experimenting with a carb..

[snowbeard]

chemist here, not a racer by any means, so if I don't know my azz from a green light, feel free to tell me ;-)

NO2 is HIGHLY flammable as a gas, it's not the cooling the air with its phase change in the carbs, that happens in the bottle, no? do NO2 bottles get frosty on the outside when used for racing? do they haave a tube down into the liquid to feel straight liquid into the engine, or do they feed from the gas in the headspace?

the hot fuel idea does sound interesting, how would an external heater of the sort suggested above sound? wrap the float bowls in something insulative, maybe even spray foam for starts? and use heat tape or wire, often used for grip heaters to heat the whole bowl?

these old GS's actually have very little juice to spare for external attachments tho. if my blinker dims the headlight, I'd say I'm using 99% of what it's making ;-)

 

[Nerobro]

chemist here, not a racer by any means, so if I don't know my azz from a green light, feel free to tell me ;-)

NO2 is HIGHLY flammable as a gas, it's not the cooling the air with its phase change in the carbs, that happens in the bottle, no? do NO2 bottles get frosty on the outside when used for racing? do they haave a tube down into the liquid to feel straight liquid into the engine, or do they feed from the gas in the headspace?

NO2 is a fairly stable gas. You can acutally use it to put fires OUT. NO2 phase changes at the injector, or at least that's the intent. A huge part of the power benifits from NO2 comes from the cooling effect.

NO2 bottles get "slightly" cooler, but they are siphon bottles so as you remove material from the bottle, liquid feeds before gas. This means the liquid in the bottle only needs to boil off enough gas to replace the volume of liquid removed.

The only time NO2 gets "funny" is when you compress it, and heat it. It needs to be at several atmospheres and over 500 degrees before it breaks down into nitrogen and oxygen.

the hot fuel idea does sound interesting, how would an external heater of the sort suggested above sound?

Racers use boxes that have alcahol and dry ice in them with a long coil of metal tube in them to chill the fuel for their engines. Cold fuel makes for a denser air charge. And therefore more power. However hot fuel does vaproize better... Expect less peak horsepower.

these old GS's actually have very little juice to spare for external attachments tho. if my blinker dims the headlight, I'd say I'm using 99% of what it's making ;-)

That's becuase you're running off the battery at that point. The GS electrical system doesn't break even untill 3000 rpm or so.

 

[snowbeard]

ok, I'll take your word for it, like I said... :-D

Thanks!!

 

[graymulligan]

Bringing nitrous into this conversation is going to start a bunch of false analogies, and probably should be avoided. We need to seperate 2 things here...the intake charge temperature, and the fuel temperature.

Colder air has more oxygen in it. Its not the temperature, its the volume of oxygen in the air. Its not about the temperature. Lets back away from the idea that heating fuel will alter the intake charge's temperature. Once the more oxygen rich air is in the combustion chamber, its not a problem if its heated. So this idea isn't going to cause issues with the intake charge. Well, it could, more on that later.

Heating the fuel, strictly from a chemical/physics thought process is a good thing. The idea of vaporizing, or nearly vaporizing the fuel charge would in theory get more energy out of the same amount of fuel. Either in the form of more Power(yay!) or better fuel efficiency(yay2!) or both(doubleyay!).

Now, the issue I see coming up is that a motorcycle is a limited amount of real estate. The "heater" may very well be heating the fuel, and also raising the temperature of the air going into the motor. Heating the intake charge and the fuel may very well cancel out the beneficial of the enar-vaporization of the gasoline.

Secondly, and probably most importantly, the heating system is going to have to be something other than electrical. If you start drawing a lot of juice out of the charging system, you're going to offset any gains you might see from heated fuel.

Oh, and a colder gasoline based fuel charge isn't necessarily a good thing. Cool air is denser and good, gas doesn't "behave" the same way.

Just my .02. I'll be watching this thread to see the results.

 

[drcoopster]

Hot fuel helps with vaporization. Large jet aircraft often use the fuel tanks as heatsinks to help cool the hydraulic fluid and the engines also run the fuel through a heat exchanger to pull some heat from hot engine oil. Granted, jet fuel (akin to diesel or kerosene) is a little different, but the basic principle is the same.

-Ian

 

[Macmatic]

Instead of trying to heat gas what about going with another fuel all together? One thats already in gas form.

I'm thinking of vehicles I've seen converted to propane or natural gas... don't know the specifics of it or if an air cooled engine would take to it well but if you could store enough energy in a small enough space and make the engine run on it...seems like it might be easier.

I'd rather have a modded gas tank with a couple of propane cylinders inside between my legs than some electric fuel heaters under my crotch...


Just an idea,
/\/\ac

 

[Energizer Bunny]

Well, I am going to weigh in on this carefully. First, it is a real bad idea to be playing with heating a volatile fuel like gasoline in or on a vehicle. I think given your well educated background that a properly designed experiment is in order.

It seems to me that this needs to be modeled using thermodynamics. In the distant past I suffered through a course related to this and I believe that the answer lies in each step of the power production process thoroughly modeled and understood.

I would think that using fuel injection to experiment would be more sensible. A carb has too complex a flow pattern to properly see the effect of heating. Fuel injection however can be insolated from the engine and temperatures of the fuel entering the injector modified through heating as it enters the fuel rail.

You could hook the engine to a dynamometer and ratch up and down the fuel temperature. Heating a fuel rail seems to be an infinity simpler task and likely much safer.

Since the air charge meets the fuel just before induction behind the intake valve, the time to affect the temperature of the air is limited. (this assumes you don't attempt direct injection.........also that it isn't a throttle body like on my Beemer)

It is good to see some technical discourse like this. I wish a had a full fledged machine shop to support this research. I currently am most interested in alternate methods of valve control.........

 

[Guest]

Wow! Lots of neat ideas flowing.

All of the cars that I owned that had carburetors had a steel tube, insulated by woven asbestos, that lead from an exhaust manifold to the intake manifold near the base of the carburetor. The tube carried exhaust gas to pre-heat gasoline in the float bowls. There might have been a spring - thermostat in the system, too. As the spring warmed, it would shut a flapper and stop the flow of exhaust gas, roughly at the same rate as the choke would go off.

With a cold engine on a cold day (someplace under 0F), gas atomized poorly. To keep the air:fuel ratio close to 14:1, a choke valve closes, "choking" the air flow. Engine speed is raised because choking reduces air flow enough that the venturi becomes ineffective. Exhaust gas is carried in a steel tube from the exhaust manifold to either the carb or the intake manifold. Heat from the exhaust gas goes to gas in the float bowl. As the fuel warms, it evaporates better, and the choke is gradually taken off. As this happens, the entire engine in warming up, which heats the intake manifold and carb by conduction, so exhaust gas flow to the intake manifold can be reduced.

Getting all of these actions to coordinate is a royal PITA. Automaitic chokes must come off at the right rate, and this must be coordinated with the rate at which idle speed and external carb heat come down. On my first two cars, I ended up installing manual chokes instead of dealing with rusted away parts.

You might want to get a basic book on carbs to start. Petersen Publishing had lots of these in the 60s and 70s. Petersen's Basic Auto Repair Manual , ISBN #0822750112 is available used through Amazon for almost nothing. Clear diagrams with scientifically correct explanations abound.

These problems aren't new. I used to read Popular Science, Popular Mechanics and Motor Trend in the 60s and 70s, when they were writing often about improvements in carburetors. They also wrote about bogus devices to improve carb efficiency. JC Whitney's catalog had dozens of these. One that supposedly worked put a disk in the fuel-air stream that would vibrate ultrasonically, to better atomize the fuel.

I purposely wrote "atomize" instead of "evaporate". If someone knows better, please correct me, but I believe that gasoline going out the venturi mostly atomizes in air instead of evaoporates. That is, it becomes suspended in fine droplets. An atomized material can eventually evaporate, which means that individual molecules exist in the gaseous phase. Evaporation is ideal, and fine atomization is very good. One reason that this matters is that liquid droplets are much denser than gaseous molecules. Every time the flow of the air-fuel mixture changes speed or direction, small droplets slam into each other, or the side of the tube, and coallesce into bigger droplets, which don't burn as well.

Don't air-cooled piston airplane engines have a different source of carb hear?

I used to work a bit with heat transfer in tire curing. The differential equations involved rapidly get too hairy to solve. A physicist was working on the project. He wrote a finite element analysis program in APL, a very strange programming language. After a year of work, he still wasn't nearly close enough. I had to make actual measurements.

You stated the concepts simply. But applying them is quite complex. My suggestions:

1) Keep it simple, very simple. Actually doing everything involved could be worth a doctoral thesis in mechanical engineering.
2) Don't do anything that could ignite gasoline. You could easily kill yourself in the process.
3) Use bench tests only. This doesn't belong between your legs until you understand everything and have solved all of the problems.
4) You need something that can be used as a dynamometer to measure power output.
5) You will need to measure fuel consumption precisely.
6) For starters, fill a picnic cooler with hot water. Put a jug of gasoline in the hot water until the temperature equilibrates. Insulate the gas tank, fuel lines and carbs. Put the warmed gas into an empty fuel system. Run the machine, test it. Repeat with different fuel temps. Check spark plugs to get an idea if the jetting needs to change at different fuel temps.

Tom

 

[gssteve]

hot gas. cant keep my bic lighter going! and i live in florida. i agree cold air cold fuel. my gs runs hot enough,so it may already be doing this theary

 

[Ludeykrus]

There's plenty of good ideas flowing through here, so I will only toss in the one thing I haven't seen mentioned yet.

Read Smokey Yunich's book "The Best Damn Garage In Town". I'm pretty sure he did something like this a few decades back.

 

[drcoopster]

I purposely wrote "atomize" instead of "evaporate". If someone knows better, please correct me, but I believe that gasoline going out the venturi mostly atomizes in air instead of evaoporates. That is, it becomes suspended in fine droplets. An atomized material can eventually evaporate, which means that individual molecules exist in the gaseous phase. Evaporation is ideal, and fine atomization is very good. One reason that this matters is that liquid droplets are much denser than gaseous molecules. Every time the flow of the air-fuel mixture changes speed or direction, small droplets slam into each other, or the side of the tube, and coallesce into bigger droplets, which don't burn as well.

I believe you're mostly correct about that. Gas is supposed to atomize out of the carb jet but before it reaches the point where it's to ignite, it should be in vapor form. Atomized fuel vaporizes easily, assisted by the low static pressure inside the carb venturi.

Don't air-cooled piston airplane engines have a different source of carb hear?

Yes, air-cooled reciprocating aircraft engines basically run an air-to-air heat exchanger to heat fresh air using heat from the exhaust. This air is then piped into the carb to help remove any ice that has formed inside the carb and/or to prevent ice from forming. This is manually-controlled, though. Fuel-injected reciprocating aircraft engines do not need carb heat because there is no venturi where ice will form.

 

[ihalterman]

Cold air is more dense( higher concentration of oxygen).
Hot fuel will vaporise more with less effort.

A cold air intake allows you to add more fuel to the mix. (more oxygen + more fuel = more power)

Hot fuel would vaporise more evenly and with less work. Not all of the fuel going into an angine get vaporised so not all of it burns. (Same oxygen + same amount of fuel Vaporised more = More power)

That's my $0.02

BJ