Login    Forum    Search    FAQ

Board index » Racing Forum » Fuel Systems




Post new topic Reply to topic  [ 42 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
 Post Posted: Wed Jan 18, 2012 6:42 am 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Quote:
Unleaded street fuels are not designed to gas in the port or to gas all the fuel anywhere else for that matter. Unleaded street fuels are to feed the catalytic converter some HC's so it can generate heat and operate. Thats why their distillation temps are so high.


Can booster design and more heat ie compression play a bigger part in getting unleaded street fuels to gas better and produce a more efficient combustion? If distillation temps are higher does this then mean that a heated manifold may give a advantage with street unleaded than say an Air gap style manifold. I know of a combo that only lost 10hp when swapping back to a eddie performer from an Air gap RPM on small block chrysler 318 on unleaded. Could the heated manifold (performer)do a better job of gassing the fuel so only lose a little to the bigger manifold? I would have thought there would be a bigger difference than 10hp with the swap.

Hysteric


Top 
 Profile  
 
 Post Posted: Wed Jan 18, 2012 7:16 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
If the engine is a low compression design then adding a heated manifold will benefit the combustion. If its high compression then it becomes more important to manage the heat input prior to the chambers input.

What you have to realize is that an engine is a machine to increase the energy level of fuel and oxygen prior to igniting the mixture. If an engine inputs zero energy to the fuel the burn will be just like tossing gasoline onto the ground and lighting it. Not very exciting is it. If you take this line of thought further you will realize that there is a finite amount of energy that can added to fuel before it detonates. Controlling the energy input to as close as possible to that point is the name of the game. We need to add energy from all the available sources in the appropriate amounts so as to not exceed the detonation point. If the compression is inadequate then we can add heat via the manifold.
The suitability of the fuel to match the energy inputs is VERY important.

The atomization size of the fuel droplets can be influenced by the booster and emulsion design. The smaller the droplets the more energy will be transferred to the fuel load of the chamber earlier along the energy path of the engine.


Top 
 Profile  
 
 Post Posted: Wed Jan 18, 2012 6:08 pm 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
So let me know if im off on this then Shrinker..............Could i hypothetically adjust the fuels ability to gasify and improve the burn by controlling and varying the manifold temp to improve vapourization as your statement below?

Quote:
Thats all fine and works a treat in a low power per cubic inch street engine that doesnt make much cylinder pressure ( read heat), use that fuel in a race engine with a high power per cubic inch and your going to reach a point somewhere where that oily goo starts to burn. If you dont complete the burn on that oily goo you will end up with radicals. They cause detonation. So if your going to use street fuel in high power engines you have to have no wet fuel trails or turbulence puddles and you have to have complete vaporization and combustion close to stoich. That is very hard to do. But if its done then you can run street fuels at very high compression pressures and power outputs.


And from the Low Comp and fuel thread:

Quote:
We made a water heated intake manifold plenum where the fuel exited side draft carbys and impacted upon the water plate,


Thanks Again

Hysteric


Top 
 Profile  
 
 Post Posted: Wed Jan 18, 2012 9:44 pm 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
Popup done.
Hysteric; Yes you can experiment around with either the fuel blend or the manifold heat or both to do whatever you want. You just have to think in the way I described as to what your trying to control and where your trying to control it. Manifold heat is not a substitute for compression when confronted with street fuels and the dangers of the goo.


Top 
 Profile  
 
 Post Posted: Thu Jan 19, 2012 12:08 am 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Quote:
Manifold heat is not a substitute for compression when confronted with street fuels and the dangers of the goo.


What would be a good starting point compression wise?

Hysteric


Top 
 Profile  
 
 Post Posted: Thu Jan 19, 2012 12:20 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
Compression is a relative question isnt it. How full is the cylinder, thats what you compress. How much exhaust residual is there supplying heat that you cant control or dont know about? How much wrecking of the atomization has been done to the fuel by the time it gets there? The thing that determines compression maximum is the amount of energy that has already been transferred to the fuel before its compressed and then also the droplet size that your compressing and how fast its gassing. vaporizing fuel removes energy from the atmosphere being compressed thus enabling more compression. I've seen street fuel lowest octane available engines with 240psi cranking pressure have no detonation issues and Ive seen engines with 165psi detonate on the highest octane available and be unfixable without a rebuild of the configuration.


Top 
 Profile  
 
 Post Posted: Thu Jan 19, 2012 1:04 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
shrinker wrote:
Manifold heat is not a substitute for compression when confronted with street fuels and the dangers of the goo.

What that means is you cant get enough manifold heat to vaporize the high temperature distillation chemicals so attempting to do that only finishes up overheating the cooler ones during the compression phase.
The ideal situation for power (not for emission control) is to use a fuel and engine that match everything up so that the fuel is in liquid form and is finely and evenly dispersed in the cylinder at the end of the induction then is nearly totally gassed during compression (but not fully gassed) by the time the ignition sequence starts. Then the ideal situation is to not disturb the growing flame kernel until its 10mm diameter then start shoving turbulence into it. Thats what timing helps control. Engines have to be visualized to do multiple things at once without compromising anything. The piston engine is a hard one to do compared to continuous combustion engines because its interrupted all the time. Jets are much better.


Top 
 Profile  
 
 Post Posted: Thu Jan 19, 2012 1:52 am 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Quote:
What that means is you cant get enough manifold heat to vaporize the high temperature distillation chemicals so attempting to do that only finishes up overheating the cooler ones during the compression phase.

Ok that makes sense, i take it your alluding to detonation with "overheating the cooler ones during the compression phase" if this happens. Is it better to vaporize the high temp distillation chemicals in the cylinder with more heat via more compression or does that create other problems?

So its safe to say that i need to design and build my engine around the fuel i choose? Since my application is street/strip its a given that im limited to 95-98 unleaded. What would you recommend as the more i read the more variables im left to ponder.........its truly fascinating getting into this technical disscussion as none of these topics are discussed in any mags or other forums.

Sorry to take this discussion so far away from its original topic.........my apologies to the earlier posters.

Regards

Hysteric


Top 
 Profile  
 
 Post Posted: Thu Jan 19, 2012 4:36 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
hysteric wrote:
Sorry to take this discussion so far away from its original topic.........my apologies to the earlier posters.

Its still on the subject of timing and jetting or fuel amounts etc.
It seems your in Australia by your octane ratings mentioned. yes ?
The engine has to be designed around the fuel. About the only option you have with the high temp stuff is to do it after ignition. Thats the only time when it gets hot enough for long enough.
It may seem that you have to know all this stuff to design a successful engine, well that is the case if you start with a blank paper but most people just do something someone else has already done. The hard part is when you try to improve things further and do it with some understanding of what your doing and how your attempting to control it.
You cant do anything about the fuel your forced to purchase by the Gov regs. But you can fiddle with the engine and get whatever improvements you want from it within the capabilities of the fuel. It depends on the whole combination as to what I may think of its potential for success.


Top 
 Profile  
 
 Post Posted: Thu Jan 19, 2012 5:21 am 
Offline

Joined: Sat Jan 07, 2012 5:22 pm
Posts: 63
Yeh im in Sydney Shrinker.

Ultimately im looking to learn as much as possible and then apply this to building more efficient engines. Im only looking to make 1.3hp per cube on 95 or 98 atm but i want to do it with factory stuff. Fuel is just 1 part of this puzzle.........how does cam timing points affect the fuels ability to fill the cylinder? Does different timing points affect the fuels ability to stay suspended in the air stream................................man where does it end

Hysteric


Top 
 Profile  
 
 Post Posted: Thu Jan 19, 2012 6:31 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
I'm in Adelaide
1.3hp per cube is easy. 1.8 is where it gets really hard and you have to be careful and know what your doing.
Cam timing doesn't affect the fuels ability to fill the cylinder it affects the air.
For whatever engine your mucking around with there will be accepted combination's that will put you into the power range your after. Once you have that then you can fiddle with stuff and learn over time. It doesn't all happen in the one thinking session.
If you do some ridiculous valve timing events then you may run into problems getting the fuel into the cylinder or you may run into problems with the fuel dropping out of suspension in the runners etc but the timings to do that are stupid. The engine would have .001hp per cube. Just build something and start fiddling. Don't worry about thinking about this stuff as a beginner, be aware of it but don't let it bother you. No one builds the ultimate engine first off. That's why we all fiddle.


Top 
 Profile  
 
 Post Posted: Sat Jan 21, 2012 11:33 pm 
Offline

Joined: Thu Jun 16, 2011 8:27 pm
Posts: 18
jmarkaudio wrote:
Two things, what I've seen with timing is that when you get to the optimum point the AFR curve will be the smoothest. <snip>


Can you clarify a bit on two points? I'm assuming by AFR curve this is AFR relative to rpm (at WOT or maybe any other fixed throttle position). And by smoothness are you referring to the overall curve or just how jumpy it looks all along?
Sorry if this is obvious to some, but I just want to be sure I understand.


Top 
 Profile  
 
 Post Posted: Sat Jan 21, 2012 11:54 pm 
Offline
User avatar

Joined: Mon Oct 29, 2007 7:07 pm
Posts: 1422
Location: Florida
What I meant was just what I said, the AFR change from to to bottom deviates the least when the timing is at the optimum point for the engine and fuel. What did we change in fuel delivery? Nothing, we changed how well the engine used the fuel going through it. What it also means is that the O2's are not just seeing the carb or injection calibration but also what the engine is doing with it. You could take an imaginary carb that metered fuel perfectly for all loads and RPM's, put it on a poorly tuned engine and the AFR would show erratic.


Top 
 Profile  
 
 Post Posted: Sun Jan 22, 2012 12:56 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
That is exactly why WB's should not be trusted. The actual Air and fuel ratio exiting the carby doesnt change when you adjust the timing does it. Its the CO that changes with timing and the WB reacts to that.


Top 
 Profile  
 
 Post Posted: Sun Jan 22, 2012 6:13 am 
Offline
User avatar

Joined: Sat Feb 07, 2009 4:12 pm
Posts: 1215
Location: Adelaide Australia
jmarkaudio wrote:
You could take an imaginary carb that metered fuel perfectly for all loads and RPM's, put it on a poorly tuned engine and the AFR would show erratic.

There is a reason for that. When the timing is on the retarded side of optimum there will be less heat so more CO is produced and LESS CO2.The HC remaining might be the same as that depends strongly on other factors as well. Were not talking about wholesale changes in timing just when its off by around maybe 2 degrees for instance. Anyway the exhaust residual of an engine is pretty unique to each engine and if you retard the timing that exhaust residual will have more CO percentage. CO is a fuel gas and it contributes to the next cycles AFR. You may think your inducting a fresh charge with a fixed AFR but you have to factor in the CO hanging around the place. If the previous burn produced less CO2 then there will be less fire extinguishing gas contamination of the incoming charge. Couple these 2 issues together and you get a hot gaseous fuel that releases very little energy (CO) that readily takes up Oxygen molecules depriving the fresh charge from achieving full conversion to expected CO2 levels SO the new fresh charge produces even more CO than the previous one. As the engine cycles downward to low efficiency via this method the CO concentration in the exhaust stream is increasing rapidly. Ive already explained many times about how CO and WB's react so you get a downward trend of AFR on your WB. Technically its true the AFR is getting richer because there is this exhaust contamination thing going on but you cant tell exactly that answer from just an AFR number, you have to use some interpretation. If you back it up with a gas bench you can tell easily that there is the wrong carbon gas species balance and you can see the relationship of HC and O2 in the whole problem. Usually there will be O2 left over because the energy will run out before final consumption. If there is too high CO production there is usually not enough energy to convert all the O2 into CO2's. the chamber has to obtain high enough energy levels to make CO2 and you can observe the HC level and O2 level and correlate them to the AFR. If the engine has to have a very rich mixture like somewhere in the low 12's to consume the O'2 then its not got enough energy and its not making optimum power and its only using the O2 by flooding the chamber with that much fuel that it cant miss using them up. The engine will have high HC and high wear. The oil in the sump will fuel up and usually the water temp will be difficult to control. A better engine can last a lot longer than most people realize and reduce racing costs and give good temp control on the street in traffic etc without using massive aluminum radiators and other tricks. Most times I find a correct combustion high power engine can use a stock radiator for the car. They will cool down to below the thermostat temp to around 150F when you flog them.
Once the cylinder has cycled downward to low efficiency it will start trying to reversion the slow burning charge hard backwards out the intake valve and that increases the energy of the incoming charge effectively improving the vaporization and even starting some low temp reactions prior to ignition and thus having a similar effect to advancing the timing. Now the cylinder starts again from a new efficient starting point ready to cycle downward again. Couple all that to the random delivery of air mass and fuel mass and its a mess.


Top 
 Profile  
 
Display posts from previous:  Sort by  
 
Post new topic Reply to topic  [ 42 posts ]  Go to page Previous  1, 2, 3  Next

Board index » Racing Forum » Fuel Systems


Who is online

Users browsing this forum: Bing [Bot] and 3 guests

 
 

 
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
cron