Turbo Charging Gas Engines ?

Discussion in 'Gas Engines' started by brian eiland, Jun 2, 2009.

  1. Jimbo1490
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    Jimbo1490 Senior Member


    This is exactly right; water serves the same function here as 'power enrichment', that is as an evaporative coolant, nothing more. Methanol is added to recover power lost by injecting water only.

    The turbo compresser outlet temp on my GN was approaching 300F, so the water injection helped quite a bit as an evaporative coolant or 'poor man's intercooler'.

    Jimbo
     
  2. flyinwall
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    flyinwall Junior Member

    Supercharged Bentley 1930's.

    Spitfire during 2nd world war.


    but mercedes had a supercharged 6 litre straight 8 in 1928 apparently it was capable of 100mph
     
  3. thudpucker
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    thudpucker Senior Member

    Fly,
    A Turbo-charger is a pump driven by the exhaust. It's different than a Super-charger, which is an engine driven pump.
    The rare air at 20,000 to 40,000 was too little for Combustion engines. A super charger used too much Horse power to make a great difference so they went to the exhaust driven Trubo's to provide power for an Air compressor feeding the cylinders.

    At sea level a Super charger works fine and I think I was told it can provide much more compressed air than a turbo charger can.
    But its more expensive in terms of the cost of energy.
     
  4. flyinwall
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    flyinwall Junior Member


    no offence but i am not stupid as i have been around supercharged and turbo'd cars for a long time and i was only making a reference to the length of time the auto manufactureres have been using forced induction
     
  5. Jimbo1490
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    Jimbo1490 Senior Member

    There is some truth to this but it is not always spot on. All turbochargers that I know of use a 'dynamic' compressors, always of the centrifugal (rather than axial) kind. These sort of devices are mass-flow devices, in that they are loaded by and perform their work on a certain mass of gas. So as altitude increases and the air becomes rarified, the centrifugal compressor continues to pack in nearly the same amount of air (actually it does fall, but gradually and linearly not exponentially and precipitously) because the dynamic compressor responds to the mass of gas, not volume.

    Contrast that with a roots type blower, which is a positive displacement device which performs its work on a certain volume of gas, a volume that contains fewer gas molecules as altitude increases.

    But then the supercharges used on all the radial aircraft engines that I know of are also centrifugal dynamic compressors, not roots blowers, so they would continue to be effective at higher altitudes.

    But the power required to do the amount of work we are discussing (1500 CFM @ 10-15 PSI for rough calcs) is not trivial; indeed it's not uncommon for there to be 100 HP or more dissipated across the shaft of the turbocharger on a modest sized diesel engine. In a mechanical supercharger installation, this power is subtracted from the output shaft while in the turbo setup, it recovered as waste heat from the exhaust. The small power subtraction due to backpressure on the exhaust side is more than made up by the pumping action on the intake side.

    Jimbo
     
  6. thudpucker
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    thudpucker Senior Member

    Thanks to all of you for the lessons and information.
     
  7. brian eiland
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    brian eiland Senior Member

    Nice explaination Jimbo
     
  8. kistinie
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    kistinie Hybrid corsair

    You think well, but you think border line... very dangerous for you peace and wallet.
    Brian, pre heating water before injecting the vapour is the principle of the Giller Pantone engine, wich is technically great, but politically incorrect.
    More generally, talking of water in positive terms, like cold fusion (http://www.scifi.com/sfw/issue151/labnotes.html or http://physicsworld.com/cws/article/print/1258 ), same for over unitary electrolyses, will get into serious business trouble !

    The wind of economic success is blowing for oil and coal, not for water and hydrogen
    http://www.ecogeek.org/content/view/667/

    So unless you are ready to retire, accept a reduction of your income and look at the world with another eye, my advice is, let the water under you boat, never think of it in your engine.
    I'm not the inventor of these wicked rules ;-)) ...Sorry for the uncomfortable position i may have put you in. ...but the positive aspect is that i and many others will be your supporter if you consider worth to go deeper in the direction of the study of water as an energy.

    May be this will give hope...

    All truth passes through three stages:
    First, it is ridiculed;
    Second, it is violently opposed; and
    Third, it is accepted as self-evident.

    -- Arthur Schopenhauer (1788-1860)



    Edited...
    It seems i have killed the line, maybe we could add a second bis state to the Schopenhauer's theory, that could be called the fear ?
     
    Last edited: Jun 27, 2009
  9. powerabout
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    powerabout Senior Member

    GM diesels before the WWII
     
  10. powerabout
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    powerabout Senior Member

    I read an SAE paper on...
    Ford tested water injection way back in early 80's on turbo charged Escorts or some small sh*t box to see how long term turbo'ed engine would hold out in the analogue electronics days.
    They had water injection and the long term tests showed cylinder damage caused by the constant steam cleaning of the cylinder ( that how you wash oil off parts right) so they shelved it for another day.

    PS Turbos work perfectly on aircraft as due to the thin air the turbo revs harder and make up for the less dense air...

    How about a 8000 hp drag race motor, the blower absorbs about 400hp..just look at the belt.
    The turbo, although an inlet and exhaust restriction, doesnt swallow the power like a belt driven gizmo BUT since there are only about 2 turbo manufacturers these days they are too expensive to use and as GM diesels proved..blowers are very reliable and cheap...
     
  11. Cheesy
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    Cheesy Senior Member

    I think you will find that they use the Roots type blower because its in the rules, a screw type blower or a turbo would be much more efficient
     
  12. Yellowjacket
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    Yellowjacket Senior Member

    Some random thoughts on this subject

    Water injection upstream of a centrifugal compressor is a good thing from a performance standpoint. What happens is that the water is evaporated during the compression process and it actually increases the pressure ratio and airflow of the compressor. If you are injecting after the compressor you don't get as much benefit of the water. Yes it does erode the impeller, that is a function of how well atomized the water is as it enters the inlet.

    It does not take a huge amount of water to supress detonation, and many folks using water injection actually over inject. Since it is safer (from a detonation standpoint) to do so and it costs little or nothing in performance, that's what happens. I did some research in college with water injection on a variable compression engine and the results were pretty amazing. A little water went a long way.

    Injecting hot water is a bad idea. You don't want heat in the water, you want to extract as much heat as you can from the air, since it takes less energy to compress cooler air that results in an improvement in cycle efficiency. Unless you are injecting tons of water, it will all be turned to steam during the combustion process.

    As Colin Campbell said in his tome "The Sports Car, Its Design and Performance" and I quote "as a means of finding the weakest link in an engine supercharging has no equal". He was right more than 40 years ago, and is still right today.

    Increasing intake pressure increases loads on the pistion, connecting rods and bearings. More importantly, it substantially increases the temperature of the exhaust gases. This is key since stress rupture life of high temperature items such as exhaust valves is cut in half by an increase in temperature of only 25 degrees F. That is, for each 25 degrees increase in exhaust valve temperature the life is cut in half. For 50 degrees increase the life is 1/4 and for 100 degrees increase life drops to 1/16th, and so forth...

    Higher exhaust temperatures cause more heat to be conducted into the areas around the exhaust port, causing increased thermally induced material stress (cylinder head crackng) and higher loads on the cooling system.

    It is easy to see why turbocharged engines require improved components such as valves and cylinder heads, and forged internals like crankshafts and rods and pistons.

    This is why increasing combustion pressures by supercharging or turbocharging a stock engine is a crapshoot since you don't know what kind of margins were designed into the engine unless you have intimate knowledge of the design process and what margins are available in the engine to withstand the additional stress.

    Turbocharging works on automotive engines primarily because they spend so little time on boost. In most cases the engine is at high loads for less than 10 seconds at a time. Consequently there isn't time for the parts to reach really high temperatures and the effect of the higher thermal loading isn't realized.

    Marine and aviation engines can be run at high percentages of maximum power for prolonged periods of time. Consequently engines run at these power settings have to be much more robust than than the intermittent duty that we see in auto engines. If you are in a "hot rod" boat application where you don't run flat out for a long period, a boosted engine can work, for a while, but you cannot expect a long life or the kind of service that you get from a normally aspirated engine, that's just not realistic.
     
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  13. Submarine Tom

    Submarine Tom Previous Member

    Water...

    Yellowjacket,

    Good summary of the thread, although using hot water for water injection wouldn't cause

    that big a difference in benefit as the majority of energy consumed is in phase change.

    I'm not sure why heating the water came up but why would you in the first place?

    When I set up my two injectors, I aimed them very near the centre of the impeller in hopes

    that if the stream didn't diffuse from the carburetor induced turbulance, that the near

    centre impact wouldn't erode the impeller too badly. It didn't, after years of service.

    Although, as you say, the "in use" time on a car engine is minimal. I was only using tiny

    windshield washer bottles with low level warning lights. Depending on the amount of "spirited"

    driving or actual racing I was doing, they only needed intermittent filling.

    As you say, it doesn't take much. Water is a pretty amazing material or substance.

    We tend to take it for granted but it's qualities are unique and merits numerous.

    Cheers, Tom
     
  14. Yellowjacket
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    Yellowjacket Senior Member

    When we did our water injection on a 6 lb/sec airflow gas turbine impeller we first injected the water at the hub. It ran onto the stationary bullet nose and pretty much went in at the blade root. Not much upstream mist at all, but we didn't get as much effect on the compression cycle that we were expecting.

    We backed the spray off about a foot from the inlet, and the stream EXPLODED due to the acoustic effect and shocks coming off the blades. I used to have some really cool video of a ball of mist just ahead of the inlet bell. The spray stream exploded and then was totally sucked into the engine inlet. You could see the shocks from the impeller leading edges rotaing in it due to the strobe effects of the 60 hz lights in the test cell. The water rate was about 6% of the total airflow or about .36 pounds per second, or 2.7 gallons per minute.... Which if you think about it is a huge amount of water to pump into any engine.
     

  15. powerabout
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    powerabout Senior Member

    how about the cylinder wear due to the steam cleaning effect?
     
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