Usage:
Many dealers and customers desire information about the use of alcohol or alcohol mixtures as fuel for Caterpillar diesel engines. The need for this information has increased because of higher fuel costs and indications of possible problems with future supplies of petroleum. The purpose of this article is to provide Caterpillar's current position on the use of alcohol fuels in diesel engines.
Generally, information is desired about two basic types of alcohol: Ethanol and Methanol. Ethanol is ethyl alcohol, and can be made from either sugar, which is available from sugar cane, sugar beets, etc., or starch, which is available from grain or cellulose material. The manufacturing processes used are generally similar to those for alcohol beverages (liquids for consumption by persons), except that later methods with better efficiency are used. Methanol is methyl alcohol, and can be made from several sources, including coal, wood, natural gas, and waste material (material which has no other use). In the process generally used, the solid material is changed to a gas and then treated with a catalyst to form liquid methanol.
According to the latest information available, the cost of ethanol in the U.S. is approximately 3.5 times the cost of petroleum fuel, and methanol is 2.0 times the cost, on a basis of the same amount of energy. Remember that ethanol has approximately 60%, and methanol approximately 45%, of the energy of diesel fuel for the same volume. The differences in cost can possibly be lowered by new methods with better efficiency now being developed.
Pure ethanol or methanol can not be used as a fuel in Caterpillar diesel engines. The low cetane number and lubrication characteristics prevent the use of these alcohols as fuels. The cetane numbers of ethanol and methanol are similar-in a range of 0 to 10. Minimum cetane numbers necessary for Caterpillar diesel engines are 35 for precombustion chamber engines, and 40 for direct injection engines. The meaning of this comparison is that the pure alcohol does not have good diesel engine ignition characteristics, and must be mixed with large quantities of cetane improvement additives for combustion. Also, in current fuel injection systems, the diesel fuel must give lubrication to the fuel injection system components. Alcohol does not give this necessary lubrication.
Caterpillar recommendations do not permit a mixture of alcohol with diesel fuel to make "diesohol". Safety is the primary reason for this recommendation, but this method to use alcohol is not practical for other reasons.
The safety factor is very important. An earlier article "Warning: Avoid Use Of Fuel Mixtures Of High Volatility. If You Are Exposed To Such Mixtures, Be Aware Of The Hazards Involved And Take Proper Precautions" told about the dangers of diesel fuels mixed with gasoline, naphtha, or other highly volatile fuels. Alcohol is one of these highly volatile fuels, and the information in the earlier article has specific application to "diesohol" mixtures. In addition to the safety factor, the use of an alcohol mixture is not practical because the alcohol can not be kept in solution with the diesel fuel when water is present. Water from any source, including either fuel component, or the normal moisture (humidity) in the air, will mix with the alcohol and cause separation of the alcohol from the fuel mixture.
The use of alcohol in internal combustion engines is the subject of an extensive analysis by Caterpillar. Some of the possible methods now under analysis are the use of alcohol in spark ignition engines, and several different dual (double) fuel systems for diesel engines. In spark ignition engines, alcohol has very good fuel characteristics, including an octane rating of 105. In diesel engines, the use of alcohol can possibly extend the supply of diesel fuel, but an analysis of several factors is necessary. Acceptable cost, practical application, and the effect on engine operation, performance, efficiency, and service life during a long period of use are important.
When the necessary analyses of all the factors are completed, the results will give an indication of the best methods to extend fuel supplies and lower costs. New recommendations will be made as soon as possible after acceptable methods are found.