Dual Fuel Liquid LPG systems

[Blu302]

Has any one had any work done with dual fuel liquid lpg systems as i'm currently sizing up a new system for my AU XR8. the new systems just out apparently use a piggy back ecu on the factory ecu. could this be done wholly and soley with the M800 running sequential injection? I know that the M800 cant run 16 injectors independently, (8 petrol, 8 lpg) but could a changeover system be implemented (when changing between "maps") where the M800 uses the same 8 injector outputs, But using an output going hi or lo, change from one "group" to the other? I was looking at running a MOSFET driver to change over between the banks (common ground for injector bank isolated by driver circuit and one selected from M800 output giving rapid changeover switching (few ns)). Other thing is how the slight RDSon resistance (0.15 OHM) will affect the injectors?


Any ideas/input much appreciated (pro and cons)

[DarrenR]

I'm not too sure what kind of current the liquid LPG injectors would need to open, but assuming the are 12V and under 8A operning current that an m800 can drive, then a switch over system 'could' work ok.
You would need to run multi maps in the ECU so you can change the injector settings, which would require the ECU to be reset meaning it not be a seemless change over. Resetting the ECU takes about half a second.

The biggest problem is switching the injectors. You can't use MOSFETs because of the reverse flyback voltage when turning off the injector the drain source diode will conduct and badly affect injector closing time amongst other problems.
The only way you could do it is with old fashioned relays! You need a switch for every injector. 4 pole relays are available so you would need two 4 pole double throw (4PDT) relays. It would be a bit messy, not recomended...

If you can wait for our new M1 series ECU, the largest ecu has 24 injector outputs so this could do what you need without any problems.

[Blu302]

I had the M800 installed a few years ago by CRD in sydney, and after working with a multi map setup to see how long it takes to change over, i got it to continue running with an idle boost to 1200 rpm. smooth as without any noticable hiccup (runs a bit rough from the cam so hard to tell). Another thing, if all the injectors run a common ground, could i just isolate one group while grounding the other bank with a 150A SPDT relay? The system is all hi resistance injectors as well?

Thanks in advance

[DarrenR]

I think you mean if all the injectors run a common 12v and the common switched by a single relay? They are grounded by the ECU so they can't run a common ground.
And the answer is still no, you can't connect any of the common side of the injectors together either.
Basically they back feed each other, it's hard to explain in words but for the injector that is turned on, the paired injector in the other set that is has its common disconnected is also turned on via the other injectors that are off.

I did have a good think about it, and the best solution i could come up with that doesn't interfere with the injector operation is two 4PDT relays like i suggested. Using high impedance injectors you only need light relays as long as there switch contact voltage is at least ~100V. Low impedance injectors would only need ~5A relay anyway.

[SportsCarRacer]

Guys, maybe a simpler more elegant solution:

Wire the 8 injectors for each fuel as paired "banks"...4 injector drivers per fuel required. Thus the 4 petrol injector "groups" goto inj1-4, and the 4 groups of LPG injectors go toinj5-8...no big disadvantage over full sequential, especially on v8.

Then, use primary & secondary injection, setup so that if lpg_on input is 1, inj5-8 do 100% of the fuelling
if lpg_oon dig input is 0, then use 100% petrol injectors (inj1-4..primary).

Then use a spark modifier table (eg user 1) to provide a spk advance adjustment when lpg is slected

This allows phasing/blending of the two fuels also...ie: cold start....the only thing you would want to do to make it spot on is ensure that a fuel gauge input from each tank has the ability to set or clear the lpg_dig_input, so that you can't select a fuel which has an empty tank.

[DarrenR]

I like your thinking SportsCarRacer! But you would have to set the ECU to be a 4 cyl 2 stroke to do that and have to run waste spark. If you're running waste spark anyway it is of no real disadvantage, and firing the injectors twice per cycle is possibly advantageous on a group fired engine??

Full sequential is only really of any power advantage if the injection timing is tuned, i suggest?

[SportsCarRacer]

Hi Darren, i agree with the waste spk (and 4 coil driver outputs), but couldn't the injection setup paramers reflect batch- or semi-sequential-fire v8 (thereby the ecu knows it fires a "pair" of injectors)...i thought this was done in fuel setup, and using negative numbers (ie:-2, -4 etc for no. of cyls/2)...have to say it's a while since i've done one of these...but this in theory should run the same as what you had suggested (4cyl 2 stroke)...besides, with a "crank" trigger, wasted spark / batch fire is easy! A ford engine (windsor?) should have the ingredients...ie 36-1 crank wheel & 50% duty sync pulse. You just need to add 8xBA V8 coils (and bosch igntors..tooo hard!) or 2x4 post windsor AU falcon coils (4x2 wasted spark)...i think this would work a treat...shame you're not in melbourne 302 man, as i think this would be an interesting project i'd be interested in taking on as a job...

It just depends on how the M800 treats the injector ouputs when a) in semi-seq / paired injector mode, and using 4 injector drivers and b) with primary/sec injector turned on....so you effectively have two seperate sets (2 fuels) of 4 pairs of injectors.

I still think this would work....but hopefully as ver3.5 software is written! I'm sure i've seen prim/seq wired gen3 v8's before, so it must be able to be done...yeah? This is the same as normal, except we are putting different fuels in the prim/sec injectors, and using the lpg_selected_ digin as an input into the pri/sec %split table to control which fuel is selected....

Worth trying on a sim3 Darren, do you think?

[Blu302]

the idea seems plausible but my head is starting to spasm just thinking about it. With being in sydney, I would still travel to Melb if the setup was cheaper than up here. (forget the travel costs+roadtrip )

[TOL]

If you can wait for our new M1 series ECU, the largest ecu has 24 injector outputs so this could do what you need without any problems.

Hi Darren,

I wonder if you could expand on the item above, and is this the M190 that you speak of which has the 24 injector channels? I might have a dual fuel application for it.

Let's assume that a person has a boosted dual fuel V8 engine. Eight gasoline port injectors, and eight methanol port injectors. The goal would be to drive around on gas, and only use the meth when under serious boost. The ECU tables would be setup to assume gas when not in boost, and to assume meth when in boost.

With the 24 injector channels you mention, could a person prescribe 8 sequential gas channels, and 8 sequential meth channels, and then flip/flop between the two groups based upon the state of boost?

My original plan was to use my M800 plus an external industrial 8 channel relay box to "toggle" back & forth between the gas injectors and the meth injectors as needed. If the M190 will handle the same function, then maybe I'll hold off until I can get my mitts on one of those instead.

The approaches above would give me either Fuel A or Fuel B. Would it be possible with the M190 to arrange for more of a fuel blender approach where fuels A & B could be phased in & out to form blends?

Where can a person read more about the M1 series ECU's?

Thanks.

[DarrenR]

SprotsCar,
I just confirmed with Mark here, and the only way to do hi/lo on a V8 is to set the ECU to be a 4 cyl 2 stroke, -4 in the number of cylinders which I think is what you're referring to anyway! That will all work fine. The only other different option is No. of cyls 48, which is 8 cyl synced once per rev, that still uses 8 inj outputs but is semi sequential, fires two outputs at the same time. It would be nice if we could fully customise the injector operation, but it would probably cause more problems than it would solve... The M1 is fully customisable tho (for hi level users).

TOL,
Yes it is the M190 I’m referring to. It has 12 peak hold and 12 saturated injector drivers. You could actually run tri fuel with this! Any switching and or blending is possible, it would need some customisation of the software which is what the M1 series is all about, with that anything is possible.

I heard of someone doing what you want to do a while ago on an NA 4 cyl with an m800, lo injectors petrol, hi injectors had a nitromethane / methanol mix! The fuels were beautifully blended to feed the power in progressively. The car had had a number of turbo and supercharges and apparently this setup was far better.

We don't have a lot of info available on the M1 yet as the finer details have not yet been nailed down. Just keep an eye on the web site for news.