Just a few off tangent points/responses

Preignition, Knock, Detonation, etc. is when the mixture is spontaneuosly ignited (it reaches it's self ignition temperature)before the flame front reaches it. Rather than a controlled burn (at a finite rate of energy release), it's all at once. This produces a significan pressure spike, and a resulting shockwave that goes across the cylinder. The shockwave also strips the insulating boundary layer off the combustion chamber surfaces, exposing the bare aluminum to the full heat of combustion (above the melting temp of AL). Where flame front speed comes into play is that if your flame front reaches the far end of the cylinder before the mixture can self-ignite, you can't have knock. Part of the reason you might get knock while towing a trailer in your truck at 3000 rpm's WOT is that you've got plenty of time for the mixture to get preheated (radiation from the flame front as well as higher pressures - PV=NRTbefore the flame front reaches it. Higher rpm's generally have more mixture motion, and flame front speed is faster (which is why most timing tables will advance the timing with higher rpms).

Chamber energy (heat & pressure) - A rough estimate is that 1/3 of the combustion energy goes to the crank, another 1/3 goes out the exhaust, and the final third is absorbed by the cooling system. If you do a thermal barrier coating on your combustion chamber, there is less heat absorbed by the cooling system, and more stays in the cylinder (w/ higher cyl pressures, pushing the piston down harder for more crankshaft torque). If you're going for efficiency, this is one reason not to run a super cold thermostat.

I'd have to say thermal barrier coating would be first in line from a benefits/drawbacks decision, and oil spray would be later.

I'll be quiet now

Andris/SPD

 

I'm gonna have to apologize to mindgame on this matter. I was a little mislead as to your position. I was emailed privately by someone who didn't bother to divulge who they were on the board and I was under the impression it was you. Between their words in that message and me misreading a post on here my temper was inflated a bit; so no hard feelings here, I always value other's opinions. I'm gonna have to go back and edit my last few posts which I made to clear things up.

 

Z28tt,

You are correct about detonation. It is spontaneous combustion due to the fuel reaching it's self-ignition temperature or pressure. Diesel engines use pressure to combust the fuel. They operate soley on detonation.

Here's the misunderstanding. Most people think that since coatings keep the heat in the combustion chamber, they can induce detonation, because of the increased temperature (as we stated above). I think this is what Mindgame was trying to say. This would be true if that was the whole story. The problem with uncoated ALUMINUM pistons is they tend to develop "hot spots". These hot spots help to raise the temperature of the incoming air/fuel, creating detonation. Coatings eliminate this two ways. First, the coating eliminates hot spots, by "distributing" the heat more evenly across the surface. Second, coatings do not absorb the heat of combustion. So, when the heat of combustion exits the chamber through the exhaust valve, the coated parts are almost as cool as before combustion began. Uncoated parts do not do this. An uncoated piston will heat the incoming air/fuel mixture much more than a coated piston. So, the combustion walls are much cooler throughout the entire process. This eliminates hot spots, and therefore eliminates detonation.

One of Vizard's book has tons of good info on this. He has even measured the temps across the surfaces of a coated and uncoated piston.

This is the reasoning behind Smokey's desire for an adiabatic engine. To eliminate heat absorption by the combustion walls. He used actaul ceramic materials for the piston, combustion chamber, and cylinder walls. Although we all know an adiabatic engine is a dream, but it was Smokey's goal to get as close as possible, thereby increasing the engine's efficiency, using all the energy of combustion (heat) to push on the piston.

It has been proven time and time again that coatings can help eliminate detonation, and increase engine longevity. Go to www.swaintech.com and read about Mike Moran's nitrous engine. Talk about on the edge of detonation!!! Yet the coatings eliminated his problem.

As for the oil sprayers, it all depends on what your trying to do. Long distance engines, turbo engines, etc might need them. For drag racing, they are not needed. Grumpy states that EVERYTHING possible has been done to eliminate oil flow through the engine. As of his latest article (from the PS Truck days), he states that most people would be amazed at the low volume of oil needed to operate a PS Truck. Sprayers go against this, consuming HP by increasing oil flow, not to mention causing issues with oil control, and oil temp. Again, for drag racing, it's not necessary, because you are only under load for a 1/4 of a mile.

Hey LTIBrutus..... That engine wouldn't be a concept by Ernie Elliot, would it?????? Maybe called "Soft Head" technology??????

Shane

 

If you coated the pistons with out coating the heads would this cause problems? My reasoning behind this question is it seems that the irregular surface of aluminum heads, would cause hot spots to form quicker with less heat being absorbed by the pistons.

 

About the "soft-head", not sure. Man, I'm gonna hang myself if my professor hears about me spilling the name, but does he have any affiliation w/ Hendrick's Motorsports??? If not, another team using a similar concept is Roush

 

96ltz - Heat is what causes the pressure that drives the piston down. By keeping more heat in the chamber through coatings, you'll get more power & reliability. Since your pistons aren't conducting as much heat away, your chamber should be slightly hotter (not much compared to the 1xxx degrees it is, but by the amout that would have been taken by the pistons). It won't cause any hot spots. The hot spots will be hot regardless (i.e. sharp edges, etc...). The best solution would be to coat everything, but budget gets in the way for most folks

A.

 

Ok, using Bernoulli's equation I calculated the gauge pressure of the air to be ~0.3psig at 125mph. Now I'm wondering what kind of vacuum do engines make at WOT on the dyno or track(assuming an NA 400rwhp 383)? Using the two above pressures, a net pressure can be calculated, right? How is the intake designed to take advantage of this? I understand that this may be beyong the scope of a simple reply so any references would be great.