I have a back ground in thermodynamics and fluid dynamics. I've been deeply involved in some modern high common rail pressure diesel combustion systems (and also petrol engines too- but that's another story)
I couldn't resist checking what our 2 stroke chambers were like and how they compare to modern engines. I did a lot of reading - SAE papers- and there are a lot of old publications from Detroit on our 2 strokes (I also find I have really gotten my arms around the oil situation and talked to former Detroit employees- but that's one for another time).
I'm attaching some pictures.
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi273.photobucket.com%2Falbums%2Fjj229%2FMarquisRex%2FDetroit%25202%2520stroke%2520chamber_zpszn1fgm4g.jpg&hash=a9f9a743e05062cf9ca19a73d99013515ac615ea) (http://s273.photobucket.com/user/MarquisRex/media/Detroit%202%20stroke%20chamber_zpszn1fgm4g.jpg.html)
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi273.photobucket.com%2Falbums%2Fjj229%2FMarquisRex%2FUntitled_zpsazchkpix.jpg&hash=a79920e55fbdb5c7363996ac26ab76859d4752f8) (http://s273.photobucket.com/user/MarquisRex/media/Untitled_zpsazchkpix.jpg.html)
The second lot of pictures are from modern day HD diesels.
The DD15 is basically a Mercedes Actros engine that's been adapted for the USA, the CUmmins ISX replaced the trusty N14 and the Volvo D13 was engineered in Sweden.
The red outline in the diagram shows the out line of the piston bowl. You'll notice the bowls are deep and carefully shaped. The ISX bowl is quite a bit more intricately shaped than the DD15- much like the MAN engines (not shown) and Hino engines (not shown). This type of design is called a 2 step re-entrant bowl with a pip (the pip is a protrusion in the centre). The bowls of late have become more shallow (not as shallow as our 2 strokes) to enable good mixing. On a diesel engine with diffusion flame combustion (that's the engineering term for diesel combustion)- mixing is very important- much more so than a petrol engine. As EGR has gotten more in use- this has displaced oxygen and the need for better mixing has increased. This is why bowls in the late 2000s onwards have gotten shallower. The common rail injection pressures are high too- about 1800-2300 bar these days.
By comparison our 2 stroke detroits are in the 200 bar region. Mixing wasn't so important then. Swirl is important to help with mixing- and our detroits have swirl from the port windows in the liner- a little anyway. The modern engines shown also have swirl induced from the inlet ports.
The fuel injection angle is the next thing that struck me- the modern benchmarks are around the 130-150 deg mark- the 8v92 is around the 165 deg mark. I'm not sure what the 8v71 is- but it SEEMS like its even steeper- may be the 170-180 mark- but hard to tell.
I would love to do my own combustion chamber design for our Detroit 2 strokes- with a higher injection pressure and a deeper re-entrant bowl.
But that's just the inner geek in me. I saw a benefit of about 12% brake thermal efficiency on a poorly combusted opposed piston 2 stroke diesel versus a well optimised one- but you wouldn't necessarily see this benefit on on-road mpg.
I talked to my friend who has helped me on many projects to optimise and develop combustion chambers for many applications and he echoed that in the real world- where you're not trying to meet Tier 2 Bin 5 emissions regs- there is no real benefit in doing do. Unless the reward is just an end in itself.
Anyway, I probably lost a load of you- but if you are interested I posted that up.
I believe Jack Bevins tried the different angle and pressures on his 8V96 (not a typo) engines.
Don Farichild a friend of mine worked on the emissions for years and got the 2 strokes approved for Tier 1 he finally threw the towel in working on a rail system and shut Clean Cam Technologies down a few years ago. Good luck
I find this very interesting. It would be great if someone could find the right combination to make a 2 cycle fuel efficient and emissions compliant. Detroit tried, but gave up. It probably will take a lot of research (and money) to work out a solution, if there is one. Some great discoveries occur by chance, but as Louis Pasteur said, "Chance favors only the prepared mind."
As long as you stay away from advanced calculus, I would be interested. :)
Have you looked into 'combustion enhancers' such as adding a small amount of propane or water/meth to mix to improve the burn? I know newer diesel with fuel injection pressures in the tens of thousands of PSI have better combustion, and our older engines basically are pissing the fuel in comparison. I know in the gasoline world, even upgrading injectors on a car from the 80s/90s with modern design injectors can improve power/economy without any other changes.
One of the drawbacks for many in this group is the exorbitant cost of a factory rebuild, let alone custom work for a moderate improvement in economy or power. However, that doesn't keep us from being interested, in the event that we can score a cheap take-out to tinker with.
cheers
Ken
Quote from: DoubleEagle on April 12, 2017, 07:07:05 PM
I find this very interesting. It would be great if someone could find the right combination to make a 2 cycle fuel efficient and emissions compliant. Detroit tried, but gave up. It probably will take a lot of research (and money) to work out a solution, if there is one. Some great discoveries occur by chance, but as Louis Pasteur said, "Chance favors only the prepared mind."
I think it wouldn't be that difficult to be honest.
I have access to the software required and I have optimised an opposed piston two stroke diesel engine such that it met Tier 2 Bin 5 and a 4 stoke MAN/Naavistar engine also.
The bowl design could be very similar to the benchmark bowls I showed above or others I have. I would use those as starting points. Just need some optimisation and fine tuning. Let me explain why...
When the ports are closed- and the exhaust valves are closed and the engine is compressing- it is- for all intents and purposes - just like a 4 stroke engine. Unlike an opposed piston engine- the geometry is similar- with a piston below and a flat head above. The only major difference is that it has more exhaust gas residual left 'hanging about' in the cylinder- due to the port timing of a 2 stroke. No big deal- this is similar to EGR of modern engines.
On the opposed piston engine (which is a very old concept) we started by adding common rail injection, first at 1600 bar, then higher etc. THEN we started on the piston and combustion system design.
The bigger problem is this- I have no doubt this engine could meet exhaust emissions- but the fuel economy could be bad due to excessive friction, or other factors.
Anyway, Investors today want a very rapid return on investment and this kind of project is unlikely to give them that. So I'm not about to start.
It's a shame in some ways.....
Quote from: luvrbus on April 12, 2017, 06:57:26 PM
I believe Jack Bevins tried the different angle and pressures on his 8V96 (not a typo) engines.
Don Farichild a friend of mine worked on the emissions for years and got the 2 strokes approved for Tier 1 he finally threw the towel in working on a rail system and shut Clean Cam Technologies down a few years ago. Good luck
I've heard of him. This is the company I once worked for when we made our 2 stroke combustion brake through.
https://www.youtube.com/user/AchatesPowerInc (https://www.youtube.com/user/AchatesPowerInc)
The problem with the Opposed piston engine is that the friction is too high. I got fed up of them continually lying and the upper leadership taking the credit for everyones work. Theres a lot of lies in that video and their major competitor has gone down (ecomotors)- who I worked with also. Lets see how long Achates last...
Anyway- I may be interested in this, but I'm too entrepenearial and realistic to really think there's a financial opportunity here.
FWIW I think a modern evolved version of the Detroit diesel style 2 stroke has much more potential than the opposed piston layout. The only advantage the OP layout has is that it imparts more heat energy to the exhaust rather than the coolant - which helps if you're turbo charging.
Excellent post and topic and keep it coming. If it is possible, by a variety of inexpensive means, to keep our old old Detroit Diesel 2 strokes on the road and operating elsewhere, by all means this is a viable world wide endeavor.
By non expensive meaning , perhaps just a piston, injector and perhaps pump modifications plus the addition of a fuel additive. Perhaps a dedicated aftermarket fuel? A new blend of whatever necessary to burn clean?
Maybe also new turbo tech? Turbo compounding? Exhaust gas filtering and exhaust gas recycling-reburning? EGR? Doable add ons? Optimized cam and injector timing? I need to learn more about all of this. Thank you.
This has probably already been done.
A few minor points-Detroit DD engines were designed along side Mercedes-Benz (parent company to Detroit and Freightliner) with Freightliner using the engines first from 2007 to 2010 when Mercedes finally decided that these engines were good enough for them also. So the DD13 became the OM471, DD15 became OM472 and DD16 became OM473.
Both the DD15 and DD16 were originally turbo compound engines. Turbo compounder is an exhaust powered turbine after the turbocharger that the exhaust will power (up to 50hp on a hill pull) back into the valve drive train at the back of the engine. This works well on hilly (west of I-25) terrain. But on the flat the turbo compounder actually robs power from the engine. Hence now the DD15 does not have the turbo compounder (DD13 never did). Only the DD16 has the turbo compounder. Another advantage to the turbo compounder is a simple turbocharger without waste gate or variable vanes can be used since the turbo compounder keeps up the flow through the turbocharger.
Funny how the engine manufacturers are experimenting with piston shapes-when Detroit engines are more fuel efficient and get the best fuel mileage of any truck or bus. Good Luck, TomC