Engine power level and piston construction

Fahlin Racing

Fahlin Racing

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Seeing quite a bit of builds on the forum with mono-therms and middle of the road, others just utilizing factory pistons, brings a question or two and many thoughts. Since the heat becomes more and more through enlarging plunger bores, extending injection periods or as simple as using a fuel with higher Btu content. Thermodyanmics is not exactly easy to comprehend and judge because the materials we use and how we configure our engines through selection of parts, especially with trial and error as the teacher...

Is there a guideline as far as pistons one can buy as he/she goes up the power ladder? Edit:maybe rule of thumb?

Being that different materials, forged vs cast etc, having different densities, expansion rates and rates of heat transfer could the overall design/dimensions/shape of each piece in the path of heat dissipation have a direct effect of our heat absorption or resistance at the crown surface dictating how well we manage our heat? Just thinking out loud.
 
Would coatings be cost effective on stock pieces rather than upgrading to more exotic pistons or is there are coating that actually stays on a diesel piston in some of the more demanding applications....
 
Anodized or anodizing is one of the strongest coatings, this being applied to the domes of pistons only. No first hand experience.

-Clinton
 
Thanks for the reply 12VRoush, do you happen to know how long this stype has been around, I have heard of ceramic coatings but this is new to me. I wonder how different the coating process is compared to the anodizing of the fittings used with stainless mesh hoses. After a little search, I came across an article Engine Builder Mag had on the anodizing you mentioned. Apparently a Type 3 of hard anodizing is technically a ceramic once its reached that point. If anyone is interested, its not a huge article though. It was written in 2009, they also touch on pricing at the time of the article which didn't seem too bad.

http://www.enginebuildermag.com/Article/68203/anodized_pistons.aspx

What do you think about the whole coatings world 12V?

I personally have never used them myself, but have always read articles on them since the barrier thermally catches me eye since engine development evolves almost constantly. I don't doubt the big boys using them to gain that extra go go power on theirs at some point.
 
Mahle's competitor Federal Mogul I guess has a Monosteel to compete against them.

Aluminum trunks seem to utilize a Ni-resist (nickel-chrome) insert that is metalurgically bonded for increasing relaibility, keeping the top rign land from excessive wear during operation.

The Ni-resist insert seems to keep the bowl edge at a higher operating temperature than the CFA (Ceramic-fiber -reinforced aluminum alloy) according to Robert N. Brady's 1996 Modern Diesel publication. From a diagram in the book provided by Cummins the picture shows the Ni-resist shows a 344 degree celcius bowl/crown area temp while the top ring area insert is at 272 degrees celcius with a top skirt area of the piston the temp drops to 184 degrees celcius.

The CFA side of the picture, the bowl/crown area is at 324 degrees celcius with a top ring land temperature of 254 degrees celcius and the top of the piston skirt area drops to 179 degrees celcius.
 
Food for thought, could maintaining a certain temperature in the crown be a way to control emissions to create the closest possible adiabatic process? I believe so myself others may think otherwise, I may be far fetched in some ideas and beliefs, I guess like Lenahan said, I do too much thinking.

Could maintaining a crown temp also benefit high horsepower production too? hmmm
 
Can anyone verify the composition of a 5.9 to a 6.7 piston? I have managed to take out a few blocks with rod and crank failure but have yet to melt a stock piston.
 
Fahlin Racing said:
Food for thought, could maintaining a certain temperature in the crown be a way to control emissions to create the closest possible adiabatic process? I believe so myself others may think otherwise, I may be far fetched in some ideas and beliefs, I guess like Lenahan said, I do too much thinking.

Could maintaining a crown temp also benefit high horsepower production too? hmmm
Click to expand...

Could you elaborate on how maintaining a crown temperature, will keep heat in the cylinder and as you put it "Get closer to adiabatic conditions".
 
If we can maintain a crown temperature closer to flame temperature or higher than usual during operation itself without turning to puddles through materials, design, part selection and coatings, hoping to, slow down the transfer rate of heat to the piston and then on. We have kept somewhat more usable heat (power) active in the cylinder for whatever amount of time longer, could be a few more degrees could be one more degree. The thought is to keep our pressure building or constant turning our crankshaft efficiently, think of the heat loss during per crankshaft degree of rotation. Since our charge of air becomes less dense with each degree of temperature rise it wouldn't be too great to heat the air before the intake valve(s) open, therefore, we must try to reduce heat dissipation to keep our expanding burn cycle usuable within the combustion chamber and cylinder parameters from TDC to wherever the the pressure may become unusuable on the power stroke.

If we can try to keep a process as close to adiabatic as possible, no heat loss nor gain during energy exchange, IMO we could see a better burn cycle with less hydrocarbons and possibly slight bit of power gain while still containing the rate of heat being relased to the surroundings once the fuel has been burned more thoroughly (piston crown, top ring, cylinder wall, headgasket ring, cylinder head, valves and injector tip and if it is there the glow plug). The Monotherms remind me of the heavy truck pistons that are articulated (2 piece) where the crown is steel and is seperated from the skirt which is aluminum. They are attached together by the wrist pin. Majority of the heat is kept in the crown but is cooled by jets spraying the bottom of the piston crown or is also cooled by what is called the 'cocktail shaker' method.

I should mention the other types of manufacturing that exist, SCFR, Squeeze Cast Fiber Reinforced and Gravity Cast. We also have forgings as we all know. Any ways my thought was maintaining a crown temp to maintain a higher resistance to quick heat absorption in the crown. Static and dynamic compression pressures involved in heat transfer rates.....??? hmmmm
 
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rjp said:
Can anyone verify the composition of a 5.9 to a 6.7 piston? I have managed to take out a few blocks with rod and crank failure but have yet to melt a stock piston.
Click to expand...

See if your local dealer may have any material information in the service manual, however you may have to contact Cummins altogether for exact info.
 
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Ceramic fiber infomartion for everyone coming from Modern Diesel Technology(from 1996) book I have been reading. Pg 397 and 398.
"Ceramic fibers have a polycrystalline structure consisting of Alumina, Zirconia, Carbon, Boron nitrate, Boron carbide and Silicon carbide."

There is also a piston heat distribution picture from Detroit Diesel's 60 series typical operating temperatures. This is a steel crown remember. The crown surface temperature near the bowl edge is apparently 602 degrees F, below that coming closer to the top ring we have 594 degrees F, moving downward to the 2nd compression ring we are down to 315 degrees F, at the bottom plane where the skirt meets the crown the temp is down to 278 degrees F. As for the part that extends down in below the center of the crown to the wrist pin, the temp becomes less in what seems to be the same gradual temperature decline.

Could this be how a Monotherm distributes the combustion heat? It would be interesting to see a heat distribution picture of. I think federal Mogul has another thing called Durabowl too not sure if its part of their Monosteel.

I am still having thoughts on if a boundary layer covering the piston (air/fuel combination) even has a effect due to it being disrupted by injection of the fuel.
 
Found this little nugget on page 405 of Modern Diesel Technology. Some valve events should be adjusted as necessary to hopefully reduce the induction heating that is said to happen from the info I quoted below.

SAE paper 910460 (The Effects of Ceramic Coatings on Diesel Engine Performance and Exhaust Emissions, 1991, by Assani, Wiese, Schwarz, and Bryzik) reports a variety of tests using plasma-sprayed zirconia-coated and insulated pistons with thicknesses of 0.5 and 1.0mm (.020 and .040 in.). The thinner ceramic coating generally resulted in improved performance over a noncoated piston due to the reduced heat loss. Fuel efficiency gains with the thinner-coated test pistons produced 10% higher thermal efficiency and 9% higher BMEP and torque than an uncoated piston with the engine running at 1000rpm. The thicker 1mm (.040in.) coated piston exhibited inferior performance to the noncoated piston. In addition, the emissions characteristics of the insulated engines at full load showed a reduction in CO (carbon monoxide) levels of between 30% and 60%, unburned HC (hydrocarbons) levels that were 35% to 40% lower, and NOx (nitric oxide) concentrations that were between 10% and 30% lower due to the changed nature of the combustion in the insulated engines compared to a non-insulated model. However, volumetric efficiencies for the ceramic-coated piston engine were lower than those of a noncoated piston engine because of the hotter cylinder temperatures and residual gases that decrease the density of the inducted air.
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Aside from that, once a certain power level is desired the cast piston looks like its going to be replaced with a forged due to the grain structure of the material is a lot tighter than that of a cast piece because the heat transfer is more efficient than that of a cast piece therefore can handle more abuse, albeit, the temperatures must still be controlled.

Anyone's thoughts on cast vs forgings please do share!
 
I've done extensive in-chamber pressure monitoring on the Duramax engines. I was after what the real world pressures were on pistons in hopes of understanding why some crack. Where that lead is another story.

In the mean time, I got to understand a lot of what was going on inside the combustion chamber. Piston temps being one of the factors I observed and how they impacted the Adiabatic curve. Additionally, I was able to see the difference in the exchange rate for coated and uncoated, cast and forged and the impact of boost pressures on exchange rates.
 
Did you see any relation to piston surface area and how the 'heat-map' of the piston when you were conducting your obervesation sessions Fingers? I see that the more we add characteristics to the crown like using a mexican-top-hat design, or if we jump back to early light duty truck engines such at the N/A 7.3L with the slight "swirl dishes" in the crown as our charge comes out of the swirl chamber or just a plain flat bottom bowl, also the area our valve reliefs create.

After speaking to another person, they had mentioned or I should say maybe hinting that a forged unit won't always have a greater efficiency in heat-transfer over a cast piston, however I am thinking the materials cool down phase may influence this (internal material structure) in addition to the overall production. We should state that any sharp edge on any piston will employee a heat sink, creating hot-spots we don't desire. The heat absorption and dissipation is quick because the edge is not that dense in material so it gives the possibility for detonation or the cocktail for preignition more readily.

Its been said that we can have a high heat transfer rate with low heat and a low heat transfer rate with high heat to engine components. Now, if we don't have something cushioning our burning charge from the crown, being either microturbulence or the main mixture (hopefully) homogenizing movements we can melt otherwise produce carbon buildup. I guess you could say I have a premiss on the boundary layer for now until further. The boundary layer is spotty if our injection impinges the crown, otherwise the boundary layer, I believe, is very thin, thinner than a gasser's boundary layer can be. I am curious as to what Greg's pistons look like after a time in service, for that matter anyones once they have torn down for a refresher or rebuild.

Here is a video showing 3 pistons I found, look at the cone within the bowl area. The one bowl is a re-entrant design, he also states that forged pistons w/o the top-ring insert end up having a longevity less than that a cast top-ring insert. What are some views on that? I am suppose its mainly the factory level build verse a high power in general
1000 HP Build Mahle Motor Sports - YouTube

http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html

Thinking about the melting points of the metals, I am sure the fibers and other materials added to the pistons alter the melting temperatures of each design as well. Hmmm :pop:

I think its time for a cold one and some tunes while thinking on this.
 
Surface area is the interface between the piston and the air charge. The more area, the more thermal transfer.

Forged, in general, will suck more heat out of the chamber. This is despite the lack of oil galleries in the pistons. I think it is because the base material conducts heat better than the cast. They seem to cool off faster too, so there may be a difference in thermal mass. (don't confuse thermal mass with weight. two different things)

At power, all pistons are going to get squirted with fuel, destroying any gas boundary layer. However, there is the quench area to talk about. Here the fuel will not burn till the pistons open up the area on the way down. It is the topic of many of the papers I have read, but I am not sure I can apply what I have read to non-typical designs. Also, Fuel only burns on the outside edges of the injection plume. Where the fuel meets the air. The whole idea of a turbulent chamber is to break up the plume and mix the fuel with the air as much as possible. We could conjecture for hours on just this one topic. I have nothing conclusive to add.

Bowl design: Another black magic topic. Even in the video you posted, he mentions the trade offs between strength, power, and efficiency. Though I did enjoy the "A lot of math went into this design" statement. Been there. I know exactly what he is talking about.

The problem with the addition of the fibers is the majority of them also reduce the conduction of heat.

That brings up an interesting topic, heat soak. The chamber temperature and density are always changing, making them a nightmare to calculate. However, they are fairly easy to observe via the pressure readings. From this you can deduce, in relative terms, how much heat is available to be transferred to the piston crown. Take this quantity and subtract whatever under piston cooling you have, and you end up with an estimate of the crown temperature.

That is simplified, but you get the gist.
 
Yeah, the calculus involved is quite the deal with heat transfer analysis. As far as strength with the fibers for the crown upon applications, the fibers create a flow of heat similar to cast iron material ie would you say? being that I am interpreting that correctly.

Now by 'thermal mass', are saying the mass of heat moved itself then by conduction heat transfer process, correct?

I view the top 2 rings as a crucial paths for obtaining crown temp as well, since diesels have such a distance from the top of the crown, we have a void or dead space allowing, when any fuel makes it to this area the perfect situation to detonate if enough heat and gas pressure is applied. You know, its like why have the space if you aren't going to have any benefit from it in certain applications. The whole bowl design can be taken many ways, its not so much a black magic topic, its more of a more than one way to skin a cat for making power since you can vary the injector in more than one way.

DSpace@MIT : A study of diesel heat transfer distribution using a rapid compression machine

I am sure fuel quantity and quality will also be involved in heat transfer, but with the bare piston itself, steel or aluminum I wonder how much the effect compression (dynamic) pressures effect the transfer rate itself. I am still goint through rewording over and over to see what there is out there as far as writings on this. I know the more heat you make the more obvious your heat absorption will be, but will different static ratios produce the same heat release as the other, turbulence has a great factor as always as does the distillation point of the diesel fuel.

If nobody has a junk piston cut in half already to post a picture I think I will cut an old Cummins aluminum trunk type piston out of a dump truck that I have in half just to see the structure. I can't really remember if I have an articulated piston or not hmmm
 
Fahlin Racing said:
Yeah, the calculus involved is quite the deal with heat transfer analysis. As far as strength with the fibers for the crown upon applications, the fibers create a flow of heat similar to cast iron material ie would you say? being that I am interpreting that correctly.

But the increase in melt point is not in proportion.

Now by 'thermal mass', are saying the mass of heat moved itself then by conduction heat transfer process, correct?

Thermal mass is the amount of energy that it takes to raise the temperature of a quantity of a material some amount. Say 2 Watts/cc or whatever. It is important when talking about the transfer of energy from the air charge to the piston. If the piston temp goes up a degree, the air charge has to go down a certain amount. That is based on the ratio of the thermal masses of the two elements.

I view the top 2 rings as a crucial paths for obtaining crown temp as well, since diesels have such a distance from the top of the crown, we have a void or dead space allowing, when any fuel makes it to this area the perfect situation to detonate if enough heat and gas pressure is applied. You know, its like why have the space if you aren't going to have any benefit from it in certain applications. The whole bowl design can be taken many ways, its not so much a black magic topic, its more of a more than one way to skin a cat for making power since you can vary the injector in more than one way.

Fuel/air mix in the space just above the ring is quenched the further down towards the ring they get. The proximity of the cool piston and cylinder wall reduces the temp of the gas below the ignition point. The space is there to protect the top ring. An active burn would destroy the top ring.

The hazard of getting fuel here is more the wash down of the already sparse lubrication.

Pressurization of the area above the ring is also vital to containment of the pressures in the bowl. Think of a fire cracker in a paper cup.

DSpace@MIT : A study of diesel heat transfer distribution using a rapid compression machine

I am sure fuel quantity and quality will also be involved in heat transfer, but with the bare piston itself, steel or aluminum I wonder how much the effect compression (dynamic) pressures effect the transfer rate itself. I am still goint through rewording over and over to see what there is out there as far as writings on this. I know the more heat you make the more obvious your heat absorption will be, but will different static ratios produce the same heat release as the other, turbulence has a great factor as always as does the distillation point of the diesel fuel.

The heat transfer is almost strictly a delta T driven event. The mass of the air charge is essentially fixed. Fuel adds ~ 5% to the mass at most. Higher chamber pressures come with higher chamber temperatures and also higher heat transfer to the pistons.

If nobody has a junk piston cut in half already to post a picture I think I will cut an old Cummins aluminum trunk type piston out of a dump truck that I have in half just to see the structure. I can't really remember if I have an articulated piston or not hmmm
Click to expand...

I have a pile of cut Duramax pistons laying around here some place.
 
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