The conditions to be met, and the difficulties to be overcome in making the gas-blowing engine a success may be briefly stated as follows:

First

Blast-furnace gas as it comes from the furnace contains a vast quantity of fine and exceedingly abrasive dust which must be completely removed before it is introduced in the cylinders of the engine or the latter will soon be destroyed by wear.

Second

The gas engine is a prime mover with little or no overload capacity, and with an efficiency which diminishes very rapidly as its load drops off. The opposite condition prevails in the case of the steam engine, which has a very large overload capacity, and which maintains its economy well at loads very much smaller as well as much larger than its rated load. Therefore, when the blast pressure required by the furnace changes, the steam engine has no difficulty whatever in accommodating itself to the change, but the gas engine must either work at the disadvantage of an uneconomically light load normally, in order to be able to carry the heavier pressures when they arise, or else it must have special devices to enable it to compress less air when a high pressure is required, at the same time increasing its speed and power.

Third

The gas engine when it began to be developed for use for blast-furnace gas was very largely a single-cylinder, single-acting engine, which, with the four-stroke cycle, meant that it received but one working stroke in two revolutions. The reason for this limitation was that it was considered almost impossible to operate piston rods with their accompanying glands at the high pressures and high temperatures involved in this type of engine.

Fourth:

Owing to the intermittent and rather complex nature of their cycle these engines were in the early days freakish, unreliable, uncertain, and difficult to operate to a degree which in the opinion of many American engineers debarred them from use, especially for blowing service.

Fifth:

Owing to the operating difficulties just mentioned, and to the high repairs which went with them, the operating and maintenance cost was very high.

Sixth:

The first cost of these engines, both for the engine proper, for foundation and for house, was and is even yet enormous, and as this first cost must be amortized at a relatively heavy rate on account of the rapid obsolescence and somewhat rapid deterioration of these engines, the fixed charges on them were very high.

Coming now to the solution of these problems and difficulties, the result desired has been achieved in each case by the same formula. A vast amount of technical work of the highest order, the endurance of a vast number of operating difficulties which resulted in deficient blast supply for the furnaces at frequent intervals of uncertain duration, and made the managers regret the day that the gas engine was born, but which led eventually to methods whereby these difficulties might be avoided or overcome, an enormous number of experiments, many of which in the nature of things were unsuccessful, and the expenditure of great sums of money for development.