35 replies to this topic

[mariner]

One of my minor but stranger obsessions is the micro cars produced in Germany in the 1950's. The most succesful was the Goggomobil with a rear mounted 600 cc two stroke. One version had an electric pre selector gearbox by Getrag. I suspect you could argue this was the first " semi automatic F1 type" box ever produced as I beleive it had dog selection via solenoids.

However even more innovative in a way were the two stroke engines in the Goliath and Gutbrod microcars - the sports versions had direct fuel injection by Bosch before the Mercedes 300SL. Bosch had developed direct petrol injection for WW2 but those were 44 litre engines run mostly at high power. The Goliath DI had to inject the tiny amounts of fuel to run a 600 cc two stroke at idle.

What is sort of interesting was that Bosch were trying ( way before CO2 etc!) to get around the fuel consumption problems of a two stoke by only adding fuel after all the air/exhaust gas mixing was largely over and so eliminate the unburnt fuel out the back problems of two strokes. If they had also gone to non petroil lubrication they would probably have had a quite efficent engine back in 1953!

Given the cars weighed about 400kg 70 mpg ( imperial) was probably within reach based on the 60 mpg of a carb. fitted Goggo.

Sadly Goliath and Gutbrod folded so the 2 stroke DI approach never went further.

[unclematt]

I believe that direct injected 2-stroke engines represent the future of the IC engine, especially for public use. The power density and efficiency of the setup are just too good to ignore. I am honestly surprised there are not already many such engines available to the public, especially in diesel form as series hybrid generators...

[cheapracer]

I believe that direct injected 2-stroke engines represent the future of the IC engine, especially for public use. The power density and efficiency of the setup are just too good to ignore. I am honestly surprised there are not already many such engines available to the public, especially in diesel form as series hybrid generators...

You're getting silly Mate, you seriously can not post and think that many manufacturers haven't investigated a cheaper more powerful engine form such as 2 strokes and rotaries.

Research Honda EXP2 400cc 2 stroke motorcycle and Honda CRM 250AR.

A few years ago I went to a few Chinese car companies with a friend from Orbital (he runs the tech side of Sprintex Superchargers now) and the story from them was all the same - "get us Euro 4 (and later 5) compliance cheap diesel and we'll buy everyone you can supply", they are still waiting.

Edited by cheapracer, 25 April 2011 - 16:07.

[malbear]

You're getting silly Mate, you seriously can not post and think that many manufacturers haven't investigated a cheaper more powerful engine form such as 2 strokes and rotaries.

Research Honda EXP2 400cc 2 stroke motorcycle and Honda CRM 250AR.

A few years ago I went to a few Chinese car companies with a friend from Orbital (he runs the tech side of Sprintex Superchargers now) and the story from them was all the same - "get us Euro 4 (and later 5) compliance cheap diesel and we'll buy everyone you can supply", they are still waiting.

when I was at Ford several years ago , the engineers said that the orbital engine was rejected because the engines would not last much over 50K and it was due to the oil starvation to pass the regulations of the time. total loss system employed, they should have gone the wet sump supercharger route. There was a small valve in the bottom of the sump that would drain off excess oil duing prolonged idling to prevent a surge of oil dissapearing out the exhaust when you accellerate when the lights go green.
I have an interesting story to tell one day regarding the shenanigans that went on involving my design , but you may get a hint from this
http://forums.autosp...w...143875&st=0

[kikiturbo2]

there was also the Ficht direct fuel injection 2 stroke, invented by guys in east german trabant factory, used by OMC and later Evinrude for 2 stroke outboards... Ingeniously simple, and efffective, but I remember them having allsorts of problems in day to day use dunno what happened afterwards..

[venator]

One of my minor but stranger obsessions is the micro cars produced in Germany in the 1950's. The most succesful was the Goggomobil with a rear mounted 600 cc two stroke. One version had an electric pre selector gearbox by Getrag. I suspect you could argue this was the first " semi automatic F1 type" box ever produced as I beleive it had dog selection via solenoids.

However even more innovative in a way were the two stroke engines in the Goliath and Gutbrod microcars - the sports versions had direct fuel injection by Bosch before the Mercedes 300SL. Bosch had developed direct petrol injection for WW2 but those were 44 litre engines run mostly at high power. The Goliath DI had to inject the tiny amounts of fuel to run a 600 cc two stroke at idle.

What is sort of interesting was that Bosch were trying ( way before CO2 etc!) to get around the fuel consumption problems of a two stoke by only adding fuel after all the air/exhaust gas mixing was largely over and so eliminate the unburnt fuel out the back problems of two strokes. If they had also gone to non petroil lubrication they would probably have had a quite efficent engine back in 1953!

Given the cars weighed about 400kg 70 mpg ( imperial) was probably within reach based on the 60 mpg of a carb. fitted Goggo.

Sadly Goliath and Gutbrod folded so the 2 stroke DI approach never went further.

The Goggomobil used engines with displacements of 250, 300 or 400 cm3. Also, Goliath (part of the Borgward group of companies) folded long after abandoning two-stroke engines. Also, as DI engines, the Gutbrod and Goliath could NOT use petroil lubrication, an oil injection pump was part of the system. A very detailed description, complete with illustrations, of the Bosch DI system and its components, can be found in Ing. Trzebiatowsky's classic work "Die Kraftfahrzeuge, und ihre Instandhandlung".

Edited by venator, 26 April 2011 - 01:39.

[unclematt]

You're getting silly Mate, you seriously can not post and think that many manufacturers haven't investigated a cheaper more powerful engine form such as 2 strokes and rotaries.

Research Honda EXP2 400cc 2 stroke motorcycle and Honda CRM 250AR.

A few years ago I went to a few Chinese car companies with a friend from Orbital (he runs the tech side of Sprintex Superchargers now) and the story from them was all the same - "get us Euro 4 (and later 5) compliance cheap diesel and we'll buy everyone you can supply", they are still waiting.

I didn't mention rotaries, and in my opinion current forms of direct injection change the game when it comes to 2-strokes (which has only recently become commercially available as a viable, available fuel delivery system).

And YES, I can seriously say with complete confidence that companies often throw out superior designs to protect egos and investments. All you have to do is know the history of the commer ts4 to understand this. I am sure most stories like the ts4 never even see the light of day. Often old, entrenched executives, engineers, and CEOs simply bury things that might reveal their incompetence, or lack of vision, or the fact they are stuck in a certain era of technology and are threatened by change to what they are familiar with...

Edited by unclematt, 26 April 2011 - 05:20.

[cheapracer]

which has only recently become commercially available as a viable, available fuel delivery system

Even previously (relative) more expensive DFI system would be easily covered by the savings of no 4 stroke valve train. DFI is in no way a new thing either.

So now that many manufacturers are converting to DFI why haven't they all gone to 2 strokes?

[mariner]

The Goggomobil used engines with displacements of 250, 300 or 400 cm3. Also, Goliath (part of the Borgward group of companies) folded long after abandoning two-stroke engines. Also, as DI engines, the Gutbrod and Goliath could NOT use petroil lubrication, an oil injection pump was part of the system. A very detailed description, complete with illustrations, of the Bosch DI system and its components, can be found in Ing. Trzebiatowsky's classic work "Die Kraftfahrzeuge, und ihre Instandhandlung".

Thank you, that is so logical it should have gotten into even my thick skull!

The only description I have of the Goliath/Gutbrod system is in a fuel injection book - is there an english translation of "Die Kraftfahrzeuge, und ihre Instandhandlung"by any chance?

Being english and not able to read German (!) my sources are limited on Goliath, I have a listing of a 1957 Goliath with a 900 cc 2 cylinder engine, would that be a 4 stroke and not a 2 stroke then?

[24gerrard]

Even previously (relative) more expensive DFI system would be easily covered by the savings of no 4 stroke valve train. DFI is in no way a new thing either.

So now that many manufacturers are converting to DFI why haven't they all gone to 2 strokes?

Good question Cheapy. I have no idea, it makes lots of sense that they do go to two strokes.

http://en.wikipedia....lls-Royce_Crecy

Check out the engine spec on this baby in 1940s.

[unclematt]

Even previously (relative) more expensive DFI system would be easily covered by the savings of no 4 stroke valve train. DFI is in no way a new thing either.

So now that many manufacturers are converting to DFI why haven't they all gone to 2 strokes?

That is addressed in my comments here:

"And YES, I can seriously say with complete confidence that companies often throw out superior designs to protect egos and investments. All you have to do is know the history of the commer ts4 to understand this. I am sure most stories like the ts4 never even see the light of day. Often old, entrenched executives, engineers, and CEOs simply bury things that might reveal their incompetence, or lack of vision, or the fact they are stuck in a certain era of technology and are threatened by change to what they are familiar with..."

It also takes time to make engine changes in the automotive industry, no one has a magic wand they can wave to insantly change anything.

[cheapracer]

It also takes time to make engine changes in the automotive industry, no one has a magic wand they can wave to insantly change anything.

There are billion dollar car/engine companies around the world right now desperately developing (and falling behind) for Euro 5/6, if a "cheaper and lighter" DFI 2 stroke worked they would be onto it quicker than you could blink. And it's not just the engine - cooling system, chassis, transmission, brakes, suspension ie; the whole bloody car is cheaper and more profitable with a lighter engine.

If it worked most would already have minor base models running around.

http://www.mynrma.co...al-ecosport.htm

[venator]

Mariner, the Goliath 900 was also a two-stroke, but was equipped with a carburettor. Only the 700 had the optional DI system, if I recall correctly. By the late '50s, an 1100 4-stroke h.o. four replaced the 2-strokes. As far as I know, "Die Kraftfahrzeuge, und ihre Instandhandlung" by Ing. Trzebiatowsky was never translated into English, which is a shame, because it is also an invaluable source of information on hot-bulb engines (as exaplified by the Lanz Bulldog farm tractor), among other things.

[Wuzak]

Good question Cheapy. I have no idea, it makes lots of sense that they do go to two strokes.

http://en.wikipedia....lls-Royce_Crecy

Check out the engine spec on this baby in 1940s.

Just what I was thinking. End to end scavenging, direct fuel injection two stroke.

It is interesting that the engine evolved from a Diesel engine to a petrol "sprint" engine, which wasn't expected to have very good fuel economy. It turned out that the fuel economy was very good at full throttle, but not so good at part throttle. RR considered the Crecy to be a full throttle engine, like early gas turbines.

The Crecy was originally designed without a throttle - engine speed and power was to be controlled by the amount of fuel being injected. But RR could not get the system to work properly - a limitation of the control technology at the time?

The head of the Crecy was also shaped for a stratified charge.

The main problem with the Crecy was that it melted pistons. Piston cooling was inadequate, involving oil pumped up through the centre of the rods. A fix would have seen external oil jets as in other RR aero engines and a few of today's engine.

[Tony Matthews]

Piston cooling was inadequate, involving oil pumped up through the centre of the rods. A fix would have seen external oil jets as in other RR aero engines and a few of today's engine.

Well, cross-thread alert there, I think!

[J. Edlund]

There are billion dollar car/engine companies around the world right now desperately developing (and falling behind) for Euro 5/6, if a "cheaper and lighter" DFI 2 stroke worked they would be onto it quicker than you could blink. And it's not just the engine - cooling system, chassis, transmission, brakes, suspension ie; the whole bloody car is cheaper and more profitable with a lighter engine.

If it worked most would already have minor base models running around.

http://www.mynrma.co...al-ecosport.htm

Volvo (the truck maker) have stated that they spend something like half of their R&D budget on passing exhaust emission legislation, clearly, if there was a cheap option availible they would have taken it.

[24gerrard]

Just what I was thinking. End to end scavenging, direct fuel injection two stroke.

It is interesting that the engine evolved from a Diesel engine to a petrol "sprint" engine, which wasn't expected to have very good fuel economy. It turned out that the fuel economy was very good at full throttle, but not so good at part throttle. RR considered the Crecy to be a full throttle engine, like early gas turbines.

The Crecy was originally designed without a throttle - engine speed and power was to be controlled by the amount of fuel being injected. But RR could not get the system to work properly - a limitation of the control technology at the time?

The head of the Crecy was also shaped for a stratified charge.

The main problem with the Crecy was that it melted pistons. Piston cooling was inadequate, involving oil pumped up through the centre of the rods. A fix would have seen external oil jets as in other RR aero engines and a few of today's engine.

I think the poor efficiency (and power output) at anything other than full throttle conditions was as a result of the fixed position of the ports.
This problem carries over into opposed piston blow scavenge two strokes as featured on another thread.
It is the main thing that prevents wide spread use along with the piston rings passing over the ports causing excess oil use and wear.
I think the idea I am looking into will cure both these problems.
Of course it will need a lot of investigation (as usual) and it may throw up other problems, so to early to say much or to be too optimistic.

[unclematt]

I think the poor efficiency (and power output) at anything other than full throttle conditions was as a result of the fixed position of the ports.
This problem carries over into opposed piston blow scavenge two strokes as featured on another thread.
It is the main thing that prevents wide spread use along with the piston rings passing over the ports causing excess oil use and wear.
I think the idea I am looking into will cure both these problems.
Of course it will need a lot of investigation (as usual) and it may throw up other problems, so to early to say much or to be too optimistic.

I believe this issue is solved by the "reverse-uniflow" engine design where the exhaust ports are at bdc in the liner, and intake is in the head through poppet valves. If one utilizes an "infinitely variable" valvetrain design for the intake valves and incorporates a long stroke, this design avoids the problems you mention, and adds a great deal of variablity to what the engine can do. It could even operate at different compression ratios on the fly without introducing quench problems...

Edited by unclematt, 28 April 2011 - 13:42.

[GVera]

I'm quite ignorant on the subject, can you lubricate a two stroke without burning oil? If not, doesn't it pollute a lot?

[bigleagueslider]

I'm quite ignorant on the subject, can you lubricate a two stroke without burning oil?

Yes you can.



slider

[Wuzak]

I think the poor efficiency (and power output) at anything other than full throttle conditions was as a result of the fixed position of the ports.
This problem carries over into opposed piston blow scavenge two strokes as featured on another thread.
It is the main thing that prevents wide spread use along with the piston rings passing over the ports causing excess oil use and wear.
I think the idea I am looking into will cure both these problems.
Of course it will need a lot of investigation (as usual) and it may throw up other problems, so to early to say much or to be too optimistic.

It may have also been due to the compressor, which was single stage single speed (IIRC) and was used to scavenge the exhaust before the fuel was injected. A relatively high percentage of compressed air was pumped straight out the exhaust.

[Myrtonos]

I found this thread and, being archived couldn't reply to it, so I'll add more on this here.

 

 

What is sort of interesting was that Bosch were trying ( way before CO2 etc!) to get around the fuel consumption problems of a two stoke by only adding fuel after all the air/exhaust gas mixing was largely over and so eliminate the unburnt fuel out the back problems of two strokes.

 

Note that the world used to be full of smoke, such as from factories and carburetted two stroke exhausts barely added to it.

 

 

And YES, I can seriously say with complete confidence that companies often throw out superior designs to protect egos and investments. All you have to do is know the history of the commer ts4 to understand this. I am sure most stories like the ts4 never even see the light of day. Often old, entrenched executives, engineers, and CEOs simply bury things that might reveal their incompetence, or lack of vision, or the fact they are stuck in a certain era of technology and are threatened by change to what they are familiar with...

 

Indeed companies do throw out more technologically advanced designs, but this is not so much a conspiracy thing. Note that fuel was much cheaper at the time than it is today. As many here know, more technologically advanced designs are more expensive. At that time fuel injection was more expensive and less reliable. Electronic fuel injection did not yet exist, and mechanical fuel injection was less reliable than carburetters. So that meant that a fuel injected two stroke may have been more expensive that a carburetted four stroke with twice as many cylinders, and with little advantage other than being more compact, and possibly lighter (though added weight of mechanical fuel injection may have offset that). Higher power to weight ratio is less important in larger vehicles where expensive engines are more finacially practicle.  The engines of many such vehicles, most notably public transit and commercial vehicles are used more often.

 

 

Also, as DI engines, the Gutbrod and Goliath could NOT use petroil lubrication, an oil injection pump was part of the system. A very detailed description, complete with illustrations, of the Bosch DI system and its components, can be found in Ing. Trzebiatowsky's classic work "Die Kraftfahrzeuge, und ihre Instandhandlung".

 

I don't know how reliable oil injection was with the technology of the time, but I realise that petroil lubrication always works as long as one remembers to mix the oil when one refuels. And when carbutretted two stroke engines were more common, serivce stations had pre-mixed petroil available straight from the pump. Direct fuel injection plus oil injection instead of a carburetter and petroil lubrication had little gain worth considering at the time, requried vehicles so equipped to stop at a different pump from other cars in the same size/price range, as well as scooters, and added at least one more thing that could go wrong.

Edited by Myrtonos, 22 May 2014 - 01:06.

[gruntguru]

The Orbital Engine Company developed DI two strokes to the point where they were demonstrably superior to the automobile engines of the time but the technology was never adopted by a car maker. Outboard engine companies did embrace the tech' but they had much lower upgrade costs - their engines being already two stroke. They were also in a position of needing to switch to four stroke to meet emission regs and demand for fuel economy. The OEC DI tech' was a cheaper alternative.

[Greg Locock]

Hang on, I drove one of the fleet of 200 evaluation cars they made. 

 

Plusses

 

torquey

fuel consumption (apparently, i didn't measure it)

 

Minuses

rapid drop in torque above peak

NVH

 

NVH had two strikes- it was a 3 cylinder which is a tricky engine to mount, and I remember the intake/exhaust noise being unmarketable. neither problem is unsolvable, but there was a suspicion that very low loss intake and exhaust might have been important.

 

Cost and reliability were also rather up in the air

[Myrtonos]

The Orbital Engine Company developed DI two strokes to the point where they were demonstrably superior to the automobile engines of the time but the technology was never adopted by a car maker. Outboard engine companies did embrace the tech' but they had much lower upgrade costs - their engines being already two stroke. They were also in a position of needing to switch to four stroke to meet emission regs and demand for fuel economy. The OEC DI tech' was a cheaper alternative.

 

That was more recent than the Goliath/Gutbord two stroke, and at a time when carburetted two stroke engines had become less common, and thus petroil pumps had disappeared. The likely reason that the OEC DI was cheaper is because these companies facilities were already tooled for two stroke engines. So switching direct injected two stroke required less changes to engine design and thus less retooling.

 Among reasons why the technology was not adopted by a carmaker, it seems, is that they were tooled for four stroke engines, furthermore a four stroke engines can meet the emission regulations with indirect injection, itself cheaper and simper than direct injection. I'm not sure how direct and indirect injection compare in reliability. Also, even with direct fuel injection, some air will still leak out the exhaust, lowering volumetric efficiency. And direct injected two-stroke petrol engines often still have crankcase scavenging as it is the probably most economical scavenging system on a smaller engines with fewer cylinders, but this means they still lack dedicated lubrication, and require oil injection, and some oil will still leak out the exhaust or get burned. Is a dedicated lubrication system any more reliable than oil injection?

 So it seems that even with direct injection, two stroke petrol engines are still only used in applications where the engine is used much less often than a car engine and the high power to weight ratio is more important.

Edited by Myrtonos, 21 May 2014 - 07:02.

[chunder27]

Even in the motorcycle world the fuel injected 2 stroke never took off really.

 

HRC spent fortunes developing it for their NSR500 racer and it was a total rocketship, more powerful, far quicker in a straight line, better acceleration.

 

But the main riders didn't like the connection they felt from the throttle and it was left to others to use it. Mick Doohan was famously staid about development, would always run what he new, rarely liked trick stuff!

 

Cagiva too tried an injected bike, and perennial tester Alan Cathcart loved it, said it felt little different to the normal bike, but they ran out of money too in 94!

 

Then you had the Bimota Due500 v-twin injected road bike that was beset by issues and nearly bankrupt the company, bit fair play to little Bimota for even attempting!

 

And finally Honda again tried to get into the off road market, they made a 2 stroke Dakar bike, the EXP2 but again would have spent fortunes developing it, trying to promote 2 stroke tech in poorer countries where maybe decent fuel wasn't available and emissions could be improved, but again it flopped and was dropped.

 

2 stroke racing bikes never really got on with fuel injection, but I think nowadays they might do better, EFI was pretty new then, and direct injection even rarer in bike tech.

 

There are revivals, a lot of guys run injection on older 500cc motocross bikes, though not sure what level we are talking!

Edited by chunder27, 21 May 2014 - 10:32.

[Myrtonos]

And note that a motorcyle engine is probably used more often, on average, than an outboard boat engine, so dedicated lubrication seems to be preffered. Remember, both the two stroke and four stroke approaches need some of the engine's power to take in air, and in any two stroke engine, some of the air will be let out the exhaust, so even a direct injected two stroke is still less efficient that a four stroke with twice as many cylinders and the same displacement per cylinder.

 

EDIT: Note that most motorcycle manufacturers seem to be tooled for four stroke engines.

 

Is there anyone here working in the engine industry who deals with industry costings every workday?

Edited by Myrtonos, 22 May 2014 - 00:02.

[manolis]

Hello Myrtonos.

The two stroke engines had (and still have) a few serious problems / issues as compared with the four strokes.


As the piston reciprocates along the ported cylinder, the piston skirt thrusts heavily onto the bridges among the ports (there is where the torque is “generated”); plenty of lubricant is necessary there, a part of which enters the cylinder degrading the combustion (read at http://www.pattakon....ssionDiesel.pdf ) increasing the emissions and the operating cost.
With less lubricant, the reliability (scuffing resistance) of the engine worsens.

The OPOC engine of EcoMotors (Bill Gates etc) has still to address this issue of the two-strokes. Otherwise it will be only for specific applications (airplane / helicopters etc).

The Achates Power two stroke engine is based on the crosshead architecture; similarly the OPRE (at http://www.pattakon....attakonOPRE.htm ) and the PatOP (at http://www.pattakon....ttakonPatOP.htm ) engines are crosshead engines; the required quantity of lubricant around the ports falls substantially (it is necessary only to prevent the contact of the piston rings with the cylinder liner) and the engine has a “like four stroke” lubrication and a better – than the conventional two strokes – scuffing resistance.


The scavenging pump is another “big issue” for the two strokes.
The crankcase scavenging is cheap, but it is not working well.
The “piston type” scavenging pump is a good and low cost solution, especially when combined with a turbo-charger (twin-charge, as at http://www.pattakon....P.htm#CrossHead )


The two-strokes fit better to compression ignition than to spark ignition. The Diesel engines (compression ignition) runs efficiently (and green) at lean and very lean burn. In case of spark ignition, you need a “rich mixture” around the spark plug. You can achieve it, but not at all conditions. In comparison to the foru-stroke, the two-stroke cannot control precisely the quantity and quality of the working medium trapped into the cylinder.


True four-stroke lubrication have the PatPortLess through-scavenged two-stroke engine (at http://www.pattakon....PatPortLess.htm ) and the PatMar through-scavenged two-stroke engine (at http://www.pattakon....takonPatMar.htm ).
Their specific lube consumption can be lower than the specific lube consumption of the equivalent best four-strokes.


So, there were significant reasons for the failure of the first “direct injected” two strokes.
The "direct injected two-strokes" could not be competitive to the four strokes because the problems they were introducing were critical, while their advantages (simplicity, specific power, size etc) were not so important.

Thanks
Manolis Pattakos

Edited by manolis, 23 May 2014 - 05:42.

[Powersteer]

The problem with two strokes is that, designers have been trying to push or supercharge exhaust volume out. You know the belief, if we pull it has direction where if pushed, it could still go anywhere, look at the dynamics of a fan where some its air pushed forwards will return back to the rear vacuum section for pressure balance. Pushing to discharge will mix exhaust with intake in turbulence, unclean compression charge.

 

What maybe they should experiment is vacuum out the exhaust and get a two stroker to operate like vacuum casting where when the extraction ports shut,.momentum would build pressure to the cast, or in this case chamber, pretty much like a four stroke scavenging and when the exhaust valve closes. It does seem counter productive for vacuum volumetric efficiency but the Achilles heel of two stroke is exhaust mixing with fresh charge. This might have cleaner fresh charge and work from there.

 

Edited by Powersteer, 23 May 2014 - 13:11.

[Myrtonos]

Hello Myrtonos.

The two stroke engines had (and still have) a few serious problems / issues as compared with the four strokes.

As the piston reciprocates along the ported cylinder, the piston skirt thrusts heavily onto the bridges among the ports (there is where the torque is “generated”); plenty of lubricant is necessary there, a part of which enters the cylinder degrading the combustion (read at http://www.pattakon....ssionDiesel.pdf ) increasing the emissions and the operating cost.
With less lubricant, the reliability (scuffing resistance) of the engine worsens.

The OPOC engine of EcoMotors (Bill Gates etc) has still to address this issue of the two-strokes. Otherwise it will be only for specific applications (airplane / helicopters etc).

The Achates Power two stroke engine is based on the crosshead architecture; similarly the OPRE (at http://www.pattakon....attakonOPRE.htm ) and the PatOP (at http://www.pattakon....ttakonPatOP.htm ) engines are crosshead engines; the required quantity of lubricant around the ports falls substantially (it is necessary only to prevent the contact of the piston rings with the cylinder liner) and the engine has a “like four stroke” lubrication and a better – than the conventional two strokes – scuffing resistance.

The scavenging pump is another “big issue” for the two strokes.
The crankcase scavenging is cheap, but it is not working well.
The “piston type” scavenging pump is a good and low cost solution, especially when combined with a turbo-charger (twin-charge, as at http://www.pattakon....P.htm#CrossHead )

The two-strokes fit better to compression ignition than to spark ignition. The Diesel engines (compression ignition) runs efficiently (and green) at lean and very lean burn. In case of spark ignition, you need a “rich mixture” around the spark plug. You can achieve it, but not at all conditions. In comparison to the foru-stroke, the two-stroke cannot control precisely the quantity and quality of the working medium trapped into the cylinder.


True four-stroke lubrication have the PatPortLess through-scavenged two-stroke engine (at http://www.pattakon....PatPortLess.htm ) and the PatMar through-scavenged two-stroke engine (at http://www.pattakon....takonPatMar.htm ).
Their specific lube consumption can be lower than the specific lube consumption of the equivalent best four-strokes.


So, there were significant reasons for the failure of the first “direct injected” two strokes.
The "direct injected two-strokes" could not be competitive to the four strokes because the problems they were introducing were critical, while their advantages (simplicity, specific power, size etc) were not so important.

 

Are you describing problems that apply even to direct injected engines. The reason that crankcase scavenging doesn't work very well, it seems is because it precludes dediceted lubrication. External scavenging, which is actually more like a roots blower, as far as I know, is only found on larger engines with higher cylinder counts, since air is taken into each cylinder sequentially, the same blower can serve many cylinders.

 I knew that two-stroke fitted better to compression ingnition but I thought it was because they just took in air, as do direct injected petrol engines.

 

Are you trying to say that direct injected two-stroke engines could not be compeditive with carburetted or even indirect injected four stroke at a time when fuel injection was more expensive and less reliable.

[mariner]

It is in diferent transport environment but the GM 567, 645 and710  rail diesel engines are direct injected two strokes with a huge history of success and reliablity.

 

http://en.wikipedia.org/wiki/EMD_710

 

They use uniflow cylinder flow, poppet exhaust ports and forced induction - many of the features discussed here.

 

Interestingly Gm has manged to keep teh two stroke  legal despite toughened rail emissions rules.

Edited by mariner, 23 May 2014 - 17:00.

[manolis]

Hello.

Powersteer,
in case of direct injection Diesel, with through scavenging (uniflow) and long stroke the mixing is minimized. With a part of the fresh air escaping from the exhaust, the mixing can be less than in the 4-stroke.
In case of direct injection gasoline, things get difficult at partial loads and stoichiometric combustion.


Myrtonos,
the lubrication is a big issue in the case of the crankcase scavenging, but it is not the only one. The inevitably large “dead volume” of the crankcase scavenge pump gives an efficient scavenging in a narrow range of revs. The exhaust can help the scavenging (Kaaden effect). The torque curve gets peaky, etc
A roots blower has its own limitations, like efficiency, rev range, pressure difference, cost, need for a gearing to drive it, need for space, added noise etc.
In the GM two-strokes (Detroit Diesels) the roots blower is only for the scavenging, not for supercharging; a turbocharger was used in some of GM models. A two stroke with exhaust camshaft and exhaust poppet valves in the cylinder head, roots scavenge pump and a turbocharger is neither simpler, nor cheaper than a four stroke providing the same power. Besides, it has reliability issues (scuffing resistance), emission issues, additional cost (lubricant lost at exhaust) etc. They are still used; the mechanics use to call them “oilers”.

The giant marine low-speed two-strokes,which are the most fuel efficient engines, have their own limitations and the makers (Wartsila, Man, Mitsubishi) try to reduce their emissions, to increase their scuffing resistance, to improve their lubrication, to reduce the cost of the lubricant (read at http://www.pattakon....nal_02_2010.pdf ).
This is what the PatMar design (at http://www.pattakon....takonPatMar.htm does.

The first "direct injected two strokes" had a lot of reasons to fail.

The interesting question is:

"Are there any new designs for two-stroke engines that have the qualifications to survive in the competition with the four strokes?"

Thanks
Manolis Pattakos

[Myrtonos]

Myrtonos,
the lubrication is a big issue in the case of the crankcase scavenging, but it is not the only one. The inevitably large “dead volume” of the crankcase scavenge pump gives an efficient scavenging in a narrow range of revs. The exhaust can help the scavenging (Kaaden effect). The torque curve gets peaky, etc
A roots blower has its own limitations, like efficiency, rev range, pressure difference, cost, need for a gearing to drive it, need for space, added noise etc.
In the GM two-strokes (Detroit Diesels) the roots blower is only for the scavenging, not for supercharging; a turbocharger was used in some of GM models. A two stroke with exhaust camshaft and exhaust poppet valves in the cylinder head, roots scavenge pump and a turbocharger is neither simpler, nor cheaper than a four stroke providing the same power. Besides, it has reliability issues (scuffing resistance), emission issues, additional cost (lubricant lost at exhaust) etc. They are still used; the mechanics use to call them “oilers”.

The giant marine low-speed two-strokes,which are the most fuel efficient engines, have their own limitations and the makers (Wartsila, Man, Mitsubishi) try to reduce their emissions, to increase their scuffing resistance, to improve their lubrication, to reduce the cost of the lubricant (read at http://www.pattakon....nal_02_2010.pdf ).
This is what the PatMar design (at http://www.pattakon....takonPatMar.htm does.

The first "direct injected two strokes" had a lot of reasons to fail.

The interesting question is:

"Are there any new designs for two-stroke engines that have the qualifications to survive in the competition with the four strokes?"

 

The inefficiency of crankcase scavenging outside a narrow speed range would be less of an issue in a motorboat engine, which runs at a constant speed when a boat is propelled and also used at full power for a greater portion of the time when the engine is used. Are the Roots blowers suited any better to bigger engines with more cylinders for the reason you mentioned? I don't see why lubrication of a roots blower would be lost at exhaust, I thought that only applied to crankcase scavenging. Those two stroke diesels you mentioned would be matted to electric transmissions, not mechanical ones and so can turn at a constant speed under acceleration. A two stroke with exhaust camshaft, exhaust poppet valves and roots blowers still produces as many power pulses per revolution as a four stroke with twice as many cylinders.

 

What reasons did the first direct injected two stroke petrol engines have to fail, other than the higher cost and low reliability of mechanical fuel injection and the inability to run on petroil, often sold on the pump at service stations in places where carburetted two stroke engines were common?

[manolis]

Hello Myrtonos.

The roots compressor does not cause additional lubricant loss.
But the ports are still there, and the piston with the piston rings passes over the ports, opening and closing them; the lubricant – a thick film of lubricant is required between the piston skirt and the cylinder liner, otherwise it starts the scuffing - finds the way to the combustion chamber, worsening the combustion and the emissions.

As I wrote, the GM (Dietroit Diesel) two-strokes had this type of scavenging (roots compressor / blower). And they had only intake ports in the cylinder liner. However the specific lube consumption in practice was too high. If I remember it correctly, they were operating at 1gr/kWh specific lube consumption (like the giant marine two stokes, which, by the way, drive the propeller directly by the crankshaft: the piston stroke is selected so that, at the “best” revs of the propeller, the mean piston speed to be around 7 - 8m/sec that give the best efficiency and reliability; for instance, the Wartsila RT96C has a piston stroke of 2,500mm and runs at 100rpm, i.e. at a mean piston speed of 8.5m/sec).

For the outboard engines that operate most of the time at full load, the crankcase scavenging is a good option (yet there is the lubrication issue and the lube consumption). For applications wherein the engine needs to operate at a wide range of revs / loads, the crankcase scavenging adds more problems than it solves.

A two stroke with camshaft, exhaust valves, roots blower, turbocharger has a better power to weight ratio than the four stroke. But there are other issues like the emissions, the pollution, the lubricant consumption, the scuffing resistance (reliability) etc. It seems the problems were more that the advantages, making the GM to phased out their two strokes for trucks and busses and to turn to four-strokes.

You still ask:

“What reasons did the first direct injected two stroke petrol engines have to fail, other than the higher cost and low reliability of mechanical fuel injection and the inability to run on petroil, often sold on the pump at service stations in places where carburetted two stroke engines were common?”

As you write it, it is like today a big percentage of cars / trucks and motorcycles are powered by direct-injected two-strokes of the second or third "generation".
A lot of reasons were already mentioned, like:
Lubrication and lube consumption, scavenging efficiency, mixing with exhaust gas, partial load operation, peaky torque, emissions, reliability.

I propose to take a good look at the PatPortLess direct-injected two-stroke:



at http://www.pattakon....PatPortLess.htm (the scavenging pump is a piston type “built-in” pump efficient at a wide range of revs, the lubrication is true four stroke, the scavenging is “uniflow”, it provides some 30% additional time for the combustion of the Diesel fuel etc, etc) and to talk about this specific design (or another specific design of your choice; but not ”in general”: it is like asking what caused the "second world war").

Thanks
Manolis Pattakos

[Myrtonos]

Thankyou for your clarifications, so it seems that a thin film of oil finds its way around the rings whenever the piston passes the ports, especially with the reasons why direct injected two stroke engines failed the first time, but "lubrication and lube consumption, scavenging efficiency, mixing with exhaust gas, partial load operation, peaky torque, emissions" don't explain the then prevelance of carburetted two-stroke engines, which do no better in those repects, and worse in some.

[desmo]

Moderator's note: I've merged this with the existing topic in the read-only archive in the interests of continuity. I can do this when an existing archived thread contains a discussion that begs for further exploration without the navigational complications of referencing a closed thread.