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

Negative pressure supercharging -comments?

  1. absolutley

    2 vote(s)
    25.0%
  2. no way

    6 vote(s)
    75.0%
  1. May 23, 2005 #1
    Hey people
    i hope ive posted this in the right section.

    this is the product. please read... how it works and as much as possible....

    http://www.impulsengine.com/kits/index.shtml

    i need some help trying to figure out exactly how this works. it is such a great idea if it really does work as said.

    the main thing i want to understand is how it pulls in the extra air/fuel mixture. any other explantions on its main operating principles would be great too

    Would this concept really work? are there any disadvantages?

    Any input would be much appreciated.
     
    Last edited: May 24, 2005
  2. jcsd
  3. May 23, 2005 #2

    Cliff_J

    User Avatar
    Science Advisor

    Ok, first off I'm not sure to read this as if it were the next tornado or if legitimate. I'm a little skeptical since the claims seem to good to be true, but here goes with some initial ideas after scanning around.

    http://www.impulsengine.com/how/operating.shtml

    Ok, a 2-cycle engine like found on a dirt bike will have a large expansion chamber, and Tri-Y headers have been known to assist in exhaust scavenging (and thus producing more power) so this is plausible.

    Next the idea is that they are going to use hot air to try to increase combustion speed. Yes, much conventional development is done to increase the speed of the flamefront with 'swirling' and other techniques. But hot air has less oxygen density and therefore would limit the amount of charge, and if more of it is present than the threshold of detonation is much easier to cross. Simply overcooling the motor and keeping the water temperature down would do little to affect the air inside the combustion chamber as its being compressed, and the compression ratios cited still seem high if they are achieving high boost ratios when the initial temperature is so high.

    The aftermarket has lots of cold-air induction kits for conventional engines (and even CO2 spray kits to reduce the air temperature even more) to assist in packing in more oxygen (and correspondingly more fuel) into the combustion chamber.

    Also the trend amoungst automakers today compared to 3 decades ago has been to use hotter running engines/water with tolerances adjusted to help increase efficiency. Also, the trends are to reduce pumping losses like the vacum produced in the intake manifold (which this is suppossed to increase).

    Anyone with a credit card with a high enough limit can call up a mail order business and get big HP increases in different parts of their powerband from many different aftermarket sources. But that still doesn't offer a great basis for analysis, its far nicer to understand what is being compared.

    If there was a baseline/control engine and a modified engine with BSFC (brake specific fuel consumption) with corresponding charts to show power/fuel it would go a long way to making me want to investigate their claims further. In addition I'd like to see a direct comparison of their modified Chrysler 360 engine against a GM LS6 or the new Chrysler Hemi that would all have similar displacement.

    my two cents is that it seems plausible but unlikely to work as well as advertised, I'd like to see what Clausis2 or others think after reading the website. This page really seems unrealistic.

    http://www.impulsengine.com/how/comparison.shtml
     
  4. May 23, 2005 #3

    brewnog

    User Avatar
    Science Advisor
    Gold Member

    Interesting.

    I'm no thermo expert, but I can't find a fault with their reasoning.

    However, the lack of any concrete performance data (as well as dubious claims like "this produces 2 times more torque from idle to midrange than naturally aspirated engines") plants some pretty big seeds of doubt in my mind. I hope I'm not being too cynical, but performance increases like that would have been instantly snapped up by large automotive OEMs, and wouldn't still be the preserve of a small Australian company. Also, their statement saying that 'Torque' means 'useful power' does set the alarm bells ringing in my head!

    Like Cliff, I'd very much like to see what Clausius, or any other 'thermo daddy' has to say on the matter.
     
  5. May 24, 2005 #4
    i though of a couple of things last night:

    to start off...

    three basic ways to improve power
    1. thermal efficiency
    2. mechanical efficiency
    3. volumetric efficiency

    this would improve thermal efficency substantially i would think, as less heat energy would be absorbed by the motor/block. how much of a difference i dont know...

    volumetric efficiency on the other hand (in normal engine operating conditions) would go significantly down. but its got different valve timing, unique exhaust system and a different cooling system which is supposedly the secret to pulling more air/fuel into the combustion chamber??

    just a couple of thoughts that got my brain ticking.
     
  6. May 24, 2005 #5

    Clausius2

    User Avatar
    Science Advisor
    Gold Member


    Daddy? I am only 23!!!! :rofl:

    I have few things to say. I do not see why greasemonkey has called this solution an "invention". This has not been invented yesterday. Current engineers do know how to increase engine power, and this method is very primary.

    Reading the link I have crashed with this statement:

    http://www.impulsengine.com/how/operating.shtml
    Of course I was waiting this statement. Current engines has an small crank angle (about 15º) over which both exhaust and intake valves remain opened. It happens at the TDC. One could think this is a very bad situation for the mixture flow, in fact intake mixture could reach the exhaust pipe if the rpm are too low. But the global result of such overlapping is an strong increasing in power. I am going to explain this.

    In this "revolutionary design", if there were such valve overlapping there would be flow from mixture intake directly to the exhaust pipe due to the "negative" pressure generated there. Fortunately, the guy who has had this "brainy" idea has forecasted this fact and so there won't be such conventional valve overlapping. If not, this direct mixture flow to the exhaust will enhance a poor efficiency.

    What happens if there is no valve overlapping?. As you may check, the most powered cars have larger angles of overlapping than usual cars, because they are thought to run at higher rpms. The control of this overlapping valve is a great topic of research in current engine industries. In fact, it is this control which is going to be the power controller in the future, instead of the accelerator pedal and throttle valve. In particular, BMW has been working on a system of "variable charging", in such a way this valve overlapping angle [tex]\alpha_o[/tex] is a function of the rpms: [tex]\alpha_o=F(n)[/tex]. This cannot be reached so far because of the camshaft "stiffness" when machinning it traditionally, and the cost of additional hydraulic-electromagnetic systems of this last BMW concept.

    If [tex]\alpha_o=0[/tex], then:

    i) the volumetric efficiency will have a good behavior at low rpms. But at high rpms it will begin to decrease strongly. It is because the intake system is not being able to take advantage of the proper inertia and compressibilty of the air. Instead of it, the intake air would crash into the intake valve if this is not previously opened before the TDC. Also, burned gases need some delay to be exhausted, so it is necessary a delay when closing the exhaust valve. Such compressible(elastic) behavior of the gas increases with rpms. At low rpms, a great angle of overlapping could cause a mixture flow directly to exhaust. It is needed a balance between these positive-negative two facts. As this engine has not any overlapping angle, its behavior at high rpms would be very worse.

    ii) so that the global efficiency should be decrased when the engine begins to run at high rpms.


    There would be some other disadvantages, but now I have to go class.
     
  7. May 24, 2005 #6

    Cliff_J

    User Avatar
    Science Advisor

    The usage of new coatings to help reduce the heat transfer from the hot gasses to components makes sense, but they don't mention this.

    The combustion process is still occuring and X amount of thermal energy is being released by that process. It doesn't matter if it occurs in 10msec or 1msec its still trapped inside the chamber. Opening the exhaust early would assist in this but it also means that expanded gas can no longer perform work on the mechanical side of things, seems like a pretty big compromise even if its only 10% mechanical loss.

    The cooling system doesn't seem to be a contributing factor, its more like their method of trying to control detonation.

    Clausius2 - Given that BMW has the abilty to modify each individual camshaft timing by 60 degrees they have an incredible flexibility to place those events where ever they choose, and with valvetronic they can adjust lift to suit as well. I wouldn't be surprised to see lab versions of this in any development engine shop, imagine being able to create a different camshaft profile with a couple keystrokes and test on an actual machine in real time. I'm almost salivating as much as when during the F1 practice broadcast here in the US they showed a clip of Aryton Senna going around the Monaco circuit in his McLaren Honda in 1990, raw unadulterated skill there compared to the extra refined machines of today.

    http://www.bmwworld.com/technology/valvetronic.htm
     
  8. May 25, 2005 #7

    Clausius2

    User Avatar
    Science Advisor
    Gold Member

    I think that BMW control system was only a concept. Currently the overall efficiency decreased due to the additional electro-hydraulic systems needed. As you can imagine, changing the profile of the camshaft in real time each revolution is a heavy task for engineers.

    But the main idea of the concept is to choose the maximum of the volumetric efficiency for each rpm varying valve delaying.

    I have seen the page of valvetronic system. It seems it only controls the inlet/outlet valve lift. I think it is designed to control power via mass flow of mixture (decreasing-increasing effective section through the valve). But I don't think it is designed to control valve angles of openning and closing. As you have said, it would be a great combination both valvetronic and a system for varying valve angles.
     
  9. May 25, 2005 #8

    Cliff_J

    User Avatar
    Science Advisor

    I'm pretty sure that both made it into production, but its not a per-revolution change but a much slower change as dicated by RPM, load, and throttle input. The 300msec time to fully change the profile would most definitely limit the per-revolution changes available (even if I'm too lazy to integrate that as a curve of change/RPM). :smile: And I don't see how else did they could eliminate the throttle butterfly to reduce pumping losses and improve throttle response without being able to vary the valve operation tremendously. Now whoever decided iDrive was a good idea is another story...

    Since Lexus and Nissan/Infiniti have production engines that vary valve timing, and since Porsche and Honda offers two switchable cam profiles and variable valve timing, this is only one more step in that direction to trump the competition with continously variable operation for both lift/duration and timing. Even the cost of implementation could likely be justified as a marketing expense, but there have been plenty of good ideas shelved to save pennies before so I see your point too.

    I do think its a large step forward in allowing the engine designing team to choose the optimum volumetric efficiency. I say optimum instead of maximum because I'm unclear on how important it truly is - with all the dangers of thinking outloud, for the 99% of the time that a non-race engine is operated at idle or part throttle I'm really uncertain how directly linked raw volumetric efficiency is to overall system efficiency. GM has their LS2 lump available with a full retail price of $6,000 and it can reliably get 30MPG on the highway and 330+HP at the rear tires. Its critized for its large relative displacement, using pushrods and have none of the variable camshaft stuff, and yet for pratical efficiency (fuel economy), value, and power output it has little competition.

    Back to our negative supercharger discussion, I was thinking this: Lets assume their high temperature air assisted 'fast-burn' happens as described with its short duration. If they were able to time it correctly and achieve very high expansion from very high temperatures its possible they could shift the peak of the pressure curve closer to 45 degrees after TDC to maximize mechanical advantage. Or, come closer to mimicing part of a diesel pressure curve (as I understand it). But how they could achieve this without detonation on 87 octane doesn't seem so likely though, and (as pointed out before) how the concept could have eluded countless engineers over the years raises even more doubts.
     
  10. May 25, 2005 #9
    Ha, Ha. The device in question is already on your car more than likely. It's called EGR---Exhaust gas reflow.

    [edit]Whoops---didn't see the technical manual. I misread the way it was supposed to work... It's still snake oil. This is not the first time I've seen this type of system nor will it be the last.
     
    Last edited: May 25, 2005
  11. May 26, 2005 #10
    this company is in australia and the minimum octane fuel is 92, not heaps more but would definitly help. there is also 98 octane as well which they may have used...
     
  12. Jun 2, 2005 #11
    Negative pressure??

    No mystery here....
    Perhaps the system simply starves the engine of fuel compared to air as RPM increases. That's happened before and worked well short time.
    If you read the rest and follow the links, you'll find that each and every stage also includes more and more aftermarket engine mods. These mods eventually lead to :
    high speed valve rocker gear mods
    valve and valve stem/shaft improvements
    camshaft duration mods
    ignition dwell and timing calibrations
    spark plug upgrades
    exhaust manifold header changes

    Mmmmmmm....sounds like any race engine to me that's naturally aspirated.

    Cheers
     
  13. Jun 2, 2005 #12
    This works due to differential pressure across the whole engine and in fact if this fellow wanted, he could leave everything stock and just use his exhaust arrangement to accomplish 'differential boost' across the engine. Provided you could maintain an absolute vacuum at the exhaust , indeed, the equivalent of thirty pounds of air could be realized entering into the combustion chamber. If this technique is being used to increase fuel economy then beyond the engine changes the final drive/ gear ratio would have to be changed as well to keep engine rpm in the lower 'torque range' .People who want to get power greater than supplied by the manufacturer do not care about fuel economy! So, why all of the other stuff.

    A 40 hp DC motor started at 120 vdc will produce close to 400 ftlbs torque (locked rotor) for up to 6 sec without harm and weighs about 75 lbs

    The ideal would be a system that costs $100 to $200 takes 15 min to install, doesn't have to interface with the existing computer and doubles your HP..........but that's just an ideal....
     
  14. Jun 2, 2005 #13
    Why do they need some delay before they can be released? Is it because they need to expand fully?
     
  15. Jun 2, 2005 #14

    Clausius2

    User Avatar
    Science Advisor
    Gold Member

    No problem here.

    Imagine you are seeing the piston going upwards during the exhaust stroke. The exhaust valve is opened. As the piston goes upwards the gas is forced to escape due to an external force of compression. IF exhaust valve would close just at the TDC, then the inertia of the gas as it goes upwards would be wasted: pressure waves travelling into the gas and caused by piston surface motion would crash into exhaust valve. These waves collaborate in the gas exhaust process. It can be experimentally checked that overall efficiency increases due to this valve delay. In such a short times and rapid motion, taking advantage of the proper gas compressibility is a vital point. In racing cars where piston speed is larger, the exhaust valve closing delay is larger too. So that, while piston is going downwards just at the beginning of induction stroke, the exhaust valve remains opened for a short time. In this short time both exhaust and inlet valves are opened. It is what I called the overlapping angle.

    If you haven't understood this stuff, please let me know.
     
    Last edited: Jun 2, 2005
  16. Jun 2, 2005 #15
    Thanks for the reply.

    This what I have understood. If there is no valve delay, the pressurized gas, instead of exiting the combustion chamber and expanding fully, some of it would be left behind in the combustion chamber and the pressure of this gas would be wasted. Therefore the exhaust valve is left open for some extra time during which the inlet valve is also opened to allow the pressurized burned gas to fully exit the combustion chamber. Is this correct?

    I have also heard of the term delay in reference to turbojet engines. What does the delay mean here where the combustion process is continuous?

    BTW, are pressure waves like acoustic waves set in motion due to particles hitting the walls of the combustion chamber after combustion?
     
  17. Jun 2, 2005 #16

    Clausius2

    User Avatar
    Science Advisor
    Gold Member

    Right.

    Sorry, I have no idea about it.

    [/quote]

    Pressure waves = acoustic waves. The acoustic field is caused by pressure spatial variations. Forget about combustion process. Pressure waves are forced by means of piston surface-gas interaction when the upwards motion is forced. The time an acoustic wave travels from piston surface to exhaust valve is comparable with the characteristic time of variation of the piston height, specially at high rpms.
     
  18. Jun 3, 2005 #17
    Thanks a lot for the help
     
  19. Jun 10, 2005 #18
    also another thing i remembered is that the hotter the exhaust gas the more it wants to exit the tailpipe, and as the gases would be a lot hotter (by the same amount of the air temp increase im sure...) so the speed of the gas would be a lot higher and that would create a larger vacumn.

    I would think this is one of its main factors in pulling through more air/fuel.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Negative pressure supercharging -comments?
  1. Electric Superchargers (Replies: 9)

Loading...