A LABOR SAVING AND MORE EFFICIENT METHOD OF DAILY ANALYSIS OF ENGINEERING PERFORMANCE
By Lieutenant Commander W. L. Moore, U. S. Navy
The need for some form of daily analysis of the performance of the engineering plant of a ship is well recognized, but the use of such an analysis is not so universal as it should be.
Among the reasons for this condition, the following three (3) may be counted as probably the most important
(a) Lack of necessary data.
(b) Time and labor required to pick off the data from performance curves.
(c) Lack of understanding of the use and value of the analysis after the form given in the Rules for Engineering Performances.
Reasons (a) and (b) may be traced largely to the universal practice of presenting performance data in the form of curves
It is true that much data can best be recorded in the form of curves and that curves are indispensable in many cases, yet practically all of the data needed by the operating engineer can be given in the form of the simple algebraic equations which are simpler and easier to use than the curves giving the same data. This is for somewhat the same reason that in many cases the azimuth tables are more convenient than Weir's Diagram.
The data needed to make an analysis is contained in the curves of total steam consumption per hour vs. H. P., or vs. some other fundamental reading of the performance of the machine. Examine the curves for a number of auxiliaries and it will be noted that these lines, the "Willans Lines," are straight within the working range of the machine, or so nearly straight that with only slight inaccuracy a straight line may be drawn through all the plotted test points which located the curve.
Any straight line can be expressed by an equation of the form
y = a + hx
Where a is a constant — the intercept on the y-axis, and 6 is a constant — the slope of the line, y and x the variables.
Applying this to the consumption curves of auxiliaries, there can be obtained the following equations:
For a reciprocating engine:
W= A+Bh
Where PF= Pounds steam per hour (total)
h= H. P.
This in some cases may be written
W=A+BR
Where R=R. P. M.
For a pump:
W=A+BS
Where S=Double strokes per minute
For a generator:
W=A+BK
Where K=Kilowatts output
Or W=A+Bl
Where l=load in amperes.
For a turbine with first stage pressure less than .58 inlet pressure:
W=A+BP
Where P=Steam chest pressure absolute A=0
(This formula corresponds to that for a flow through an orifice W per sec =AP/70).
A number of equations derived in this way for destroyer auxiliaries are given at the end of this article. Several are taken from curves given by Lieutenant Commander Osgood in an article on "Daily Analysis." in the August 1920 number of the Institute Proceedings. These equations should be checked against the corresponding curves to check the validity of the assertations made herein.
It is to be noted that all the equations represent actual test data and are not theoretically derived. Also, that an equation is applicable over only the same conditions that the corresponding curve is applicable, i.e., if the equation is given for the consumption of a pump at 300-pound discharge pressure, and 5-pound back pressure, another equation would be necessary for 100-pound discharge pressure or 15-pound back pressure, just as another curve would be required.
Note also that the equations for the consumption of turbines based on inlet pressure are independent of H. P., R. P. M., Discharge Pressure, Air Pressure, and within the ordinary range of pressures of Back Pressure.
Consideration of the equations at the end of this article will show the following advantages over curves
(a) They are so simple that they can be worked out in many cases by mental arithmetic.
(b) They are very compact. A number can be included in very small space.
(c) They give data in a form which can be duplicated and disseminated by the typewriter or printer. This eliminates the need of tracings and blue prints and the expense and labor of making them. The Department could compile a great amount of data in a small pamphlet, and keep this pamphlet up to date through the confidential bulletins, a service of which the cost would be prohibitive if curves were used. Each engineer officer of a ship, when he conducted a water-rate test, could report his results in a form which would be immediately available for dissemination to the service.
(d) For reasons (a), (b), and (c), the data for all auxiliaries can be printed on one form for the daily analysis as illustrated in the sample form appended. This relieves the engineer officer of the necessity of thumbing through a sheaf of blueprints each time he makes an analysis.
This idea of presenting data in the form of equations for the use of the operating engineer can be carried further than is attempted here and probably for all classes of machinery. As an example, take the boiler test curves given in Lieut. Commander Osgood's article
Curve C, page 1229, ''Equivalent evaporation lbs. water per gallon oil per hour vs. gallons of oil burned per hour," and curve, page 1230, "Factor of Evaporation vs. F. W. Temperature."
From Curve C, it may be assumed that for port use the equivalent evaporation per gallon of oil is constant at 120. Combining this amount with the data, from curve, page 1230, the equation is derived
E = 93+.1T
where E is the actual evaporation per gallon oil burned, and T is the Feed water temperature.
This equation gives the actual amount of water which would have been evaporated had the boiler been in the same state of cleanliness and upkeep, and had been operated under the same conditions and with the same skill as on test.
A further line of development leading from this may be shown using a Sturtevant forced draft blower turbine—equation W=9.8 P. Assume port service feed temperature 220°, then E= 93-1-22=115 lbs. water per gal oil. Then the gallons of oil required to run the blower per hour is
G = 9.8 F/115 or .085 P (roughly 1/12 P).
A scale can be made out of this equation showing the fuel consumption of the blower and pasted on the dial of the throttle gauge for the instruction of the fire-room force in economical operation.
Returning to the point (c) mentioned in the second paragraph where lack of understanding of the application of the analysis was given as one reason for the non-universal use of daily analysis. This is perhaps natural when it is considered that the final result of the form as given in the Rules is a percentage scarcely more informing than the per cent obtained by dividing fuel allowance by fuel used.
The daily analysis can and should be carried much farther toward a definite determination of the location of faults. The sample form for a destroyer port analysis attached takes it a few steps along this line. Even the best analysis merely affords the foundation upon which the engineer officer can base his efforts to eliminate causes of inefficiency.
The quantities which are required to be determined for this more complete analysis are
(a) Pounds of water which would have been used had all machinery operated at its test efficiency.
This is determined by adding up all individual consumptions calculated by the equations discussed above.
(b) Pounds of water actually used.
Determined by actual measurement — timing given quantities of water collected in feed tank and from that calculating the total amount used in the day.
(c) Gallons of oil burned.
(d) Pounds of water which should have been evaporated had boilers operated at test efficiency.
Calculated from oil burned using boiler formula given above.
(e) Pounds of water actually evaporated.
Add make-up feed to pounds of water actually used.
(f) Gallons of oil allowed by Engineering Competition Rules.
From these quantities the following percentages are obtained:
(a) divided by (b) gives the relative efficiency of the steam ends of steam-using machinery compared to their test performances.
(e) divided by (d) gives the relative efficiency of the boilers compared to their test performances.
(b) divided by (e) gives the relative efficiency of the whole plant including boilers and auxiliaries.
(f ) divided by (c) gives an "Efficiency of Operation which, although dependent upon the suitability of the competition allowance, takes into account not only the efficiency (b)/(e) but whether machinery is run too fast, too many auxiliaries are operated, or for too long a time, and such operating features.
The difference between (a) and (e) is a measure of leaks inside the steam systems ; through leaky valves, traps, piston rings, drain seals, heating systems, etc., where the water is not lost, just as the make-up feed is a measure of- leaks where the water is lost.
With all these efficiencies worked out the engineer officer's task of locating each cause of lowered efficiency is much simplified, and more so as he has each day an itemized list of test consumptions for each piece of machinery for comparison with other days. The results he obtains are thereafter dependent upon his engineering ability.
The daily analysis has here been worked out for port use only, and the equations for auxiliaries. Both have been used underway, however, involving a few more complications but none that are prohibitive.
It is hoped that the ideas presented in this article will be found of value to the service and by facilitating a wider dissemination of information and reducing the drudgery of analysis contribute to raising the level of Engineering Efficiency.
Equations Derived From Curves in August United States Naval Institute Proceedings
(Check Against These Curves to Prove the Validity of the Formula)
Back Pressure in All Cases, 10 Pounds Gauge Boiler.
E = 93 + .iT.
Main air pump. 15x30x30x24 at 28" vacuum.
W= 350 + 90S
Auxiliary air and circulating pump. 5 ½ x 6 x 8 x 7 at 2" vacuum 15 pounds press.
W = 90+4.25S, or roughly, W=100 + 4S
Main feed pump. Blake 16 ½ x 24. Disch. press. 500 pounds gauge.
W=500+220S
Auxiliary feed. Blake 16 ½ x 11 x 18. Disch. press. 300 pounds gauge.
W=400+ 150S
F and B pump 7x7x12. Disch. press. 75 pounds gauge.
W=120+13 S
When pumping bilges or when used as flushing pump (DS = 35 to 40 and disch. press. 15 pounds) allow 75 lbs./hr.
F. O. Booster. 6 ½ x 7 x 8. Disch. press. 30 pounds.
W=70 + 4.5S
F. O. Service. 6 ½ x 4 ½ x 12. Disch. press. 150 pounds.
W=80+11S
Lubricating oil pump. 7x8x12. Disch. press. 40 pounds.
W=100+ 10.5S
Oil cooler circulating pump. 8x9x12. Disch. press. 35 pounds.
W=100+11S
Air compressor Westinghouse.
W= 25 X Pressure.
Fresh water pump. 3.5x4x4. Disch. press. 30 pounds.
W= 40+1.5 S.
Evaporator feed pump. Disch. press. 60 pounds,
W=110+ + 5.5S
Formulae From Curves Furnished by New York Shipbuilding Co. With 16th Division
Back Pressure o Pounds Gauge
Main air pump. Warren 11x32x21. Between 10 and 25 DS. 28" vacuum. Add 2.5% for each 5 pounds back pressure.
W= 1800+100S
Main feed pump. 300 pounds discharge pressure. Warren 16x12x24. Add 2% for each 5 pounds back pressure.
W =1000 + 225S.
Auxiliary feed. 300 pounds disch. press. Warren 15x10x16. Add 2.5% for each 5 pounds back pressure.
W = 800+100S
Augmenter condenser — throat 13/32 inch.
W = 6.6y + P where P = absolute pressure.
Fuel oil service pump. Disch. press, 150 pounds. Warren 6.5x4.5x12. Add 4% for each 5 pounds back pressure.
W= 70+12S
Lubricating oil pump. Warren 6 x 8 x 12. Disch. press. 40 pounds. Add 3 ¾% for each 5 pounds back pressure.
W= 20+22S
Oil cooler circulating pump. Warren 6x7x8. Disch. press. 35 pounds. Add 5 ½% for each 5 pounds back pressure.
W= 0+10S
F. & B. pump. Warren 7x7x12. Disch. press. 100 pounds. Add 3% for each 5 pounds back pressure.
W=160+21S
Evaporator feed pump. Warren 4 ½ x 6 x 6. Disch. press. 160 pounds. Add 2 ¾% for each 5 pounds back pressure.
W = 20 + 9S.
Distiller F. W. pump. Warren 3 ½ x 4 x 4. Disch. press. 30 pounds. Add 6% for each 5 pounds back pressure.
W= 20+9S.
Auxiliary air and circulating pump. 6x8x8x7. Water press. 15 pounds. Vacuum 20" Hg. Add 5 ½% for each 5 pounds back pressure.
W= 2S + 10S.
Westinghouse air compressor. Steam pressure 200 pounds.
W=3180 + 6 P where P = disch. press.
Generator 25 KW. Back pressure 10 pounds gauge.
W=600+46KW
Note that this is lbs./hr. and that KW is not KWH. Fuel oil heater.
W= .3 gals, oil/hr.
Forced draft blower. Terry turbine.
W= 33 P with all hand valves closed.
W= 41.5 P with one hand valve open.
W= 50.5 P with two hand valves open.
W= 59 P with three hand valves open.
W= 67.5 P with four hand valves open.
Note that these figures are independent of RPM back pressure or air pressure so long as throttle pressure (abs) is more than 1.7 back pressure (abs), i.e., about 35 pounds gauge.
The figure for oil consumption by the blower with all hand valves closed is 33 F/115 or .287 P gal./hr.
Formula From Test Data, Journal A. S. N. E., August, 1918. Sturtevant Turbine
P Inlet Pressure Absolute
W = 9.8 P with all hand valves closed.
W1 = 14.2 P with one hand valve closed.
W2 = 18.8 P with two hand valves closed.
Formulas From Curves From Bu. Engineering (For Bethlehem Destroyers)
Auxiliary Air Pump—Simplex Featherweight, 6x10x8
W = 90 + 4S. Estimated.
Generator 25 KIV, G. E. turbine 3600 R. P. M. Steam at 200 pounds, 0° superheat.
On 28" vac.
W= 300+32 KW.
On 25" vac.
W = 320 + 34 KW.
On 0 pounds gauge
W = 410 + 35 KW
On 10 pounds back pressure
W = 500 + 48 KW
Auxiliary condenser circulating pump 3x3 reciprocating.
W = 50+ .3 RPM. Estimated.
Main air pump. 15x30x30x24. Worthington.
W =100+ 100 S. Estimated.
Main auxiliary F. & B. pump. 7x7x12. Worthington.
W = 140 + 15S
Lubrication oil pump. 7x8x12 V. S. Worthington.
W = 290 + 7S Estimated.
Distiller fresh water pump. 3 ½ x 4 x 4 V. S. Worthington.
W = 20 + 1S. Estimated.
Oil cooler circulation pump. 8x9x12 V. S. Worthington.
W = 420 + 8 S. Estimated.
Main and auxiliary feed pump. 16 ½ x 11 x 16. V. S. Worthington.
W = 250+125 S Estimated.
Evaporator feed pump. 4 ½ x 6 x 6. Worthington.
W = 5 + 2 S. Estimated.
Fuel oil booster pump. 6 ½ x 7 x 8 V. S. Worthington.
W = 140 + 3S
Fuel oil service pump. 5 ½ x 4 x 8 V. D. Worthington.
W= 340+19 S