Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Better fuel efficiency through vapor carburators?

  1. Mar 11, 2004 #1
    I'm sure everybody has heard all the stories about high mileage carburators and the oil companies etc. But why has this problem not been solved? Approximately two thirds of the fuel we burn in our cars goes out the tail pipe. I've read that someone has used catalytic cracking to breakdown the fuel into a more user friendly vapor and got incredible mileage. Naturally I'm a bit of a sceptic but I'd like to hear what people have to say about the idea.
     
  2. jcsd
  3. Mar 11, 2004 #2

    Cliff_J

    User Avatar
    Science Advisor

    The fuel delivery and combustion process aren't the issue so much as the design of the ICE itself.

    The design of the diesel ICE offers better efficiency with its higher compression ratio to create higher average cylinder pressures and slower burning fuel to allow longer periods of high cylinder pressure, but still loses plenty of BTUs out the tailpipe and into the cooling system.

    I think its a lost cause to search for better efficiency with the fuel itself like trying to gain aerodynamic efficiency by changing the type of carpet used on the floor of the car. But hey, I enjoy paying $$$ at the pump - NOT!

    A high-output and cheap to manufacture fuel cell would double our efficiency instantly even from the existing fuel sources, and allow further flexibility into others. That's the answer, IMHO anyways.

    Cliff
     
  4. Mar 11, 2004 #3
    1.) ALL of the fuel I burn in my car goes out the tailpipe.
    2.) Almost all of the fuel I put in my tank gets burned.
    3.) I can prove it.
    4.) So can you.
     
    Last edited by a moderator: Mar 11, 2004
  5. Mar 11, 2004 #4
    This sounds like a "hoakey" explanation of EGR. EGR shows a minimal improvements in milage but it doesn't do it by altering the exhaust gasses into some magical vapor. Moreover, combustion is an oxidation process--how much energy would be required to reverse that process? Answer: A significant ammount (more than required for the original reaction). Where is this extra energy coming from?

    High milage carbs are around and fairly easy to manufacture. The problems associated with these are power and emissions.
     
  6. Mar 11, 2004 #5
    All around the globe are thousands of racing teams who spend every waking moment thinking about how to get an extra horsepower out of an engine, and how to get a tenth of a mile per gallon more on their fuel mileage. At the same time, there are tens of thousands of mechanical engineers working for automobile manufacturers(maybe the most competitive industry in the world) who would dearly love to get any possible edge on the competition. A lot of people would have you believe that it has never dawned on any of these engineers to improve the efficiency of their products. What do you think these engineers do all day?
     
    Last edited by a moderator: Mar 11, 2004
  7. Mar 11, 2004 #6

    russ_watters

    User Avatar

    Staff: Mentor

    Well put.

    Lamar, there are certain fundamental restrictions on the efficiency of internal combustion engines. It is extrordinarily difficult to get an otto cycle engine above about 35% and the efficiency is directly related to compression ratio as you can see from THE EFFECIENCY EQUATIONS. Compression ratio is why the diesel cycle (similar to, but not exactly the same as the otto cycle) is a fair amount more efficient than the otto cycle.

    One thing not talked much about though is tighter computer control over the combustion process. Its really not that expensive and though it only adds a few percent to the efficiency, it reduces the nastier emissions by a considerable amount.
     
  8. Mar 30, 2004 #7

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Since higher compression ratio's also produce more NOX's, two different environmental concerns come into conflict with each other here - efficiency and NOX pollution. I assume that we are forced to seek the middle ground on this point.

    Does anyone know how efficiently the fuel is atomized in modern fuel injection systems as compared to the theoretical ideal, and to what degree does this impact the final fuel efficiency?

    My preferred solution: Go Hydrogen.
    https://www.physicsforums.com/showthread.php?s=&threadid=4127
     
  9. Mar 30, 2004 #8

    Cliff_J

    User Avatar
    Science Advisor

    The lean burning of H2 in an IC engine with a high compression ratio (to give us high efficiency) will still result in the production of NOx. Given that H2 used on an existing ICE will suffer a 15% decrease in power output, it won't be until the technology of direct injection makes it way from the lab to a production line that we'll see a 15% increase in power output compared to a gasoline engine. Not bad, lots of promise once the compromise over higher efficiency of fuel spent/NOx produced is optimized.

    Also, there are researchers working on devices to reduce NOX emissions by 90% or better via a fuel powered chemical scrubber. They are retrofitting this device to existing ICE engines like on a bus to cut down on its output, same could easily be applied to an H2 vehicle espcially since the size could be much smaller. I don't remember the details, but it was on a science channel show like 'TechKnowledge' or one like it.

    I've also read of a place that uses a metal hydride as the storage mechanism for H2, offering a greater density per volume than even liquid H2. It is low pressure and should the container become ruptured its not flammable even if in direct contact with a flame. It suffers from high cost and is can be easily destroyed by exposure to components in regular air. Some place was using in a Corvette they retrofitted to run on H2. I'll see if I can dig up some links.

    Cliff
     
  10. Mar 30, 2004 #9

    Cliff_J

    User Avatar
    Science Advisor

    Here's a couple relevant to what I posted:
    http://www.eere.energy.gov/hydrogenandfuelcells/fuelcells/pdfs/fcm03r0.pdf
    http://www.unitednuclear.com/h2.htm

    Also, why no support for E85 and biodiesel as interim fuels that can readily replace fossil fuels and utilize the same infrastructure? They definitely would be accepted with open arms from our shrinking agriculture industry, reduce our dependence on foreign oil, and require no expensive fuel cells or public education about the safety of H2. Instant green IMHO.

    Cliff
     
  11. Mar 30, 2004 #10

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Great links! Thanks.

    Again, if anyone is interested in this - Hydrogen powered cars, and a Hydrogen Economy in general - please see the link that I provided.

    https://www.physicsforums.com/showthread.php?s=&threadid=4127

    There are many other good links contained within the thread. I feel that H2 cars, and H2 production generally are some of the most important emerging technologies. As for options like biodiesel, in principle I support anything that could help reduce our need for oil, but I also feel that we need a coordinated effort to get hydrogen off the ground...so to speak. :rolleyes: In this sense I prefer to see a focused effort for H2. As for E85, there seems to be a lot of problems with cars that run this stuff. At the least I have heard such talk from technical people. I'm not sure of any specifics. I know that home produced ethanol for farms has or had [at least] really taken off. In the long run though, I worry about the implicit wisdom of putting food in competition with energy.
     
    Last edited: Mar 30, 2004
  12. Jul 23, 2004 #11
    To: Lamar
    Why has the problem not been solved? Goood question! Answer: (A) You pay for all the unburned fuel going out the tailpipe. (B)This represents positive cash flow for refiners and petroleum companies. (C) They get very upset at people who want to increase fuel efficiencies by factors of 2, 3. 5, etc. (D) What happens to good hearted people who want to cut BIG OILs cash flow by factors of 2, 3, 5, etc? In the 1920s a lot of work was done to improve gasoline mileage. For some strange reason, it is very difficult to locate records of this work. On the Internet, "This page is not available" comes up many times. I wonder why? Nevertheless, there is a lot of valuable information on the internet. It will just never be implemented in the United States. Think perhaps China, Russia, India, etc. Good luck.
    Freddie
     
    Last edited: Jul 23, 2004
  13. Jul 26, 2004 #12

    megashawn

    User Avatar
    Science Advisor

    Ok, hopefully noone will beat me up.

    I had heard that buy running your fuel through a copper tube, and wrapping this tube around the heater core water line will heat the fuel, causing it to expand, thereby burning it more effiecently. I don't know the technical reasons why.

    Anyhow, something similar to this is used with propane conversions, where they use hot water from the cooling system to expand the propane before it is fed to the engine.
     
  14. Jul 26, 2004 #13
    Megashawn: No one will beat you up. But, if there was a whiff of publicity re large capital investment to commercialize, Poof - you would vanish!
    If you have droplets of fuel, the droplets cannot vaporize and burn in the short time available in the cylinder. So maybe a little of the outer layer of the droplet vaporizes and burns and the rest goes out the exhaust to heat your catalytic converter. Vaporizing fuel was the basis for many improvements. Your reference to propane vaporization is astute.
    The big jump in fuel economy is the introduction of water vapor into the cylinder to:
    1. Lower peak temperatures thereby reducing heat losses.
    2. Extending the time during which cylinder pressure is relatively high. This is significant because high pressure early in the cycle does very little while moderate pressure when the crank is at 90 degrees does a lot.Vizualize a sine curve.
    I read a reference which stuck with me but I cannot relocate, but the reference was to an Oldsmobile 88 idling at 80 rpm. Typical "normal" idle speeds are about 500 rpm and up. My personal belief was that this was an example of water vapor introduction.
    There are many references on the Internet which can be found, also many books available giving more details on specifics. Try "unusual engines" on Google and be prepared to give up several hours, days, weeks, depending on your interests
    Good luck
    Freddie
     
  15. Jul 26, 2004 #14

    megashawn

    User Avatar
    Science Advisor

    I've heard of water injection, is this what your talking about? That is one of the greatest developments for engines in sometime.

    I've also understood, perhaps incorrectly, that a turbo system increases the efficency by reintroducing unburnt fuel back into the system.
     
  16. Jul 26, 2004 #15

    ShawnD

    User Avatar
    Science Advisor

    Turbo is when more air is forced into the cylinder to give higher compression.
     
  17. Jul 26, 2004 #16

    russ_watters

    User Avatar

    Staff: Mentor

    Please keep this nonsense out of the engineering forum. Do you have any idea how many engineers there are in the world? How easy do you really think it would be to keep such technology off the internet? A halfway competent physicist can build an H-bomb (the CIA did a test to find that out). How much harder do you think it is to make a new carburetor? The idea that there is some secret technology out there that is being suppressed is absurd.

    Have a look at the efficiency equations I posted. They don't leave a whole lot of room for 100mpg cars.
    Yes. Pre-heating reduces the activation energy needed inside the cylinder. You can also recover heat from exhaust gas for the same purpose. But here's the catch: it takes energy to pump the gas through the extra piping and extra money to build the engine and the benefit is maybe an extra percent or two of efficiency.
    A turbocharger and supercharger both increase the airflow to the engine - turbocharger by using exhaust gas to spin a turbine (losing some energy in the process), and a supercharger by using the drive or cam shaft to run the blower (using some energy in the process). In practice, neither result in higher efficiency, just higher peak power output.

    Also, water injection isn't nearly as exciting as its made out to be. It can give a few percent more power or a few percent more efficiency. It doesn't overcome the laws of thermodynamics.

    The fact of the matter is that 100mpg is possible with existing technology, but it'll never happen because people don't want it. They want horsepower, air conditioning, power windows, and space. Those things and fuel economy are mutually exclusive. An in-line two seater that looked like a glider fuselage could easily achieve 100mpg (they were sold in the '60s as a matter of fact) - but no one would ever buy it.
     
    Last edited: Jul 27, 2004
  18. Jul 27, 2004 #17

    Cliff_J

    User Avatar
    Science Advisor

    A turbo or supercharger increases volumetric efficiency - the ability to get air/fuel mixture into the combustion chamber. More mixture, more power. It doesn't change the efficiency of the system in terms of the energy input/output ratio but instead just the amount you can input/output.

    Where is this increase in efficiency from water injection coming from? My understanding is using water as a means of controlling detonation (heat control) which means any gains are the result of some other factor (like high compression ratios) and not from the water injection itself. A better formulated fuel could be used in the same engine with the same result without any water in that case, its just the water allows the usage of a lower grade fuel.

    Oh, and if you're talking about getting 100mpg the same way the grassroots approach is to building electric cars where every compromise is optimized for efficiency, I'll pass. I've been in a couple fender benders, I wouldn't want to be the guy with no legs having a Zinardi bar named after me. Build a hybrid motorcycle instead, at least it'd be fun. :smile:

    Cliff
     
  19. Jul 29, 2004 #18
    ShawnD:
    You are right re the turbo. It put more air into the cylinder, which = more oxygen, which can burn more fuel to give more power. I don't see any effect on efficiency.
    Re water vapor, which does affect efficiency, you also get reduced NOx as a side benefit of reduced peak temperatures.
    Megashawn: You are referring to a specific technique to vaporize the fuel (copper tube). Numerous techniques have been used. The reason it works is that liquid fuel cannot access enough Oxygen to burn properly. In vapor form it can and does burn readily. The droplets of liquid fuel are the nasty critters you want to get rid of (unless you are an oil company).
    Freddie
     
  20. Jul 29, 2004 #19
    I thought about designing something that would create large amounts of ozone to feed into the intake. This, along with changing over from gasoline to *propane. Being as my vehicle is already fuel injected, I don’t see any other choice for me.

    *That’s a spicy meatball!!* :D
     
  21. Aug 13, 2004 #20
    My apologies to all. I just discovered that I do not have permission to access this page. And I don't know the routines that I need to get authorized. So thanks to all who participated in what I thought was a worthwhile discussion. Just goes to show ya.
    Freddie
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Better fuel efficiency through vapor carburators?
Loading...