which can be obtained with the recorder by correcting the errors due to faults in installing the engine and its accessories. The fifth record is particularly interesting because it shows the influence of the ignition-tube on the power of the deflagration of the explosive mixture (Fig. 150). This record was obtained with an engine provided with two contiguous tubes. The communication of each of these tubes with the explosion-chamber
could be cut off at will at any moment. The last record (Fig. 151) was obtained at a time when the effective load of the engine was changed at two different intervals. This record shows how regularly the engine was running and how constant were the initial pressures. These pressures, however, which is the case in most engines, manifestly diminish when the explosions succeed one another without idle strokes of the piston. This shows, also, the influence of "scavenging" the products of combustion and the effect it has on the efficiency of explosion-engines.
Analysis of the Gases.—It has already been stated that one of the tests which should be made consists in measuring the calorific value of the gas. Just what the calorific value of the gas may be it is necessary to know in order to obtain some idea of the thermal efficiency of the installation. If a suction gas-producer be employed (an apparatus in which the nature of the gas generated changes at each instant), calorimetrical analyses are indispensable in appreciating the conditions under which a generator operates.
These analyses are made by means of calorimeters which give the calorific value either at a constant pressure or at a constant volume.
Constant-volume instruments give a somewhat weaker record than constant-pressure instruments; but according to Professor Aimé Witz, the inventor of an excellent calorimeter, the constant-volume type is almost indispensable in gaging the efficiency of explosion-engines.
Fig. 150.
Fig. 150b.
