posted September 04, 2001 10:26 AM
Just wanted to add this to the data base of info for swithing to alky, methanol or alcohol fuel.
RIGHT at this point it might be as well to point out to readers that the handling of alcohol fuel, even in small quantities, is dangerous since poisonous Methyl Alcohol is the basis of most of these fuels.
In some cases to prevent it being used for drinking an additive is used, called Pyridine, about one half per cent being the amount.
This gives it a nasty smell and a vile taste, but pure fuel is, of course, without this deterrent.
The problem still remains, however, since it can get into the system by absorption through the skin or cuts, and can be inhaled from exhaust gases.
The effects are cumulative and if enough build up is allowed it oxidizes forming Formaldehyde causing blindness and insanity.
The use of rubber gloves, avoiding splashing and handling in confined space and in general treating with commonsense, however, reduces the risks to acceptable proportions.
Should, however, any get in the eyes immediate medical attention is necessary.
For those who have not handled alcohol fuel it might be as well to say it is a clear, colorless liquid, cool in touch, with an odor different from petrol, and has an attraction to moisture in the atmosphere.
ADVANTAGES AND DISADVANTAGES
Let us now investigate the advantages and disadvantages of going over to this fuel, and at all times taking petrol as our reference level, having in mind the basic requirements of fuel in the heat engine.
The first question must be is it easy to obtain and the answer is there are a number of garages retailing the fuel, in certain cases with other fuels added in specified quantities.
Having obtained the fuel, as already explained, it must be handled with care and commonsense.
There is no real problem in keeping in store any quantity left over from one meeting to another, provided it is kept in a can, or tank for that matter, with the cap kept on during the store period, which can extend into years, contrary to popular belief.
Cost of the alcohol depends on what other fuels have been incorporated, but as guide pure alcohol is, in small quantities, about just over half as much again as the cost of top grade petrol. You must bear in mind at this point, however, you will require double the amount of alcohol as compared to petrol for reasons which will be explained later.
Another point to consider is that alcohol is a solvent and so far as certain paints are concerned it acts as a perfect paint stripper. Alcohol also has a very thorough scouring effect on tanks, pipe lines and so on, not forgetting it can on certain
types of fiberglass tanks cause them to disintegrate into a rather nasty sticky mess.
Consumption of alcohol will be, in rough figures, double that of petrol, due to the calorific value being about half that of petrol.
The correct air-fuel ratio for petrol is 14.1 to 15.1, but for alcohol it is 7.1 to 9.1 so that means we must pass at least twice the weight of fuel, in the case of alcohol, to heat the same amount of air to the same temperature as we need for petrol.
Since the specific gravity of the two fuels is near enough the same it means in effect we have to pass through the jets double the quantity of the fuel.
Apart from doubling up the flow capacity of the jets, and we would add here that this does not mean doubling up the diameter of
the jet hole as many people think, but, in fact, increasing the diameter by 1.4 times or if you like by 40 per cent since a little thought will remind you of the fact you are dealing with the area of the hole in the jet and not the diameter.
It is of little use increasing the capacity of the jet to pass double the amount of fuel unless steps have been taken to establish that the fuel lines, taps, float chambers and so on are also capable of passing double the fuel and the actual flow should be measured.
Now unlike petrol you will find alcohol fuel will continue to provide increased power for a mixture well above the ideal mixture strength and you can always tend, therefore, to jet up on the rich side, and so avoid any possible chance of running into troubles through weak mixture causing burnt valves and holed pistons.
This larger amount of fuel compared to petrol and especially as it is a fuel with much higher latent heat value tends to do two things. The density of the charge entering the engine is higher than petrol and a greater weight of mixture is therefore being exploded.
This is a fuel with a large cooling effect provided by part of it evaporating after it has reached the combustion chamber and so tending to cool the valves, piston and so on.
Some may well get into the combustion chamber as liquid, due to the reduction in temperature of the induction system, pipes, carburetor, etc., and so extending the cooling effect, in the process counteracting the effect of the high internal temperature.
In view of this amount of fuel entering the chamber, with possibly some of it in liquid form, the ignition system must be beyond reproach since if the spark is weak the mass of fuel will just soak the plug and then at once ignition troubles arise affecting starting in particular.
Owing to the use of alcohol a higher compression ratio can be used with this fuel as compared with petrol, another consideration is the type of plug used which will be a hotter type than used before with petrol.
NINETEEN TO ONE
We have just mentioned the higher possible compression ratio used with alcohol and the limit that can be used with any particular fuel depends on the tendency of the fuel to detonate.
As a rough guide the ratio for petrol is limited to about ten to one, or with certain additives to as much as 12 to one. With alcohol, however, you can go up to 19 to one or higher in certain cases. (For all practical purposes however, 14 to one should be considered the maximum usable ratio in modern short stroke automotive engines.)
The possible use of a much higher ratio, of course, means we get a higher power output from the engine, and this, in fact, is almost the main advantage of alcohol fuel.
Detonation with alcohol fuel is really not a problem, but pre-ignition is, or could be unless the mixture is kept well on the rich side.
The reason for this is that if the mixture is on the weak side it burns slowly and can still be so doing when the exhaust valve has opened which then becomes overheated. This in turn ignites the next charge before the correct time, the whole process becoming a chain reaction causing even more rise in temperature and so it goes on until the piston holes and other damage then follows.
The first signs of this process taking place are a loss of power, a general rise quite quickly of overall temperature, the head in particular.
To avoid this, run on the rich side always and use plugs with a good heat capacity.
It might be worth mentioning at this point that an engine set up correctly for running on alcohol, even though on a rich mixture, will be found to be (compared to petrol), a much cleaner running engine inside the cylinder head, and provided the ignition side is up to its job there will be less fouling of plugs than on petrol.
Due to the different rate of burning of alcohol compared to petrol the ignition setting will have to be changed.
It will have to be advanced and the amount necessary will depend on the shape of the cylinder head and general design.
For example, on a well designed hemi-head an extra five to six degrees might well be enough, whereas on a poor designed head it might be something like 15 degrees.
Optimum ignition setting is tied up with the air-fuel ratio and it will be found that with alcohol it is not so critical as with petrol, that is to say the drop off of power is not so progressive as will be seen later.
Provided the engine is set up for running on alcohol correctly there should be little trouble in starting except perhaps on a very cold day and it should be possible to start up on the fuel mix used for the actual racing.
The main problem, due to the cooling effect of the fuel, is to get the engine to operating temperature in the short time available from fire-up to staging.
For this reason so far as motor cycle type engines are concerned, you will note,
in many cases, the finning on the cylinder barrels and heads is almost eliminated. This, by the way, also helps to increase the power to weight ratio, or if you like tends to counteract the weight of the extra amount of fuel carried as compared to petrol.
From reading this far, you should have come to the conclusion that if your engine is now on its limit running on petrol, while large increases of power are obtainable by the use of higher compression ratios it is possible to get a reasonable increase in power output, ten per cent or so, with the existing ratio, provided you make quite certain you get enough fuel through to the engine and, in fact, that you tend to run on the rich side.
Once you have gone over to alcohol and obtained satisfactory running, you have commenced an extension of your power output by anything up to 25 per cent as you adapt the engine to run with the new fuel.
The rather attractive feature that you tend, even with the increase of power to stand less chance of doing damage to the engine than when on petrol should also be considered.
One final point to consider. If you change over to
alcohol from petrol where you were using a mineral oil, it is not necessary to change over to a castor based oil. For modern engines, the present type additive mineral oils offer a higher performance level than the additive castor based oils, and under controlled conditions the light viscosity oils have an advantage where the warm up time is limited.