Stack temperature observations were also made during each test as indicated by an electric pyrometer, the most accurate method yet devised for high tem perature measurements. This temperature varied on different watches and conditions in the fire room, but in every case where other conditions were nearly the same we find a fall in the stack temperature with an increase in CO.. The average stack temperature for the trip was found to be 715 degrees F. which is easily 50 degrees lower than the temperature in the front connection where the heat in the gases is no longer available for evaporation. The temperature in the port side of the stack was found to be about thirty degrees lower than in the starboard side under given conditions, showing the effect of the retarders in the port side. But even then the temperature was about 670 degrees under the best conditions for ordi nary running.
The following table, together with its graphical representation, will serve to indicate the average re sults of each day's test : The above table represents the average results of 225 analyses, a portion of which were obtained each day during the trip.
Draft readings were also taken in several cases and it was found that under normal running conditions the furnaces required a draft of about 0.42 inches of water for proper combustion.
The inboard furnace on the forward starboard oiler equipped with the cast iron secondary damper was found to admit of more perfect control and draft regulation than the old type. Almost perfect com bustion was obtained from this burner as 14.0 per cent of CO. was produced with no indications of carbon monoxide of CO.
The oil readings were obtained by a meter in the feed line which serves only as an indicator of the fuel consumption because it is bad practice to assume that a meter measures oil accurately.
Without accompanying indicator cards it is not possible to determine the oil consumption per indi cated-horsepower-hour, but it can be seen from the table that where conditions are quite similar there is always an indicated decrease in the oil consumption corresponding to an increase in CO* in the flue gases.
During one period when the r.p.m. of the engine room was reduced to 75 on the 8:00 to 12:00 p. m. watch, we noted an unusual stack temperature of 550 degrees. This would tend to the conclusion that the boiler capacity is rather low for the power required in order to obtain the maximum results from the fuel. A material reduction of draft, whether it be by retard ers or any other means will, in our opinion result in an insufficient supply and for that reason it seems that the boilers are being crowded when the engine has to turn up to 84 r.p.m.
The average CO. content of 11.18 per cent only represents a preventable fuel loss of 2% per cent with conditions as prevailing in this case and it seems un reasonable to expect better results where the firing must necessarily be guess work.
A calibration of each furnace against a differen tial draft gauge would no doubt be of value in better regulation of the fires, but the ordinary type of draft gauge is not suitable to marine work because of the unsteady motion of the ships.
A glance at the attached graph will indicate imme diately the various effects by any definite change in conditions as it is merely a graphical representation of the table contained on page 207.