andereck

Ya well my point is that the fuel will cool the intake charge making it more dense and allowing more of it to fit in the same space. I never said anything about excess fuel, only more power potential. I'm not going to debate it with you.

DarricksZ28

I'm with you! That's the way I've always understood it to be cooler/denser charge means more oxygen to burn in a given space then add more fuel equals more power. This excess fuel replacing air and robbing power is news to be. No sense in debating nonsense!

chuntington101

ok well i haven't exsplained it very well (i dont even thing i was getting was i was talking aobut lol) so im going to go through it agian! lol

right, liquid fuel is dence but gasious fuel (ie fuel that is above its boiling point) is not very dence! now im not sure what factor is with fuel but water steam takes up something like 4000 times the volume as water does! now thats a big diffrence.

so you are using fuel to cool the intake charge (nothing worng with that). so the temp of the air charge goes down as the fuel in injected/drawn in/how ever the fuel gets in there, and some of the fuel will boil and turn from a vapour into a gas! now as a gas lets say it takes 1000 time the volume of what it does as a liquid (and thats very conservative). this gas takes up the space of the air that could otherwise be there.

now on a maximum performance engine this is "weasted" space. sapce that air could be taking. so in a race engine where getting as much air into the engine as pos is the aim of the game (and thus the most power), this system of cooling the intake with fuel is not a great idea!

also, as steve said before, why not use a higher octane fuel to cool the intake? that way there is even greater dept resistance than with a cool intake.

make sence??? im not saying that a blow through system will not give you cold intakes, just its not the "best" way to do it! if that makes any sence.

as for the fuel efficenty thing in F1 its a very big thing! where races are won on pits you want to spend the least amount of time in there, filling up, as possable! not very apropiate to this forumbut there you go!

thanks, and hope this makes more sence this time guys, sorry!

Chris.

stevieturbo

moot point....but dence and sence, should be "dense" and sense"

Another factor is....if the air is so hot its vapoursing the fuel, doesnt matter whether its a carb or injection, you have charge cooling issues that need sorted first !!!

DarricksZ28

andereck

Liquid fuel does not burn. You need vaporization for engine to even start. You tried to make a point about fuel mileage. I promise you that if fuel is just in a liquid state in the cylinders your mileage will be for crap. Carbureted engines under max choke in the dead of winter often start with a 2:1 AFR by weight. This is because at low temperature the fuel does not readily vaporize and great quantities are required to ignite. This is why we see fuel blended for different temperatures. This is also why methanol engines are often started on gasoline and why E85 is E85 and not E95. E85 will actually contain varying ammounts of gasoline depending on the time of year. Try starting an alcohol fueled car below about 50f. The fuel just doesn't readily vaporize and therefore doesn't ignite.

I could go on, but its just not an issue with this discussion. The point is that the introduction of fuel into the airstream lowers its temperature and raises its density. This is what supercharging and intercooling is all about.

While I'm not sure why you're trying to hypothesise my findings away without data I certainly wish you wouldn't for the benifit of people that are actually interested in supercharging with carburetors.

Good day.

chuntington101

very good point steve! my english is crap. lol

as for the other guy (sorry but cant even be bothered to look for your name anymore) i was mearly disscussing the disdavantages of useing fuel as a "chargecooler". and, like steve said above, if you are relying on it that much, thats its an advantage over injection, then you need to look for a diffrent method of cooling the air from your supercharger or turbo.

and i never said liquid fuel burns.

also if carbs are sooooo great for really powerfull engines why is it most builds dont retro fit carbs and run them?? and the like of Nelson racing and W2W (to name just two) use injection on their turbo engines??? (ps drag cars dont count as the regs dont allow them to, if im not misstaken)

thanks Chris.

PS, sorry if there are any spelling mistakes!

sb427f-car

You're thinking about a diesel. Diesels consume the same amount of air no matter the amount of fuel injected, because they are throttle operated off of fuel, NOT AIR. Gas engines OTOH with a throttle body or butterfly in between the mixing bowl or manifold controls air flow.

Staged injection (or two injectors per cylinder) are nothing new. Hell, look @ a Big Stuff III ECU, it has the software and hardware to drive up to 16 injectors!!! It is actually quite a brilliant idea, and I wonder why the diesel guys haven't gone to trying this to be able to vary injector pusle widths even more (since auto ignition, spray width, ect. in an injector is even more important than with a gas motor).

As far as control and efficency, I don't think anyone can argue against EFI being more A) user friendly (once properly installed) B) critical engine feedback being acquired.

I'm not going to deny that there are some differences between carburators and EFI in the fuel vaporization and distribution, but you have to be MUCH more skilled to properly get a carb to not pool fuel in the manifold than you do with EFI. Additionally, if "The Professor" has been lobbying for EFI in NHRA Pro Stock for a few years, rest assured there are reasons for that. That means to me that the differences are negligible, and this really shouldn't even be a debate.

DarricksZ28

What I was saying by that an engine will consume the same amount no matter the given fuel quantity meaning that "gaseous fuel" as described by chuntington would not replace air volume. If a given engine moves XXlbs/min of air at a given RPM/throttle position, it's going to move that amount no matter the volume of fuel that is introduced at the given RPM level/throttle position. Whether or not that is burned efficiently is different. That's the way I've always understood it to be. Is that incorrect? But I see how my statement would seem I was thinking diesel. But that's what I was saying just in a short sentence. Sorry.

I was also under the impression that an engine won't run properly/efficiently on vaporized fuel because it would be more of an explosion than a controlled burn. I thought fuel was atomized into the incoming air charge in the form of small liquid droplets and if you don't get proper atomization then the engine will not operate properly. To me vapor means "gaseous form" and atomizing is "a mass suspension in gaseous medium". I always thought that if your fuel was vaporizing before it entered the combustion chamber there was a problem.

sb427f-car

If you flood an engine...you're introducting far too much fuel and it is not atomising, as you said suspended in a gaseous medium. Sure...it'll still burn, but eventually, it'll work just like water on a big bonfire. Fuel itself DOES NOT BURN. It needs oxygen to have that happen. In the correct conditions (granted this would be in a lab environment) I could litterally put out a fire in a trash can by dumping raw gasoline on it. WHY? If done properly, it'll sufficate the oxygen. So there for it is replacing the oxygen or air.

The two obviously have their own different densities and will take up phsyical volume. Considering the volume inside that of an intake manifold is fixed, theoretically, you could in fact replace all the air with raw fuel, not just in liquid state, but also the fuel vapors (the flooded engine situation).

That's why in order to clear that you mat the throttle and keep cranking it because evntually it'll draw enough air to get a proper A/F to ignite (as well as push some of those fuel vapors out the exhaust valve).

kmracer

iTrader: (1)

im not sure if this holds any salt, but recently, steve morris built the worlds most powerful pump gas motor at 1740hp on 93 using a blow through setup and an A2W ic.

http://www.stevemorrisracingengines....ticle-SMRE.pdf

not that im a big fan of BT setups, i really am not. im more of an efi supporter when you have the money and plan on doing street driving, especially at those power levels, but thats just my opinion.

DarricksZ28

Well we weren't talking about flooded engine. And it's obvious that the three elements (fuel, oxygen and heat) need to be present in correct quantities for combustion. My statement was made concerning a properly operating engine using the correct air to fuel ratio range for a gasoline engine. My argument isn't that. My argument is that in blow through carb setups, I don't think vaporized fuel is replacing air that the engine would otherwise use because the engine will not operate properly if fuel is being vaporized in the intake manifold as what was suggested was happening using fuel to cool the air charge. For an engine operating with a a/f mixture 10-17:1, the same amount of air will be pulled into the engine regardless of the fuel ratio. I've always understood this to be correct. Theoretically, yes you can replace the air with fuel vapor, but we don't race in theory. If fuel is being vaporized anywhere in the intake tract outside of the combustion chamber then there is a major problem that needs to be addressed, and it has nothing to do with a blow through carb setup is my point. Also air is compressible where as liquid fuel is not which is why I make my statement. The engine's vacuum(or positive pressure in this case) will draw/force the same amount of air into the cylinder no matter the fuel volume because the air is what is being compressed not the fuel. Whether this mixture will light off properly or not is the issue. If you completely fill a cylinder with fuel and no air then try to compress it then engine damage will follow. Internal combustion engines take in atmospheric air, mix it with atomized fuel, compress it, ignite it, then expell it. That drawn/forced in amount of air remains constant relative to air density and volumetric efficiency. If I'm wrong then I stand corrected, but you haven't proved this point wrong.
And yes I am very aware that twin injector setups are in use and are effective, and I never doubted that. I've just never heard of 2 stroke direct injection referred to as "motorbike style injection". Which I don't even know if that is what he was referring to as I only assumed he meant a 2 stroke engine because they light off twice as often.

But I hate theory because it doesn't win me races, and in reality blow through carb setups work for BOTH supercharged AND turbocharged applications. No ifs, ands, ors, buts about it. It works, plain and simple. And there are cars solidly in the 7s using blow through setups. Is it harder? Possibly, depends on what school of thought you were brought up on. If you're used to a carb, and hate laptops then go blow through. If you're a wired individual then EFI. Either way ET/Power goals can be met in either case. Other goals concerning driveability and economy are another concern that need to be addressed as needed.

chuntington101

thanks sb427f-car, now i think i owe you a piant

guess us brits cant put our word across very well! lol

Kmracer, he does build some MAD blow through motors!

thanks Chris.

chuntington101

DarricksZ28 you said that if you have vapourised fuel anywhere in the intake track then its a bad thing? (correct??) so, if you think that is the case, then how is a blow through setup cooling the intake charge if its not by vapourising the fuel (or some of it)??

and i dont think anyone has said that there aren't big BHP blow through setups. just saying its not the "best" (if there is such thing lol) of going about it.

as for the motor bik injection is was refering to 4storke bike engines. thye fire the injector once as per a normal injector, and then once when it would normal be closed. it the injector fires twice per the cylce instead of the usual once. does that make sense???

thanks Chris.

sb427f-car

Ok, on another level, charge cooling with fuel depends upon where introduced in the intake tract...no denying that. But I think the arguments can be made against a carb just as well as an injector.

I would think that the difference in charge cooling do to fuel evaporation, vaporization, or atomization are negligible and probably unmeasurable. When you think about introducing fuel right at the port, it cools the charge there, and along with modern chamber designs to promote proper swirl and fuel mix, you're probably getting the same effect. Additionally, injecting it closer to the ignition point, as well as LATER in the intake cycle, it would have less time to reheat due to the laten heat in the engine and manifold. This is what makes direct injection so great. You can design better swirl, get all the air in there you can, shut the valve, inject the fuel, cool off the charge a bit, prevent it from heating up too much to prevent detonation and then light it off.

I really don't see how there would possibly be ANY measureable differences between using fuel to cool the A/F mix. Prove me wrong and I'll eat crow though

As for Steve Morris, IIRC in that article...it did mention that you could make more and have a bit better driveability with EFI.

The difference is in the feed back. A monkey could tune an EFI car with a laptop and the proper reading / training with knowing how to read the data that the ECU spits out. Try teaching a monkey to read spark plugs, change metering rods and secondaries and I'll give ya my bank account balance

DarricksZ28

Vaporization doesn't occur in order for the fuel to cool the air charge. Also in order for the fuel to vaporize as it's introduced to the charge air the charge air temperature would have to apply enough heat to exceed the latent heat of vaporization for the fuel being used. Or basically boil the fuel. In or at the carburetor. That ain't ideal. In a gasoline engine. If any amount of fuel is being vaporized by the charge air then the owner/tuner/tester of any aptness is/will be correcting that situation. Once fuel is vaporized it's ready to be ignited, you don't want your fuel air mixture ready to ignite BEFORE it enters the combustion chamber BEFORE it is compressed do you? I would hope not. So therefore I remain at my last statement, that yes it is possible to vaporize fuel in the intake tract via charge air, BUT if this is occuring then the charge air temps are WAY too high period, carb, EFI, or mechanical fuel injection. That problem would need to be solved. The fuel cools the charge because of atomization not vaporization. The latent heat of vaporization is increased when liquid fuel is suspended in the charge air therefore absorbing more heat allowing for a denser charge. The more heat absorbed the cooler the temperature. Up to a certain point(power/pressure level) the fuel introduced to the charge air can no longer absorb all the heat and begins vaporizing. BIG Problem. Now it's time for an intercooler.

As far as the twice per cycle as opposed to once per cycle injector firing, it sounds like you're referring to batch fire fuel injection. And yes it makes sense.

DarricksZ28

I'd have to disagree with you on the fact that the effect wouldn't be measurable, and only because of real world results. A blow through carb setup, from the results and stories I've heard/seen, is more lenient when there isn't an intercooler present. So in order for there to be a noticeable difference there has to be a measurable gain. But neither one of us can prove that with factual data at this point.
I'd have to agree with you on the fact that it is better to inject fuel as close to ignition as possible. Because the less chance you give the fuel to precipitate out of the mixture the better.
In my opinion EFI would be the ideal fuel delivery system for a street driven medium to high HP vehicle. I've worked with both and once I grasped the EFI concept I took it ran, didn't look back and hid it far away! But to someone who doesn't want to step outside of their comfort zone(old carb guys mainly) blow through carb setups will get the job done. But I don't dispute EFI has many advantages and I prefer EFI.

chuntington101

DarricksZ28, two great post! clearly you have a VERY good understanding of whats going on!

sorry if i came across abit abrupt, i didn't intend to offend you.

and the cooling properties of the carb make sence now. i allways thought that as fuel evaporates at around 220k (-50degrees c) that there would be some evaportaion of fuel in the intake track, but i guess not! i supoose it does relly have much time to vaporate as it will very quickly be inside one of the cylinders??

thanks Chris.