I need a reliable test that can determine the percentage of gasoline in diesel fuel after they have been mixed together. My boss seems to think (I think he's wrong) that we wound up with a considerable amount of gas in our last diesel delivery. One or more ways of finding out would be helpful. The analytical company we sent samples too say there is no real way of telling from their standpoint.

 

flamability to an open flame????

 

I'd find a different analytical company if they can't tell a difference between diesel and gas

 

Specific Gravity of liquids:
Gasoline, Vehicle .....60 F......... 737.22
Diesel fuel oil ..........15 C .........820 - 950

 

The question is if there is any gas mixed in with our diesel and if so how much.

 

Yea we tried that but it didn't really prove much. Fresh diesel from another source extinguished a match (duh). Mixed with 20% Gas is ignited (again duh) Diesel drawn from our storage tank also extinguished a match. Seems to me that that points to it being less than 20% gas if any in the fuel but there are entirely to many variables in that for it to be proof.

 

How do I determine that when they are theoretically mixed together in the same container? My suggestion was to put some in a jar and let it settle for a few days. (how many I'm not sure) I would think that since they have different specific gravities that the gas (if any) would float. Then simply skim whatever was on the top layer off and send it in for analysis. From there determine by volume what the approx percentage was.

How this all came about was that we have a Cat in a Pete that blew two injector nozzels and scored the cyls. Company is trying to make the fuel jobber pay for the repair and I think it is BS. IMO the ratio of gas to diesel would have to be severe (like to the point of smelling it) to cause any serious damage and there is no way the driver would have made it the distance he did before noticing something wasn't right...

 

Alright, I was going to be the first reply, but I had to go to my Digital Design class.

This is kind of cool. In chemistry for engineers we are given various senarios where some company sends us samples of things and our team makes a conclusion about it to report back. It's the same thing as this.

You need pure diesel and pure gasoline. Find the density of each with Denisty=mass/volume. Make your volume and mass measurements very accurately. Next, take a sample of your diesel-gas and find it's density. Using a larger sample will give better results. There is only one possible mixture for any density of the diesel-gas that you may find. To find out how much gas is in the diesel use the following equation: X(gas_density) + (1-X)(diesel_density)=diesel_gas_density; where X(100) is the percentage of gas in the diesel.

For density you might use kg/L, but all it really has to be is some ratio, even pounds per gallon. Just use the same ratio for each "density" measurement.

 

As that ancient Greek, (whose name escapes me) said while sitting in the bathtub thinking about how to determine if the king's gold was mixed with lead (Pb): "Eureka!"

 

So in laymans terms SAY WHAT?
Is there a simple test he could do without needing a lab?

 

Uh ok so that is - - - -
Density = Mass devided by volume (need one clean sample of each fuel)

the density of the gas + the density of the diesel minus the density of the gas = the mixed density or X
and then X devided by 100 gives you the percentage???

Am I reading that right?

 

No, I don't think so.

X(gas_density) + (1-X)(diesel_density)=diesel_gas_density

In other words:
[(mixed fuel density minus diesel density) divided by (gas density minus diesel density)] all multiplied by 100 equals the percentage of gas in the fuel.
You do the stuff in parentheses first.

In other words:
M = density of mixed fuel
D = density of Diesel
G = density of gasoline
(you have to find all those)
P = percentage of gas in fuel

P = ((M-D)/(G-D))*100

 

Take ShovelHead's numbers for the fuels' specific gravity and plug them into Drolex's equation, along with your empirical measurement of the mixture in question... please report the results of your homework in the morning.

BTW - even straight unleaded won't necessarily hurt a diesel, since the fuel is not injected until combustion is needed. The obverse (#2 in a gasser) is far worse due to diesel's relatively low octane, causing preignition and detonation.

If your test sample won't ignite with an open flame, I don't see how it could have damaged the injectors.

 

Sorry, do not use Shovelhead's posted numbers. Those are not the needed numbers. Anyway, this calculation will be more accurate if you measure the desities of the pure forms of the diesel and gas that actually went into this mixture.

 

But he can't measure the exact blends that went into it. And Diesel can vary as to it's spefic gravity.

But I agree with XLR8R, if it will extinguish a match, it should be fine. Dump some PS in it if you are woried, for a little bonus lubricity.

And maybe shop for a new supplier