Shock storing conrod arm mod

[cajunfj40]

Hello DieselJan,

Huh, this is interesting. I did some rough calcs using a Chevy Duramax Diesel engine at 4,000RPM (a bit higher than recommended, but it can get there) because I could find the relevant numbers. 4.06" bore by 3.9" stroke, 850 gram piston. After converting everything to SI units, I got a peak acceleration force on the piston of about 5kN when it is slowing down from max speed at half-stroke to 0 speed at BDC. With a peak combustion pressure of ~2500PSI, the force exerted on the piston is ~143kN, or about 30x that of the accelerating piston. At least that means that if you have the right spring for peak cylinder pressure it won't move much due to piston acceleration forces.

Trouble is, that high a force will require a spring that won't fit the available space. Converted back to US units, that's a bit over 16 tons of force at peak cylinder pressure. Think needing ~4 main suspension springs from a fully-loaded tractor-trailer rig (80 tons).

You could use a gas spring, but to do that you'll essentially end up with two pistons within the same cylinder, one a "free" piston in contact with the combustion gases, and the other trapping some 2500psi+ gas between it and the combustion piston, with some means to keep them from getting further apart than the height needed for proper compression ratio. Unfortunately, that doubles your piston ring friction and you have to figure out how to keep that gas pressure topped up. Packing the gas spring into the con-rod/piston package would mean higher pressures and more elaborate sealing methods, which may add less friction than a second set of piston rings, but it still is quite an addition.

I don't think you'll get sufficient efficiency gains to offset the additional parasitic loads from the added friction, rotating mass, etc. that your re-design adds. Sorry.

I know you didn't really want a different way to get the same effect - just a critique of your idea - but there are some other things out there that may interest you, so go ahead and ignore the rest of this if you want.

A simpler way of getting more leverage at peak cylinder pressure/TDC is offsetting the piston bore relative to the crankshaft, or offsetting the wrist pin in the piston. Basically, when the piston is at TDC, the crankshaft is rotated a bit beyond the point where the crank arm would be vertical. When peak cylinder pressure occurs, it will be working on a lever arm right away, rather than pushing straight down the vertical stack of piston/wrist pin/conrod/crank bearing/main bearing/main bearing cap, and trying to squeeze the oil films between those parts.

You can also play with combustion pressure profiles by changing how the mixture reacts. There's some really neat work being done out there.

You mention that you are an electronic engineer - check into "Reactivity Controlled Compression Ignition" or similar (U of Wisconsin has some good stuff here: RCCI (Reactivity Controlled Compression Ignition) Engine - Wisconsin Engine Research Consultants - Engine Research Center) where they use multiple injections of fuel of varying or modified octane/cetane rating to control the reactive species mix in the combustion chamber, with a lot of control over peak temperature, peak pressure, etc. They have achieved brake mean thermal efficiency up to 57% with cetane enhancer modified gasoline (example of their work here: High Efficiency, Low Emissions RCCI Combustion by Use of a Fuel Additive). They have an early version ("only" about 47%-52% brake mean thermal efficiency depending on fuels used) that has both port (octane-rated fuel, or "low reactivity") and direct (cetane-rated fuel, or "high reactivity") injection compression ignition in a high-compression engine. This may be in your area of expertise - figure out how to graft the port fuel injection system from a flex-fuel spark ignition engine onto a modern common-rail direct injection diesel engine, and get the two ECU's to talk to each other or be controlled by a third computer, in order to get the RCCI results. If you can come up with the way to get that sort of thing to work, you could open up some really interesting aftermarket modifications that don't require heavy engine wrenching - just appropriate junkyard scrounging and code work, plus an auxiliary fuel system.

[kach22i]

Originally Posted by Frank Lee

Seems like excess complexity to me, especially for a critical component that has many harsh demands placed upon it.

Consider how such a part would wear too.

I've read about spring-loaded detonation dampers located in the cylinder head which would be orders of magnitude simpler.

Interesting, I could not find it, but I found the below. Uses air/gas and oil for "shock abortion" (spring-like) and increasing chamber size (more power).

Detonation control device for an internal combustion engine
https://www.google.ch/patents/US5063883

The fixed geometry of combustion chamber 16 causes very rapid pressure rise from 2.5° B.T.D.C. to 5° A.T.D.C. by the squish chamber 16-A in combination with the rapid response of piston 11 and without the use of such, curve 3-A would follow curve 2 to where the first response of piston 11 takes place, then curve to the right in much the same manner as indicated by curve 6. Therefore a considerable gain is made from using the squished chamber.

The valve 30 is preset to release near the detonation limit of engine 5. When the pressure of combustion chamber 16 exceeds the predicted detonation pressure, valve 30 will bypass the oil medium 47 in part, thus allowing piston 11 to move further within cylinder 11-A. This enlarges the fixed combustion chamber until oil can be replaced to cylinder 13 by way of line 27. The time required to replace oil 47 would be determined by the pressure within line 27 and the diameter of the line 27 or an orifice leading to cylinder 13.

[cRiPpLe_rOoStEr]

Originally Posted by Frank Lee

I've read about spring-loaded detonation dampers located in the cylinder head which would be orders of magnitude simpler.

Nowadays that direct-injection is going mainstream, some mechanical provision to overcome detonation seems more likely to become redundant anyway.

[freebeard]

Four pages in two days?

To everyone else:
I am not very interested in different technology engines. Please comment on why this concept won't work or why it could and what can improve. If there is something similar or very relevant please let us know.

Here's a one word answer : Hysteresis.

I think the picture of the con rod bent in half says it all. Are we talking about an I-beam or H-beam con rod.

What is to be gained over offsetting the wrist pin in the piston??

The only thing I can see surviving in that environment would be a sintered-metal 3D printed nano-scale structured beam that is rigid in X and Y but compressible in Z (for certain values of X,Y and Z).

[DieselJan]

Hi Everyone involved
Thanks for helping me understand the limits and problems of this design, especially Cajunfj40. I never knew there was such high forces on the piston, wow. The problem was that I didn't know where to start to calculate these things, so I decided to just ask. Thanks for all the comments and suggestions.

I am into electronics and still think that the internal combustion engine's biggest gains will be mechanical or in the way the fuels is used. In my opinion electronics is there for "fine tuning" or making it possible. There is constantly gains made due to things being changed around the engine, but I still think a change in the operation of the engine will have a jump in gains.

Originally Posted by cajunfj40

I know you didn't really want a different way to get the same effect - just a critique of your idea - but there are some other things out there that may interest you, so go ahead and ignore the rest of this if you want.

Let me quickly explain the reason I said I am not interested in other technologies. I am actually open to any suggestions.
I have been reading on Ecomodder for about 4 years. Looking for modifications I can do to improve FE. It could have taken me 2 years if a lot of threads weren't "Hijacked/off topic". Take the Centurion build thread which is excellent and full of useful information, currently 63 pages. It could have been much shorter and condensed if it weren't for some people who want to add their one idea the whole time.

Just an suggestion. If you are very concerned with a certain topic, start a thread about it which can be discussed in detail. Then just comment in other people's threads with a link. This will benefit everyone reading ecomodder in future. So let's keep one topic/ one related topic per thread.

As you can see I have just hijacked my own thread.
Thanks
Jan

[cajunfj40]

Hello again DieselJan

Hi Everyone involved
Thanks for helping me understand the limits and problems of this design, especially Cajunfj40. I never knew there was such high forces on the piston, wow. The problem was that I didn't know where to start to calculate these things, so I decided to just ask. Thanks for all the comments and suggestions.

Not a problem - I like to share.

I am into electronics and still think that the internal combustion engine's biggest gains will be mechanical or in the way the fuels is used. In my opinion electronics is there for "fine tuning" or making it possible. There is constantly gains made due to things being changed around the engine, but I still think a change in the operation of the engine will have a jump in gains.

Well, writing from the perspective of a mechanical engineer that's been studying efficiency gain concepts for over 25 years as a hobby, and who also favors mechanical changes because I understand them better than the other areas, the standard reciprocating piston engine design actually doesn't have much left in it for gains, IMHO. At least, this appears to be true for the two areas you focused on - spreading out peak combustion pressure load so that more of it can get to the crank in both normal and abnormal (knock/ping) operating regimes. kach22i found that fascinating pneumatic/hydraulic controlled mechanical "detonation relief" dynamic compression release device for the abnormal conditons, but that's an extremely complex way of solving a simple problem. The thing is, those conditions are abnormal for a reason. By changing things like intake mixture tumble and swirl, squish geometry, mixture profile in the cylinder, etc. the abnormal regime can be avoided entirely - and generally there are efficiency gains in doing those things as well. For general thermal efficiency, most of the mechanical gains are in lightening the rotating assembly, reducing the overall mass for faster warmup, lower viscosity oils to reduce drag, better finishing/tolerances to reduce friction, better tuning of intake/exhaust for the dominant operating RPM's, etc.

In terms of how the fuels are used, you are back to electronics, at least if you want a responsive engine that runs well/clean at several different operating regimes. Today's fast computation and multiple sensors allow real-time control of mixture, timing, cam phasing, valve timing, dynamic compression ratio, all sorts of things to keep the combustion process operating as efficiently/cleanly as possible.

Let me quickly explain the reason I said I am not interested in other technologies. I am actually open to any suggestions.
I have been reading on Ecomodder for about 4 years. Looking for modifications I can do to improve FE. It could have taken me 2 years if a lot of threads weren't "Hijacked/off topic". Take the Centurion build thread which is excellent and full of useful information, currently 63 pages. It could have been much shorter and condensed if it weren't for some people who want to add their one idea the whole time.

In another context, I moderate a weekly in-person informal discussion group. I also, as part of my job, run a technical update meeting. It takes a lot of work to keep a discussion focused on a single topic/agenda. I think this site does rather well wrangling a disparate group of enthusiasts with widely varying interests/knowledge bases/communication skills, etc. Sure, there are lots of digressions in threads. Topic drift is basically inevitable under those conditions if you don't have someone riding herd on a given thread. That and sometimes really interesting things come out of the topic drift, sometimes spawning new threads.

It's also free, as in you are not required to pay anything to be able to contribute to/gain from the site.

Just an suggestion. If you are very concerned with a certain topic, start a thread about it which can be discussed in detail. Then just comment in other people's threads with a link. This will benefit everyone reading ecomodder in future. So let's keep one topic/ one related topic per thread.

This is a decent suggestion overall, and might be worth working into a general "rule of conduct" for a FAQ/sticky on how to comment here, preferably with some general guidelines like when to start a new thread, how to split off into a new thread and/or how to request that the mods do a move/split. Unfortunately, it comes across a bit like CATFOTFIC when phrased like this as part of a general complaint about how the site is run/presented. I see the mods already splitting threads, moving them to different areas, etc. Making them the topic police in every thread is asking a bit much, IMHO. Maybe you could start a thread in Forum News & Feedback on creating a "how to comment" sticky? Possibly I've missed an existing FAQ - there may already be a general comment guidelines sticky beyond the sub-forum guidelines.

As you can see I have just hijacked my own thread.

See? Topic drift is inevitable. Even when you have total control over your own post.

Keep thinking up ideas, read widely in the available literature, and keep contributing - I found your post interesting. Even ideas that aren't practical generate lots of related thoughts/ideas. Threads that have an unworkable idea to start with can generate lots of avenues of exploration as folks chime in with other ideas, however tangentially related.

(and yes, I did add some emoji here, even though I generally avoid the things because I am not that swift at picking up how they are supposed to be used. )

Thanks,
-cajunfj40

[freebeard]

Topic drift is your friend. 'Nuff said.

Internal combustion was 'settled science' by the end of WWII and was thoroughly regression tested on the drag strips of Southern California. You can go faster by drilling holes in the tops of the pistons. Who knew?

In my opinion electronics is there for "fine tuning" or making it possible.

That's two things, right? Electronics is the window to plasma physics.

In terms of posting; I've seen some threads managed by the OP updating the first post to TLDR the whole thread. Another thing is the wiki: Main Page - EcoModder

[craysus]

Perhaps simplify your thought a fraction..

Adjust the cylinder head combustion chamber profile based on the timing requirements..have a lower compression at TDC, and increase the compression a few degrees after TDC...this would effectively perform the same function as your sprung piston?

CSRV vs. Poppet Valve - Coates International Ltd.

Using a cammed intake system similar to above, and taking changing the profile based on simple rotation. You could imagine taking this to the next phase, and implementing a Wankel style interface as the cam, instead of the twin cams used byu coates...and therefore simplifying the movement down even further..

Alternatively, electrically controlled "valves" could be utilised on a more conventional head...and if the valves opened / shut normally, but could be extended INTO the cylinder, to increase compression at the desired part of each scycle..(Making the valves a solid tube to take up volume..maybe twisting open / closed to vary between a solid tube and a fuel delivery / exit path)

Just some random thoughts to help with overcoming the requirement for 4 x truck springs being inside a 4" cylinder bore.. (Havent invented a Tardus as yet...sorry..)...

[cajunfj40]

Internal combustion was 'settled science' by the end of WWII and was thoroughly regression tested on the drag strips of Southern California. You can go faster by drilling holes in the tops of the pistons. Who knew?

Is that the go-faster trick of drilling down behind the compression ring so combustion pressure increases the sealing force on the power stroke? Allows you to run lower ring tension for reduced friction on the rest of the strokes at the cost of a bit more oil consumption. A nice example of using gas pressure instead of mechanical spring force. Could potentially work in a "burn and coast" optimized vehicle that spends almost no time off peak bsfc.

[LittleBlackDuck]

Originally Posted by cajunfj40

Is that the go-faster trick of drilling down behind the compression ring so combustion pressure increases the sealing force on the power stroke? Allows you to run lower ring tension for reduced friction on the rest of the strokes at the cost of a bit more oil consumption. A nice example of using gas pressure instead of mechanical spring force. Could potentially work in a "burn and coast" optimized vehicle that spends almost no time off peak bsfc.

Historically, that approach does not tend to do well on the street. The small gas ports tend to clog easily, and then you end up with an oil burning bucket of crap. There is a lot of conjecture on which type of port (horizontal or vertical) is more suitable for street cars. Also, the benefits are more from better ring control than lower friction, and more so with much higher RPMs and power outputs than we are talking about here.

Simon