Forged Piston Problems
- Thread starter Diesel power
- Start date
Does the flame front travel to the piston faster with nitrous? If this is the case, then I can understand backing of the timing.........Right?
Here's how it works:
As the piston comes up higher and higher, the temperature of the air in the cylinder increases, but the head and walls are cooling it down, so it's not exact. Starting about when the air is ~900 F, you can begin to shoot fuel into it. If you shoot it in too fast, the fuel will actually cool the air back down too much, and bursting happens, which is "unstart", and the fuel just vaporizes into a white gas and exits the tailpipe unburned.
But if it does light, the injector continues to spray fuel in as the piston travels upwards and the pressure rises. But diesel burns slow relatively speaking, and most the fuel isn't even in the cylinder yet, so the peak pressure hasn't occurred yet. The pressure peak happens shortly after TDC (~3 deg). But the piston cannot really push very hard to rotate the crank, since the crank is nearly straight up. It's only when the piston is way past TDC that it has any "leverage" to push down with and spin the engine. So it's the pressure that is "contained" in the cylinder doing the work, the peak pressure is just a necessary evil that bends rods and cracks pistons.
When you have nitrous in the mix, it's first thing is that it makes bursting happen earlier since it cools the air down, hence the wild nitrous backfires and unstarts you see sometimes with it. The peak pressure is always going to be very close to TDC, but you should always keep after TDC if possible or you lose power. Since nitrous makes the pressure rise faster, pushing 4 degs or so is hopefully going to keep it ATDC, and reduce the odds of bursting/unstart.
IMO...
As the piston comes up higher and higher, the temperature of the air in the cylinder increases, but the head and walls are cooling it down, so it's not exact. Starting about when the air is ~900 F, you can begin to shoot fuel into it. If you shoot it in too fast, the fuel will actually cool the air back down too much, and bursting happens, which is "unstart", and the fuel just vaporizes into a white gas and exits the tailpipe unburned.
But if it does light, the injector continues to spray fuel in as the piston travels upwards and the pressure rises. But diesel burns slow relatively speaking, and most the fuel isn't even in the cylinder yet, so the peak pressure hasn't occurred yet. The pressure peak happens shortly after TDC (~3 deg). But the piston cannot really push very hard to rotate the crank, since the crank is nearly straight up. It's only when the piston is way past TDC that it has any "leverage" to push down with and spin the engine. So it's the pressure that is "contained" in the cylinder doing the work, the peak pressure is just a necessary evil that bends rods and cracks pistons.
When you have nitrous in the mix, it's first thing is that it makes bursting happen earlier since it cools the air down, hence the wild nitrous backfires and unstarts you see sometimes with it. The peak pressure is always going to be very close to TDC, but you should always keep after TDC if possible or you lose power. Since nitrous makes the pressure rise faster, pushing 4 degs or so is hopefully going to keep it ATDC, and reduce the odds of bursting/unstart.
IMO...
No, boost psi dosent tell you much, but drive psi does!
Tune from DP and you will learn alot.
Yes everything will happen faster with nitrous. like pat said nitrous will ignite the fuel faster so if you are injeting fuel sooner you are trying to "hydrolock" the piston, so by backing the timing off you somewhat delaying the ignition and allowing the charge to work in the " leverage" part of the stroke......
nos
I agree on the bursting. Why would it make the pressure rise quicker? You still need heat, pressure. I don't see what would change from 80 or 90 psi with a given amount of fuel versus 50 psi and nos. The only difference I see is you have to watch and not cool it down to much. Then you have bursting. Jeff
I agree on the bursting. Why would it make the pressure rise quicker? You still need heat, pressure. I don't see what would change from 80 or 90 psi with a given amount of fuel versus 50 psi and nos. The only difference I see is you have to watch and not cool it down to much. Then you have bursting. Jeff
Think in piston terms....
TDC is top dead center if you have an explosion before TDC you are hurting parts and wasting HP right?
now if you combust after TDC you are working WITH the rotation of the assemblie.
Combusting Before TDC would" kind of hydro lock or delay the rotaion of the assemblie
Boosted air is hot!!(150-400*) and still only 23% oxygen at best..
Nitrous is cold -120* and it is 36% oxygen all the time..
cool dence more "volitle" air WILL ignite things faster
Last edited:
nos
your still not telling me why it would burn faster with nos. I need a reason, Not because everyone thinks so. I want to learn but nobody can give me a reason why it would burn faster in a diesel. Jeff
your still not telling me why it would burn faster with nos. I need a reason, Not because everyone thinks so. I want to learn but nobody can give me a reason why it would burn faster in a diesel. Jeff
nos
So a water to air intercooler you would run lower timing? It would run alot cooler than nos in a short burst like a drag race.
So a water to air intercooler you would run lower timing? It would run alot cooler than nos in a short burst like a drag race.
The droplets take time to completely dissolve into a gas, only fuel vapor burns, liquid fuel doesn't. Nitrous+heat makes the droplets burn off their outer layer faster since there is more oxygen atoms available to "hook" onto the fuel molecules, hence raising the pressure faster.
Nitrous works as catalyst, making a reaction happen faster than it would without it.
No, water to air IC will never cool like nos will. no need to touch the timing there.
now when it's injected into the air stream or intake manifold then you have yet another thing to consider.
I'm not saying either way but high O2 will make for a faster burn. Burn a match in the air and time it. Then lite one and stick it in a jar filled with O2 and time it.
nos
I guess I will agree to disagree. diesel power my inlet temp are never that high! Your's shouldn't be. Pat I still do not see how in a boosted condition that there is a difference. Will it burn hotter? Yep! But it still doesn't change the burn rate. Jeff
I guess I will agree to disagree. diesel power my inlet temp are never that high! Your's shouldn't be. Pat I still do not see how in a boosted condition that there is a difference. Will it burn hotter? Yep! But it still doesn't change the burn rate. Jeff
Assuming that your nitrous is in check(not to much) wouldnt its cooling effect delay the peak temp time, therefore delaying ignition(fake timing retard)? Hope this makes sense!
turbo outlet temps are very high sometimes, that is where i inject my nos at, right before the IC, see there is a lot of tricks to makeing nos work for you.
the burn rate should increase because the oxygen consentration increased...more oxygen- more power!..........to a point
I would imagine they are through the roof if you are running your turbo at a 5:1 P/R
And to bring it back on topic, aluminum atoms when exposed to high oxygen levels, at high pressures and temperatures, ignites. Atmospheric oxygen is usually not enough to burn aluminum, unlike magnesium (it's chemical cousin). But add a catalyst like nitrous, and the pressure/temp required goes down.