This lack of standardization is also exhibited in the figures quoted in certain fuel oil specifications for Diesel engines.
The Anglo-American Oil Company gives the follow ing for an oil suitable for use in engines where ignition is produced by the temperature due to compression— No reference is made here to ash content or to viscosity, both of which are important points.
The specifications preceding this arc for engines in which an injection is employed, and it is there fore apparent that the solid injection type restricts the descriptions of oils suitable for this special system.
In regard to tar oils, the following is stated to have been used with success. This is the specification laid down by the National Fuel Oil Company.
In tests carried out with mixtures of Mexican cnide and Diesel oil in various proportions, it was shown that, if Mexican oil only was employed, the consumption would be 3 per cent higher than when burning Diesel oil only. This result would be more helpful if the characteristics of the Diesel oil used were given.
Another instance of the effect of oil mixtures in regard to viscosity and flash point is shown in the mixing of Mexican oil with Scotch shale oil. With 100 per cent shale oil the viscosity at 60° F. was .115 x 10.3 and flash point 237° F. With 50 per cent shale and 50 per cent Mexican the viscosity was -865, and flash point 167° F. The 100 per cent Mexican oil was 72, and the flash point 145° F. These figures need no comment, and this principle of intermixing is un doubtedly worthy of more serious consideration than has hitherto been given to it.
Even in the Fuel Oil Specifications laid down by the British and United States Admiralties there exist striking differences. In the former the flash point must not be lower than 175° F. (close test) and, in the case of oils of exceptionally low viscosity, the flash point must not be less than 200° F. The viscosity of the oil shall not exceed 2,000 secs. for an outflow of 50 cu. centimetres at a temperature of 32° F. The American specification calls for a fuel oil having a fla*h point of not below 140° h., of a specific gravity of from .85 to .96 at 150 C.
it should flow readily at ordinary atmospheric tempera tures and under a heat of 1 ft. of oil through a 4 in. pipe It) ft. in length it should have a calorific value of not less than 18,000 B.T.U.'s per lb. In regard to sulphur the British specification allows up to 3 per cent, while the American places the limit at 1 per cent.
The data I have given and the general trend of the evidence prtKluced reveal what an extraordinary diversity of practice exists throughout the world and there appears to be little agreement among experts on this aspect of the subject. Yet, as has been indicated, its importance is great, for in it undoubtedly lies the future progress of the oil engine for marine purposes, and every effort should be made to introduce a far greater uniformity of practice in this respect. The statements made even by experts arc frequently of a very vague character and do not assist in attaining that precision which one has a right to expect, and which alone can advance oil engine practice.
It is necessary also in concluding this brief review to utter a protest in regard to incorrect nomenclature of oils for use in Diesel engines. The term " crude " oil is frequently employed in referring to heavy oils. Crude oil is the liquid obtained direct from the well, and contains the lighter fractions as well as the heavier oils which have to be removed before the ordinary fuel oil is available. There arc few crude oils which could be used in an oil engine in their natural state, and, even if this were possible, their use would involve the loss of highly valuable products. There appears, indeed, to be no definite practice in this terminology of oils for fuel purposes. In some instances, one finds the vague terms fuel oil and Diesel engine oil employed, which are altogether too vague and convey nothing to the engineer. Valuable service would be rendered by one or other of our associations if this question of nomen clature were seriously taken up, and a well-defined classification formulated.
A table giving the ultimate analysis of various fuel oils is included in the appendix.