The Naphtha Engine

By Staff
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The naphtha engine. Naphtha is a clear liquid hydrocarbon that is produced during the fractional distillation of crude petroleum oil or coal tar.
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Cross section of naphtha engine. A small piston pump, shown in this figure, is driven by a crankshaft eccentric at the rear of the engine to supply naphtha after the engine has started.
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Section view of the naphtha pump.
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The hand air pump, shown in this figure, was operated two to five times to pressurize the fuel tank up forward and thereby supply naphtha vapor to the circular burner under the boiler.
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This figure illustrates the position of the retort (boiler) that converts the liquid naphtha to vapor for powering the engine.

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 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.

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.

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.

As soon as the engine starts, the operator would give the naphtha pump a few last strokes and then open wide the injector valve and the damper. Thereafter, the boat speed and retort pressure (65-75 pounds) would be regulated with the injector valve and damper. Not unlike a steam engine, reverse could be obtained at any engine speed by turning the hand wheel to the right. The air pump that was used to force naphtha vapor to the engine for starting can also be utilized to provide air pressure for the ship’s whistle.

Pressurized naphtha and open flame obviously suggest that the naphtha engine would have trouble passing today’s OSHA regulations. Gas Engine and Power Company claimed in 1896 that there were nearly two thousand naphtha engines in use without reports of mishaps based on foundation. To demonstrate their confidence in their engine, the manufacturer offered $500 to any person who could explode the boiler engine. ‘We will furnish, without charge, a launch for the test, requiring a deposit of $ 100 from the party making the experiment, to be forfeited in case of failure.’ In essence, they bet $500 against $100 that a person could not explode their engine. In an 1891 booklet of cautionary notes, the company went so far as to advise owners of naphtha launches to give wide berth to steam vessels. Not everyone agreed with the manufacturer about the degree of safety offered by the engine and in 1890 two bills to bring naphtha launches under regulations governing steam craft were introduced in Congress. Neither bill was able to get through committee examination. Bills of the same design were introduced again in 1894 and 1895, also to no avail. Fire was no doubt much more likely than explosion, and the company noted in the operator’s manual that occasional small fires could have an adverse effect on timid operators. I suspect that the brass lined engine pit came in handy in such events.

Not very many naphtha engines survive. They were sold all over the world in their day, but the brass scrap value would diminish chances for longevity.

The Adirondack Museum in Blue Mountain Lake, New York, has a 21 foot, 2 horsepower naphtha launch on display. I am relatively sure that the Henry Ford Museum, Dearborn, Michigan, has a naphtha engine on display.

The ‘Lillian Russell’ is a fully restored naphtha launch that is on display at the Mystic Seaport Museum in Mystic, Connecticut. I want to express my appreciation to this museum for research materials made available by their G. W. Blunt White maritime research library.

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