A review of an engine model kit for a Sombart non-compression gas engine.
Type: Sombart non-compression engine.
Maker: Wayne Grenning, Lockport, N.Y.
Availability: Casting and full material, kit, finished model.
The model reviewed this month is the latest offering from Wayne Grenning, the fellow who brought the scale model of the Otto-Langen into the world. Keeping in line with his first project, we are presented with a model of a prime mover from the past, the likes of which has never been seen before. The model in question is of a Sombart non-compression gas engine, manufactured under Bisschop patents, by the Sombart Mfg. Co., in Hartford, Connecticut. Figure 1 in the Image Gallery shows a period print, complete with 'Sombart' misspelled, which illustrates the engine as it appears in the Young Mechanics Own Book, printed in 1897. The engine was designed for light work and was rated in terms of manpower. (One manpower was about 1/12 HP). It was a non-compression engine, with open flame ignition, and used coal gas or illuminating gas as fuel. The model is scaled from a 5 manpower engine which is owned by Tom Stockton, of Ann Arbor, Mich. This is the only Sombart known to exist.
Its mode of operation is as follows: The piston starts at the bottom of the stroke, with the spool valve in a position to admit gas and air through large check valves. As the piston rises it draws in gas and air, and they are mixed in the valve chamber before entering the cylinder. About halfway through this stroke, the piston uncovers a flame port with a flap valve over it. Since the pressure in the cylinder is slightly below atmosphere, the flame at this port is drawn through the flap valve, and ignites the charge in the cylinder. This slams the flap valve shut, blows the gas and air check valves shut, and forces the piston to the top for the power stroke. The spool valve then shifts position via an eccentric on the crankshaft, and on the down stroke of the piston, the burned gases are expelled through the exhaust port at the bottom of the engine. Since the ignition of the charge usually blows out the ignition flame, it is equipped with an auxiliary flame to re-light the ignition flame.
The model is comfortably large, with a 9-3/4 inch flywheel. Most of the engine is iron with smaller pieces in brass, iron and steel, and an aluminum sub-base. The model represents the Sombart quite faithfully, right down to the flame ignition. Figure 2 shows the model in operation. Since it was running at about 100 RPM, the engine appears to be standing still. Note the gas connections and ignition flame to the left of the photo. It uses propane for the flame, and acetylene for the operating fuel. The model features a spool valve, elegantly finned cylinder (Figure 3), and unusual offset crank, just like the big one. It also has a curved spoke flywheel, rope pulley, and, on the finished model, an oak skid. The finished model is painted green, with the pulley and cylinder painted with black manifold paint, because it runs very hot. The only real departure from scale that I can find is the flame ignition chimney. The original had a cast flame box and chimney. This model uses a stainless steel sheet metal chimney. I suppose this is because "you can't scale down a candle flame." Another small departure is the misaligned rocker arm, which is not as the original was. I understand that this was due to a problem with the pattern for the brass casting. The finished model comes with the necessary care and feeding instructions, a brief history, and extra stainless steel for making new flap valves. Available as options are a nicer looking gas valve and the LP regulator for the flame. There is no governor: the big ones didn't produce enough power to need them, and were usually loaded.
Starting the model is straightforward, but a bit of tinkering with the flame location and height, and gas mixture is necessary. Otherwise, you just turn on the ignition supply, set your model on fire, turn on the fuel, and start flipping. Beware of leaking gas lines. They can lead to some exciting moments in your shop. Also, as should always be the case, keep a fire extinguisher on hand. If common sense is used in your gas supply plumbing, there should be no problems at all. There is a list of safety suggestions in the operating manual that should at least be glanced at. Another point to watch is if the model stalls. The acetylene entering the cylinder will go out through the flame port and light up the area quite brightly. This isn't too alarming or dangerous, but it probably should be watched. As may be expected, the model is very sensitive to wind. The original used illuminating gas, which was naturally high in carbon. This was all that kept the piston lubricated. The carbon from the acetylene lubricates the piston on the model, and oil should NOT be used on the piston or spool valve. These run so hot that oil would burn off, leaving a tarry deposit. This could cause the piston to bind, or cause the spool valve to stick to the point of breaking the rocker arm or pivot pin.
The model runs quite well. It pops along from about 100 RPM on up. It doesn't deliver much power, just enough to keep it clipping along. The crosshead/connecting rod arrangement provides for a unique geometric movement. It is very simple, mechanically, and designed such that nothing in the valve setting can get out of alignment.
The only trouble will probably be in the ignition flame. As I have mentioned before, it is rather sensitive to location and atmospheric conditions. My model has one small modification. The rocker arm has a section silver-soldered into it to bring it in line properly with the spool valve and eccentric. This doesn't change the operation of the machine. I did it because my model was neither a finished model, nor a casting kit. It was a pseudo-mechanics kit which is NOT normally available. I had to make the link from the eccentric to the rocker arm, and managed to break the thing trying to bend it into place. To forestall a similar incident on my next try, and to make it more to scale, I modified the rocker arm.
This is an excellent model overall. It is a unique model of an engine that came into being before the advent of the mass-produced farm engine, at a time when the smaller operator needed a cheap alternative to the steam engine. Its flame ignition and unusual mode of operation make it a real conversation piece.