(67) Installation and Consumption of Diesel Plant.
An English gas-electric station was completed at Egham, England, that is a good example of the changes that have been made recently in the electricity supply abroad, with Diesel power.
The generating plant comprises two 94 K. W. Diesel engines built by Mirrlees, Bickerton and Day, direct connected to single phase alternators generating at 2,000 volts. The exciters are direct connected to the main shaft, and the plant is capable of generating an overload of 10 per cent for two hours. Space has been left for the installation of two more units of a larger size.
The following fuel consumption was guaranteed for a load of unity power factor, and the official tests show slightly better figures than the guarantee.
| Full load | 0.68 lb. oil per K. W. H. |
| Three-quarter load | 0.72 lb. oil per K. W. H. |
| Half load | 0.79 lb. oil per K. W. H. |
| Quarter load | 1.15 lb. oil per K. W. H. |
Cross-Section Through Egham, England Municipal Plant.
Particular attention has been given to the water supply for the jackets of the engines; the circulation being by two electrically driven, direct connected centrifugal pumps, one of which is a spare. A Little Company’s cooler has been installed, which consists of a horizontal cylindrical chamber, the lower part of which contains water. In the tank are arranged a number of concentric metal cylinders spaced about ¼-inch apart, and in several sections, that are carried on a slowly revolving shaft, driven from the fan shaft. The cylinders are all of the same length, and are open at both ends.
The lower half of the cylinders dips into the water in the casing, and as they revolve, a thin film of water on each side of the plate is carried into the upper portion of the casing where it meets a blast of cold air from the fan. The fan is driven from the circulating pumps, and passes the air through the chamber in a direction opposite to that of the water, baffles being placed so that correct circulation is maintained.
The small loss is made up by connecting the ball cock in the tanks with another tank charged from the works well by means of a self-starting rotary pump, electrically driven. Very little power is required for the pumps and cooler. Fuel oil is stored in a tank outside the building, the oil being supplied to the tanks from an oil wagon by means of a small hand pump.
Oil is taken from the tanks and forced into the engine room by a rotary pump, from which it enters two graduated tanks located in the roof of the station. The graduations on the tanks allow the consumption of oil to be carefully recorded by alternately filling and emptying the two auxiliary fuel tanks.
The entire building is electrically heated, and the kitchen of the flat above the station is equipped with an electric cooking-stove for the use of one of the engineers who make it his residence.
DIESEL HORSE-POWER FORMULA
P. A. Holliday, in the Engineer, derives a new formula for computing the horse-power of the four stroke cycle, single-acting engine. For each horse-power developed by these engines about 21,000 cubic inches of displacement is necessary, per minute.
| D = | Cylinder bore in inches. |
| S = | Stroke in inches. |
| M.P.S. = | Mean piston speed in feet per minute. |
| R = | Ratio of stroke to bore. |
| N = | Revolutions per minute, then |
| √B.H.P. × 2220 | |
| D = | |
| M.P.S. |
| 6 M.P.S. | |
| Knowing the value of D, N = | |
| S |
For high speed, low ratio (R), four stroke cycle engines, approximately 22,000 cubic inches displacement per minute is required.
| √2,330 B.H.P. | |
| D = | |
| M.P.S. |
In both formulae, the air compressor for fuel injection is included.