View Full Version : R0N93 + 15% of 50/50 watermeth = RON?

09-08-2010, 08:55 PM

I would like to know how much octane value I would get if I would inject 15% of 50/50 watermeth mix with RON93 gas.

I would also be interest to know which RON value would I get if 10 or 20% would be injected instead

Richard L
11-08-2010, 12:16 AM
Hello Zak,

I have been told in the past, 15% is worth about 5-6 points. It is difficult to be exact on M50:W50.

Methanol raises the octane chemically (raise the auro-igniton threshold) whereas water regulate the burnt rate (as race fuel) and suppress peak tempearture spikes (onset of knock).

I think there are lots of information of this topic on this site, just need to spend some time on searhing.

12-08-2010, 08:06 AM
Thanks Richard.
so I would guess 20% should be around 6-7 point. well I would thing it all depends on which octane you start with... the lower octane you got first the more point you get... so starting from RON93, the lovely RON100 figure should be reachable if 20% 50/50 watermeth is injected
this is pretty mutch good news :)
I tried to search info on this but couldn't find any.

Richard L
14-08-2010, 04:51 PM
I did a calculation of the equivalent heat removed by various water/methanol ratio at different a/f ratio. You migh have seen this before but in case you hadn't.

The following charts are calculated based on:

10Kg of air, Gasoline's latent heat capacity of 350KJ/Kg
Water's latent heat capacity of 2256KJ/Kg
Methanol's latent heat capacity of 1109KJ/Kg

Injection water at different ratio to fuel at 100% water and 75% Water/25% Methanol. You can see the at 100% water injection, only 3% of w/f fuel ratio is enough to replace 2.5 point of a/f ratio (dotted line). As soon as 25% of Methanol is added, the a/f ratio is dropprd to 12.0 - loosing some cooling capacity

http://www.aquamist.co.uk/forum/gallery/afmr/100w.gif http://www.aquamist.co.uk/forum/gallery/afmr/75w.gif

Each of the following chart show a 25% percent increase in Methanol concentration of the mix.

http://www.aquamist.co.uk/forum/gallery/afmr/50w.gif http://www.aquamist.co.uk/forum/gallery/afmr/25w.gif

lastly, just methanol is added and no water. The chart on the right is 100% water

http://www.aquamist.co.uk/forum/gallery/afmr/0w.gif http://www.aquamist.co.uk/forum/gallery/afmr/100w.gif

The two charts show (first and last) that you will require to inject twice the amount of methanol to equal the latent heat of water alone. Methanol is relatively low cost and very effective as a coolant so what is the problem?

When higher concentration of methanol is injected, you need to lean your engines a/f ratio to accommodate the extra fuel or your engine will bog down and loose power. Consequentially - one runs the risk of putting the engine into heat stress if the supply of methanol is suddenly interrupted. Injecting water does not affect the a/f ratio. It appears that 50/50 mix has the best of both worlds.

In either cases, having a good w/a injection system with reliable "system fault" diagnostic capability is essential especially if you are running a high concentration of Methanol.

02-09-2010, 09:43 PM
those are very interesting info indeed.

quick question.
for an engine that was runing 11.7:1 A/F ratio at 1.4 bar, is it safe to say 12.5:1 a/F ratio sounds like a good target when running with 18% 50:50 water/meth?

03-09-2010, 12:57 AM
those are very interesting info indeed.

quick question.
for an engine that was runing 11.7:1 A/F ratio at 1.4 bar, is it safe to say 12.5:1 a/F ratio sounds like a good target when running with 18% 50:50 water/meth?

Mixture strength is a really interesting topic, both in theory and in practice some insight can be gained.

In the ratio's of water injection you are talking about the excess over stoich of the petrol has a large effect on the anti knock capability of the "whole system" (point 2) where the power starts to come good depends on many things and other variables like ignition strength (point 3) not as important to us is the total fluid use both petrol and water, this is only for real racers like F1 to pick a field.

From my tests over a period of time (some say long) I found that the area of ~11.3:1 > and higher is where you want to be for great power and still excess margin for knock protection (at the ratio's you are talking about). You may need to go weaker on the mixture (towards 12.5:1) if you are lower on power mainly due to other factors like the ignition system capacity, just be mindful that doing this greatly reduces your overall anti knock threshold.

In summary the excess fuel (petrol) always has a large bearing on the anti knock, even up to 60% water injection (by mass to the main fuel supply). I work in a band of 11.3 to 11.7:1 you can see detailed results in my members project thread. Howerton eng and Richard both agree you will need to test your own situation and set up to find its sweet spot, something to keep in mind as well.