ENGINES WORKED BY PRODUCER-GAS
These engines are worked by a special gas generated in an apparatus called a "producer." If air is forced through incandescent carbon in a closed furnace its oxygen unites with the carbon and forms carbonic acid gas, known chemically as CO2, because every molecule of the gas contains one atom of carbon and two of oxygen. This gas, being the product of combustion, cannot burn (i.e. combine with more oxygen), but as it passes up through the glowing coke, coal, or other fuel, it absorbs another carbon atom into every molecule, and we have C2O2, or 2 CO, which we know as carbon monoxide. This gas may be seen burning on the top of an open fire with a very pale blue flame, as it once more combines with oxygen to form carbonic acid gas.
The carbon monoxide is valuable as a heating agent, and when mixed with air forms an explosive mixture.
If along with the air sent into our furnace there goes a proportion of steam, further chemical action results. The oxygen of the steam combines with carbon to form carbon monoxide, and sets free the hydrogen. The latter gas, when it combines with oxygen in combustion, causes intense heat; so that if from the furnace we can draw off carbon monoxide and hydrogen, we shall be able to get a mixture which during combustion will set up great heat in the cylinder of an engine.
In 1878 Mr. Emerson Dowson invented an apparatus for manufacturing a gas suitable for power plant, the gas being known as Producer or Poor Gas, the last term referring to its poorness in hydrogen as compared with coal and other gases. While the hydrogen is a desirable ingredient in an explosive charge, it must not form a large proportion, since under compression it renders the mixture in which it takes part dangerously combustible, and liable to spontaneous ignition before the piston has finished the compression stroke. Water-gas, very rich in hydrogen, and made by a very similar process, is therefore not suitable for internal combustion engines.
There are many types of producers, but they fall under two main heads, i.e. the pressure and the suction.
The pressure producer contains the following essential parts:—
The generator, a vertical furnace fed from the top through an air-tight trap, and shut off below from the outside atmosphere by having its foot immersed in water. Any fuel or ashes which fall through the bars into the water can be abstracted without spoiling the draught. Air and steam are forced into the generator, and pass up through the fuel with the chemical results already described. The gases then flow into a cooler, enclosed in a water-jacket, through which water circulates, and on into a scrubber, where they must find their way upwards through coke kept dripping with water from overhead jets. The water collects impurities of all sorts, and the gas is then ready for storage in the gas-holders or for immediate use in the engines.
A pound of anthracite coal thus burnt will yield enough gas to develop 1 h.p. for one hour.
Suction Gas Plants.—With these gas is not stored in larger quantities than are needed for the immediate work of the engine. In fact, the engine itself during its suction strokes draws air and steam through a very small furnace, coolers, and scrubbers direct into the cylinder. The furnace is therefore fed with air and water, not by pressure from outside, but by suction from inside, hence the name "suction producer." At the present time suction gas engines are being built for use on ships, since a pound of fuel thus consumed will drive a vessel further than if burnt under a steam boiler. Very possibly the big ocean liners of twenty years hence may be fitted with such engines in the place of the triple and quadruple expansion steam machinery now doing the work.