Liquid injection versus gas injection

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marek
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Liquid injection versus gas injection

#1 Post by marek » Fri May 22, 2020 10:48 am

I imagine the number of people running old style mixer systems is very low by now.
Do any of the professionals on the board have an idea of how many liquid injection setups there are out there as opposed to the standard multipoint reducer fed gas setups? (These will presumably run Vialle LPi/Keihin CNG injectors, or others?)

kind regards
Marek

Gilbertd
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Re: Liquid injection versus gas injection

#2 Post by Gilbertd » Fri May 22, 2020 11:11 am

Not many and about 3 times the price of a vapour injection system https://tinleytech.co.uk/shop/lpg-kits/ ... ction-kit/

I still run lambda controlled mixer systems and wouldn't change. Hardly any difference in economy and performance, no, or negligible, petrol consumption (runs on gas from stone cold, no warm up on petrol), stand alone system so not affected by petrol system faults, reliable, easy to fault if there is a problem, minimal number of parts, etc.
96 Saab 900XS, AEB Leo, sold
93 Range Rover 4.2LSE, Lovato LovEco, sold
97 Range Rover 4.0SE, multipoint, sold
98 Ex-Police Range Rover 4.0, AEB Leo, daily motor
96 Range Rover 4.6HSE Ascot, AEB Leo, my spare


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LPGC
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Re: Liquid injection versus gas injection

#3 Post by LPGC » Fri May 22, 2020 8:00 pm

My very rough guess of proportion of the different LPG fuel system types/methodologies of vehicles currently running in the UK, listed roughly in the same order as the system types were introduced to the market...

1. After market mixer systems. This includes mostly older vehicles, mostly fitted more than 10 years ago but also some recent conversions of older vehicles with carb or fairly simple fuel injection systems (a conversion today using this type of equipment would most likely be on something like a 1990's camper van, something with a carb or basic fuel injection system) 10%. Could split this type of system into open loop and closed loop, in which case I would expect open loop (1A) would be around 3% and closed loop (1B) would be around 7% from the total of 10%. A new install of a mixer system would most likely be on a carb / KJetronic older vehicle (because most customers / installers would rather / can only fit type 7 below) which means that in time that 1A 3% : 7% 1B ratio may come closer together then 1A may become more common than 1B.

2. After market gas carb type systems. Very similar to mixer systems but gas is fed under slight pressure to the gas carb. Includes some of the Impco stuff fitted on e.g. American RVs, some of which might even have been converted to LPG in the US before being imported to the UK. 0.4%. But if we included LPG converted boats (on which Impco is popular) this figure would be higher. We could break the 0.4% down to open loop (2A) 0.1% and closed loop (2B) 0.3... Unless we included boats which would increase 2A a lot more than it increased 2B. If we included forklifts 2A would be very much higher!

3. After market continuous port vapour injection injection systems (e.g. Etagas), all closed loop. 0.3%
4. 'Factory fitted' continuous port vapour injection systems (e.g. early Koltec on 'factory converted' Vauxhalls / Fords / etc and some oddballs including BRC on Sprinters/Transits), all closed loop. 0.5%

5. Aftermarket electronic pulsed port vapour injection none slave none-sequential systems (almost standalone LPG fuel systems that don't use pinj as the basis for ginj, such as OMVL C), all early variants closed loop. 0.05%. Unless we included some of the more recent re-introductions (or the only re-introduction whatever the case may be!) of this type of system which is open loop, which might add another 0.02% for a total of 0.07%. And unless we included one-off systems based on Megasquirt etc which might add another 0.02%.

6. 'Factory fitted' pulsed electronic port vapour injection none slave systems (usually standalone but tie in with the petrol ECU, at least causing the petrol ECU to run open loop or avoid OBD mixture errors etc, e.g. later 'factory converted' Vauxhalls / Fords / etc) 1.2%

7. Aftermarket sequential port vapour injection slave type systems for petrol port injection engines (the type most readers are likely to be most familiar with) 83.68%
8. 'Factory fitted' sequential port vapour injection slave type systems (almost entirely the same as the line above but 'factory fitted', e.g. BRC on Sprinters/Transits (not the same type as in listing 6) 0.05%. This type is distinct from type 6 because it is a slave type system (type 6 is usually standalone).

9. Aftermarket sequential slave port liquid injection systems for port injection engines. 0.2%
10 'Factory fitted' sequential slave port liquid injection systems for port injection engines (e.g. some Subaru Tribecca's) 0.1%

11. Aftermarket sequential port vapour injection slave type systems for direct fuel injection engines (the petrol system is direct injection but the LPG system is port injection) 2.5%. 11B a very small number of direct injection vehicles 'factory fitted' with this type of system <0.02%

12. Aftermarket liquid direct injection systems for direct injection petrol engines (inject LPG through petrol direct injectors) 1%

13. As far as I am aware there are no liquid port injection systems available for converting direct injection engines but this type could be produced (though would offer no advantages over types 9 and 10 and is likely to have disadvantages over vapour injection type systems).

I agree with Gilbert that a mixer system and/or gas carb type system, where possible (vehicle permitting) isn't a bad bet if the user/owner is prepared to manually switch back to LPG when the gas has run out. The upsides of this type of system is as Gilbert has said that it's a completely independent fuel system which doesn't rely on many (if any) aspects of a vehicle's petrol system to be working properly in order for the LPG system to work properly, plus this type of system often allows starting the engine from cold on LPG. The downsides are that the driver has to know when to manually switch back to petrol (when the gas has run out) to prevent a potential backfire and these types of systems aren't suitable for a lot of modern vehicles (where modern mostly means post 2000).

'Liquid injection' can mean any of types 9/10/12.
9 & 10 are closely related but type 12 is a very different type of system.

Regards 9&10 it may seem a good idea to have liquid LPG port injection on a petrol port injection engine but in practice the port vapour injection systems are better and the results are better. Liquid port injection systems rely on high pressure in-tank pumps that can fail, the ECUs (and firmware etc) are not as well thought out or as configurable, early systems relied on old tech petrol injectors to inject liquid LPG (including on factory fitted) - the specific old tech petrol injectors were the only injectors at the time that could withstand the pressure of liquid LPG at high enough pressure to avoid vapour locks. The range of available modern liquid LPG injectors is small. Some (older) setups injected vapour anyway(!) including on the factory fitted... the injectors were remote from the manifold and by the time the liquid reach the manifold it would be vapour (lost most of any positives we might read into liquid injection while suffering the downsides of a less than ideal ECU). Quite a lot of liquid injection systems run a multiplier of less than 1 so fuelling accuracy could be worse than a vapour injection system even if the liquid injection system had a good ECU (range of available injectors).

I see 11 (port injection on a direct injection engine) as a fudge which will never deliver ideal results. It means having to run some petrol direct injection to avoid overheating and lack of lubrication of petrol injectors and it means any advantage of direct injection (localised correct mixture, cylinder wide lean mixture at part loads) is lost. The installer is at the mercy of the ECU designer getting aspects of firmware correct (sometimes adding short multiple burst of petrol DI injector pulses per intake stroke / allowing some of the petrol injection pulses to reach petrol injectors and detracting this from the total pulse length) to arrive at a single pulse length for the LPG injector... The installer can adjust the map *multiplier map / rpm correction / etc) but cannot adjust the way in which the ECU interprets petrol injection pulses. In contrast on a port injection engine the ECU only has to measure the length of a single petrol injector pulse (and maybe filter a very short additional injector pulse) per intake cycle so there isn't much in the way of 'interpretation' for the ECU designer and firmware designer to get wrong (yet still the designers of some ECUs get this aspect wrong for port injection).

I believe 12 is the best way forward for converting direct injection engines but this can have it's own type problems too (cold starting problems and problems associated with fuel changeover).
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marek
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Re: Liquid injection versus gas injection

#4 Post by marek » Sat May 23, 2020 7:16 pm

Thank you.
As I suspected, near zero.

kind regards
Marek

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Re: Liquid injection versus gas injection

#5 Post by LPGC » Mon May 25, 2020 11:48 am

You're welcome.

There are still a lot of mixer systems and mixer systems are still fitted but there have never been many liquid port injection systems.
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