posted September 04, 2001 10:30 AM
SINCE fuel-air ratios are quoted by weight of both parts it will be necessary to establish the actual weight of each component before we can determine the correct ratio we require.
To put this into practice you must take the cubic capacity of one cylinder in inches, since we are considering weight in pounds, multiplied by the number of cylinders that are fired per revolution, times the total revolutions per minute for a normally aspirated engine, but for a supercharged engine this figure will be increased as indicated previously.
This total figure will be the volume of air consumed per minute, which must now be converted to weight of air in order to find the amount of fuel necessary to mix with it at the nominated ratio.
In order to carry out this calculation it is necessary to know that you convert cubic centimeters to cubic inches by dividing the total figure by 16.4, which must be converted yet again to cubic feet by dividing by 1728.
Since one cubic foot of air weighs 0.081 pounds at a temperature of 32 degrees F, or alternatively one pound of air equals 12.4 cu. ft., it is now possible to determine the weight of air in pounds involved per minute.
The next step is that of ascertaining, from the previous calculation, the actual amount of fuel involved by considering the fuel-air ratio.
SIX PARTS TO ONE
In the case of pure methanol a ratio of approximately six to one, that is to say six parts of air to one part of fuel by weight.
This means a total of seven parts, one will be that of the fuel itself, that is to say a seventh, but since the actual weight of the fuel is eight pounds per gallon of methanol, we will have to divide that figure by eight to convert to gallons.
The final figure so obtained is the fuel required at full throttle in gallons per minute.
Since this is assuming 100 per cent efficiency it means in effect this will be a mixture on the rich side, but as methanol is insensitive to small ratio changes this is unimportant and in fact a built-in safety factor, avoiding lean mixture troubles such as burnt pistons.
From this calculation it will be possible to determine the total amount of fuel required to carry in the tank, plus the rate of flow to the carburetors or injectors, single or multiple as the case might be.
Providing the actual fuel flow can be allowed to take place as it would under normal operating conditions, it will be possible to check the jet sizes related to the actual amount of fuel they will pass per minute.
If this is not possible, for example in the case of an engine driven pump system, either the maker's figures will have to be used, or the displacement per revolution or stroke established, times the number of these per minute, giving the estimated flow.
These figures are empirical but will at least provide a basis on which to start and experiment, and will prove whether the pump has sufficient capacity or not, and for the particular application in mind, this figure should be at least twice the estimated flow rate.
READY TO START
At this stage we are ready to start up and from the actual running of the engine, commence to see if the mixture is about right by the normal methods, but -it must be appreciated our estimated requirements have been taken at full throttle or maximum fuel demand.
Tuning, insofar as intermediate settings of the throttle, follows normal practice, but for starting conditions, it may be slightly different, as in most cases of fuel other than petrol, it is unnecessary to provide an excessively rich mixture for starting as this will only cause plug wetting, making it difficult or even impossible to start.
As previously stated when the engine is set up, which is often not the case, and in tune, it will be possible to start up and run right away. However for those that may find starting a problem, especially in cold weather conditions, it may be advisable to add some volatile component to the fuel, or even start up by the simple means of introducing another fuel, such as lighter fuel, by the simple means of squirting a small amount into the air intake of the engine.
A warning at this stage would not be out of place in the use of Ether or compounds containing a high proportion of Ether, such as Easistart, . or similar aerosol packs, except those specifically formulated for spark ignited engines, as opposed to diesel, due to the danger of flash fires, and also damage to the engine caused by possible detonation.
The preferred method of obtaining easy starting is that of blending certain other fuels with the methanol in controlled proportions, for example the use of Acetone up to a maximum of 5 per cent by volume, petrol also up to the same maximum amount, or Ether, but at a maximum of 3 per cent.
With regard to Ether, the blending of this with the fuel should, for reasons of safety, be left to the fuel supplier due to the extremely low flash point of this material, in fact, a figure of minus 40 degreesF.
Since as stated before, these fuels, if by any mischance, get into the eyes immediate medical attention is necessary.
If this is impossible due to circumstances, to obtain, the following action will do until professional attention ca n be secured.
The eyes should be continually washed out with clean water for a period of at least 15 minutes, needless to add, with care.
Clothing contaminated with fuel should be removed to stop the fuel penetrating to the skin, and if it has, the area effected washed thoroughly with soap and water.
It may seem some stress is made of the dangers of fuel, but it is better to know the dangers and take the necessary precautions, which after all only amount to common sense, rather than go along in total ignorance.