Two Stroke Engines vs "normal" engines

-westy-

-westy-

-westy-

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Hello,

I've got an interview tomorrow for a company that makes Paragliders, specifically the engines and control systems. Reading from the job brief, it mentions that a good working knowledge of engines and two stroke applications is preferable, so I thought I'd do some reading up :p

For the more knowledgeable among us, what are the actual differences between two stroke engines and other engines, for example a simple car engine? Why are they called "two stroke" for example?

Thanks :)
 
This isn't a good start for a "good working knowledge".......

In simplicity, two stroke are oil in fuel, four stroke are similar to all modern engines - oil in sump with pump/oil galleys etc.
 
kae2 said:
This isn't a good start for a "good working knowledge".......

In simplicity, two stroke are oil in fuel, four stroke are similar to all modern engines - oil in sump with pump/oil galleys etc.
Click to expand...

Well, no - I'm fairly good at diagnosing and servicing the engines themselves, just wasn't too clear on the actual inner workings of them.

Wikipedia has given me more of an insight on them, along the lines of the whole revolution of the engine being complete in a single turn of the crankshaft, rather than two....?
 
kae2 said:
This isn't a good start for a "good working knowledge".......

In simplicity, two stroke are oil in fuel, four stroke are similar to all modern engines - oil in sump with pump/oil galleys etc.
Click to expand...

Thats missing the point / key facts by a long long way... wiki is op's friend here :) (hint the clue is in the 2 and 4 ;) :)
 
Flukester said:
Thats missing the point / key facts by a long long way... wiki is op's friend here :) (hint the clue is in the 2 and 4 ;) :)
Click to expand...

From what I've gleaned from Wiki, the "stroke" applies to the movement of the piston, "2 stroke" being a combustion cycle completed with an upwards and downwards stroke, as opposed to double the number for a 4 stroke engine?

Is kae2 correct in saying about the oil being in the fuel for 2 stroke engines, as in they have no sump and oil pump operation?
 
Firestar_3x said:
You sound like the ideal person for the job :p
Click to expand...

:D

In fairness, I have a good working knowledge of car engines etc, just need to brush up on two stroke. At least I'm doing my homework instead of making myself look like an arse during a technical interview ;)
 
2 strokes are used when high torque isnt needed but where you need a large rev range, as in cases where gearboxs arent used.
4 strokes make higher power but over a shorter rev range making the use of a gearbox a must.
there are also 3 strokes as well, but guess you dont need to know about them.

There is a lot more to it but thats the basic reasons to use on or the other.
 
robj20 said:
2 strokes are used when high torque isnt needed but where you need a large rev range, as in cases where gearboxs arent used.
4 strokes make higher power but over a shorter rev range making the use of a gearbox a must.
there are also 3 strokes as well, but guess you dont need to know about them.

There is a lot more to it but thats the basic reasons to use on or the other.
Click to expand...

Useful, thanks :)
 
-westy- said:
From what I've gleaned from Wiki, the "stroke" applies to the movement of the piston, "2 stroke" being a combustion cycle completed with an upwards and downwards stroke, as opposed to double the number for a 4 stroke engine?
Click to expand...

Fundamentaly yes. A stroke is one motion of the piston, either up or down. A 4 stroke engine requires, unsurprisingly, 4 strokes to complete an entire cycle i.e. suck, squeeze, bang, blow.

A two stroke engine combines some of these cycles to get the entire cycle completed in two strokes, so you get twice as many power strokes as a four stroke engine.

-westy- said:
Is kae2 correct in saying about the oil being in the fuel for 2 stroke engines, as in they have no sump and oil pump operation?
Click to expand...

In general terms no. Because the crankcase of a conventional two stroke is used to pump fuel and air into the cylinder, you can't use a pressurised oil feed and plain bearings to lubricate the crank bearings, piston and little end. Instead the lubrication system is "total loss", i.e. all the oil used for lubrication eventually gets pushed out of the exhaust. Adding oil to the fuel is the most simple method of providing lubrication, but most modern engines will use an oil pump to inject oil directly into the crankcase. This will be linked to the throttle in order to inject more oil under higher engine load.
 
robj20 said:
2 strokes are used when high torque isnt needed but where you need a large rev range, as in cases where gearboxs arent used.
4 strokes make higher power but over a shorter rev range making the use of a gearbox a must.
There is a lot more to it but thats the basic reasons to use on or the other.
Click to expand...

Sorry but no. Two stroke engines are hardly famous for providing large flat torque curves; it's easier to get a four stroke engine to deliver this.

Choice of engine will be dictated primarily by cost, power density, emissions and fuel consumption requirements. If you need something small, light and powerful but fuel economy and emissions are of secondary importance then the two stroke is the obvious choice e.g. a microlight or powered hand glider. Two stokes provide a further advantage for powered flight by their natural ability to work in any orientation (provided fuel delivery to arranged to suit). Trying to run a four stroke engine upside down requires a lot of lubrication issues to be solved, even with the added complexity and weight of a dry sump.
 
two strokes have vulcans in the cylinders. real ones, and theyre massive.

they flap their ferocious wings fore and after (bird looking down at the piston crown) and hence creates a power stroke

on the exhaust stroke the bird has to "duck" in order to avoid being nutted by the piston

win
 
Two strokes are used when you want to ride an offroad bike up and down in a residential street at 2AM ****ing off your neighbours as they provide maximum annoyance due to sounding like a swarm of high pitched angry bees.

The Crazy Frog ringtone was based on the sound of a two stroke engine. Also the security robots in the first Bioshock used two stroke engines. Remember how annoying those bloody things sounded?
 
robj20 said:
2 strokes are used when high torque isnt needed but where you need a large rev range, as in cases where gearboxs arent used.
4 strokes make higher power but over a shorter rev range making the use of a gearbox a must.
there are also 3 strokes as well, but guess you dont need to know about them.

There is a lot more to it but thats the basic reasons to use on or the other.
Click to expand...

Well in Motorcross bikes it's opposite.
A 250 2t makes more power and torque than a 250 4t and the 4t will rev higher. (by a good few thousand rpm)


The biggest difference is that a 4t has valves and cams and fires every other revolution. A 2t doesn't have *valves or cams and fires every revolution. *(not including power valves)
 
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Two strokes often sound like buzzy little mosquitos, where as 4 strokes have a much lower sound..

Go to a local kart track, you'll soon work out which ones are 2 and which ones are 4 :)
 
-westy- said:
Well, no - I'm fairly good at diagnosing and servicing the engines themselves, just wasn't too clear on the actual inner workings of them.

Wikipedia has given me more of an insight on them, along the lines of the whole revolution of the engine being complete in a single turn of the crankshaft, rather than two....?
Click to expand...

twostroke are so easy to work on a lot less parts than a fourstroke so if you have any experience with fourstroke you will soon pick it up

i cut my teeth in the 70`s tuning twostroke engines, i love them
 
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