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Aviation History
1934
1934 - 1424.PDF
SUPPLEMENT TO FLIGHT MAY 31, 1934 THE AIRCRAFT ENGINEER (A) B.M.P. at various speeds. (B) Minimum fuel consumption and available mixture range at 1,300 r.p.m. (c) Heat to cylinder and head water jackets at 1,300 r.p.m. (D) Detonation tendency at 1,300 r.p.m. (E) Maximum cylinder pressure and rate of combus- tion pressure rise (1,300 r.p.m.). Except in the detonation tests, a non-detonating fuel was used throughout. t20 z KliO a: si 10 * 6 t- z g K 0 OCTANC -75 1 NUMSER -•—/fcae/rst -2 -1 -. -^ A B SWIRL RATIO % 0 2 I 4 FI6.II. y 5 e EFFECT OF SWIRL ON DETONATION : 1,300 r.p.m., central sparking plug. The letters F.S.-O.M. indicate " fre- quent, slight, occasional, moderate detonation." The results of these tests are shown in Figs. 8, 9, 10, 11 and 12 respectively, while the figures obtained at 1,300 r.p.m. are summarised in the following table: — Table 2. Figures obtained at 1,300 r.p.m. 5. P. fc •>' Si QQ ^" -1-6 0 0-851-75 3-354-6 5-6 6-8 -1-50 0-851-75 3-354-6 5-6 6-8 s cS B 4 1 73 2 5 g 6A 4A 1A7A 3A 2A 5A 8A Max. M.E.P. lb./in.t Brake lnd. 143 141-2lit 8 14*-5144 140 137 129 140 139 144-8145-5 143 139 137 129 15!) 157-2 160-8 160-5160 156 153 145 156 155 160-8161-5 159 155 153 145 tiojjl •«, £ lic — gx""ft is "f ° Central Plug 40 37 36 3729 28 13 8 37 34 3241 29 24 10 9 0 465 0-4560-456 0-4440-450 •0-458 0-470 0-506 20 16 18 18 17-515 12-5 12-5 Offset Plug 0-450 0-4640-450 0-4500-450 0-4520-455 0-485 2° 20 2522 20 15 12-512-5 2| d —0-605 0-600-625 0-650-695 0-745 — 0-630-625 0-6350-66 0-760-805 _—. O °'" 75-7 75-7— 75-575-9 76-5 — to i "o lir e per ^•s —40 47 40 38 34 — 38 35 39 37-535-5 — 620 640 615 605 585 — 635 660 630 600 600 All readings (except fuel consumption) at maximum power mixturestrength. • For maximum power mixture strength. Detonation Tests. Series D. These were of two kinds. In the first series the engine was run throttled on a fuel of relatively low octane number and the throttle opened to give a standard intensity of detonation. This was done with various swirl conditions and the B.M.P. giving standard detona- tion taken as an (inverse) index to the detonation tendency. These B.M.P. figures are shown in the upper curve of Fig. 11.. 700 IN P500 .50 S^40 < M a: 50 ISO z is 150 FIG 12. REVERSE SWtRL MAX/MUM PKCSSV/I& B.M.e.p. 20| I 2 3 •* SWIRL RATIOS (AT 1500R.P.M) EFFECT OF SWIRL ON MAXIMUM CYLINDER PRESSURE AND RATE OF PRESSURE RISE: 1,300 r.p.m. Max. power mixture strength. Full line refers to central sparking plug, dotted line to offset plug. In the second series of tests the engine was run at 1,300 r.p.m., full throttle, and benzole added to the petrol (D.T.D. 134) to reduce the detonation to standard intensity. The " octane number " of this mixture was then measured in a C.F.R. engine by the " Aircraft Method " (900 r.p.m., shrouded inlet valve, mixture temperature 260 deg. P.). This process was repeated for various swirl rates, giving the results shown in the lower curve of Fig. 11. COMMENTS ON TEST RESULTS Series A. B.M.P./Swirl (Fig. 8).—The highest output is given, at all speeds, by a swirl ratio (swirl-meter speed/engine speed) of about 2-2.5. The curves are fairly flat, on the low-swirl side of the maximum, giving an available swirl range, without serious loss of perform- ance, of 0.5-3.5. The motoring M.E.P. was found to be independent of swirl, at any rate within the limits of engine variation (±1.0 F.M.P.) so that the above conclusions apply to I.M.P. as well as B.M.P. Scries B. Fuel Consumption and Mixture Range at 1,300 r.p.m (Fig. 9).—In these respects also a swirl ratio of about 2.0 gives the best results. There is little difference between the central and offset plug positions, except that the latter appears to mitigate the increase in consumption due to excessive swirl. Why this im- provement should exist is not clear, especially as the mixture range and the ignition advance requirements at these high swirls are the same as with the central • plug. In all these mixture range tests the ignition advance was adjusted to suit each mixture strength. The ignition advance requirements decrease steadily with increasing swirl. Series C. Jacket Losses at 1,300 r.p.m. (Fig. 10).— The minimum gross loss is at zero swirl, but the mini- mum loss per b.h.p. is at a swirl ratio of 1, that at the optimum power swirl ratio of 2 being some 6 per cent, higher. ' Incidentally, the ratio h.p. in water/ b.h.p. is very low, being only 0.6 at a swirl ratio of 1. 540^
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