Misfuel ratios page

[Julian]

I've started a page on misfuel ratios put up the graph of rug-derv mixes here ... http://www.biopowered.co.uk/wiki/Calculating_misfuel_ratio

I'm just in the process of writing some blurb about using the graph and going back over a VOD thread Keith highlighted recently ...

http://www.vegetableoildiesel.co.uk/forum/viewthread.php?tid=14224&page=2

The method put up by scottydog, originating by zebedee I believe, implies that if a litre of misfuel weighs 744 grams, it equates to an SG of 0.744.  Surely that's only correct if the liquid is water.

But in the same thread glycer-rides gives this equation ... % of petrol in misfuel = 922 - (1.11 x MFW).  Where MFW = misfuel weight.

Having trouble getting my head round this at the moment can anyone help!

[Keef]

The method put up by scottydog, originating by zebedee I believe, implies that if a litre of misfuel weighs 744 grams, it equates to an SG of 0.744.  Surely that's only correct if the liquid is water.

No, but it's always relative to water. So if misfuel weighs 744g, it has a sg of .744 of 1 (misfuel of water).

Sorry Julian, I'm struggling to explain it any better than that and I'm still working on the 922 - (1.11 x MFW).

[Julian]

In the clear light of morning, that was a pretty stupid question ... it obviously relates to the misfuel SG because that's what you are weighing ... either a blond or senior moment on my part, sorry.

Like you I'm still puzzled by glycer-rides's formula, I'll U2U him if no one on here can help.

[Julian]

Finished off the page with a bit more text and added weights for a litre of misfuel to the graph.

[Tony]

Nice work Julian - it's always good to get information like that down somewhere accessible

[scottydog]

I dont know the ins and outs of it Julian but i have been using it for a good while with great results for blending-winterising
and if good enough running it straight in the genny so it must be in the ball park.

ps the genny hasnt puked yet 

I think the original tables came from a guy who collected the stuff in tanker loads and needed to work it out properly but dont
quote me on that it was quite a while ago.

SD

[Julian]

I don't use misfuel, but I guess it's not necessary to know the percentage mix too accurately.  Hopefully it's good enough for our proposes and will be of use others.

[Ross.Dunmall]

But in the same thread glycer-rides gives this equation ... % of petrol in misfuel = 922 - (1.11 x MFW).  Where MFW = misfuel weight.

Having trouble getting my head round this at the moment can anyone help!

Petrol specific gravity 0.737 = Mass of 737g/l
Diesel specific gravity 0.830 = Mass of 830g/l

You're always weighing 1l of Mis-fuel to find it's Mass or Weight (MFW). And assuming the Misfuel Weight Vs Composition Graph is a straight line.

Using the formula at opposite ends of the scale yields the following

MFW of 737g
% of petrol in misfuel = 922 - (1.11 x MFW)
% of petrol in misfuel = 922 - (1.11 x 737)
% of petrol in misfuel = 922 - (818.07) = 103.93% Petrol. So we assume there also is something lighter  than petrol (perhaps an additive) and ignore it deeming the composition as entirely petrol.

MFW of 830g
% of petrol in misfuel = 922 - (1.11 x MFW)
% of petrol in misfuel = 922 - (1.11 x 830)
% of petrol in misfuel = 922 - (921.3) = 0.7% Petrol. So this Misfuel is composed almost entirely of standard Petroleum derived Diesel

Final example of a random Weight I've made up somewhere in between. Let's say MFW of 761g
% of petrol in misfuel = 922 - (1.11 x MFW)
% of petrol in misfuel = 922 - (1.11 x 761)
% of petrol in misfuel = 922 - (844.71) = 77.29% Petrol in your Mis-fuel.

Hope that helps? if not feel free to tell me.

Nice work with page and the graph very beneficial to have it there, but I would suggest a few minor alterations if it's at all possible.

State the average values for Specific Gravity or g/l of Petrol and Dino Diesel somewhere in the body text.
And here's the tricky one. Mark the intersections at 100% Dino Diesel and 100% Petrol on the graph with the values recorded next to it for further clarity.

Oh and with regards to the formula, supposedly 100% pure petrol will have a Specific gravity of 740.54g/l ie 0.741, but that's not entirely what is stated in any post. ie (922-100)/1.11 = 740.54

Worth mentioning that the test when performed with a hydrometer must have it's reading taken in the 17-20^oC and with the hydrometer roughly in the centre after spinning it and without it touching any side.

[Julian]

If I remember correctly (which is unlikely) it was the 1.11 that was confusing me.  I assumed it was a correction factor.  If that's what it was and petrol and diesel have different SGs then the correction factor should surely be different for each.

Then when you are looking at mixtures of the two, what correction factor do you apply without knowing the ratio of the mix?

I think in the end I decided it was better to work from actual figures and amalgamated two sets of tests, resulting in the graph.

It would appear that the SG of both petrol and diesel can vary and that was the reason for not putting them in but if you feel it would make things clearer, I can do so.

Not too sure what you mean regarding 100% dino and 100% petrol ... the top and bottom of the graph is marked as 100% of each.

17-20°C is mentioned for the weights, but you're right, it should be mentioned for the SG too, along with no air bubbles and a centralised hydrometer.

Many thanks for the comments, I'll make the changes.

[Ross.Dunmall]

The correction Factor of 1.11 is so that once the MFW is used there is a difference of 100 between Petrol and diesel.

Using Diesel at 830g/l (0.83) and Petrol at 740 (.74), which seem to be the rough average that I've found on the interwebs.

(830 - 740 * Factor) = 100
(90 * Factor) = 100
Factor = (100/90) = 1.11

At least that's how I understood it. Even if using 1.11 actually gives it as 103 if we use the SG of Petrol as 0.737.