The Naphtha Engine


| October/November 1991



The liquid naphtha

The naphtha engine. Naphtha is a clear liquid hydrocarbon that is produced during the fractional distillation of crude petroleum oil or coal tar.

Author's note: The information in the attached article was obtained from a pamphlet of Cautionary Notes dated 1891, a Naphtha Launch instruction book dated 1907, and from a Naphtha Launch catalogue copyrighted in 1896, all of which were published by Gas Engine & Power Co., Morris Heights, New York. The original company is no longer in business. The information in the article concerning Frank W. Ofeldt was obtained from a monograph published by the Adirondack Museum, Blue Mountain Lake, New York.

Before we go too far, let me explain that there are two basic types of naphtha engines. One type is an internal combustion engine. The two cycle Simplex naphtha engine built by Charles P. Willard & Company, illustrated on page 555 of American Gasoline Engines Since 1872, exemplifies this type of engine. This article is about the other type of naphtha engine, which is an external combustion engine. It isn't very likely that you will come across a running naphtha engine of this second type at an engine show, because it would require a substantial supply of moving cold water for safe operation. This engine was used exclusively for powering small boats and yachts just before the turn of the century.

Naphtha
Naphtha is a clear liquid hydrocarbon that is produced during the fractional distillation of crude petroleum oil or coal tar. Naphtha distills off between gasoline and kerosene. Today naphtha is sold in hardware stores as a wiping solvent and paint reducer. The naphtha used for boat engines was special in that it had a specific gravity of 76 degrees Baume, whereas naphtha used by painters had a specific gravity of 60 degrees (0.68 vs 0.74). Naphtha has a heat of vaporization lower than water, which means that for a given amount of heat input naphtha will produce more vapor than water would produce for the same amount of heat input.

History
After steamboats got a reputation of danger from explosion, the Coast Guard required operators to be licensed, thereby removing steamboats from small owner/operator utilization. The outboard motor would solve this problem eventually, but in 1885 it didn't exist. In 1883 Frank W. Ofeldt took out a patent on a naphtha engine which was essentially a closed loop steam engine that used naphtha instead of water. The engine was developed by the Gas Engine and Power Company of Morris Heights, New York. A few years later the company was in production, meeting the urgent market for small, powered launches that could be operated by owners without the need for a licensed engineer. In 1896, the company joined with Charles L. Seabury & Co., and together they manufactured naphtha launches and yachts that ranged in size from a 1 horsepower, 16 foot launch up to a 76 foot twin screw yacht powered by two 12 horsepower engines.

Engine design
As mentioned earlier, the design features a closed loop where the exhaust, naphtha vapor, is liquefied by a condenser which consists of a pipe running along the side of the keel forward to the fuel tank. The engine consists of three cylinders, as shown in figures 1 and 2. Figure 3 illustrates the position of the retort (boiler) that converts the liquid naphtha to vapor for powering the engine. A small portion of the vapor was used to feed a burner located under the retort coils. A small piston pump, shown in figure 2, is driven by a crankshaft eccentric at the rear of the engine to supply naphtha after the engine has started. The fuel tank sits in the bow in a water tight compartment. Water from outside was admitted around the tank through holes where condenser pipes enter through the hull bottom. The engine was located in the stern, in a boxed-in area with brass sheeting on all surfaces. This metal lined engine pit was necessitated by the inevitable fire which would result if any leaks developed around the shaft stuffing glands. Figure 4 shows the complete engine with the controls mounted on a small bulkhead just in front of the engine. The brass stack above the retort was a visual trademark. Working pressure was 65-70 pounds, and the design of the retort and burner would allow a boat to get underway in two to five minutes in mild weather. Engine lubrication was provided by adding one-half gill (2.5 fluid ounces) of pure sperm oil to the closed loop system for every 10 hours of operation. Note that the naphtha itself has some natural lubrication qualities. Engines were built in 1,2,4, 8, 12 and 16 horsepower sizes. The 1 horsepower engine weighed 150 pounds, and the 16 horsepower engine weighed 1000 pounds. A 2 horsepower engine would consume about one gallon of naphtha per hour of operation and naphtha sold for 9 to 11 cents per gallon in 50 gallon barrels in those days. Compared to steam, the naphtha engine provided a launch with lightweight, efficient power that required no license to operate.

Starting
The hand air pump, (E) in figure 4, was operated 2 to 5 times to pressurize the fuel tank up forward and thereby supply naphtha vapor to the circular burner under the retort. This vapor was ignited by a match introduced through a hole in the base (A).. Next, the naphtha valve (D) was opened and the naphtha pump (P) was given 10 to 20 quick strokes to pump liquid naphtha from the tank in the bow to the retort coils. The air pump would continue to be used to maintain the flame on the retort coils and the liquid naphtha contained therein. In about two minutes the pressure gauge would indicate 10 to 15 pounds and the operator would open the injector valve (C). This would allow pressurized fuel vapors to supply the retort burner. The funnel-shaped device just below the injector valve is an air damper which is used to control the air-fuel ratio. Next, the Starting/Reversing/Forward hand wheel (G) is used to turn the engine over and operate the slide valves. Once the engine starts, the previously mentioned piston pump will supply naphtha to the retort.