eyefi Posted January 22, 2003 Share Posted January 22, 2003 Originally posted by Terminator Any chance of a link Syed, this sounds interesting. here Link to comment Share on other sites More sharing options...
Nathan Posted January 22, 2003 Share Posted January 22, 2003 Seeing as it's safe to return..... It's been a long while since I did physics but I'll have a stab. And I'm quite prepared to be shot down! Don't take any of the below as gospel but it's what was floating around in my head at 9pm last night. I've pasted this from my word doc so I hope it works... I think the thing to bear in mind here is that I don't think it's as much to do with LHE (latent heat evaporation) as much as SHC (specific heat capacity) and LHV (latent heat vaporisation). Specific heat capacity tells you how much energy you need to put into a substance to increase it's temperature by 1degC. I always thought water injection was to do with the massive cooling found from expansion exhibited by water on vapourisation. (around 4000 times, IIRC). A good point was made by Phil but unfortunately although getting hydrogen from injecting water into a car engine would be very 'interesting' it won't happen. A change of 'state' ie water to steam does not imply 'inter'molecular bonds are broken (i.e. molecules don't disassociate into their respective atoms.. it remains 'water'). However the 'intra'molecular bonds do break... the bonds that hold water molecules together in their 'liquid state'. It takes energy to do this and its called the latent heat of vaporisation.... changing water liquid into a 'gaseous state' i.e. water vapour. Breaking water in to hydrogen and oxygen is a whole different ball game... and it doesn't even follow the same rules. You wont even do this in a top fuel dragster. As for the queries regarding amount injected relative to the swept volume it's actually very small. Using a pretty crude calculation, I was only injecting 0.0057% of the total cylinder volume (it wil obviously vary depending on rpm- the example was made at 7K rpm). And that didn't even take into account pressurization from the turbos. I based that on atmo so the actual amount would be even less. It shows that you don't need a lot of water to make a difference. It is suggested that 10 to 25% of the total fuel injected should be water. I was injecting far less than that. I did work that out as well but I can't for the life of me remember what it was. It was well under 10% though. Some theory suggests that water injection can actually have a positive effect on power output simply because of the huge exapansion taking place when water turns to steam. Oh look. A steam engine ;-) Aside from the fact that I've seen a lot of so-called theory fall down when it comes to practical testing I'm very sceptical of any power increases found purely from adding water mainly because of the small amount used relative to swept volume as shown above. Moot point though and quite interesting. In the grand sceme of things, and to answer the original question, I wouldn't bank on making any meaningful power by injecting water. It does however allow you to push the boundaries as regards to boost pressure and combustion temperatures. My thoughts on water though have always remained the same. I don't agree with (or see the point) for using it on engines that don't detonate (ie any stock supra or BPU one). If an engine is not detting or doesn't have excessive EGT's then fitting water injection will simply be an exercise in getting ones wallet fleeced. I don't subscribe to the 'cooler must be better' idea with water (as opposed to a bigger intercooler) because you will do nothing by injecting it into a non detting/non high EGT engine except create unuseable steam. It doesn't create a 'denser charge' in the way people assume, unless you consider a dense charge of water vapour to be beneficial. Dense charge of air, yes. Water, no. If anyone has any data which shows a benefit on an engine like the above I'd like to see it. If you do decide to use water to push the boundaries then be it on your own head. I for one wouldn't use water on an engine that would det without it unless it was on a race engine where it doesn't really matter and every bhp counts. I fitted water to my car purely because at flat-out speeds although it wasn't detting it was hitting 1000 degC. I fitted water, injecting at the amount shown and never saw over 900 which I was happy with. There was no point in injecting any more. I never noticed any loss in power and neiter did I feel any gain. I felt that it did the job perfectly. It's still not the best solution because pumps can fail as can other parts in the system but I was happy to keep an eye on EGT's (and the 3 led WI diagnostic system) more than I was to try and get an even bigger intercooler in there along with the associated costs. As for claiming higer bhp when mixing methonol (or any other alcohol) with the water think back to just how much you are injecting.... Just something to think about. Cheers Nathan TDI PLC Link to comment Share on other sites More sharing options...
Gaz Walker Posted January 22, 2003 Share Posted January 22, 2003 Originally posted by Nathan I fitted water to my car purely because at flat-out speeds although it wasn't detting it was hitting 1000 degC. I fitted water, injecting at the amount shown and never saw over 900 which I was happy with. Very interesting Nathan, that was precisely why I want the Aquamist system on my car... To me thats a significant improvement... Gaz. Link to comment Share on other sites More sharing options...
eyefi Posted January 22, 2003 Share Posted January 22, 2003 nice post, but scheme has a h in it Link to comment Share on other sites More sharing options...
Nathan Posted January 22, 2003 Share Posted January 22, 2003 Originally posted by eyefi nice post, but scheme has a h in it A thousand apologies Damn those fiddly laptop keys.....should have dunged out my old Vic20... Nathan TDI PLC Link to comment Share on other sites More sharing options...
THOR Racing Posted January 22, 2003 Share Posted January 22, 2003 I don't agree with (or see the point) for using it on engines that don't detonate (ie any stock supra or BPU one). If an engine is not detting or doesn't have excessive EGT's then fitting water injection will simply be an exercise in getting ones wallet fleeced Nice post Nathan. I agree with the general point of the post and with particular reference to the above quote this is precisely why the boost controller I am designing (yes, one day I'll finish it!) will have sensor inputs for temperature and output controls for boost control as well as water injection (or spray, whatever...) So the idea would be to have a boost controller that would act as a normal boost controller but if you add the additional temperature sensors you can decide at which point to turn water injection on (if you have it) or reduce boost as EGT's go above a set threshold. It will also be able to automatically monitor the water flow from the pump and should the water run out or pump fail then the boost can be reduced (gradually to avoid unstable driving but fast enough to avoid destroying anything.) But as Nathan says I wouldn't want my car on such a thin tightrope. Regards Pete Link to comment Share on other sites More sharing options...
Steve W2 Posted December 8, 2003 Share Posted December 8, 2003 Originally posted by Nathan Some theory suggests that water injection can actually have a positive effect on power output simply because of the huge exapansion taking place when water turns to steam. Oh look. A steam engine ;-) The energy released by the expansion of steam is nothing in comaparison to that of an chemical explosion. This is why we dont have steam powered Supra's. The amount of steam required to produce energy sufficient enough would require something as large as a, errrrr.....steam engine! LHV in engineering and combustion terms is lower heating value:) Personally, i would just pay the money and get a bigger IC. I can't see how adding water to the combustion process helps at all. As i have mentioned in previous posts I work for a combustion engineering company and one of the worst cases of combustion can be attributed to having (albeit high) levels of water inbound in the fuel properties. All I can see this does is add water to the fuel thus decreasing the amount of fuel being burnt in the combustion process. This is effectively lowering the calorific value of the fuel (LHV) and will cause less of an explosion on a volumetric basis. My 2p anyway! Link to comment Share on other sites More sharing options...
Digsy Posted December 8, 2003 Share Posted December 8, 2003 I remember an experiment at school which (among other things) underlined very graphically why pouring water on a burning chip pan is a Bad Thing. Basically Teach got some oil very very hot, lit it, then poured a small amount of water on it. The resultant fireball nearly touched the classroom roof. Can't remember what the mechanism was, or if it would work the same in an engine though. Does it ring bells with anyone??? Link to comment Share on other sites More sharing options...
Mark Ayling Posted December 8, 2003 Share Posted December 8, 2003 Blimey, this thread came back from the dead!! Link to comment Share on other sites More sharing options...
Steve W2 Posted December 8, 2003 Share Posted December 8, 2003 Originally posted by Mark Ayling Blimey, this thread came back from the dead!! Surprise!! Just saw it thought I would throw a few comments in. Did the same chip pan experiment on a fire prevention day! The expansion ratio is something 2700:1 Not as much as an engine though, and not as controllable. Link to comment Share on other sites More sharing options...
ChrisR Posted December 8, 2003 Share Posted December 8, 2003 Originally posted by Mark Ayling Blimey, this thread came back from the dead!! Didnt it, always catches me out especially when i pay no attention to dates and see peoples names who walked from this site ages ago. Good though as i missed it first time round and it answers some questions i had. Cheers Link to comment Share on other sites More sharing options...
Digsy Posted December 8, 2003 Share Posted December 8, 2003 Originally posted by Steve W2 Not as much as an engine though, and not as controllable. I'm sure you could map it. One big Mazola injector, and one water injector. It would smell lovely too. Link to comment Share on other sites More sharing options...
Wez Posted December 8, 2003 Share Posted December 8, 2003 I found that pretty informative. I have always thought water injection was just a fudge fix for a problem caused elsewhere, ie to prevent det due to high temps etc. Link to comment Share on other sites More sharing options...
Timwildman Posted December 8, 2003 Share Posted December 8, 2003 I know it's not the same as a car, but i've worked on an airplane that used water injection, to get extra thrust. It does work, it was proven to shorten the take off run, or keep it the same in extra hot countries. It also make a lot more noise, could feel the ground shake on the othere side of the airport when it took off. So there you go, but I think its mainly to used on cars for a temp control thing, (haven't read the rest of the post tooo lazy) but it will lower air temp increase density, allow more air..and inturn more fuel for bigger bang..bla bla bla.. My 2p Link to comment Share on other sites More sharing options...
Barnstormer Posted December 8, 2003 Share Posted December 8, 2003 A lot of older aircraft did have water or water/methanol injection on turbo jet engines. Basically it did two things.. 1) Lower the exhaust gas temps (EGT) a little and most importantly 2) increased the mass flow through the engine resulting in higher thrust. Jet engine thrust is proportinal to the mass of air ejected out the back. As water increases the density of the airflow the result is more thrust. Normally only used on take off to get airbourne when very heavy or on a short runway. The Trident was an example of such a beast and in the cockpit were 3 green lights - one for each engine. When required to use the water/methanol injection on takeoff the co-pilots job was to watch the lights. If any one of them failed to illuminate it mean't you were not going to get airbourne! ATB Link to comment Share on other sites More sharing options...
Timwildman Posted December 8, 2003 Share Posted December 8, 2003 I was thinking of a BAC1-11 with just water. Link to comment Share on other sites More sharing options...
heckler Posted December 8, 2003 Share Posted December 8, 2003 From what I have read, and know (not a lot) from been in the RAF, The ONLY reason a Harrier can hover (besides thrust vectoring) is WI. In hover, that amount of thrust required is huge, so much that the engine has to run at %105 (might be %103) MAX thrust (yes, I know this is impossible but...) the only method that makes this possible is WI as it allows the engine to be slighly cooler - going back to cooler engine, higher boost pressure. Thats also why a harrier can only hover for about 3 mins I think, water runs out. Anyone remember that Harrier that crashed at Lowestoft (Norfolk) airshow? Ran out of water, ironic thing that it crashed into the sea... My 2p si Link to comment Share on other sites More sharing options...
Mark Ayling Posted December 8, 2003 Share Posted December 8, 2003 Originally posted by heckler From what I have read, and know (not a lot) from been in the RAF, The ONLY reason a Harrier can hover (besides thrust vectoring) is WI. In hover, that amount of thrust required is huge, so much that the engine has to run at %105 (might be %103) MAX thrust (yes, I know this is impossible but...) the only method that makes this possible is WI as it allows the engine to be slighly cooler - going back to cooler engine, higher boost pressure. Thats also why a harrier can only hover for about 3 mins I think, water runs out. Anyone remember that Harrier that crashed at Lowestoft (Norfolk) airshow? Ran out of water, ironic thing that it crashed into the sea... My 2p si I can't believe it, but I actually found that really interesting! Link to comment Share on other sites More sharing options...
MONKEYmark Posted December 8, 2003 Share Posted December 8, 2003 can you uses methonol say 50/50 miixed with water. ian with the big power cortina with 4wd 4l v8 super charger and nos and water injection uses 100% metonol i had aqumist fitted for another safety factor to help fmic would like to know if you can use isopropal alchol too? can get it Link to comment Share on other sites More sharing options...
Barnstormer Posted December 9, 2003 Share Posted December 9, 2003 The Harrier can hover without WI but only when the ambient temp is low and the aircraft is light ie low fuel and no weapons. The main problem for a jet engine is density altitude - if the ambient temp is high and/or the air pressure low the thrust of the engine decreases. WI simply increases the density of the airflow so increasing the thrust. Most jet engines run at more than 100% thrust. Indeed the plane I fly today is rated at 108%! When an a/c engine is first tested and certified it normally has rated thrust ie 100% but often over time the engine manufacturers increase the design efficiency, thrust etc to give a but more oomph! Also a/c manufacturers increase the basic weight of an aircraft by adding bits and so the engines need to be uprated. If anybody is REALLY interested to know I can explain more but it won't help you get any more BHP from a Supe. ATB Link to comment Share on other sites More sharing options...
Steve W2 Posted December 9, 2003 Share Posted December 9, 2003 I think that the principles for using WI on a plane are very different from that of a car. I also think that the only way the WI may have a slight advantage is if it's used in ADDITION to the fuel requirements of the car and not in place of any fuel. I dont know that a car squirts extra fuel into the cylinders for a 'cooling' effect. Even if it does it is a design factor by Toyota to have the car running minusculely richer as opposed to leaner and melting a piston. Howver, if you guys are using to effect then thats great. I would be weary though. Flames/explosions and general combustion does not like water. Link to comment Share on other sites More sharing options...
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