Bulletin of the Tomsk Institute of Technology

Volume 41, Issue 2

1918

Prof. V. L. Maleev

TESTING OF TWO LOCOMOBILES OF 250 H.P.

BULLETIN

of the Tomsk Institute of Technology, Siberia, Russia

Vol. 41, Number 2

1918

Prof. V. L. Malejev

TESTING OF TWO LOCOMOBILES 250 HP. EACH

Tomsk
1919

Testing of Two 250 hp Locomobiles

Professor V. L. Malėev.

1. Preface.—In the summer of 1914 the author had occasion to carry out tests of two locomobiles from a certain foreign works, installed at the municipal electric station in the town of K—, Tobolsk Province. In the author’s opinion, these tests deserve to be described for several reasons: first, the locomobiles in question represent a new and interesting type in point of construction, and the locomobiles tested were in general the first of this type to be installed in Russia; further, in the supply of these locomobiles a very low steam consumption had been guaranteed, which on the whole was achieved; finally, installations of comparatively large locomobiles, such as these, developing from 225 to 270 indicated hp, are at present of particular interest from the standpoint of competition among various heat engines.

2. Description of the locomobiles.—Both locomobiles are completely identical in dimensions and construction, bearing the works mark B.K. 11. The only difference is that in the one sent and installed first, which we shall call No. 1, the piston rods are not through rods, while in the other, No. 2, they are through rods. The firm’s fitter reported, however, that the works would also send to No. 1 new through piston rods with external supporting slides and, correspondingly, new covers with guides.

The boiler has smoke tubes; the superheater is made of solid-drawn tubes coiled in a spiral; the outside diameter of the tubes is 50 mm, the length of each tube 14.67 m, and their number 19. The heating surface of the boiler, according to the works data, is 41.68 m²; the heating surface of the superheater is 43.8 m². The grate area is 2 m²; the firebox is set forward and adapted for wood firing.

The working steam pressure is 15 atm gauge; the temperature of the superheated steam is stated by the firm as 350° C; however, there are no devices for its regulation, and, as the tests showed, it varies depending on the load of the engine and the manner of firing.

For feeding the boiler there is an injector and a rocking pump, located on the extension of the rod of the condenser air pump. When using the pump, the feed water may be heated by passing it through the tubes of the heater, warmed by the exhaust steam on its way to the condenser.

Engine. The principal dimensions of the engine are: diameter of the h.p. cylinder \(D'=260\) mm, of the l.p. cylinder \(D''=520\) mm; piston stroke in locomobile No. 1 \(H=461\) mm, in No. 2—\(H=462\) mm; diameter of the piston rods \(d=60\) mm. The cranks of the shaft are at an angle of \(180^\circ\) to one another; the normal number of revolutions \(n=214\) rpm; degree of non-uniformity of rotation of the shaft

\[ \delta=\frac{1}{180}. \]

The distributing organs: admission of steam into the h.p. cylinder is effected by a round piston valve \(a\), Fig. 1, under the action of a flat governor; exhaust of steam from the h.p. cylinder is effected by the same piston valve \(b\); it also admits steam into the l.p. cylinder, while serving as a Trick valve with double admission, but with internal edges; the exhaust of the spent steam from the l.p. cylinder is effected first through the ports \(d\), Fig. 2, situated in the middle of the cylinder and opened and

Fig. 1.

closed by a wide piston, as in straight-flow steam engines; the subsequent exhaust of steam for reducing compression, which begins approximately only after 20% of the piston stroke from the dead point, is effected through special exhaust slots, closed by piston slide valves \(c, c\), seated on a common rod with the admission slide valve \(b\).

along 1-2-3-4-5-6.

Drawing 2.

The movement of steam is clearer in Drawing 2, which represents a schematically developed longitudinal section of the cylinders and slide valves along the broken line \(1-2-3-4-5-6\), Drawing 1. Solid arrows show the movement of the steam entering the cylinder, and dashed arrows that of the steam leaving it.

In assessing the features of this steam distribution, it may be noted that the separation of the admission passages from the exhaust passages at the high-pressure cylinder considerably reduces the cooling of the admitted steam and, from the standpoint of reducing its consumption, is quite expedient; a similar separation is also encountered in other good designs, for example in the locomobiles of the Lyudinovo Works of the Joint-Stock Company of the Maltsov Works. The inevitable increase in harmful space is of only slight significance and is offset by the advantage obtained.

As regards the low-pressure cylinder, the separation of admission and exhaust in it is not carried out so completely: one of the two steam passages at each end of the cylinder is washed by both the admission and the

with the exhaust steam. However, the main part (about \(3/4\) by weight) of the exhaust steam flies out through the exhaust ports in the middle of the cylinder. Therefore the initial condensation of the steam is also greatly weakened.

Another advantage of this design is the very small dimensions of the cylinder exhaust slide valve, since with a cylinder diameter of 520 mm the round slide valve has a diameter of only 150 mm, with an axial length (height) of the port of 38 mm; the travel of the slide valve is \(h = 2r = 112\) mm. For a machine making 214 rev./min., the small weight and travel of the slide valve are very important.

The exhaust of the steam is usually led into a mixing condenser with a vertical wet air pump, driven from the main shaft by means of a belt drive. The ratio of pulley diameters is \(840 : 1100 = 0.764\), so that the pump makes about 163 double strokes per minute. On its way to the condenser the steam passes through the above-mentioned heater for the feed water.

3. Conduct of the tests.—Quantities measured: during the test the consumption of firewood and feed water was measured, as were the pressures and temperatures of the steam at entry into the engine and at exit from it, the temperatures of the feed water, of the cold water before entering the condenser, and of its mixture with the condensate after the condenser; indicator diagrams were taken; the number \(n\) of revolutions per minute of the engine was measured, then the voltage and current strength for calculating the electrical work, and also, by special meters, directly the magnitude of this work in kW·h; and, finally, the content of \(CO_2\) in the products of combustion was determined.

Methods of measurement. The consumption of firewood was determined by weighing it on decimal scales in half-sazhen batches of 15 poods each.

The consumption of feed water was at first intended to be measured by means of a Leinert-type water meter with swinging tanks. However, when it was checked by weighing the water passed through it, it was found to have a rather considerable insensitivity, over \(\pm 1\%\); moreover, when using this water meter it would have been necessary to adjust the duration of the experiment to the moment when the whole tank had been used up, the capacity of which was \(7\frac{1}{2}\) poods, i.e., to work an extra 5–10 minutes. In view of this, the consumption of feed water was determined by weighing it on verified decimal scales in portions of 10 poods; the scales with the tank stood on trestles, next to which there was a second tank, into which the weighed water was let down and from which it was taken by the injector. The same scales were used to weigh the water for pri-

…bringing, after the end of the test, the level in the second tank to the same height as at the moment the test began.

In view of the fact that the units were tested under an entirely constant load, the accidental fluctuations of which were immediately equalized, we considered it possible to limit the duration of each test to exactly 6 hours, with intermediate reports in the middle of each test. By dividing each 6-hour test into 2 halves by means of these reports, and calculating the steam consumption per unit of power for each half, we obtained figures that differed from one another only within the limits of the possible accuracy of the test.

Of course, all measures were taken to ensure the necessary accuracy: the test began only after a fully steady state had been attained; at the moment of the end of the test (and, as far as possible, of the intermediate report of water consumption), the steam pressure, the water level in the boiler, and the condition of the furnace were brought strictly to the initial state. The boiler was fed by an injector receiving steam from the same boiler, which made it unnecessary to introduce any corrections and, in view of the arrangement of the measuring tank, ensured greater accuracy than when using the engine feed pump.

The carbon-dioxide content in the flue gases was determined by an automatic analyzer—the Eckardt “econometer”; in this connection, the position of the zero line was checked each day by drawing in clean air.

The scales and, in general, all measuring instruments were checked before and after the tests, and the corresponding corrections were introduced into the test results given below. The only instruments not subjected to checking were the pressure gauges on the boilers and the vacuum gauges at the condensers. However, bearing in mind that the pressure gauges were quite new and of good manufacture, their readings may be regarded as sufficiently reliable. As for the vacuum gauges, then, on the one hand, the oscillations of their needles under the influence of the periodic impulses of the air pump were so considerable that, when recording the “mean reading,” an error greater than the possible error of the instrument could in any case be introduced; on the other hand, we used the vacuum-gauge readings only for a rough setting of the quantity of cooling water and to check whether the exhaust steam was superheated; for thermodynamic calculations, however, we determined the vacuum from the temperature of the exhaust steam, since, as it turned out, it was always wet.

Proof of the wetness (absence of superheat) of the outgoing steam was provided, on the one hand, by the readings of the vacuum gauge; on the other hand, by the fact that

the circumstance that random fluctuations in the temperature of the freshly superheated steam, reaching as much as 50° and more, were not reflected in the temperature of the exhaust steam and, finally, the heat diagram, Fig. 26.

Separate devices. First of all, mention may be made of the device for taking indicator diagrams: indicators were placed at each end of the cylinder, directly on the corresponding nipples. On the H.P. cylinder there were two of the newest Maygak indicators of medium size with a cold spring; on the L.P. cylinder, two Dreyer, Rosenkranz and Droop indicators, likewise model II, of the latest type, with a cold spring working in compression, a plate piston, and an instantaneous stop. To the inner indicator, i.e. the one nearest the shaft, were attached roller motion-reducers of the corresponding plant; the ends of the cords from the motion-reducers were hooked onto special pins made of strip iron, screwed to the machine crossheads; each of the cords was guided by several rollers so that the part of it adjoining the pin had a direction strictly parallel to the axis of the engine cylinder. To avoid stretching, a particularly thick cord was used for one pair of indicators, and for the other a cord of no lesser thickness, in two strands; moreover, the instruments were so arranged that the cords were as short as possible.

With the given numbers of revolutions and the length of piston stroke, it is impossible to hook the indicator hook onto the above-mentioned pin on the machine crosshead in the usual way. It was necessary to resort to the “self-hooking” hook shown in Fig. 3: the strong, but light, steel hook has a bent spring tongue a; the length of the hook is \(l = 100\) to \(120\) mm. To hook the hook onto the catch-pin c

Fig. 3.

on the machine crosshead, the hook must be held so that this pin, on reaching the left dead position, strikes the angle formed by the tongues a and b; during the return motion c slides past the rigid tongue b and catches the hook. To remove the hook, i.e. to stop the indicators, it is sufficient to take hold of the cord d.

The fittings for the thermometers in the steam pipes were brass; care was taken that the mercury bulb should be located approximately at the center of the cross-section of the steam pipe, and that the temperature reading...

oil, which was poured in for better heat transfer, could drain off; in the pipe with fresh, highly superheated steam, at least by 20–30° above the steam temperature.

The load resistance was of a special design, since, despite the fairly considerable power—up to 170 kW—owing to the three-phase current system and the high voltage of 3000 volts, the current flowing into the resistance amounted to only a few—up to 32—amperes. The resistance consisted of a wooden vat, about 1.4 m in diameter and about 0.9 m high, into which the ends of three iron rods \(a_1\), \(a_2\), and \(a_3\), Fig. 4, 5–6 mm thick, attached on insulators \(b,b\) to a triangle \(f\) of angle iron fastened with bolts, Fig. 5, were immersed by several centimeters; the triangle \(f\) was suspended by means of intermediate ropes \(c,c,c\) from the rope \(d\), passed over a pulley; flexible conductors \(e_1,e_2\), and \(e_3\) from all three phases of the current to be destroyed were connected to the immersed rods.

Figs. 4 and 5.

The load was regulated by immersing the ends \(a_1\), \(a_2\), and \(a_3\) to a greater or lesser depth \(h\). To remove the heat into which the electrical energy was converted, the water in the vat was continuously renewed, entering through the hemp hose \(g\), the end of which was lowered almost to the bottom of the vat; na-

the heated water flowed out through a cut in the upper edge of the vat along the spillway \(i\) into an attached trough, and along the latter ran off into the river. In order that the conversion of electrical energy into heat should proceed quietly, the water had to be changed at such a rate that it did not have time to heat above \(50\div55^\circ\) C.

However, even when this condition is observed, the discharge through the thin rods \(a_1, a_2, a_3\), which are immersed to a small depth, proceeds rather unsteadily and is accompanied by a phenomenon resembling a voltaic arc; the ends of the rods \(a_1, a_2\), and \(a_3\) burn away. For operation to be as steady as possible, the ends \(a_1, a_2\), and \(a_3\) must lie in one horizontal plane, i.e., be immersed to exactly the same depth. As the ends burn away, which for some reason usually occurs unevenly, they must be aligned again. For the uniform immersion of the rods \(a_1, a_2\), and \(a_3\), it is necessary that the supply wires \(e_1, e_2\), and \(e_3\) be as flexible as possible; for this purpose it is useful to make them, up to the fixed insulators, as long as possible and twisted in the form of spirals.

In view of the high voltage of the current, the entire apparatus was enclosed by a fence, which prevented access by unauthorized persons; the water, flowing out of the charged vat, quickly loses its charge owing to the mixing of streams charged with different phases.

4. Results of the tests.—In the following Table 1 a summary is given of the results of the tests on steam and fuel consumption. In addition to what was said above, it may be noted that the pressure in the condenser, line 17, was determined with the aid of steam tables from the temperature \(t_0\), line 13; the quantity of cooling water \(W\), line 18, was calculated from the quantity of feed water \(G\) and the temperatures \(t_0, t_1\), and \(t_2\), lines 13–15, on the basis of the heat balance, according to the expression, self-explanatory without further comment,

\[ W = G \frac{t_0 + x_0 r_0 - t_2}{t_2 - t_1}, \tag{1} \]

where \(r_0\) is the latent heat of evaporation at pressure \(p_0\), and the value of the steam content \(x_0\) was determined graphically from the \(J\!-\!S\) diagram, under the assumption that expansion takes place adiabatically from the point determined by the pressure \(p\) and temperature \(t\). The actual value of \(x_0\) should be somewhat lower under the influence of cooling of the steam at admission, but we were unable to measure it. In all probability, the value \(W\) found by us is somewhat exaggerated, but in view of its secondary importance one may confine oneself to this method.

As regards the values of \(n\) rev/min, p. 19, it should be noted that the governors were not sufficiently adjusted; almost up to each test the fitter was tinkering with them, now tightening, now loosening the governor springs, as a result of which in tests II and V \(n\) proved to be above normal. However, an increase of \(n\) by 1–2% is, from the thermodynamic point of view, entirely immaterial.

As regards the mean indicated pressures \(p_i\), pp. 20–23, they were determined as the arithmetic mean of all \(p_i\) for the given working stroke of the corresponding test, found by planimetering. For checking, in each test \(p_i\) was also determined, in addition, by Simpson’s rule on one or two series of diagrams as close as possible to the mean. The results obtained did not differ from the results obtained with the aid of the planimeter.

In conclusion it should be mentioned that the author carried out tests I and II, relying on the fitter who vouched for the correctness of the assembly of the machine. Examining the diagrams obtained and comparing them with the diagrams of machine No. 2, the author discovered that the rear cover of the high-pressure cylinder had been installed incorrectly, shifted by one bolt clockwise. Since the ports are arranged almost entirely in the cover, as a result of this they proved to be greatly narrowed, especially the steam-inlet port. The result of this was a reduction in the area of the diagram of this end and of the low-pressure cylinder end paired with it, Drawings 6 and 7. When the cover was reset correctly, the indicator diagrams proved considerably better, the mean pressures almost became equal, and the work of the individual ends likewise. Thus test I, from the point of view of acceptance of the machine, should be rejected. We have included it only to clarify the influence of the indicated incorrectness of assembly. Unfortunately, lack of time did not permit repeating the test with \(1/2\) load with the cover correctly installed. It may, however, be stated with confidence that the results

Drawings 6 and 7.

would be, approximately, by as much better than the results of test II as the results of test V are better than test I.

Table 1.

In Figs. 6–13 are presented series of diagrams from all five tests, the series being selected as nearly as possible to the corresponding mean diagrams. The pressure scale of the diagrams is $m_1 = 2.5$ mm/kg·cm²; the scale $m_2 = 10$ mm/kg/cm² of the l.p. cylinder diagrams is to be taken with such a calculation that the ratio $m_1 : m_2$ is approximately—

tively, the ratio \(F_1:F_2\) of the areas of the pistons of the H.P. cylinder and the L.P. cylinder; then, with equal diagram lengths, their areas express the works on one scale. The Roman numerals on the diagrams denote the number of the test from which the diagram was taken.

The diagrams, as was already indicated above, were taken from each working cavity with a separate indicator, while in Figs. 6–13 they are placed in pairs in order to save space.

The diagrams of tests I and V are placed so as to make the constriction of the passage clearer.

With the exception of the diagrams of tests I and II, the rest show good outlines and a satisfactory distribution of the work. The dotted line on the diagrams of the H.P. cylinder shows the steam pressure in the boiler, and in the L.P. cylinder—the exhaust lines of steam from the H.P. cylinder, giving the magnitude of the fall in steam pressure during its passage from the boiler into the H.P. cylinder and, correspondingly, from the H.P. cylinder into the L.P. cylinder; taking into account the high speed of the engines, the drops are not large, and for this reason they are more significant on the crank side of the L.P. cylinder of both engines.

Fig. 12 and 13.

The following Table 2 gives the results of processing the figures presented in Table 1.

Table 2.

In explanation of it, it must be said, first, with regard to the effective power \(N_e\). The point is that in the contract with the firm the figures for steam consumption per 1 effective horsepower at \(1/1\)- and \(1/2\)-load were guaranteed, p. 13. At the same time it was stipulated that the guarantee was still to be considered fulfilled if, during the test, the steam consumption proved to be 5% greater than the guaranteed figure, i.e. the actual guaranteed figures were 5% higher than the nominal ones and are indicated in parentheses, p. 13. However, the difficulty, or rather the oversight, consisted in the fact that the contract did not specify the method for determining the effective power \(N_e\). It was not possible to measure the value \(N_e\) directly, for example by means of a brake, owing to the considerable power of the machines in question. Two courses remained: either to determine \(N_e\) from the indicated power \(N_i\), for which it is necessary to know the mechanical efficiency \(\eta_m\) of the machine; then

\[ N_e = \eta_m \cdot N_i , \tag{2} \]

or to determine \(N_e\) from the electrical work on the collecting busbars, \(K\) kW, in which case it is necessary to know the efficiency \(\eta_e\) of the electric generator; then, with the generator shaft directly coupled to the shaft of the engine,

\[ N_e = K / 0.736 \eta_e . \tag{3} \]

Unfortunately, neither \(\eta_m\) nor \(\eta_e\) was stipulated in the contract. A further difficulty lay in the fact that, although under the contract both units were supplied by Siemens-Schuckert, in reality it supplied only the electrical part, while the locomobiles were supplied and delivered by the representative of the locomobile works. In view of this, for checking the guarantee of steam consumption the acceptance commission agreed to use the value \(N_e\) found from eq. (2), where, according to the firm’s indication, \(\eta_m = 0.93\) was adopted for full load; for half load the author, using the results of tests of similar machines, adopted \(\eta_m = 0.86\). However, for purposes of verification it was decided also to determine the steam consumption from the electrical work, i.e. by means of eq. (3). According to the firm’s indication, for the generator \(\eta_e = 0.93\) was adopted for full load, and for half load, relying on experimental data for similar machines, the author adopted \(\eta_e = 0.88\).

The values of \(N_e\) calculated from eq. (2) are given on p. 8. Lines 9–12 represent the steam consumption per unit of the various powers and are clear without further explanation. Comparing the corresponding figures of pp. 11 and 13, it may be noted that at full load both locomobiles satisfied the guarantee; at half load, locomobile II [[unclear: continuation cut off]]

hold, while locomobile I was not, probably because of improper installation of the cylinder cover, etc. Comparing the consumption figures for locomobile I with those for II, we see that locomobile I, which had been operating for several weeks before acceptance and had had time to run in, gave better results than locomobile II, which was tested immediately after assembly. Other causes that adversely affected the steam consumption of locomobile II were a lower superheat, poorer vacuum in the refrigerator as a result of air leaking into the cold-water pipeline, assembled with couplings instead of flanges, and, finally, the circumstance that locomobile II operated not with carefully made patented packings, which had not yet been delivered for it by that time, but with simplified temporary packings.

On p. 14 the consumption of firewood per 1 indicated h.p. is given; it turns out to remain almost constant for all tests, at least within the limits of the accuracy of the tests, varying very little with load. This is explained by the fact that the inevitable decrease in the thermal efficiency of the engine itself with decreasing load is balanced by an increase in the efficiency of the boiler. This circumstance suggests the question whether the relative dimensions of the boiler and the engine were chosen altogether successfully by the factory. Unfortunately, our tests cannot give a more definite answer to this, since we were unable to measure the temperature of the flue gases and to make a more detailed analysis of them.

On p. 15 \(Q_d\) is given—the heat consumption per 1 indicated h.p. according to the quantity of firewood consumed, with the average useful calorific value of birch firewood taken as \(H_n = 3400\) heat units/kg.\(^1\)

Since the useful calorific value of firewood is subject to considerable fluctuations, chiefly depending on its moisture content (for dried firewood \(H_n\) reaches 4490 heat units/kg, while for firewood with 40% moisture \(H_n\) falls to 2400 heat units/kg), and since we did not measure the moisture content, but rely only on the statement of the station superintendent that the firewood had been lying, i.e. contained about 20% moisture, the figures on p. 15 cannot claim particular accuracy. An error of \(\pm 10\%\) is possible. However, for comparing the tests with one another, the figures on p. 15 may be considered sufficiently accurate, since the firewood was taken from one woodpile, i.e. its true calorific value was indeed the same for all the tests.

On p. 16 the heat consumption per 1 indicated h.p.-hr. of the engine itself is given, i.e. according to the steam consumption, taking into account the heat of the water at

\(^1\) K. Blakher. Heat in Factory Practice. Riga, 1905, pp. 93 and 94.

entering the boiler \(i' = t_{\mathrm{n}}\) and the temperature \(t\) of the superheated steam upon entering the cylinder, etc.; the calculation was made from the steam tables according to the expression

\[ Q_{\mathrm{n}} = D_i \left[i' + r + c_p (t-\vartheta)--t_{\mathrm{n}}\right]. \tag{4} \]

The thermodynamic efficiency \(\eta_t\), p. 17, shows what part of the heat \(Q_{\mathrm{n}}\) contained in the steam upon entering the engine is converted into indicated work. Since part of the total heat, even in an ideal engine, must inevitably be lost, the merit of the engine is more clearly shown by comparison with an ideal engine, i.e. by the so-called indicated efficiency \(\eta_i\), p. 18, where

\[ \eta_i = \frac{632.3}{D_i (i-i_0)}; \tag{5} \]

the work of 1 kg of steam in the ideal Clausius-Rankine engine, \((i-i_0)\), we determined from the \(I-S\) diagram by \(p\), \(t\), and \(p_0\), while the work of 1 kg of steam in the tested engine, \(623.3/D_i\), we obtained from p. 10. For comparison we took the Clausius-Rankine engine, and not the Rankine-Meyer engine, for the sake of simplicity of calculation; the difference due to neglecting incomplete expansion is not especially great. Moreover, in the new Russian rules for testing steam engines and turbines, nothing is said about the Meyer engine.

The values \(\eta_i\), p. 18, show that, from the thermodynamic point of view, the engines tested are very good.

On p. 19 the economic efficiency \(\eta_{\mathrm{ek}}\) of the whole unit is given, calculated according to the expression

\[ \eta_{\mathrm{ek}} = \frac{632.3\,K.h}{0.736BH_{\mathrm{n}}}. \tag{6} \]

Although the values \(Q_{\mathrm{d}}\) and \(\eta_{\mathrm{ek}}\) are considerably inferior to those obtained with internal-combustion engines, they nevertheless exceed the average values usually adopted at the present time for steam engines of corresponding power.

In conclusion, let us explain pp. 23 and 24 of Table 2: since the values of the efficiency of electric generators \(\eta_{\mathrm{e}}\) are determined much more accurately than the values of the mechanical efficiency \(\eta_{\mathrm{m}}\) of steam engines, are less subject to variation from accidental influences, and, finally, are the same both for a new engine and for one that has been run in, it seemed of interest to the author to determine, conversely, the values of \(\eta_{\mathrm{m}}\) from \(K\), \(N_i\), and \(\eta_{\mathrm{e}}\). On p. 23 are given the resulting values of the total efficiency of the whole unit \(\eta_{\mathrm{a}} = \eta_{\mathrm{e}}\eta_{\mathrm{m}}\), and on p. 24 the values of \(\eta_{\mathrm{m}}\) for \(\eta_{\mathrm{e}} = 0.93\) at full load and \(\eta_{\mathrm{e}} = 0.88\) at half load. The tests-

tests II—V gave results very consistent with one another and rather close to the values of \(\eta_m\) adopted by us. Test I, carried out with incorrect sections of the steam passages on the cylinder-cover side, etc., and therefore with large losses and an improper distribution of work among the individual working cavities, gave a value of \(\eta_m\) approximately 0.03 lower than the values from tests IV and V. At \(1/2\) load, test II, the narrowing of the passages did not affect the value of \(\eta_m\), probably owing to the smaller steam consumption.

In general, p. 24 confirms the sufficient correctness of the values of \(\eta_m\) and \(\eta_e\) adopted by us above.

Start of the test at 11 a.m., end at 5 p.m.
Drawing 14.

Finally, in Drawing 14 a specimen is given of the economograph diagram taken during test V. It gives not only the average content of \(\mathrm{CO}_2\) in the flue gases, equal to 14%, but also shows that the \(\mathrm{CO}_2\) content fluctuated very little, only within the limits from 12 to 15%.

Regulation. After the steam-consumption tests, tests were made of the regulation of the machines: with an almost instantaneous reduction of the load from \(1/1\) to approximately \(1/9\) of its normal value, from 250 to 28–30 hp \(^{2}\), the number of revolutions \(n\) increased from 214 to 229, but after 10 sec. settled at 224, i.e. the greatest overspeed was \(+7\%\), and the remaining change \(\Delta n = +4.7\%\). With a rapid increase of the load, the number of revolutions drops from 224 to 209, and after 10 sec. settles at 214. Thus it may be considered that the governors on these machines are sufficiently powerful and reliable, but with a rather considerable degree of insensitivity. In view of the latter circumstance, bearing in mind the parallel

\(^{2}\) It was not possible to carry out a complete unloading while working with the condenser, since the centrifugal electric pump supplying water for cooling the steam and the load resistance would then have stopped; the energy for the pump amounted to about 30 hp.

For the operation of both units the regulators are provided with devices allowing the number of revolutions to be changed while the machine is running by up to \(\pm 5\%\).

Next, the degree of non-uniformity of rotation of the machines was investigated by means of a Horn tachograph. In view of the complete identity of the machines, the identical dimensions and weights of the flywheels and generators, and the identical controllability of the machines, tachograms were taken from only one unit, II. The pulley for setting the tachograph in motion had to be fitted on the generator shaft, behind the Zodel-Voith coupling, so that the degree of non-uniformity found from the tachogram,

\[ \delta = \frac{1}{235}, \]

refers to the generator; the value of \(\delta\) for the locomobile, up to the elastic coupling, will be somewhat greater and, it must be assumed, approximately equal to

\[ \frac{1}{180}, \]

as specified in the contract with the firm.

Fig. 15.

In Fig. 15, as an example, is given a photographic print of a piece of a tachogram taken at full load, \(N_e \simeq 250\) effective h.p. and \(n = 214\) rev./min.; the ordinate scale is 4 mm \(= 1\%\) fluctuation of speed. The nominal speed of the paper tape was \(c = 10\) mm/sec, i.e. one revolution of the machine on the diagram should correspond to a length

\[ l = \frac{10 \cdot 60}{214} = 2.8 \text{ mm}; \]

however, owing to slipping, on the one hand, of the friction wheels in the tachograph itself, and on the other, of the tape on the aluminum pulley, the length corresponding to 20 revolutions of the machine came out to be 48 mm, i.e. the length corresponding to 1 revolution is only 2.4 mm, the slip being about 14%.

Turning to the diagram, Fig. 15, we see that one complete period, from one tooth of a minimum to the next, is quite accurately 4.8 mm, i.e. it embraces exactly 2 revolutions of the machine. The explanation of this phenomenon must, in all probability, be sought ...

in the interaction between the flywheels and the governor. However, as is known, Horn’s tachograph gives diagrams which make it possible to measure, with sufficient accuracy, the limits of fluctuation of the machine speed, i.e. to determine the degree of non-uniformity \(\delta\) of its rotation, but they cannot convey the true character of the curves of speed variation, especially with so considerable a number of revolutions as \(n = 214\) per min.

Additional investigations. After the completion of the described acceptance tests, the author decided to carry out at least a cursory investigation of the operation of the machine under other loads, and also when working without a condenser, exhausting to atmosphere. In these experiments, in establishing the desired load, they confined themselves to taking indicator diagrams and to simultaneously recording the number of revolutions of the machine \(n\). The experiments were made with locomobile No. 1, with the valve cover correctly installed.

On Figs. 16 and 17 a series of diagrams is given for operation with an overload of about 20%; on Figs. 18 and 19—with the smallest load, about \(1/9\) of the normal value; on Figs. 20–25 are given series of diagrams for operation exhausting to atmosphere with \(1/8\), \(1/2\), and full loads. The machine could not carry a larger load when operating with exhaust to atmosphere. The pressure scales in Figs. 16–25 are the same as in Figs. 6–13. The inscriptions on the diagrams themselves make further explanations unnecessary.

Figs. 16 and 17.  Figs. 18 and 19.

In general the diagrams, except for the smallest load, have a proper appearance; the unavoidable loops do not present anything dangerous

as a result of the use of piston slide valves. When operating with full load on the exhaust, Figs. 24 and 25, at the end of compression in the l.p. cylinder, etc., the safety valves opened. All diagrams of the l.p. cylinder when operating on exhaust show a large resistance in the exhaust line: compression in the l.p. cylinder should begin 20% before dead center, whereas in the diagrams of Figs. 20, 22, and 24 it begins as if at 75, even 80%. Apparently the auxiliary ports, which release steam after the exhaust edges \(d\) of the piston have closed and are controlled by the piston slide valves \(c, c\), Fig. 2, are insufficient for exhausting steam at atmospheric pressure, whereas for exhausting less dense steam, at a pressure of about \(0.15\ \mathrm{kg}/\mathrm{cm}^2\) abs., their cross-section is sufficiently large. This assumption is also confirmed by the magnitude of the steam velocity: the area of the auxiliary ports is only about \(132\ \mathrm{cm}^2\), which, at an average piston speed of \(3.29\ \mathrm{m}/\mathrm{s}\), gives an average steam velocity in the ports of about \(52.2\ \mathrm{m}/\mathrm{s}\), and a maximum, near the middle of the piston stroke, of as much as \(83.5\ \mathrm{m}/\mathrm{s}\). Since the machines are intended for continuous operation with a condenser, this circumstance is not particularly important.

Further, in Fig. 26 there are given first the Rankinized diagrams of locomobile No. 1 with correct assembly and full load, Figs. 6 and 7, and then they have been transferred by the well-known method of Boulvin¹ into thermal coordinates \(T—S\). To determine the losses of the actual machine, diagrams of an ideal machine have also been drawn in the coordinates \(T—S\), and also in \(P—V\)—without clearance space, without losses from the influence of the walls and from friction, but with incomplete expansion. The pressure in the receiver of the ideal machine is taken equal to the pressure in the H.P. cylinder at the moment of the beginning of the return stroke, point \(f\), Fig. 26, and the volume of the receiver is assumed infinitely large.

Fig. 24 and 25.

In Fig. 26 all scales are indicated and the required curves and lines are marked with inscriptions. By way of explanation it may be added that the great difference in the boundary curves for the H.P. and L.P. cylinders in both coordinate systems is due to the fact that during the period of compression in the clearance space of the H.P. cylinder there is, by weight, considerably more steam than in the corresponding period in the L.P. cylinder, namely 0.0186 and, respectively, 0.0026 kg; since 0.0413 kg of fresh steam is admitted per 1 stroke, the total quantity of steam taking part in the work during 1 period amounts, in the H.P. cylinder, to 0.060 kg, and in the L.P. cylinder, to only 0.044 kg.

The thermal diagrams of the tested machine show that the superheating of the steam at the end of admission into the H.P. cylinder, point 2, is preserved, and only the temperature of the steam is lowered from \(368^\circ\) to \(290^\circ\); into the L.P. cylinder the steam enters still superheated, and even at the moment of cut-off in the L.P. cylinder has a temperature of about \(122^\circ\), i.e. several degrees above the corresponding temperature of saturated steam. However, the—

the passage of the indicator diagram of this cylinder into the superheat region is so insignificant that, with sufficient accuracy, one may simply consider that at the moment of cut-off the steam is unquestionably dry, i.e. that in this cylinder there is no phenomenon of initial condensation. The preservation of steam superheat up to the low-pressure cylinder explains the low steam consumption of the engine, and this, in turn, must be explained by the location of both cylinders directly on the steam boiler, by the very short steam passages, and by the separation of the windows for admission and exhaust of steam.

The losses in this engine, in comparison with the above-mentioned ideal one, are revealed by the deviation of the outlines of the diagrams, both in the coordinates $T—S$ and $P—V$. For clarity, the corresponding areas are hatched with inclined lines, while with horizontal hatching the areas $dmnfed$ and $ioki$ mark the losses from incomplete expansion for the ideal engine. In the $P—V$ diagram the area $ioki$ is not shown, since in any case it would not fit entirely on the drawing.

For a quantitative determination of the losses it must be remembered that, of the quantities of steam participating in the working process, there is only $0.0413$ kg of fresh steam, whereas the diagrams are drawn for the full quantities, i.e. $0.060$ kg for the high-pressure cylinder and $0.044$ for the low-pressure cylinder. Therefore, having measured the areas of the ideal diagrams, both in the coordinates $P—V$ and $T—S$, they must be reduced in the ratios $\frac{0.0413}{0.0600}$ and $\frac{0.0413}{0.0440}$; to do this graphically when drawing the diagrams is inexpedient, since then the visibility of the losses in the separate parts of the diagrams of the actual engine would disappear.

Bearing this in mind, it must be admitted that the losses in this engine are not very great. Even the losses due to clearance space and at admission, considerable at first sight, turn out not to be especially large: in all, all the losses equal only $0.13$ of the area of the ideal diagram. Even if an engine without losses from incomplete expansion is taken as the ideal engine, the losses equal only $0.22$ of its area, which is in very close agreement with the value found above, p. 18, Table 2, $\eta_i = 0.79$.

5. General conclusions.—If one sums up the results of the tests of the locomobiles under consideration and compares their merits and shortcomings, and also tries in general to evaluate this type of machine, then first of all one must acknowledge in their favor the comparatively small consumption of fuel and steam, i.e. economy; the second merit is the comparatively small area and, in general, the small space required for their installation. This, however, exhausts the positive side, and further one must point out several negative properties.

![Drawing 26: indicator and related curves for the cylinders; visible labels include “curve \(p-t\),” pressure graduations, and cylinder-volume annotations.]

Visible annotations in the drawing:

• curve \(p-t\)
• \(15\ \mathrm{kg}/\mathrm{cm}^2\), abs.
• H.P. cyl.
• L.P. cyl.
• [[unclear: slanted label near lower curve]] curve
• atmos.
• \(V\ 0{,}4\ \mathrm{m}^3\)
• \(0{,}05\)
• \(0{,}1\) [[unclear: unit abbreviation]]
• pressure scale: \(50,\ 100,\ 150,\ 200,\ 250,\ 300,\ 350\)

\[ \begin{aligned} \text{H.P. cyl.:}\qquad & \text{L.P. cyl.:}\\ m &= 0{,}116; \qquad & m_2 &= 0{,}055;\\ a &= 0{,}40; & a_2 &= 0{,}50;\\ e &= 0{,}10; & e_2 &= 0{,}20;\\ c &= 0{,}48; & c_2 &= 0{,}20;\\ D &= 260; & D_2 &= 520;\\ d &= 60; \qquad H &= 461; \qquad n &= 218{,}6;\\ G_{\mathrm{ч}} &= 1057. \end{aligned} \]

Drawing 26.

With regard to the economy we achieved, it must also be stipulated that, although our tests, in respect of the condition of the machines, cannot be called entirely “show” tests, nevertheless they were not carried out under the ordinary working conditions of the station; namely, throughout all the tests one especially capable and indefatigable stoker worked. In view of the considerable power, the locomobile consumes at full load such a quantity of firewood that one stoker is compelled to throw in wood almost continuously, which is very fatiguing; at the same time, two stokers cannot work simultaneously, since they interfere with one another. When we tried to replace the most experienced stoker with others at full load, the results obtained each time were deplorable: the steam pressure fell, its temperature did likewise, and the other stokers were never able to raise them to the required magnitude.

Thus, if the locomobile operates with a load close to full, and still more with an overload, the actual consumption of firewood will undoubtedly be higher than that obtained in our tests, when only the best stoker worked, and he, moreover, made special efforts. Of course, the use of a self-recording instrument for gas analysis and the awarding of bonuses for economy of firewood can improve the quality of the stokers’ everyday work and the economy of the machine, but only in part.

With a reduction of the load, or with machines of smaller power, the stoker’s work becomes more within his strength. Conversely, for locomobiles of still greater power, firing with firewood is inapplicable, unless it proves possible to design a mechanical furnace or a furnace permitting the simultaneous work of two stokers.

As regards the given machines, it is also necessary to note their sensitivity, in terms of steam consumption, to the temperature of the live steam and to the vacuum in the condenser, as well as to the care of assembly and the degree of running-in of the rubbing parts, as is evident from a comparison with one another of the results of tests I, IV, and V.

Among the definite shortcomings, one must note the high temperature at which many parts of the machine have to operate. Some parts, such as the stuffing boxes, the piston and valve-cylinder rods, etc., have a temperature above \(100^\circ\) owing to contact with strongly superheated steam. This heating is also transmitted in part to the guides and the crosshead of the cylinder, etc. The remaining parts are heated as a result of heat transfer and radiant heat from the walls of the steam boiler. Thus, the temperature of the air around the main

the shaft during operation at full load is about 50° C.; the temperature of the main-bearing shell reaches 60°, even 70° C.; and this is considered normal; when touching the handrails at the flywheel, one is afraid of being burned by them. Although this plant is distinguished by the use of high-quality materials and careful machining of the parts, their operation under the indicated severe temperature conditions must inevitably produce rather heavy wear and in any case requires extremely attentive maintenance.

Further, maintenance is greatly hampered by the inaccessibility of individual parts: in order to pass from inspection of the guides to inspection of the main-shaft bearing, situated at a distance of 1–1½ m, one must go down a ladder from a height of about 2 m, climb up again by a similar ladder, and walk about 10 meters in the horizontal direction; the same is true for inspecting the other cylinder or guide.

As for the advantage of small and medium locomobiles—the possibility of making do with one person who performs the duties of fireman, engine driver, and oiler—there can, of course, no longer be any talk of it. And in general the designation “locomobile” is quite unsuitable for such a machine, which is about 7 m long, 3 m wide, and 3.5 m high, and weighs about 60 tons (3600 poods!), since there can be no question of moving it.

However, as regards the inconvenience of maintaining the machines owing to the numerous separate ladders, this reproach applies not so much to the type of machine as to the unsuccessful design of its installation. In general it must be noted that the given station was poorly designed and built: evidently, for the sake of economy, the building was made of such a length that two units of the first stage could barely be fitted into it, and there is absolutely no room for installing a third when the need arises to increase the station’s capacity. At the same time the height of the building was made, quite uselessly, nearly twice as great as necessary. Further, owing to the unfortunate placement of the switchboard, the width of the building turned out to be so great (almost equal to its length) that it is impossible to install an overhead traveling crane, the absence of which was keenly felt during the installation of the machines and will be felt at every disassembly and assembly.

We have already spoken above about the unfortunate wording of the clause of the contract concerning the guarantee for steam consumption.

It remains to touch upon the question of the choice of machine type. Unfortunately, it must be admitted that the choice of locomobiles for a municipal station of such dimensions was unsuccessful. The fact is that the output of energy by such a station after several years is usually so—

…which increases, so that one has not only to add new units, but also to remove the former ones in order to install in their place new ones of greater capacity. If the station is equipped with reciprocating engines or turbines supplied with steam from independent boilers, then only the machine equipment has to be changed, while the boiler house only has to be enlarged. When equipping a station with so-called “locomobiles,” the former equipment has to be removed and all the equipment acquired anew, which costs almost twice as much.

In general, locomobiles, like every separate type of prime mover, have their own field of application, in which they compete with other machines and often deserve preference—namely, small- and medium-capacity stations with units of 100–120 hp each. The considerably larger locomobiles now encountered are a kind of fashion, a craze. The guaranteed low consumption of steam and fuel by no means justifies this craze, even if the actual consumption during the station’s day-to-day operation proves to be close to the guaranteed one.

As for the mistakes made in the construction of this electric station, it is, unfortunately, by no means an exception: the author has had to take part in the expert examination and final acceptance of several municipal power stations, in the design of which, and in the selection and ordering of machines and the conclusion of contracts, various, at times very gross, mistakes had been made. If municipal administrations turned to the appropriate specialists not only for guidance in the acceptance of a completed station, but beforehand, during the development of the design and the contract, then such mistakes would be eliminated; with the same expenditures, towns would obtain stations better arranged and equipped and more economical in operation, and could also reduce the costs of constructing and equipping and of further expanding their stations.

However, even on the basis of his own practice, the author may note that timely recourse to the appropriate specialists is apparently already beginning gradually to become customary among municipal public administrations. Let us hope that this custom will spread both in breadth and in depth, i.e., that both the number of consultations and the variety of questions raised will grow. Then the latest achievements of technology will more quickly and more directly benefit our towns and raise their general cultural level.

Tomsk. November, 1914.

V. L. Malkev.

1. See, for example: Dubbel, Steam Engines. Petrograd, 1907; Hugo Ancona, The Entropy Diagram and Its Applications. Petrograd, 1910. ↩