The invention of a self propelling engine, capable of working without fuel economically and for a considerable time, has often been attempted, and was, perhaps, never before so nearly accomplished as about the time of the introduction into practical use of Faure's electric storage batteries; but at the present moment it appears that electric power has to give way once more to steam power. Mr. Honigmann's invention of the fireless working of steam engines by means of a solution of hydrate of soda - NaO HO - in water is not quite two years old, and has in that time progressed so steadily towards practical success that it is reasonable to expect its application before long in many cases of locomotion where the chimney is felt to be a nuisance. The invention is based upon the discovery that solutions of caustic soda or potash and other solutions in water, which have high boiling points, liberate heat while absorbing steam, which heat can be utilized for the production of fresh steam. This is eminently the case with solutions of caustic soda, which completely absorb steam until the boiling point is nearly reached, which corresponds to the degree of dilution.
If, therefore, a steam boiler is surrounded by a vessel containing a solution of hydrate of soda, having a high boiling point, and if the steam, after having done the work of propelling the pistons of an engine, is conducted with a reduced pressure and a reduced temperature into the solution, the latter, absorbing the steam, is diluted with simultaneous development of heat, which produces fresh steam in the boiler. This process will be made clearer by referring to the following table of the boiling points of soda solutions of different degrees of concentration, and by the description of an experiment conducted by Professor Riedler with a double cylinder engine and tubular boiler as shown in Fig. 2:
+---------------------+------------------+---------------------- | | Boiling point in | Steam pressure above | Solution of soda. | Centigrades. | atmospheric pressure | | | in atmospheres. +---------------------+------------------+---------------------- |100 NaO HO + 10 H2O | 256 deg. C. | 40 atm. | " + 20 " | 220.5 " | 21 " | " + 30 " | 200 " | 15 " | " + 40 " | 185.5 " | 10.2 " | " + 50 " | 174.5 " | 7.7 " | " + 60 " | 166 " | 6.1 " | " + 70 " | 159.5 " | 5.1 " | " + 80 " | 154 " | 4.2 " | " + 90 " | 149 " | 3.6 " | " + 100 " | 144 " | 3.0 " | " + 120 " | 136 " | 2.2 " | " + 140 " | 130 " | 1.6 " | " + 200 " | 120 " | 0.95 " | " + 300 " | 110.3 " | 0.4 " | " + 400 " | 107 " | 0.3 " +---------------------+------------------+----------------------
Experiment No. 15.3 - The boiler of the engine, Fig. 2, was filled with 231 kilogs. water of two atmospheres pressure and a temperature of about 135 deg. Cent.; the soda vessel with 544 kilogs. of soda lye of 22.9 per cent. water and a temperature of 200 deg. Cent., its boiling point being about 218 deg. Cent. The engine overcame the frictional resistance produced by a brake. At starting the temperature of both liquids had become nearly equal, viz., about 153 deg. Cent. The temperature of the soda lye could therefore be raised by 47 deg. Cent, before boiling took place, but, as dilution, consequent upon absorption of steam would take place, a boiling point could only be reached less than 218 deg. Cent., but more than 153 deg. Cent. The engine was then set in motion at 100 revolutions per minute. The steam passing through the engine reached the soda vessel with a temperature of 100 deg. Cent.; the temperature of the soda lye began to rise almost immediately, but at the same time the steam boiler losing steam above, and not being influenced as quickly by the increased heat below, showed a decrease of temperature. The difference of the two temperatures, which was at starting 1.3 deg. Cent., consequently increased to 7.2 deg.
Cent, after 17 min., the boiler having then its lowest temperature of 148.8 deg. Cent. After that both temperatures rose together, the difference between them increasing slightly to 9.5 deg. Cent., and then decreasing continually. After 2 hours 13 min., when the engine had made 12,000 revolutions, the soda solution had reached a temperature of 170.3 deg. Cent., which proved to be its boiling point. The steam from the engine was now blown off into the open air during the next 24 min. This lowered the temperature of both water and soda lye by 10 deg. and re-established its absorbing capacity. The steam produced under these circumstances had of course a smaller pressure than before, in this way the engine could be driven at reduced steam pressures until the resistance became relatively too great. The process described above is illustrated by the diagram Fig. 1, which is drawn according to the observations during the experiment.
The constant rise of both temperatures during the first two hours, which is an undesirable feature of this experiment, was caused by the quantity of soda lye being too great in proportion to that of water, and other experiments have shown that it is also caused by an increased resistance of the engine, and consequent greater consumption of steam. In the latter part of the experiment, where the engine worked with expansion, the rise of the temperature was much less, and by its judicious application, together with a proper proportion between the quantities of the two liquids in the engines, which are now in practical use, the rising of the temperatures has been avoided. The smaller the difference is between the temperatures of the soda lye and the water the more favorable is the economical working of the process. It can be attained by an increase of the heating surface as well as by a sparing consumption of steam, together with an ample quantity of soda lye, especially if the steam is made dry by superheating. In the diagrams Figs. 3 and 4, taken from a passenger engine which does regular service on the railway between Wurselen and Stolberg, the difference of the two temperatures is generally less than. 10 deg.
Cent. These diagrams contain the temperatures during the four journeys a b c d, which are performed with only one quantity of soda lye during about twelve hours, and show the effects of the changing resistances of the engine and of the duration of the process upon the steam pressure, which, considering the condition of the gradients, are generally not greater than in an ordinary locomotive engine. It can especially be seen from these diagrams that an increase of the resistance is immediately and automatically followed by an increased production of steam. This is an important advantage of the soda engine over the coal-burning engine, in consequence of which less skill is required for the regular production of steam power. The tramway engines of more recent construction according to Honigmann's system - Figs. 5 and 6 - are worked with a closed soda vessel in which a pressure of 1/2 to 1½ atmospheres is gradually developed during the process. While the counter pressure thus produced offers only a slight disadvantage, being at an average only 1/2 atmosphere, the absorbing power of the soda lye is materially increased, as shown by the following table, and it is, therefore, possible to work with higher pressures than with an open soda vessel.
Besides this great advantage, it is also of importance that the pressure in the steam boiler can be kept at a more uniform height.