The Diesel or slow-combustion oil engine; a practical treatise on the design and construction of the Diesel engine for the use of draughtsmen, students, and others

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 Excerpt: ...the same as at B. The air is now compressed again to Pt at F and discharged. The curves BC and EF are compression curves PV" = constant, and in each of the cylinders n is supposed to have the same value. The work done in compression is the sum of the two shaded areas, i.e.--Fig. 53.--Diagram of Work in a Two-Stage Compressor. For U to have a minimum value, it is necessary that the sum of the two variable terms within the brackets, i.e., shall be a minimum. In these terms Pi and P.2 are fixed values, Fm. 54.--Diagram of Work in a Four-Stage Compressor. being the initial and final pressures, so it is necessary to find that value of P3 which shall make u a minimum; by differentiation--_=!-P_L=0. dP3 P2 P3-' n-l where P = (P)""; hence for a minimum value p 2-p p. ra--rtrl and consequently fv P2, and P3 are quantities that are in geometrical progression. In a similar manner it may be shown that the terminal pressures at the end of each stage in a multistage compressor are quantities that form a geometrical progression. For example, in Fig. 54 is shown a diagram similar to that in Fin. 55.--Diagram showing Gain due to Stage Compression. The gain due to stage compression is well shown by the diagram in Fig. 55 where compression is carried on from P0 to P3 in three stages. Starting at A, the air is compressed along the curve as far as B where the pressure = Pt; here it is discharged into the cooler and its volume shrinks at constant pressure to C, when the second cylinder compresses it to D at a pressure P2. Here the air is again cooled at constant pressure, its volume shrinking to E. Finally the third cylinder compresses it to P3 at the point F. The shaded area shows the saving of work over that necessary if the compression had been done in one cyli...