Maximum Value for PW and injectortiming?

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Re: Maximum Value for PW and injectortiming?

Postby billr » Tue Jun 12, 2012 7:48 am

I'm thinking it might not be all that hard to test the injector flow. Take the injector "rail" loose from the manifold and point one into a big collapsed plastic bag, with the bag sealed to the injector with tape. Then do the flow test in "test mode" and weigh the bag afterward. I have used (for other purposes) thin bags that hold about 1 cubic meter, that should be enough.
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Re: Maximum Value for PW and injectortiming?

Postby Activate » Tue Jun 12, 2012 1:57 pm

Hello Bill,

With normal gas maybe it can be done that way but I dont't think that will with LPG?
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Re: Maximum Value for PW and injectortiming?

Postby billr » Tue Jun 12, 2012 2:41 pm

Why not? Once it exits the injector it will vaporize and take up a lot of volume, but that's what the "big bag" is for. As long as you can trap it all in the bag, a pound (or kg) of fuel is still a pound, no matter how much is liquid or vapor. That's really what we are looking for in fuel-flow, mass of fuel. Volume ratings, like cc/min, have to be converted/corrected to mass for real fuel calculations.
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Re: Maximum Value for PW and injectortiming?

Postby racingmini_mtl » Tue Jun 12, 2012 3:45 pm

You can't weigh gases like that due to the atmosphere. Just imagine you were going to weigh the helium in a balloon: you know there is a mass of helium in there but you wouldn't be able to find it using a scale.

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Re: Maximum Value for PW and injectortiming?

Postby billr » Tue Jun 12, 2012 6:51 pm

Oh, yes you could Jean. But with helium you would be measuring "lift" (negative weight); we all are familiar with that, right? Remember, I'm figuring to start with a collapsed bag with little air in it. Not a perfect vacuum, of course, so not a perfect flow test. But I think it would be within 5%, which is a whole lot better than what he has now... nothing. If I did my arithmetic right, that one- cubic-meter bag of propane vapor would weigh 1.5# in room-temperature air (plus, of course, the tare weight of the bag). A limp bag, by the way, not a rubber balloon that would require the propane be at some pressure to inflate it.
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Re: Maximum Value for PW and injectortiming?

Postby racingmini_mtl » Tue Jun 12, 2012 9:31 pm

How can you measure the weight of the helium from the lift without knowing the exact volume (and therefore the weight of the displaced air)? Or are you saying that you know precisely the bag volume and that you also think you can fill it precisely to that volume? And measure the exact pulse width to get there? You also need to measure the gas temperature accurately to know its density.

If you can do all that then ok, you can get the injector flow rate. But that seems unlikely to me (but I could be wrong).

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Re: Maximum Value for PW and injectortiming?

Postby billr » Tue Jun 12, 2012 10:26 pm

I think you are making it more complicated than it needs to be. You don't need to know the exact volume of the vapor. You just need to start with a bag as empty of air as possible (ideally no air) and know the density of air and propane at the ambient temperature and pressure. No problem with the propane temperature being unknown, I'm patient and would let the bag sit for several hours until the propane was at same temp as air. And the pressure would be same as ambient, remember this is a "limp" bag and not an elastic balloon. Measuring the injector pulse-widths (and number of them) would be exactly the same as testing for a liquid fuel. Can't that be done pretty easily in "test mode"? You are correct that the measured weight of propane in the bag would not be the actual weight of propane flowed, because of buoyancy of the air displaced, but you would have all the data needed to calculate actual weight of propane flowed into the bag.
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Re: Maximum Value for PW and injectortiming?

Postby racingmini_mtl » Tue Jun 12, 2012 10:39 pm

I think you're making it simpler than it is. The fuel coming out of the injectors is going to be quite cold due to the gas expanding. That means you have to evaluate how many pulses will be needed to fill the bag once the gas expands when going to room temperature. It seems there would be a lot guess work and time spent on this with possibly quite random results unless you're very meticulous.

One thing is certain, that's definitely not as straightforward as measuring liquid fuel injector flow rate.

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Re: Maximum Value for PW and injectortiming?

Postby Activate » Tue Jun 12, 2012 11:26 pm

The partnumber for the Bigas injector is DISTB2F400F with 3.0 mm Nozlle.

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Re: Maximum Value for PW and injectortiming?

Postby jamies » Wed Jun 13, 2012 6:00 am

having done VSI injection myself, with similar injectors, you will find you need to modify the p&h boards for the injectors to open correctly, and then to stay open after the peak phase.
btw "speedup" relates to peak time, they are recommending 4ms peak.
solder some 0.22 ohm resistors over the top of the 0.1 ohm resistors to give you a 6 / 1.5 amp peak and hold and you will find that this will reduce your pulsewidths and possibly solve some issues for you.
Your 3 ohm injectors are probably not peaking correctly at 12 volts (12v, 3 ohm, 4 amps, take any losses in wiring etc its marginal), therefore relying on the peak timer on the p&h boards.

Also inject the lpg using end of squirt, use a timing table similar to this to get up and running.
If you have a single plane intake injector timing is more critical as other cylinders can steal the gas if incorrectly timed.
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Re: Maximum Value for PW and injectortiming?

Postby Activate » Wed Jun 13, 2012 9:20 am

Thanks for the reply james.

I already have placed the extra resistor over the original ones.

I have the stock intake, I will try the Timing table as you suggested.

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Re: Maximum Value for PW and injectortiming?

Postby Activate » Thu Jun 14, 2012 1:03 am

Another qeustion :

My Fuelload goes up to 175% the timing table only goes to 100% can that be a problem?

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Re: Maximum Value for PW and injectortiming?

Postby Marek » Thu Jun 14, 2012 3:49 am

For testing purposes, why not use a compressed air supply at something at or near the desired constant operating pressure at measure the volume of water displaced from an upside down graduated cylinder?

Assuming ambient temperature doesn't vary and the capacity of the compressor is high compared to the volume metered out, you could simply log how many injection pulses it takes for the cylinder to overflow in each case at different pulsewidths and plot that it the usual manner.

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Re: Maximum Value for PW and injectortiming?

Postby jsmcortina » Thu Jun 14, 2012 3:58 am

Marek wrote:For testing purposes, why not use a compressed air supply at something at or near the desired constant operating pressure at measure the volume of water displaced from an upside down graduated cylinder?

Indeed! I feel like a dummy for not remembering my school chemistry lessons.

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Re: Maximum Value for PW and injectortiming?

Postby racingmini_mtl » Thu Jun 14, 2012 6:20 am

I thought of that but you would need to keep the water level inside the graduated cylinder at the same level as the water outside. Otherwise you have more or less pressure than ambient and that would affect the measurement. And you would need to do it in real time to keep the pressure differential at the injector constant. But after checking this again, that would only be a few percent of pressure differential with any reasonably sized setup so that should work.

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Re: Maximum Value for PW and injectortiming?

Postby billr » Thu Jun 14, 2012 4:19 pm

Oh my, I had decided to let this one die a couple of days ago, after we had debated my "big bag". I see two potentially serious problems with using air in place of propane. First, propane and air have considerably different viscosities; so substituting would involve complex (for me) compressible-gas mathematics with things like Reynolds numbers. Maybe even have to open up an injector to measure actual physical sizes of stuff. Second, I question whether the injector is even flowing propane gas; I expect it is liquid in the injector and then flashes to vapor after it exits the injector nozzle. So testing with a gas (air) wouldn't be nearly the same as the flow with liquid propane. I, too, admit that I might be all wrong; but I think my concerns merit serious consideration/discussion.
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Re: Maximum Value for PW and injectortiming?

Postby Marek » Thu Jun 14, 2012 11:17 pm

Bill,
The typical setup for "LPG" or "autogas" is to have a reducer (or vaporiser) to convert liquid lpg to gas using the the car's cooling circuit as the source of heat. The unit reducer also regulates the pressure using a set screw, spring and rubber diaphragm to feed a gas injection rail which houses per cylinder injectors together with a pressure and temperature sensor. Typical operating pressure is 1.2 to 2 bar referenced to MAP.

The setup you refer to would be described as "CNG" and would run liquid straight to the injector for direct injection - that is not being considered here. It is a much more rarely seen system.

(The reason it finds favour in Europe is mainly due to taxation - the cost of filling up is almost halved from the current petrol rate of around USD10 per gallon. The logic behind that is that it is a cleaner burning fuel than either petrol or diesel.)

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Re: Maximum Value for PW and injectortiming?

Postby billr » Fri Jun 15, 2012 8:03 am

OK, thanks for educating me on that. I knew the old propane forklifts I have worked on vaporized before mixing in the "carb", but I figured FI would handle only the liquid. I probably should have known better from the physical size of the injectors I saw in pictures.
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Re: Maximum Value for PW and injectortiming?

Postby Activate » Mon Jun 18, 2012 10:03 pm

can anybody tell me if it is a problem that there the feulload table goes to 175% and the injectortiming goes to 100%?

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Re: Maximum Value for PW and injectortiming?

Postby racingmini_mtl » Mon Jun 18, 2012 10:28 pm

Do you mean the VE table goes to 175? That could be possible. And do you mean the duty cycle goes to 100%? If so, that's not good. You want to keep it less than 85%. If it goes higher than that, your injectors are too small.

If you meant something different, then you need to use the exact name for the values you see. Also posting an msq and log showing what you mean is always less ambiguous.

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