liquid propane fuel system, not vapor. 2

[ncnichol]

I have a h/p SB chev eng that i'm thinking of changing to propane power. The most common systems change the liquid to a vapor before it enters the eng. I have heard of systems that inject liquid into the eng. does anyone know of such a system? Does it need some type of direct injector, or mybe some kind of carb-mixer that would spray liquid into the intake? The problem I have with direct injection would be high cost.The possible high performance gains of a system like this could be huge. Thankyou for any help.

 

[patprimmer]

There are several previous threads on this very subject that you will find if you simply search. One was very recent.

Franz Hoffman is the resident expert on this subject and I believe another member here was actually directly involved in design and development of one liquid LPG injection system.

As far as I know, none are direct injection, but are EFI and can be used in place of OEM EFI injectors on modern cars so long as you have a method to tune to adjust the injector pulse width to correct for different injector flow rates and different fuel flow rates required.

It also helps if you can remap the ignition timing.

It also helps power if you can adjust the compression to around 11:1, the exact optimum number depending on you inlet valve closing point among several other things.

Don't expect real gains in power over high octane petrol.

You can get real gains in power and economy over old gas phase carbies or mixers.

You might get small gains by replacing low to mid 90s octane pump petrol and carbies if you go to liquid injection propane and raise the CR a few points.

Remember, although gains can be had from the higher octane, there will also be losses from the lower energy content per unit weight of the fuel vs petrol.

I deliberately use the British terminology of petrol instead of gasoline so as to avoid confusion between gas (gasoline) and gas (LPG or propane).

If you can source reasonably pure propane you get a somewhat higher octane than if you only get a commercial grade LPG fuel which often contains quite a lot of butane in many parts of the world. Butane lowers the octane considerably.

Regards
Pat
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[franzh]

Several major propane equipment companies have working platforms of GDI fuel systems. The vehicles reportedly work very well. They can only be installed on engines specifically built for GDI and not a conventional engine.

The other member is Turbo Cohen, his expertise is invaluable.

Franz

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[TDIMeister]

I'm working on adapting a petrol DI multihole injector nominally for 120 bar operation to convey LPG in liquid form. Because the the LPG tanks are usually limited to around 200 PSI (and my project does not want to use an additional pump), the injector and all components contacting the LPG must be kept below approx 40°C in order to ensure that the LPG remains liquid and doesn't flash into vapour anywhere except once it gets sprayed. This means that direct injection is dispensed with (the injector tips are subjected to high temperatures, being directly in the combustion chamber), but the injector is placed very close to the intake valve in a composite runner/holder.

Actuation of the injector is by peak-and-hold solenoid; we'd be controlling this with a Opal-RT HiL controller and the "ECU" realised in Simulink.

 

[franzh]

You will not be able to overcome cylinder pressure at TDC with LP vapor pressure in your tank. All of the DI projects I have reviewed use the petrol HP pump at the engine to boost the LP pressure to the same as petrol for direct in-cylinder injection. All of the DI projects I have reviewed utilize the adaptive fuel trim capabilities of the original ECU.

Part of your post states in-cylinder injection, but the last portion describes an in-manifold injection (very close to the intake valve in a composite runner/holder). Different strategies, different technologies.

Franz

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[TDIMeister]

Franz, I'm using GDI Injectors but placing them in the intake ports... I thought this was amply clear. We're thinking outside the box, this is not for a passenger car engine application.

 

[franzh]

Got it, I didnt make the immediate connection. The use of GDI injectors is an unnecessary expense and added complexity. Siemens makes liquid bottom feed injectors, as does Keihn and Bosch. You will need to do some leg work. They are the same ones as used in the Roush LPI trucks, injecting liquid propane just behind the intake valve.

They must use a pump because the radiant heat of th engine will cause the propane to flash to vapor at the rail. The pump raises the relative saturation pressure. No one has worked out a means of keeping propane liquid at lower pressures or higher temperatures at the given saturation pressure.

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[turbocohen]

Atchooly there have been a few low pressure DI LP projects we supported when I worked at Siemens which is not the same operation but owned by Continental. Synerject later on put LP through their poppet valve DI boosted by an 85psi air pump.

in the late 90's a student in Canada adapted a modified CNG injector I made out of a DI prototype and I think it was on a Chrysler 2.4.. Ran damn good and smogged well within ulev II. Heat was the issue as it so often is.