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Old 06-11-2010, 11:26 PM   #1
azkid110
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running on fumes? mpg mod idea

ok well, I drive a 1994 jeep cherokee 4wd, automatic, with the HO 4.0l I6, and I'm lucky to get 18 miles to the gallon. From what I understand, engines burn gasoline vapors, or an atomized fuel/air mixture, the gasoline vapors (fumes) are the most volatile, and bigger drops of gas do not burn as efficiently.

I'm thinking about making an intake/induction system, where the injectors would spray into a "mixing box" which would have a drain going back to the gas tank, a vacuum line with a needle valve to the intake manifold, a bigger hose to the throttle body, and an intake with a filter, plus flame arrestors everywhere to minimize the risk of explosion. So the gas that is evaporated, or finely atomized would get sucked into the engine, but bigger drops of gas would fall to the bottom and drain back into the tank. I think it will work, but the engine will probably run hot, because there will be no liquid gas to cool the cylinders, so maybe water/ethanol, or steam injection can fix that. shell engineers in the late 50's did something similar and made a car that got over 350 miles per gallon (article here: http://www.treehugger.com/files/2008...d_down_old.php) they heated the fuel so it evaporated into a lean vapor, plus a ton of other mods, but for 350+ mpg it doesn't look very special.

thoughts? comments? all are welcome. This is just an idea, and I think the jeep engine may be too complex for this without modifying a lot more than I would like to, If I'm going to actually build something, it will likely be on something that isn't my daily driver lol.

idea #2 was to kill 2 out of 6 cylinders to cut fuel consumption by 1/3 http://car-forums.com/talk/showpost....72&postcount=7
post #9 was a little revision on the cylinder kill idea http://car-forums.com/talk/showpost....76&postcount=9
post #10 was a bit of revision on the original vapor box idea, included thoughts of adding EGR http://car-forums.com/talk/showpost....3&postcount=10

Last edited by azkid110 : 06-22-2010 at 09:45 PM.
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Old 06-12-2010, 04:43 AM   #2
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I don't know where in the engine the fuel is injected, but if it is throttle body injected it might work. Multipoint fuel injected might be a little more difficult. I think it would be easiest on a carbed engine. Biggest problem would be to control the air:fuel ratio. Temperature changes are going to effect the rate of atomization of the fuel, so will the car stall at high RPM on a cold day? will you need to heat this "mixing box" to be able to get a usable amount of vapor in the air?

Don't forget the other modifications that where done. the deletion of the transmission, the reduction of drag, the reduction of weight, and the reduction of rolling resistance. Never mind that holding a steady 30 MPH is nowhere near typical driving conditions.
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Old 06-13-2010, 03:02 AM   #3
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I think you are right about a carb'd engine being easiest to convert, and I would expect the a/f ratio with something like this would be leaner, but I think efficiency would be better. Other people have made carburetor replacing fuel vaporizers, some work like bongs (http://www.youtube.com/watch?v=uxnmH3sEXts) others use ultrasonic pulses to break up gasoline into mist, works like a cool mist humidifier. the jeep engine is port injected, one injector per cylinder, for my idea I would probably heat the fuel on a coolant line, and set up the intake to pull air from around the exhaust manifold. Gasoline produces vapor even at low temperatures, as low as -40c, but you're right, heat does help with evaporation. the idea is to get an even burnable mixture of gasoline vapors into the engine, instead of spraying atomized gasoline directly into the engine, so it can use less fuel, at the cost of power.

I found a video about the 1959 shell car http://www.youtube.com/watch#!v=II1_...eature=related
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Old 06-13-2010, 04:42 AM   #4
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http://www.youtube.com/watch?v=Fz6XTJKagOE
As you can see, the biggest problem will still be regulating the mixture entering the cylinders. I would imagine the gas:air ratio in the "mixing box" is going to vary depending on the temperature, engine RPM, atmospheric pressure, type of/additives in the fuel (E10/E85/invigorate/nitrogen), etc. Just not sure how you are going to regulate it, unless you use some complex computer controls.
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Old 06-13-2010, 09:45 PM   #5
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yeah regulating the mix would be tricky on a hand made system, but hey, even the 2 stroke motor in that video is running on it! as long as it runs, and is enough to run the a/c and drive, plus get good gas mileage and not melt the pistons, I would be happy. this guy put something similar on his truck, it isn't put together very well, but it runs! http://www.youtube.com/watch#!v=jCs4...eature=related
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Old 06-16-2010, 10:05 PM   #6
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Driving a 1994 Jeep with a 4.0 6cylinder engine is asking for it to go through petrol quickly. Heavy, unaerodynamically efficient, an engine that is probably getting to the stage where its worn and a drivetrain which loses considerable power compared to a FWD car. You've done well to get 18mpg (USA mpg is different to rest of world as your gallon is smaller). There's a huge scope for improvement before you even start on the trick inlet system but that depends on how far you want to go.

You may want to read up on direct injection engines as Porsche has used it to great effect in their LMP2 RS Spyders where they can get same horsepower and better fuel consumption. The difference is very noticeable but requires high level of engineering.
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Old 06-18-2010, 12:11 AM   #7
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I have another idea, which may be able to cut my fuel consumption by 1/3rd, basically I would remove the rocker arms, pushrods, and lifters off of two cylinders, I would be sure these cylinders were 180 degrees from one another, so while one is at TDC the other is at BDC, then I would remove the spark plugs from the two cylinders, and connect a braided steel line from one spark plug hole to the other, and disconnect the fuel injectors for the two cylinders.

the valves would stay closed so it wouldn't disturb vacuum or exhaust, there would be no compression in them because the air would exchange between the cylinders, and I would still have 4 running cylinders totaling about 2.7l of displacement. sure I would lose power, but I don't ever really stomp on it anyway, and it would be easily reversible.

thoughts on that one?
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Old 06-18-2010, 05:42 AM   #8
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remember you have a 4-cycle engine, you would want both cylinders at TDC, which would cause your braided line idea to no longer be valid, and your power output will still be uneven. Also, it will totally screw up your computer and that might well neglect any efficiency you may have gained. Same problem with running on fumes, sure you could get it to run, but any deviation from your ideal air:fuel ratio is going to negate any gain in efficiency, and possibly destroy your engine. Also, expecting it to be able to run the AC and make it up a hill is quite a demand.
If you could make it so that the "mixing box" contained only gasoline in the gaseous state, you could use something similar to a propane carburetor to regulate the fuel ratio. The only difficulty would be that a gas is more sensitive to changes in temperature, atmospheric pressure, elevation, etc. so it may be necessary to adjust the carburetor depending on the weather for optimum efficiency.

No matter what you do, with a computer controlled engine, unless you reprogram the engine for the new system, it is bound to give you a headache. I think you would be better off trying your ideas on a scrap lawnmower first, then trying them on an old beater car with a carbed engine without computer controls.

wouldn't you be better off trading your jeep in for a little subcompact? you wouldn't want to try any of this stuff on your daily driver and get stuck stranded without a vehicle anyway, so why not get a more efficient vehicle for everyday use? not sure how far you commute or what you have to carry, but there are other options; walk, bike, moped, motorbike, carpool, mass transit, etc. other stuff to try before you go ripping your engine apart.

did you try stuff like reducing as much weight as possible, hypermiling, etc?
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Old 06-18-2010, 06:10 AM   #9
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yeah a new car would be great, I would love to get a 1996 or newer geo metro 3 cyl with manual transmission, it's my dream car.

I thought about it today, and thought instead of trying to tie the cylinders up with a braided line, maybe just get a tube that screws into the spark plug hole and goes to a small filter, and possibly remove the exhaust valve to lessen the turbulence threw the small spark plug hole.

I would love a smaller engine, I may be able to get my hands on a lawn mower engine to make an air conditioner/ generator, or maybe a leaf blower engine to set it up on a bike, that would be neat. I need to get my hands on a paycheck first though
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Old 06-22-2010, 08:35 PM   #10
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So where is vwhobo anyway? with his vast knowledge I'm sure he could add something useful to this thread.

I've been thinking about this idea, the vapor/fume intake especially, I want it to pass emissions tests, and the emission I'm worried about is NOX because it will be running a lean mixture. I was thinking of incorporating an EGR system to lower combustion temperature, and reduce NOX emission, I haven't seen a home made system with egr, but I think that if I build something I will incorporate it. I was also thinking of having the system computer controlled, because tuning air bleeds, and egr valves while driving is a little bit much for the year 2010, so I was thinking about using an O2 sensor as an input, for the computer to determine what to do, well the o2 is inevitably going to be high because of the lean mixture (not enough gas to consume all of the air) that is where egr will come in and reburn some of the exhaust, so it will dilute the intake air with enough exhaust so that the final end product has a normal or lower o2 reading, hopefully normal nox emission, low co2 and hc. I think if I can work the egr, air bleed, and vapor box to burn clean enough I can reduce or eliminate the need for a catalytic converter or post combustion, but we'll just have to see.
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Old 06-22-2010, 10:54 PM   #11
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vwhobo is right here. But you don't want to hear what I have to say. Your idea is so bad on so many levels that I don't have the time or energy to address them all. I'll just briefly touch on the last post.

You won't pass the emissions test because even if you got past the sniffer, you wouldn't make it by the visual. Especially without a cat. If any of your ideas would actually work in the real world, why wouldn't car manufacturers, not even one, who spend billions on designing new models and engines already be using those same ideas.

The reason is that they don't work. Think about it.
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Old 06-26-2010, 12:04 AM   #12
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maybe instead of trying to evaporate the gasoline, I should focus on better atomization of the gasoline. I am thinking maybe a higher fuel pressure, and a smaller injector nozzle, or the same fuel pressure with an updated style of injector which has several smaller outlets, instead of one larger one, to get a finer spray of gasoline. Then the pulse width of the injectors could be tuned, and no further modifications would be required, but combustion efficiency would be increased due to the smaller sized gasoline drops. Even at low rpm I think a finer atomized fuel mix could increase power output, and fuel economy, while reducing emissions.

thoughts?
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Old 06-26-2010, 02:18 AM   #13
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I think you're grabbing at straws, you would spend how much $$ for an increase of say 0.5 mpg? You would be better off getting a motor bike that gets 3 times your MPG , have reliable transportation, a backup vehicle to use in bad weather/hauling large objects, and only have to spend several thousand dollars max. Could easily pay for itself in 15k miles.
I still don't think it is wise to go tearing apart your daily driver for such little improvement. Would be cool for the theory, to see what you could get it to do, but not the thing to try to do to save money when you are on a tight budget.
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Old 06-26-2010, 07:36 PM   #14
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I concur for all of the reasons stated above.

Even if you did a substantial amount of modifying/re-engineering the best you could hope for is a 5-10% improvement, which would translate into .9-1.8 mpg (based on your figure in the OP). You could gain that amount essentially for free.

How? First, make sure that all of your maintenance items are 100% up to date and done right. This includes fluid types and levels as well as underhood items such as ignition components and filters. None of this is actually free, but because you're supposed to be doing it anyway you can't include the cost. Run 5w30 in the engine and synthetics in the transmission, transfer case and differentials.

Second, don't do the "warm up" thing. Get in, start it and drive. No matter what wives tales you've heard it's actually better for the engine and trans, as long as you don't flog it.

Third, don't flog it.

Fourth, don't use drive thrus, and if you're too lazy to get out and go inside, shut it off while waiting.

Fifth, crank up the tire pressures to the maximum listed on the sidewall.

Sixth, drop the driveshaft to the front differential.

Or you can do what my son did. He got tired of feeding his Dodge Ram at $60-$75 per fill up. He couldn't ride his Honda 919 to work most days because he either had to drop off or pick up his son from daycare or Grandpa. So we scored him complete but neglected '95 Ford Aspire (Kia) for $300.

He added another $500 worth of parts and tires, a couple of evenings in the shop and then a weekend of detailing. He now has a commuter car that is clean, relatively comfortable for two adults, a kid and a dog and stone reliable. The best part is it does right around 40 mpg depending on if the A/C is in use or not. Even including the cost of registration and insurance, he amortized the cost in less than six months by leaving the truck parked most of the time.

I guess the moral to that story is the best way to get better fuel economy might be to start with an economy car. Think about it.
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Old 07-03-2010, 05:23 AM   #15
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vwhobo! Thanks for the advice on removing the front drive shaft, you definitely have the right idea, I've been having a noise issue, a ticking noise which would happen while decelerating, braking, going into dips, I suspected it was the front drive shaft because I didn't feel anything in the pedal, and it ticked with the speed of the drive train. so I marked the relationships with some paint, and removed it, then test drove and immediately noticed it was faster, then hit the brakes and the noise was gone! problem solved! after inspecting the drive shaft I wasn't surprised, it didn't feel smooth, was very dirty, and the joints made noise moving them around by hand. I'm very happy with the result, the jeep feels a lot better to drive, it coasts longer, and is faster, I'm sure this will help my gas mileage as well!

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