Ceramic coated pistons

[mic*]

Angle ATDC varies with relationship of bore dia to stroke length yeah? 15-20deg ATDC as a generalisation. I would have thought crank up the compression increasing burn speed even more to the point where your timing is almost at TDC or at least close enough so that there is no significant flame front before TDC causing knock, and surfaces are cool so next to no chance of RSI.

I got the whole oil squirt thing from the start too. My assertion was that their existance shows how much heat is dissipated through the piston, and that coating the top will stop this and blah blah blah.

[oldcorollas]

well. i suppose you are usually limited to the fuel quality, which in turn determines the maximum dynamic compression you can run... higher gas temp or boost or static compression or lower overlap cams will all increase dynamic compression...

i don't know if it would actually increase or decrease the gas temp prior to ignition.. from my understanding, it could go either way, depending on the heat generated during compression and the heat flux from the walls...

intention to boost? of course not sure there is a huge amount to gain in an NA motor (where things seem to take care of themselves pretty well anyway)..

i suppose one way to test it would be to assemble motor, wind in timing till it pings, then coat everything, and do same.. and see which requires less timing.. that will tell you which has higher burn rate..
but changing compression ratios to determine which is best is a little expensive for my liking.... UNLESS you have a boosted motor, and then changing your dynamic compression is as easy as a bleed valve or larger pulley..

I would have thought crank up the compression increasing burn speed even more to the point where your timing is almost at TDC or at least close enough so that there is no significant flame front before TDC causing knock, and surfaces are cool so next to no chance of RSI.

yes it's a generalised number and engine dependant but.... you are assuming that knock only happens prior to TDC... doesn't it also occur after TDC (from that net available paper on detecting knock signals)

i suppose the only way to truly tell would be to assemble identical engines with and without coatings.. test.. and see what happens... but that is beyond the scope of mere mortals with bank accounts...

however.. if you do coat an engine, and then after dyno testing at same boost levels (with same turbo/SC as someone else) and you find that you need 3psi less boost and 5deg less timing to make same power.. then you have a pretty good case... but i think it will only be small gains like this... i would be more interested in longevity of things like rings.. which tend to have a habit of making a mess of things...

[oldcorollas]

edited to one post

[mic*]

Fuel quality... Ahh yes.

Its the be all and end all really isn it...

[oldcorollas]

Fuel quality... Ahh yes.

Its the be all and end all really isn it...

perhaps, but you shouls always build an engine to the rpm you want, and the fuel available... methanol would be great for a boosted engine, but not practical

vapour injected LPG however....

[mic*]

Knock after TDC

Cant say ive read that paper.

I thought the whole phenomenon was caused by the pressure spikes of separate flame fronts meeting - doppler effect - and then that is further amplified by the further increasing pressure as you approach TDC.

You could still easily experience the doppler effect of separate burns meeting ATDC but... oh ok i guess they will still have an impact on the maximum pressure point and if it occurs between TDC and ideal angle of max pressure (call it 20 deg ATDC) then power is not delivered...

Wouldn be such an engine killer tho would it? I imagine that only the instruments could pick it up coz you wouldnt really even get the noise since comp is reducing as it occurs.

Still = bad for power = bad!

[mrshin]

Stu, please don't start getting me excited again...

[oldcorollas]

Knock after TDC
Cant say ive read that paper.
I thought the whole phenomenon was caused by the pressure spikes of separate flame fronts meeting - doppler effect - and then that is further amplified by the further increasing pressure as you approach TDC.
You could still easily experience the doppler effect of separate burns meeting ATDC but... oh ok i guess they will still have an impact on the maximum pressure point and if it occurs between TDC and ideal angle of max pressure (call it 20 deg ATDC) then power is not delivered...
Wouldn be such an engine killer tho would it? I imagine that only the instruments could pick it up coz you wouldnt really even get the noise since comp is reducing as it occurs.
Still = bad for power = bad!

here's the first one i pulled up..
http://www.iop.org/EJ/article/0957-0...319/e20719.pdf
figure 5 shows the knock occurring about 15deg ATDC..

heres an SAE paper about inaudible knock detection.. also about 15-20deg ATDC
http://www.visteon.com/utils/whitepa...03_01_3149.pdf
regarding your point of detection, they say that it is sometimes good fro efficiency to have some inaudible knock...
but i think a knock sensors sensitivty is pretty terrible, and if you wanted to be really serious about it, you would start into ion-sensing.. as some companies are already doing (and also the MS guys were discussing). because a piezo knock sensor is not so good, buy the time your ECU is compensating, the damage could have already been done!!

i am not sure it is caused by flame fronts meeting.. i thought that theory had been discredited ?

[myne]

Interesting stuff.
Stu, you ever read any of the Endyn dynamics mob's gear?
They have some very interesting ideas on engines, which are not really what you'd call conventional, but what they write seems credible somehow.

For example their article on "soft head" mention engines with 19:1 static compression and 92 octane petrol. It sounds rediculous, but they do go to great detail into why it works and the applications it's been used on.
http://www.theoldone.com/articles/

I find it interesting, but I cant help wonder; If it really works like that, why dont more people do the same thing?

Also, is that a *K head you have pictured?

[oldcorollas]

yup, the old one has some interesting stuff... (i read all his stuff i could get my hands on )
remember tho, that they are using pretty wild cams in nascar, and so although the static compression is up there, dynamic compression will be lower... but the squish area idea seems pretty good... i suppose it's hard to detonate a quenched mixture...
more people don't because of cost, and lack of resources to custom make everything.
i don't understand why more people don't use twin screw superchargers instead of turbos...

hmm... this is getting OT, but people need to remember to distinguish between;
1 pre-ignition - ignition from some hot part of cylinder,
2 detonation - spontaneous ignition, like diesel concept,
3 too much timing advance - starting the burn cycle too early.

preignition is solved usually by good chamber design and no sharp edges (which are more likely to get hot, since more surface area, less cross-sectional area = heat build up... like with spark plug design)
detonation is due to temp, compression and fuel... it's the fuel breaking down too early.

too much advance is something we can control. most cars have problems with the this instead of the other 2... since if you remove timing, problem goes away.

nope, it's just from the HPC site.. probably some generic V8 head (which looks remarkably similar to a K head in terms of shape and valve proportions )

anyways, i think coating is a good idea.. most ppl don't do it for cost reasons.. i figure if you are spending X thousand dollars on motor already.. whats another $500 or so

[RWDboy]

One problem i can see with ceramic coating of piston tops is the longevity of the coating in a highly tuned motor. If there is any pinging/knocking (high pressure waves, built from resonance or otherwise) then the coating could get very easily eroded by the 'impulse' flow of extremely hot air at the surface.