Converting a GM Gen-V 6.2L direct injection engine to Propane

Propane, Butane, LPG, GPL, C3H8, C4H10
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turbine guy
Posts: 44
Joined: Tue May 06, 2008 10:51 pm
Location: Fort St. John, BC Canada

Converting a GM Gen-V 6.2L direct injection engine to Propane

Post by turbine guy »

Ok folks, my 2005 GMC Denali, liquid injection truck is getting long in the tooth. (Actually, I just have new truck envy.) This truck has an ex-Bi-Phase straight liquid injection system, 6.0l engine and has 145,000km total accumulated. It still runs well, but I simply want a new pickup truck, specifically a new GM Silverado with the direct injection 6.2l engine. My question to you, or more accurately, please tell me why it won't work:
- I want to eliminate/remove the vehicle gasoline tank & low pressure lines to the camshaft driven high pressure fuel pump.
- Move my pump-in-tank Bi-Phase propane fuel tank from the old truck into the new truck and run the liquid propane lines to the high pressure pump. (I will retain the return feature of the "low" pressure propane system to help eliminate vapour lock.)
- Reprogram the ECM to "think" the engine has smaller gasoline injectors than it actually has to compensate for the lower BTUs per litre of propane vs. gasoline. (I have and am adept with HP Tuners.)
- Hit the key and drive away in my new EcoTec3 6.2l powered pickup.

Please tell me why this will not work and any mods suggested to make it work. I don't give a darn about the GM warranty, if I wreck the engine, so be it, and lesson learned. I look forward to your input.

Robin.

C3H8
Posts: 1129
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Converting a GM Gen-V 6.2L direct injection engine to Propane

Post by C3H8 »

I'm surprised. I thought this post would have piqued some of our members interest. Some of the manufacturers have dabbled in this area in Europe already. Turbine Guy and I have already had some PM on this. I see the main issue actually being on the low pressure side of the system. The gasoline pump pressure is controlled by pulse width modulation and the pressure varies according to RPM and load. This means the propane system can likely use the same control, however vapourization within the low pressure side will remain an issue on start up. On a dedicated system the lines will require purging to ensure liquid fills the lines as far as the high pressure regulator. This will necessitate designing some kind of return system that can possible be closed once the line is purged.

On the high pressure side the pressures are substantially higher ranging from 500 PSI to 2800 PSI. This should easily maintain the LPG in a liquid state.

TG mentions putting in smaller injectors to compensate for the increased liquid to vapour state of the LPG. Also he has skills on tuning of ECU's providing he can gain access to the newer style of ECU's GM has used on this model. There is a possibility this may not be required. The DI systems have a very broad range of controls. In the European installations they still remain dual fuel. This allows the usual gasoline start giving the ECU time to go through any preliminary testing while on gasoline. They then shut off the gasoline side and start up the propane which has been purging while the gasoline is running. No hard to do as they just put lockoffs for both the gas and LPG right at the high pressure regulator. Although I have no direct experience or confirmation it appears they operate through the same injector for both gasoline and propane. To use DI for both fuels they have to or the injector tip overheats and is destroyed.

The only other way DI can be converted is to put in a sequential injection system on propane and then program the system to use a tiny bit of gasoline all the time to keep the injector tip cool. What's a tiny bit, I don't know. The issue with doing it this way is you lose the efficiencies of DI which can be substantial over sequential.

The last factor is compatibility with the gasoline ECU. Most of the European systems show the addition of an LPG ECU. I am not sure of all the functions of that ECU. It may actually modify injector PW or it may just be a glorified superfix. Hopefully more information will come out as DI systems become more widely available.

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Converting a GM Gen-V 6.2L direct injection engine to Propane

Post by storm »

C3H8 wrote:
Mon Nov 16, 2020 12:57 pm
I'm surprised. I thought this post would have piqued some of our members interest.
Interest = yes, knowledge to answer = not much.
C3H8 wrote:
Mon Nov 16, 2020 12:57 pm
TG mentions putting in smaller injectors to compensate for the increased liquid to vapour state of the LPG. Also he has skills on tuning of ECU's providing he can gain access to the newer style of ECU's GM has used on this model. There is a possibility this may not be required.
That's not quite what he meant.
turbine guy wrote:
Fri Nov 13, 2020 9:56 pm
Reprogram the ECM to "think" the engine has smaller gasoline injectors than it actually has to compensate for the lower BTUs per litre of propane vs. gasoline. (I have and am adept with HP Tuners.)
This means that TG believes he needs to change the "value" (basically a flow value) within the OS for this particular engine to suit LPGs lower energy output.

@Turbine guy: I wouldn't be doing this to start with simply because Liquid LPG has a much greater potential to remove latent heat from the air and surrounding components as it is injected into the engine. This has the effect of rapidly and dramatically increasing the density of the intake charge which in turn increases potential energy output. I would make sure the injectors are of an appropriate and comparable size physically and then leave the injector value alone until I was able to get some datalogs and then check the O2 readings (try to have it set to lambda rather than AFR), STFT and LTFT, and the MAF.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

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