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only crankcase scavenged engines do this.



thats what i have been thinking about



really? i think this is just a limitation of the crankcase scavenged design. maybe there is simply not enough oil going to the main bearings. any more oil in the mixture and the charge will not burn efficiently enough.



lotus has their own design. the others have their own designs too. yamaha calls it e-tec. bombardier licensed it to them i think. or is it evinrude? chrysler all have their hcci engines in 2 stroke. if all of them redesigned an engine from scratch they would use a direct injected 2 stroke using hcci.

the advantage of air blast assisted fuel injection is just too much hype. e-tec uses a voice coil solenoid to inject fuel. others use a more conventional common rail.



those are mostly carbureted, crankcase scavenged, crossflow designs. good for the power range and applications they were designed for. no more no less.



not generally true. cargo vessels almost exclusively use 2 stroke diesels in the large tens and hundreds of liters displacement. this is only possible because diesels are direct injected. medium sized 4 strokes are already too complex. how much more for the really huge ones.



exactly. if it can be scale up...

Hows the vibration on this engine layout? is it a single plane crankshaft with 2 shared crank pins with 3 main bearings?

I meant that to illustrate the point that going lean is bad for reasons other than not enough oil.
Kristian

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The BIG marine slow-speed Deisels (approaching 1000mm - yes 1 Metre bore, 110 RPM max continmuous rating of about 1,000 HP per cylinder or more) are all two strokes. As I recall, they take in (super or tubocharged of course) air through cylinder ports but exhaust through a single exhaust valve in the head. Being Deisels, obviously they use direct injection.

The last one that I saw up close and personal was about ten years ago when I visited a Hapag Lloyd container ship in Halifax. A prominent feature of the engine room was a spare piston and rod, and a spare exhaust valve, each securely held in brackets. There may even have been a cylinder/head as well (these engines use integral cylinders/heads like rotary aircraft engines). The Chief engineer advised me that they could change out a piston or valve during 18 hour port calls, if necessary.

So what? Well, it does suggest that non-motorcycle two-stroke arrangements are possible. And don't forget an early two-stroke string that reminded us that the current OMC (Johnson/Evinrude) 2 stroke outboards are based upon an Australian design originally developed as a lightweight automotive engine, that arrived just in time to be scuttled by emerging emissions regulations in the US and the EU. Given the ability of these engines to meet new marine emissions standards, I wonder if the proposed automotive 2 stroke might not have been more successful had it arrived later, when emissions control was better understood, and electronic engine controls better established.

So, what about outboard motors, recalling that earlier string?

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Back about 20 yrs or so, Smokey Yunick produced a two-liter turbocharged engine that had more power and torque than it "should have" (on regular gas) and got 50 mpg (alledgedly.) The suspicion was that he converted it to a two-stroke. I wonder why we couldn't do the same; changing the cam is easy, though going to direct port injection would not be, but it's an interesting idea, basically doubling the power without having to spin it faster. Or, use a much smaller and lighter engine for the same power.

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I did forget the Johnson Outboard and yes thats from using Orbital's direct injection system (the Australian company you mention).

I talk to Ben of Orbital 2 or 3 times a week by email and he says that they are struggling with the latest emission requirement challenges with the 2 strokes and they are the world leaders so it's not promising.

Very simply, as with the Lotus concoction (not sure they have anything but 3D and theory?), you need a lot of mechanical parts to make a 2 stroke work in the real world and it ends up not much if at all cheaper than a 4 stroke with headaches in other areas (exhaust valve, direct injection and variable compression for starters).

this picture has been getting around for years now...

and suddenly you now have the major problem of all racing 4 strokes, high valve speed - you have just suggested that we double the current speed, ie; if it did 7,000rpm before the valve train now has to perform as if the engine was doing 14,000rpm.

Why go for the case where it doesn't work well - run it half as fast and have it produce the same power, and have lower rotational friction losses. Remember, we're in, "In theory..." where we're unencumbered by costs.

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excuse me? a stock 1984 rx7 injects oil into the fuel reservoir (aka float bowl) in the carb, an injected one has ports with oil injectors in them mounted in the intake tract. also happens to draw its oil supply from the engine sump but thats separate point. a yamaha 2 stroke(eg. rd250/350/400/r5/rz350/banshee) with an oil injection pump puts the oil into the intake throat, etc, etc.

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the 1984 rx7 is a rotary engine right? i guess you need the oil to lubricate the seals. a yamaha 2 stroke is most probably crankcase scavenged. the purpose of all this is to put lubricating oil where its needed because there is no other practical way to put it there.

it works fine until you start controlling emissions.

and it was emissions control that doomed the bigger automotive petrol 2 strokes.

wikipedia says likewise



thats very interesting. do they still use air blast injection? but i don't think theirs is the only viable design out there.



but still the lotus engine has advantages over a 4 stroke like packaging and emissions. in a generator that engine is perfect. hcci and all. they have a running single cylinder research engine by the way.

hcci is being marketed as the only way towards meeting all future emissions standards. both in diesel and petrol engines.

a simpler non hcci 2 stroke design has other more interesting possibilities.



wonder if the fabrication technique can be scaled down...

exactly why i think using poppet valves in a 2 stroke is not as easy as in a 4 stroke. uniflow engines have a simpler valve train but it has to run at crankshaft speed. ok up to a certain rpm limit whatever that is. but considering that you need less rpms to produce as much power,it can still be done.

i dont think i would want to clutter the cylinder head though. if there is no moving part in the head then the cylinders can be made unitary. and that opens up a lot of design possibilities.

actually i was told elsewhere that direct injection is what made "non-motorcycle two-stroke arrangements" possible and i agree. diesels are naturally in that category.



yeah, i got interested after i stumbled upon a post in another forum about a 1973 mercury inline-6 2 stroke outboard engine.

well is it that simple?

same weight same power but longer fatigue life?

There is a problem with this train of thought. While the valves would be operating 2x as much, the speed would remain the same. Instead of one operation every 4th cycle, it is now one operation every other cycle. The power would be increased due double the combustion cycles, not double the rpm.

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