types and despite all the fuss between the 2 engines, i think 2 stroke will be around for a while longer, as they are getting cleaner.  |
| Read all comments (1)|Write your own comment |
|
Ads by Google
|
