The Hornsby-Akroyd Vaporizing Oil Engine
By John Wilcox
Hornsby-Akroyd #3121, built by De La Vergne about 1902. 35 hp. 16 X 20 bore and stroke, 220 rpm. Flywheels are 72 dia. X 7? face. Shipping weight 16,000 Ib.
Photo by John Wilcox
This month's article is about a historically important engine that is little known in America - the Hornsby-Akroyd vaporizing oil engine. It uses heavy oil fuels and was significant in the development of today's Diesel, but has lots of peculiarities of its own. I have a couple of them in running shape, so can speak from experience a-bout the adventures of operating one. They are vaporizing oil engines, a type distinct from Diesels in that they gassify the fuel before mixing it with air by bringing it into contact with a hot surface. A combustible mixture is then formed and burned as in a gas or gasoline engine.
The earliest vaporizing oil engines were marketed in England and on the Continent in the 1880's. Most of them had exhaust-heated vaporizers into which the oil was sprayed or dripped, the engine proper being no different than those running on ordinary gaseous fuels. The heat developed was insufficient to keep the tarry ends from condensing out, so that these engines were continually in trouble with stuck valves and a general accumulation of gum and goo. However, since prohibitively high insurance rates made it impractical to use gasoline in that part of the world, they were the only liquid fuel engines available and a number of companies made them.
The first really effective solution to the oil engine problem was found by an English inventor, Herbert Akroyd Stuart. His idea was to vaporize the oil within the combustion chamber itself. Sufficient heat would then be available to keep the vaporizing surfaces red hot, and any deposits formed would see the flame itself. Stuart seems to have been pretty much of a backyard tinker. Working on his own and with limited resources, he perfected his engine and obtained an important patent in 1890. He then set out to find a machine shop to produce it, and reached an agreement with Richard Hornsby and Sons of Grantham that resulted in marketing of the Hornsby-Akroyd oil engine in 1892.
As can be seen in the accompanying cross section, the vaporizer is mounted in place of the head on a four cycle engine. It is a large chamber in constant communication with the cylinder proper through a narrow restriction, only the half nearest the cylinder being water-jacketed. When the engine is running, the outer half is kept at a dull red by the heat of combustion. Oil is injected against this surface at the beginning of the intake stroke, so that the duration of a full revolution of the crank is available for it to vaporize. Air is pulled into the cylinder proper at the same time, but does not mix with the vapor until the piston comes up on compression, forcing some of it through the restriction with a high degree of turbulence. Somewhere around top dead center, a combustible mixture is formed and the hot walls of the vaporizer light off the charge. Only the air which actually enters the vaporizer is used in combustion. Since a-bout half the charge of air remains in the clearance volume of the cylinder and valve boxes, the pressures developed are very low, and the power output of a Hornsby-Akroyd is only about half of a natural gas or gasoline engine of the same displacement and speed. Cylinders tend to be large in comparison to the rest of the engine, and speed ratings were pushed to the verge of disaster in an effort to appear competitive.
The Hornsby-Akroyd was an immediate commercial success. It could be used away from city gas lines without the need for the coal or wood fired gas producer, which tended to be nearly as large and cumbersome as a steam boiler. Hornsby's prospered and must soon, to judge by the serial numbers attained, have been turning out more engines per year than any other English maker. In 1895, John De La Vergne visited Europe in search of a promising gas engine he could license and build to drive the ice machinery he was making in New York City. He came home with the patent rights for the Hornsby-Akroyd, and soon began turning them out in this country in almost exact duplication of the English design. They were never very popular here because of the competition from gasoline, but sales were sufficient to start the De La Vergne Refrigerating Machine Co. into the gas engine business in a big way. By 1908. the company had dropped the 'Refrigerating' from its name, had taken up the manufacture of huge steel mill engines, and was well on its way to becoming America's most respected engine builder.
The development of the solid injection Diesel, which was brought out for stationary service immediately after WWI, can be clearly seen in the progression of De La Vergne's models during the early teens. Although its evolution was of course motivated by Dr. Diesel's air injection engine of 1898, the Diesel as we know it today evolved more directly from the Hornsby-Akroyd by a gradual process of increasing the compression ratio, retarding the injection, and opening up the restriction between the cylinder and the vaporizer. A more immediate descendant was the hot bulb engine, generally credited to Carl Weiss of New York City in 1895. The essential distinction here is that the hot bulb is a relatively small device that ignites a flame which then spreads into the cylinder proper.
Meanwhile, back in England, Hornsbys' were still building the original model without basic change when they merged with Ruston, Proctor, and Co. in 1917. The new firm of Ruston and Hornsby, Ltd. continued it for several more years the total production run lasting for at least thirty years and totaling over 100,000 units.
The two I have arc a 10 1/2 horse built by Ruston and Hornsby in 1922 and a 35 horse built by De La Vergne a-bout 1902. The smaller one powers the 'waterworks' over at the farm, and so gets exercised every couple of weeks during the summer. it has the less common arrangement of the intake valve above the side shaft which was used on some of the smaller English models. The fuel pump is driven by a separate cam, but is still timed to inject as the intake valve opens. Like many English engines, it has only one flywheel. The 35 horse is belted to a triplex pump to load her down and make her boom. We generally fire up and roll some echoes up and down the valley when company comes.
Both engines run on Pennsylvania grade crude direct from a neighboring well. The only difficulty is with a fibrous material in suspension in this oil that clogs the strainer screens and occasionally fouls the injector valves. Hornsby-Akroyds are able to run on dirtier fuels than any other engine ever built, because the abrasives are deposited in the vaporizer and never reach the cylinder walls. Engines used in Texas have operated without damage on local crudes so dirty that it was necessary to remove accumulated matter from the vaporizers every day.
Starting a Hornsby-Akroyd is something of an operation, since the whole end of the vaporizer must be heated to around 1000 degrees. An ordinary gasoline blowtorch is sufficient for the small engine, but the big one requires a more elaborate job that burns kerosene atomized by compressed air. It takes a-bout ten minutes to heat the engine, burns a gallon of kerosene in the process, and sounds more or less like a jet engine. It also has an unfortunate tendency to flame out like a jet engine, filling the engine room with highly combustible vapor in about three seconds. You don't want to smoke while operating it. An experienced hand can tell whether the engine is ready by injecting a little fuel and watching the reaction at the cylinder cock. Lazy wisps of white smoke mean she's just getting warm. If a vigorous funnel of vapor comes out, she's pretty hot. When she sends out a couple of preliminary puffs and then shoots fire you'd better get the oilers turned on.
Once hot, the engine can be started either by 'shooting' with compressed air in the cylinder, or by 'tramping' with one's foot on the flywheel spokes. Tramping is quite easy with this model and lots more fun. It is only necessary to inject some fuel and roll the wheels forward onto compression. The engine will fire and kick back with increased vigor, rolling itself onto compression backwards after making one revolution. The second kick generally imparts enough energy to take her over compression, and off she goes! Occasionally, though, three kicks are required or one is sufficient. In either case, the engine will start and run backwards, which it is perfectly happy to do even though four cycle. The engineer will not be so happy, though, since the exhaust is coming out the intake pipe and the engine room is receiving 4000 cubic inches of blue smoke with every cycle. The only solution is to sit down on the fuel pump handle, wait for her to slow down, and try to bounce her into forward motion just before she stops.
One's troubles art: not necessarily over when the engine comes to speed in the right direction, either. If the vaporizer was not hot enough, this will not become evident until the governor cuts back. Then the engine will cease to fire and start lo slow down. Since lime is important lo the ignition process, it will begin lo lire again when the speed becomes low enough to allow sufficient time under compression. By this time, though, so much unhurried oil will have been pumped into the vaporizer that the. governor looses all control and the engine goes lickety-split. It then coasts for a while before the governor allows any more oil to be injected, pumping cool air through the cylinder and getting colder yet. Being colder, it has to go slower than before to begin to fire, gets more raw oil in the vaporizer, and goes even faster once it recovers. If allowed to continue, these oscillations will lead to a shut down one way or another, so it's better just to turn off the fuel and light the torch again.
We know of only one other Hornsby-Akroyd still in operation in the U.S. Mr. R. C. Hoover of Fairborn, Ohio writes that he saw one run in 1905 and we are hoping that he will remember the location, although the probability of its still being there is pretty slim. It will be interesting to hear if other readers have found any. Some of you fellows in Wisconsin and Minnestoa ought to explore the grain elevators in Canada. There are probably lots of them up there.