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From: Austin Shackles on 12 Apr 2006 02:36 I've been thinking about liquid phase injection... The injection system on the sierra (K-jet) runs, IIRC, at a nominal 5.5 bar (or something around that, anyway). This is not far different to the pressure that you get in a propane tank, provided the temperature is something reasonable. is there any reason why I can't feed liquid LPG from the tank to the fuel distributor inlet on the K-jet system? OK, it'd presumably need adjusting to get the fuelling right - but since the fuel contains less energy but is at a higher pressure, it might not need that much adjustment. Actually that was just an example, what I was wondering about really was more modern injection systems - for example, if I buy a 2-litre ford minibus which I have my eye on, I imagine it has the injection version of the DOHC engine as fitted to later sierras. I don't think it's new enough to be a duratec, even if there is a 2-litre duratec. But the same applies - you already have liquid injection and a metering system for it. dunno what pressure it runs at, mind you, but to be effective an injection system has got to be fairly high pressure. [aside: the book says the lucas hotwire in the later rangies is 2.5 bar] However, there ought to be scope for regulating the input pressure, and in fact, if you get the input pressure right, it should be possible to vary the pressure by just enough to compensate for the different specific energy of the fuel, and not have to adjust the metering at all. e.g. if the fuel has 10% less specific energy, then upping the pressure by 10% should deliver more fuel. Get the ratio right and it should run on LPG or petrol with no other adjustments. OK, tell me why it won't work... -- Austin Shackles. www.ddol-las.net my opinions are just that "The woods are lovely, dark and deep. But I have promises to keep, And miles to go before I sleep." Robert Frost (1874-1963) from Stopping by Woods on a Snowy Evening
From: Stewart Hargrave on 12 Apr 2006 14:59 On Wed, 12 Apr 2006 07:36:17 +0100, Austin Shackles <austinNOSPAM(a)ddol-las.net> wrote: > >I've been thinking about liquid phase injection... > >The injection system on the sierra (K-jet) runs, IIRC, at a nominal 5.5 bar >(or something around that, anyway). This is not far different to the >pressure that you get in a propane tank, provided the temperature is >something reasonable. > >is there any reason why I can't feed liquid LPG from the tank to the fuel >distributor inlet on the K-jet system? My Bosch book on fuel injection systems says, re. K-Jet: "Primary pressure regulator...holds the delivery pressure (system pressure) at about 5 bar." "The injection valves...open of their own accord when the opening pressure of e.g. 3.5 bar is exceeded." "The control pressure is tapped from the primary pressure through a restriction bore. This restriction bore serves to decouple the control pressure circuit and the primary pressure circuit from one another...When starting the cold engine the control pressure is about 0.5 bar. As the engine warms up, the warm up regulator increases the control ressure to about 3.7 bar." My understanding of the system is that there are two regulated working pressures - the 'main' pressure (5 bar) which delivers fuel to the injectors, and the 'control' pressure (0.5 - 3.7 bar) which makes all the gubbins in the distributor work which controls how much fuel is delivered to the injectors. Thing is, because these are pressures that are regulated by a return to the tank, the pressures are relative to tank pressure - ie the absolute pressure (relative to atmosphere) is going to be up to 14 bar. You are still going to need a pump so that the pressure regulators work (they depend upon an over-delivery of fuel from the pump - the regulators bleed the excess back to the tank, hence maintaining the required working pressure). I wouldn't want to guess whether the seals, pipes, unions, etc., are up to this. My other initial thought is, that as the injectors open simply when the pressure behind them gets above 3.5 bar, then even when you have turned the engine off, they are going to continue venting LPG. You'd either need a shut-off solenoid on each injector, or find a way of increasing the opening point to somewhere comfortably above 7 bar. I guess you would also need to consider injector freezing, too. -- TSH For email, replace 'SpamOnlyToHere' with my initials LPG info. page: www.tshargrave.co.uk Now with added Biodiesel (and getting a bit out of date)
From: Tom Woods on 12 Apr 2006 16:39 I was googling about the possibility of using LPG in a k-jet system the other day and i'm sure i found one of your (Austins) old threads in the LPG group where the pressure of the LPG inside the system was given at different temperatures - and it ended up being a very wide range that was outside the scale of the K-jet system.
From: Tom Woods on 12 Apr 2006 16:40 On Wed, 12 Apr 2006 21:39:02 +0100, Tom Woods <news(a)NOPSAMtomwoods.co.uk> wrote: > i'm sure i found one of your (Austins) old threads >in the LPG group D'oh. this is the LPG newsgroup!. I cant tell it apart from A.F.L!
From: Austin Shackles on 12 Apr 2006 17:36
On or around Wed, 12 Apr 2006 19:59:54 +0100, Stewart Hargrave <SpamOnlyToHere(a)MiserableOldGit.Me.uk> enlightened us thusly: >On Wed, 12 Apr 2006 07:36:17 +0100, Austin Shackles ><austinNOSPAM(a)ddol-las.net> wrote: > >> >>I've been thinking about liquid phase injection... >> >>The injection system on the sierra (K-jet) runs, IIRC, at a nominal 5.5 bar >>(or something around that, anyway). This is not far different to the >>pressure that you get in a propane tank, provided the temperature is >>something reasonable. >> >>is there any reason why I can't feed liquid LPG from the tank to the fuel >>distributor inlet on the K-jet system? > >My Bosch book on fuel injection systems says, re. K-Jet: > >"Primary pressure regulator...holds the delivery pressure (system >pressure) at about 5 bar." > >"The injection valves...open of their own accord when the opening >pressure of e.g. 3.5 bar is exceeded." > >"The control pressure is tapped from the primary pressure through a >restriction bore. This restriction bore serves to decouple the control >pressure circuit and the primary pressure circuit from one >another...When starting the cold engine the control pressure is about >0.5 bar. As the engine warms up, the warm up regulator increases the >control ressure to about 3.7 bar." > >My understanding of the system is that there are two regulated working >pressures - the 'main' pressure (5 bar) which delivers fuel to the >injectors, and the 'control' pressure (0.5 - 3.7 bar) which makes all >the gubbins in the distributor work which controls how much fuel is >delivered to the injectors. > >Thing is, because these are pressures that are regulated by a return >to the tank, the pressures are relative to tank pressure - ie the >absolute pressure (relative to atmosphere) is going to be up to 14 >bar. some error there. absolute pressure in a vented tank is going to be more or less 1 bar... >My other initial thought is, that as the injectors open simply when >the pressure behind them gets above 3.5 bar, then even when you have >turned the engine off, they are going to continue venting LPG. You'd >either need a shut-off solenoid on each injector, or find a way of >increasing the opening point to somewhere comfortably above 7 bar. You'd have shut-off solenoids, of course. But point taken; although how does the petrol system avoid this, or perhaps it doesn't? > >I guess you would also need to consider injector freezing, too. I doubt they would, they're on the top of the engine just beside the combustion chamber. Likesay, I wasn't really considering it for the K-jet anyway, that runs OK on a single-point system. I was thinking more of feeding LPG to such as the Ford EEC IV system on a 2-litre twin-cam, which is an electronic injector thing running the injectors in pairs - it's not multi-point sequential. I imagine it's a bit like the lucas hotwire type. Main thing as I see it is to find a way of supplying LPG at the right sort of pressure. This should be possible with some kind of regulator, but I don't know exactly what. Either that, or you have to have a circulatign pump and return to tank system. -- Austin Shackles. www.ddol-las.net my opinions are just that "Carpe diem, quam minimum credula postero" (sieze today, and put as little trust as you can in tomorrow) Horace (65 - 8 BC) Odes, I.xi.8 |