Figure 351 shows the results of a test on an 85 h.p. Bes semer engine, installed in a cotton gin and using Texas distillate of 36° Baume. The full-load value closely approximated the factory test in Fig. 350; the increased fuel consumption at the lower loads is due, no doubt, to misadjustments in the fuel pump and injector nozzle, since the engine had been operated one season by an inexperienced engineer. Even with this handi cap the results are surprisingly good.
Figure 352 is a test on a 50 h.p. Fairbanks-Morse vertical Type Y engine. The engine was of the single-cylinder design and was installed in a combination electric light and flour mill plant. After the engine had been in service for some time, the question as to its fuel consumption in actual operation was raised. A test, consisting of three one-hour runs at the various loads, was conducted. The fuel was carefully weighed, while the tempera ture of the cooling water was maintained as constant as possible by operating the inlet valve; the actual amount of cooling water used was measured by two tanks of known value. The engine car ried a 10 per cent. overload with ease, but at 25 per cent. overload the exhaust became very smoky, showing that part of the fuel was not being consumed. The engine labored considerably and lost speed slightly. Since no oil engine should he expected to carry more than a 10 per cent. overload, the behavior on the 25 per cent. overload is not open to criticism.
The fuel was a 38° Baume distillate weighing 6.94 pounds per gallon. The builder's guarantee of fuel consumption at full load was .694 pound. This guarantee was more than fulfilled. The efficiencies at the lower loads were also good.
Figure 353 covers tests on a 16 h.p. Petter oil engine. This engine was built at Yoevil, England, and was imported for experimental purposes by a firm which was entering the low pressure engine field. Curve a covers the test using 26° Baume Peruvian crude oil; b covers 28° fuel oil, while c covers the use. of 42.5° distillate or stove oil.
Figure 354 covers tests on a 60 h.p. De La Vergne Type D.H. low-pressure oil engine. These were factory tests and are much lower than the company's guarantee. In fact, they approach the performance of the Diesel engine.
Figure 355 is the result of a test on a 75 h.p. Buckeye-Barrett oil engine using Lima Ohio crude. These results are quite representative of low-pressure engine practice.
Operation Costs.—The fuel consumption in actual operation is much greater than the values obtained on a test. In the latter case all conditions are well-nigh perfect, whereas in ordinary opera tion many things serve to preclude ideal results. The engineer should be guided by his judgment in determining whether he is obtaining fair efficiency, rather than by comparison with factory tests. Even though the efficiency be considerably lower than that reported by the testing engineers, the operator should not feel that the engine is not giving satisfactory service. This,
of course, applies only to plants where a reasonable amount of attention is given the various engine parts and necessary adjust ments made.
Table XVIII covers a monthly report on a small combined water and light plant. In this plant a 50 h.p. low-pressure oil engine was belted to an alternator and a waterworks pump. Even though the engine was not carrying its rated load, the fuel cost was reasonable. The lubricating oil consumption was somewhat high, but this was evidently due to the lack of a filter. It is in such plants as this one that the low-pressure engine finds its greatest field. Such a plant could not exist if a steam engine were used since the operating expenses would exceed the gross income. In this plant the engineer's wage was not high, but the matter of wages is largely determined by the cost of liv ing in the particular locality. This plant was situated in a small Texas town where living expenses were low; the engineer's salary of $70 probably was as high as was paid to any workman in the town.
While it is in the smallwater works and electric light plants that these engines are in greatest demand, industrially they are meeting the requirements of low fuel and maintenance charges.
In those larger centers where electric power can be purchased for 3 cents per kw.-hr., it is problematical whether the low pressure oil engine can be used successfully. In communities where electric power rates range from 5 cents upward and where the power demand is under 100 h.p., the owner of a small manufacturing plant should install some make of the low pressure oil engine and thereby reduce his factory costs. For example, a small 100-barrel flour mill, if running twenty-four hours daily and producing the rated capacity, will use be tween 600 and 700 kw.-hr. per day. At the low rate of 5 cents per kw.-hr. the power charges would run from $30 to $35 daily. Since it requires approximately 10 h.p.-hr. to pro duce a barrel of flour, a 50 h.p. oil engine would handle the plant with ease, being able to operate the elevator machinery as well. Such a unit on a load of 40 h.p. would not consume in excess of 100 gallons of distillate oil per day. The fuel would cost less than $5 per day. On the basis of three hundred working days the net saving, including fuel, lubricating oil, etc., as well as the wages of an operator, is more than $6000 yearly. The only argument against the use of an oil engine in such installations is the poor results obtained from engines erected several years ago. During the last few years the improvements in design have converted this type of engine into a very reliable mechanism. Records of one hundred to one and fifty days of twenty-four hours' service without a single stop are not extraordinary.