So, Why Oval?
- Thread starter Fingers
- Start date
They "might" be less efficient. I don't know for sure either way.
The pistons have more head exposure, yes, but also have less quench area.
They might not be the best for maintaining swirl, but I would say that they promote turbulence in the chamber. Which is better?
Really people, they are no where near pigs economy wise. Head clearance, injectors, cam, and tune have way way more influence on the economy of your engine than going conventional chamber to oval.
I noticed zero mileage difference on my stock motor to my built motor with oval bowls. Same tune.
I thought you liked the arias pistons Jeff? They are 2618.
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Jon are you against less quench than .070 or am I misunderstanding here?
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The thing I don't understand is how the flame can get snuffed out if the components necessary for combustion are present? IE, fuel, oxygen and heat...is it that htere just isn't enough volume for the chemical and physical reaction to take place, or something like that?
To answer the last two posts at the same time:
Diesel will not burn below about 400° F. Compressing the air charge raises the air temp above that in a diesel engine, but there is a lot of that heat lost through contact with the piston, head and cylinder walls. In the quench areas, there is enough metal contact to wick away enough heat to drop the local air temp below the ignition point of the diesel. In effect, quenching the fire. It ends up being a ratio between the mass of the air and the surface area surrounding it.
This effect seems to come on strong when the air gap gets to about 0.070" or smaller.
So, what I am saying is either keep the gap in excess of 0.070" or make it as small as possible.
That is, keep your valve reliefs 0.070" or deeper and your head to piston clearances tight.
Diesel will not burn below about 400° F. Compressing the air charge raises the air temp above that in a diesel engine, but there is a lot of that heat lost through contact with the piston, head and cylinder walls. In the quench areas, there is enough metal contact to wick away enough heat to drop the local air temp below the ignition point of the diesel. In effect, quenching the fire. It ends up being a ratio between the mass of the air and the surface area surrounding it.
This effect seems to come on strong when the air gap gets to about 0.070" or smaller.
So, what I am saying is either keep the gap in excess of 0.070" or make it as small as possible.
That is, keep your valve reliefs 0.070" or deeper and your head to piston clearances tight.
Thanks again Jon for another great reply...I had no idea that the thermal exchange between the air charge and exposed metal within the cylinder, could affect the AFR temp at all, let alone enough to lower the temp below the diesel's ignition point...thats CRAZY.
Out of curiousity, What is the quench spec on a stock 04.5+LLY/LBZ and LMM?
I ask on all 3, bcuz I would guess they're probably the same...
Out of curiousity, What is the quench spec on a stock 04.5+LLY/LBZ and LMM?
I ask on all 3, bcuz I would guess they're probably the same...
There has to be a formula for this somewhere...we know that compressing air makes heat, but how much heat per bar or xyz of psi increase? Also, pressurizing the fuel creates heat too, right? Now how much does the IAT temps change from the compression stroke? If we say the ECT is a constant at 200, then isn't is safe to say that the lowest temp that could possibly be read on the cylinder and head walls is 200°F ??? So technically that tiny quench area that's cooling the quench area to 200° has the ability to cool the entirety of the compressed air/fuel ratio hundreds of degrees °F in the short amount of time that the piston travels into its quench point?
I simply find it amazing and fascinating that the air charge can be cooled so drastically and so quickly in such an environment...
I'm trying to dig into this a little further on my own and hit a huge wall of ignorance...physics...
From what Ive quickly gathered, in Thermodynamics there are different fundamental THERMODYNAMIC PROCESSES namely Isobaric, Isthermal, Isentropic, and Polytropic and Isochoirc processes. Yet the diesel engine represents an adiabatic relationship/process... And every thermal dynamic process seems to have different variables and constants and formulas, all of which far exceed my comprehension.
I just want to try to wrap my head around this
Can anyone simplify these perameters into a basic equation?
Ie...using the IAT as a constant 120°F, a compression ratio of 17.1, find the final temperature gain of the volume of compressed air, and then figure out the cm3 of the exposed cylinder wall and head, and using a constant temp of 200°FF for that surface areas temp, and figure out the potential of the thermal exchange?
Thanks to anyone that wants to TRY to make sense of that :rofl:
:hug:
I simply find it amazing and fascinating that the air charge can be cooled so drastically and so quickly in such an environment...
I'm trying to dig into this a little further on my own and hit a huge wall of ignorance...physics...
From what Ive quickly gathered, in Thermodynamics there are different fundamental THERMODYNAMIC PROCESSES namely Isobaric, Isthermal, Isentropic, and Polytropic and Isochoirc processes. Yet the diesel engine represents an adiabatic relationship/process... And every thermal dynamic process seems to have different variables and constants and formulas, all of which far exceed my comprehension.
I just want to try to wrap my head around this
Can anyone simplify these perameters into a basic equation?
Ie...using the IAT as a constant 120°F, a compression ratio of 17.1, find the final temperature gain of the volume of compressed air, and then figure out the cm3 of the exposed cylinder wall and head, and using a constant temp of 200°FF for that surface areas temp, and figure out the potential of the thermal exchange?
Thanks to anyone that wants to TRY to make sense of that :rofl:
:hug:
Last edited:
Pistons
Yep Shane I meant to say Like the 2618 and don't like the 4032. The 4032 has a higher silicon content and is harder but more brittle. In a higher hp motor I like the 2618 better.
Yep Shane I meant to say Like the 2618 and don't like the 4032. The 4032 has a higher silicon content and is harder but more brittle. In a higher hp motor I like the 2618 better.
That will work then. But a piston with no reliefs would work differently then. You would want to see one with no reliefs at .070 at the smallest? That goes against what most engine builders are doing and the factory clearance as well.
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Yes, the equations are not difficult to find temperatures at each point in the diesel cycle if you know the air temperature, pressure, static compression ratio, and energy transferred to the working fluid in the cycle.
However, to say that pressurizing the air creates heat is not technically correct. Heat is energy. The law of conservation of energy states that energy cannot be created nor destroyed. With this, energy is only transferred or converted. Yes, the temperature does rise when you compress a fluid, but that energy has to come from somewhere.
I know I did several calculations similar to this back when I was in my undergrad. I will go and see if I can dig some examples up when I have some free time.
However, to say that pressurizing the air creates heat is not technically correct. Heat is energy. The law of conservation of energy states that energy cannot be created nor destroyed. With this, energy is only transferred or converted. Yes, the temperature does rise when you compress a fluid, but that energy has to come from somewhere.
I know I did several calculations similar to this back when I was in my undergrad. I will go and see if I can dig some examples up when I have some free time.
There has to be a formula for this somewhere...we know that compressing air makes heat, but how much heat per bar or xyz of psi increase? Also, pressurizing the fuel creates heat too, right? Now how much does the IAT temps change from the compression stroke? If we say the ECT is a constant at 200, then isn't is safe to say that the lowest temp that could possibly be read on the cylinder and head walls is 200°F ??? So technically that tiny quench area that's cooling the quench area to 200° has the ability to cool the entirety of the compressed air/fuel ratio hundreds of degrees °F in the short amount of time that the piston travels into its quench point?
I simply find it amazing and fascinating that the air charge can be cooled so drastically and so quickly in such an environment...
I'm trying to dig into this a little further on my own and hit a huge wall of ignorance...physics...
From what Ive quickly gathered, in Thermodynamics there are different fundamental THERMODYNAMIC PROCESSES namely Isobaric, Isthermal, Isentropic, and Polytropic and Isochoirc processes. Yet the diesel engine represents an adiabatic relationship/process... And every thermal dynamic process seems to have different variables and constants and formulas, all of which far exceed my comprehension.
I just want to try to wrap my head around this
Can anyone simplify these perameters into a basic equation?
Ie...using the IAT as a constant 120°F, a compression ratio of 17.1, find the final temperature gain of the volume of compressed air, and then figure out the cm3 of the exposed cylinder wall and head, and using a constant temp of 200°FF for that surface areas temp, and figure out the potential of the thermal exchange?
Thanks to anyone that wants to TRY to make sense of that :rofl:
:hug:
It's roughly .020-.025" stock figured .015" out and a B grade HG with .035-.040" thickness
That would be really neat, and FWIW, appreciated...
Yeah, I started reading this, about just because the compression happens, doesn't mean the temperature necessarily changed, I think that's the adiabatic thermal dynamic property, yes?
But which property is the thermal transfer from the compressed gasses/fluid mix, to the metal...
I guess none of that is as important as finding the temperature change of the compressed AFR...bcuz, if its total temperature is only slightly above diesels ignition or flash point, then I can now easily see how quench would snuff out the flame, and how it get more profound as the quench gets tighter...as Jon had explained...
Took quite a bit of reading for me to grasp it, now it would be cool to find an answer to the pressure/temp relationship and how much it indeed changes and what the end twmp is, using an IAT of 120
Finding the bulk temp of the air charge is easy. Simply adiabatic. The heat loss through conduction to the surrounding metal however can be tricky.
A useful analogy would be to think of a red hot piece of metal with thin and thick dimensions. The thin section will cool off in air very quickly while the thick portions will remain hot longer.
The same thing happens in the chamber. The thin sections of air charge lose their heat very quickly.