596.    COKE AND SMOKELESS-FREE AGE.  Diesel Fuels From Coal.  Vol. 2, 1940, pp. 70-71; Ztschr. Ver. Deut. Ing., vol. 83, No. 47, 1939, pp. 1240-1241.

      Synthetic hydrocarbons of the Kogasin type, made by the Fischer-Tropsch process, have a cetene number of 120, and when about 38% is mixed with tar oil of 20 cetene number, a diesel fuel of 60 cetene number is obtained, which is equal in ignition qualities to commercial diesel oil of petroleum origin.  Blended fuels must, however, be examined critically as regards miscibility, separation in storage, corrosive action, and coking qualities.  Attempts to increase the ignitability of coal-tar oils by additions of ethyl nitrate and organic peroxides appear to have been abandoned for reasons of cost.  H. Kölbel claims to have developed stable diesel fuels from coal-tar oil and Kogasin, utilizing the selective solvent action of the latter to remove constituents liable to cause coking.  The process is said to be applicable also to low-temperature tar oils.  The latter have inherently higher cetene numbers.  Data relating to a 45-55 Kogasin-coal tar-oil mixture show this to have properties better than those of an unnamed petroleum fuel.  An illustration compares a mixture of this type with a commercial gas oil as regards:  (a) Fuel consumption in gm./metric hp.-hr. (100 gm./metric hp.-hr.=0.22 lb./hp.-hr.) in a 30- to 35-hp., 1,450-r.p.m., 4-cylinder engine; (b) exhaust temperatures; and (c) CO content of exhaust gases.  The low CO content of the exhaust gases from the mixed fuel is specially interesting as it indicates the suitability of this fuel for use underground, in mine locomotives and the like.