New engine type

[disenfranchised]

Anyone heard of the Sthil 4-Mix engine
http://www.popsci.com/popsci/bown/20...537079,00.html

The article seems to be pretty old, but given the claimed performance increase over a 2 stroke, and cleaner emmissions you'd think it might hve made it's way to motorsport

[Wired1]

Yeah it looks pretty interesting but I gather it's not going to be as powerful as a pure two-stroke machine but is better on the emissions. I'm always interested in new engine designs and would love to build a steam bike eventually - I'm just not sure how the gas station guys would react to you pulling up with a flaming fire box on board. It would also be a challenge to build a steam powered off-road bike.
What about that multi cylinder circular thing a kiwi built a few years back, i seem to remember it didn't always run but he reckoned it was way more efficient than a standard piston engine.
And then there the wankel rotary, they have phenominal power to weight ratio, maybe you could build a smaller one for your strimmer?

[Coyote]

Where does all the fuel/oil that goes to the crank go? Does it just stagnate around it like normal oil?

I've never understood why they don't have a 2 stroke with a sump, instead of adding oil to the fuel.

[Wired1]

Good question, I'm sure it's something to do with the four strokers having valves so they have to get oil to the top of the cylinder or something.

[car]

And then there the wankel rotary, they have phenominal power to weight ratio, maybe you could build a smaller one for your strimmer?

That's already been done. They're handy in chainsaws, apparently -- great power to weight as you say, and relatively low vibration. Or so I read, somewhere, some time.

[Wired1]

Bugger, for once I'd like to have a good idea BEFORE every other bastard.

[breakaway]

Wouldn't this engine configuration mean that the fuel mixture that goes to lubricate the crank would stagnate? Isn't htat bad?

[Ixion]

Where does all the fuel/oil that goes to the crank go? Does it just stagnate around it like normal oil?

I've never understood why they don't have a 2 stroke with a sump, instead of adding oil to the fuel.

Cos the mixture in a two stroke passes through the crankcase. So (a) the crankcase has to be as small as possible (b) if you had it full of oil (b1) the petrol would dissolve in said oil and (b2) the oil would be sucked up the transfer ports (instead of fuel mixture), so you would end up trying to run on oil.

A two stroke using direct fuel injection can use a wet (or dry) sump, and some VERY promising work is being done in this area.

The mighty ringa-ding-ding will live again! We it we does

[Ixion]

Incidentally, I can't see the advantage of this "new" design. it's still an Otto cycle so I can't see where any extra power will come from. Its only advantage seems to be being able to run upside down, but any normal dry sump engine can do that. Aviation engine designers sorted that one out years ago. The hard part is the carburetion not the lubrication. And I bet it doesn't go ringa-dinga-ding.

[Coyote]

Cos the mixture in a two stroke passes through the crankcase. So (a) the crankcase has to be as small as possible (b) if you had it full of oil (b1) the petrol would dissolve in said oil and (b2) the oil would be sucked up the transfer ports (instead of fuel mixture), so you would end up trying to run on oil.

A two stroke using direct fuel injection can use a wet (or dry) sump, and some VERY promising work is being done in this area.

The mighty ringa-ding-ding will live again! We it we does

I know how the 2 stroke engine works (there are very pretty pictures on the net showing them moving), but direct fuel injection sounds like what I was hoping was possible. Cut out having the ports that feed the fuel/oil mix from the crank to above the piston. Instead just have a sump of oil for the crank and just have a standard piston like a 4 stroke but which a 2 stroke cycle. I thought some clever boffin would've already thought of this, and one of the drawbacks of a 2 stroke - burning oil - would be ridden of.

Good to hear some European dirt bike manufacturers keeping the 2 strokes alive. TM have come out with a 144cc MXer designed to keep up with the 4 strokes (because all this time 4 strokes have been better only because they've had the cc advantage) and they're pushing the idea of bringing 144's into racing.

[Coyote]

I'm pretty keen to see the pivot engine in a bike. I'm assuming this is a radically different design with no concepts from 50 years ago that were ignored

http://www.pivotalengine.com/index.html

[Mental Trousers]

I know how the 2 stroke engine works (there are very pretty pictures on the net showing them moving), but direct fuel injection sounds like what I was hoping was possible. Cut out having the ports that feed the fuel/oil mix from the crank to above the piston. Instead just have a sump of oil for the crank and just have a standard piston like a 4 stroke but which a 2 stroke cycle. I thought some clever boffin would've already thought of this, and one of the drawbacks of a 2 stroke - burning oil - would be ridden of.

In a 2 stroke the piston acts as a pump to push the air/fuel/oil mixture into the combustion chamber. If you close off the sump and fill it with oil you then have to fit a pump (supercharger or turbocharger) to the intake side. Without a positive pressure on the intake side the scavenging efficiency of a 2 stroke is woeful.

[Coyote]

In a 2 stroke the piston acts as a pump to push the air/fuel/oil mixture into the combustion chamber. If you close off the sump and fill it with oil you then have to fit a pump (supercharger or turbocharger) to the intake side. Without a positive pressure on the intake side the scavenging efficiency of a 2 stroke is woeful.

Which are some of the problems I thought someone would've overcomed by now.

Looks like I'll have to learn how to design and cast engine blocks...

[Mental Trousers]

It's a matter of economics. Adding a supercharger or turbocharger instantly adds a lot of dollars to the cost of an engine. Then there's the parts supply chain once the engine is sold etc. Technically it's piss easy. Economically, it's just too expensive.

There is an alternative though, ie the Stepped Piston Engine.

[Ixion]

Turbocharger won't work. No way to get mixture into the cylinder other than forcing it in with the turbocharger. But turbocharger doesn't provide any pressure until the engine is running. How are you going to start the engine?

Supercharger could work in theory, but you need a valve system to stop the combustion explosion flashing back through the supercharger and blowing it up (which used to be a problem even on four stroke sc engines). So far noone's come up with a practical way.