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PostPosted: Sun Aug 20, 2017 11:32 pm 
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Bit of advice please. Been told by some installers that conversion on the above is not recommended because it is direct injection. Only one who has said " no problem" is an approved Prins installer who claims he has a kit specific to my CITREON C4 - but I am not keen on getting a Prins installed. What is the view on here re pros and cons ?

I also have a motorhome - 2.8jtd engine. I see that Autogaspol are now advertising conversions on diesel engines. I firist enquired about conversion when I bought the motorhome in 2005 but was told that it was either impossible OR not recommended. Has there been progression in converting diesel engines. ?


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PostPosted: Mon Aug 21, 2017 1:53 pm 
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Location: Yorkshire
I'd probably advise the same as 'some installers'. Several firms make systems to convert DI engines including AEB (OMVL / Emer), AC(Stag), KME, Prins. Most of the systems are LPG port injection and very similar to LPG port injection systems we fit on petrol port injection engines, using the same injectors, reducer, etc, except the electronics are special... electronics have to be special to interpret DI injection pulses and emulate DI injectors. Port injectors are usually pulsed only once (sequential injection) or twice (group injection) per cylinder intake cycle but DI injectors may be pulsed several times per cylinder intake cycle and the various pulses per intake cycle can be of different lengths (hence 'interpret'). DI engines may even pulse injectors during the compression stroke.

The LPG systems referred to so far involve fitting an LPG port injection system onto a petrol direct injection engine. DI engine cylinder heads are designed around the petrol DI injectors, we cannot fit a second set of DI injectors inside the cylinder head, the tips of DI injectors fire directly into the cylinder / combustion chamber. When we convert a port injected petrol engine we can fit the second set of injectors (the LPG injectors) very close to the factory petrol injectors and can achieve results that are indistinguishable from driving on petrol because the principals/methodology between port petrol injection and port LPG injection are much the same. But if we fit an LPG port injection system onto a petrol DI engine the principals/methodolgy isn't the same (port versus direct, single LPG injector pulse on the intake stroke versus multiple DI pulses that may occur during the intake and/or compression stroke) - So for example, the special LPG electronics have to add up the total duration of DI pulses per intake cycle to derive a pulse length for LPG port injectors / fitting port injection onto a DI engine means you lose any advantage that direct injection might give (local/pocketed correct mixture in the combustion chamber which allows di engines to run what would otherwise be a cylinder wide very lean burn) / the DI injectors must in any case still flow some fuel (petrol in this case) because the flow of fuel is what prevents the DI injectors being damaged by overheating (DI injector tips inside the combustion chamber) / so they don't run on 100% LPG even when running on LPG.

Then there are fuel shunting type systems, where either petrol or LPG is fed to the vehicle's factory fitted petrol direct injectors. The greatest challenges for manufacturers of this type of system seem to be more plumbing related rather than calibration related - Two fuels both use the same set of injectors (the vehicle's original DI injectors), so there could be potential for backflow of one type of fuel into the other type of fuel's tank via the other tank's fuel lines etc. A bit of petrol finding it's way into the LPG tank might not have ill effect but a bit of LPG flowing into the petrol tank via petrol lines could be disastrous, a petrol tank cannot take LPG pressure. Some vehicles with this type of system have cold start problems if the engine was turned off when running on LPG.

Prins make both types of system (port injection and fuel shunting). Another manufacturer of the fuel shunting type system apparently went under a year or so ago, not many manufacturers make shunting systems.

The diesel will never run on 100% LPG but it's fuelling can be supplemented with a small proportion of LPG (and make more power with a bit of LPG in the mix too). Claims are up to running on around 30% of total fuelling (30% LPG + 70% diesel). Set the system up to put too much LPG into the mix and diesel engines can be wrecked by 'starfire' or by very high exhaust gas temperatures. Better results can be had on older diesel engines rather than newer diesel engines because some of the gains come from increasing the proportion of diesel that burns in the cylinders versus diesel that is only partially burned or not burned at all / wasted. Newer diesel engines are more efficient in the first place than older diesels because they don't pump as much unburned diesel out the exhaust. Some LPG supplementation systems for diesels monitor exhaust gas temp and will back off LPG fuelling if it gets too hot.

Simon

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PostPosted: Wed Aug 23, 2017 5:50 pm 
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Thanks for the info and advice. Much appreciated.


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