By this construction it will be seen that the naphtha first passes through the entire coil AV upward, thence down into the tube 0 and through the an nular space between this tube and the in ner tube P. Thence the greater portion of the gas enters through the pipe 0 to the steam - chest, and thence through the cylinders. At the same tune a portion of the highest grade of the gas, or that which has the least density, pass es up. as indicated by the arrow, into the inner tube P, and thence to the injector, in passing through which latter it draws air through the vent and thus charged with air passes into the burner. Draft for the bunter is provided by side openings at the lower end of the combustion-chamber, and the gas of combustion passes up through the smoke-stack.
In starting the engine the air-valve B is opened, and the air-pump E (Fig. 7) given a suffi cient number of strokes to force gas from the tank through the outlet-pipe to the burner, where it is ignited and heats the retort. The naphtha-valve D also is opened, and from fire to ten strokes given to the naphtha-pump F. This pumps naphtha from the tank in the bow of the boat into the retort. and. if the latter has been sufficiently heated, pressure will at once he indicated on the gauge. The injector-valve C, as already explained, regulates the flow of gas to the burner. and hence the speed and pressure. The consumption for a 2-horse-power engine is given at from three quails to one gallon per hour, and for a 4-horse-power engine at from four to six quarts per hoar. The vapor consumed is practically that which goes to the burner, since that which performs work in the engine is exhausted into condens ing-pipes running along the bottom of the boat, and is forced by the engine back to the tank, being thus used over and over again. The builders recommend the use of deodorized naphtha. A 2-horse-power engine weighs 200 lbs., a 4-horse-power. :100 lbs., and an 8-horse power, 600 lbs., or, as the builders claim, less than one fifth the weight of other engines and boilers of the same power. It takes only about two minutes to get under headway.
Experiments with the Naphtha-Engine.—Beeent ex periments have been made by the Gas-Engine and Power Co., the builders of these engines, to test the relative value of hydrocarbon vapor and ordinary steam as an evaporating agent to produce work from heat in small motors, with the following results: A small ordinary steam-engine was used, with a friction-brake on a fly wheel to measure the useful power. while indicator-dia grams taken from the cylinder showed the power devel oped by the working agent. A vertical steam-boiler was heated by a large gas-burner, so that. the exact quantity of heat could be obtained and regulated by the gas-nie ter record. In one case steam was taken from the boiler to the working cylinder in the usual way, and the ex haust steam from the cylinder was condensed in a coil of pipe immersed in water, allowed to flow into a hot-well.
passed on to the feed-pump of the engine, and forced back into the boiler, thus making a complete circuit. With constant water-level in the boiler, the steam-pressure was 50 lbs. per sq. in. at the start, and it was brought up to this at the end of each trial of three hours' durit lion. In the case of naphtha, a copper coil was fitted inside the steam-space at the upper part of the same boiler, so that the boiler efficiency should be the same as in the previous ex periment. Naphtha of specific gravity was pumped into the coil and vaporized by the heat of the steam. The vapor passed to the engine, worked the same piston in the cylinder, was led into a condensing coil, passed to a hot-well, and finally pumped beak into the coil inside the boiler.
The tests made alternately with steam and naphtha gave the following results: Thus, with nearly the same rate of gas-consumption. the power obtained on the brake was in the ratio of about. 5:0 for steam and naphtha—that is, the same quantity of heat was turned into nearly twice as much work by the expansion of vapor as by the expansion of steam tinder the same conditions.
Naphtha, being a complex mixture of various hydrocarbons, evaporates far more rapidly than water. Proper care MINI. he taken in using the naphtha. as the more volatile vapors pass at the ordinary atmospheric temperature. Other vapors escape a..s the temperature rises, and there is not uniformity in the rate of evaporation when naphtha is heated. Experi ment shows that a given quantity of heat will evaporate nine times as much of this naphtha as of water at atmospheric pressure. On time other hand, this naphtha only expands to the volume of vapor that water yields. Hence, a given quantity of heat can produce times the vidnine of vapor from naphtha of gravity that it would of steam at the ordinary atmos pheric pressure. Now we know that the greater the range of temperature I hrough which we can cool a by its own expansion. doing work in a perfect heat-engine, the greater the fraction of its sensible heat will be turned into work. To turn all its sensible heat into work would require infinite expansion to the absolute zero of temperature, which is impossible: Izesides, the gas would he changed into the liquid and solid states long before that extreme degree of cold could he readied. \Vitt, exhaust at atmospheric pressure, the lower limit of the working range of bunperature in every case is the boiling-point of the liquid. In the ease of the naphtha used in the above experiments, this lower temperature was 130' P., being cooled through a range of 90° F. Under these mmlitions, steam eould Only be cooled tc 212' P., through a range of P. to 212' P., or F. Therefore, since the efficiency in a perfect heat-engine depends only on the working-range of temperature, we see that this efficiency with steam and naphtha would be in the ratio of about 5 : 9.