From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Analysis of the physical characteristics and water tolerance of Isopropyl Ether as an aviation fuel.
| Identifier | ExFiles\Box 150\1\ scan0209 | |
| Date | 29th September 1936 guessed | |
| - 3 - Physical Characteristics The physical characteristics of Isopropyl Ether are shown in Table I, along with corresponding values for pure Iso-Octane and benzene shown for comparison. Although a low boiling material, its vapor pressure is below the maximum allowed for aviation gasolines and when blended therewith, vapor pressures will be entirely suitable. Freezing point is low and thus it does not have this disadvantage of the benzene or benzol blend fuels. Latent heat of vaporization while lower than for benzene is comparable with that for Iso-Octane and consequently the same maximum engine horse power would be anticipated from considerations of mixture cooling effect, and no increase in tendency to cause carburetor icing due to excess refrigerating effect would be anticipated. Heating value on both a weight and volume basis is lower than for either Iso-Octane or benzene and this normally would be expected to give a reduction in miles per gallon or conversely would require greater tank capacity for a given cruising radius. The magnitude of this disadvantage is in proportion to the quantity of Isopropyl Ether used in the final blend and as will be shown later, may be wiped out in practical blends by permitting of leaner air fuel ratios without excessive head temperatures. In considering the physical characteristics of aviation gasolines, the subject of water tolerance is of major importance. The existing specifications for water tolerance of aviation fuels require only that, when 80 ml. of the fuel are shaken with 20 ml. of water at room temperature, the increase in volume of the water layer shall not exceed 2 ml. This requirement is directed against the use of alcohol blends from which the alcohol is usually easily separated by the addition of water. Isopropyl Ether has only very slight solubility in water and the above water tolerance test usually shows no measurable increase in the water layer, even when concentrations of 40% are used in blends with aviation gasoline. The low solubility of Isopropyl Ether in water was demonstrated by a more accurate analysis than the above rough test. 503 ml. of a 40% blend of Isopropyl Ether in aviation gasoline were shaken with 497 ml. of water until equilibrium was established. The final contraction of the gasoline layer was 2.63 ml. or 0.52%. The water content of the gasoline layer was then determined (by a method described below) as 0.09%. Since no change was found in the total volume (1000 ml.) of gasoline and water the total loss of Isopropyl Ether by solution in water was 0.61% on the basis of the original blend or 1.5% of the Isopropyl Ether itself. The above results indicate the magnitude of the loss of fuel that might possibly be suffered if a blend of Isopropyl Ether were stored over water for long periods of time. This possibility has practical significance in view of the occasional use, for example in the U.S. Army Air Corps, of water displacement storage systems. However, another aspect of the problem of water tolerance, which is sometimes of importance, is the tendency for aviation gasoline to dissolve water which may later be deposited at freezing temperatures as ice in the fuel feed systems of airplanes in flight. This difficulty has occasionally been encountered in the past with aromatic blends. | ||