Infra-Red Radiation from an Otto Cycle Engine Part I. Apparatus and Technic SYDNEY
T
HE research reported in this Paper is Part of a general investigation of combustion in an engine cylinder being conducted in cooperation with the National Advisory Committee for Aeronautics; results will appear later in one of their technical reports. The importance of infra-red radiation in the study of flames and explosions has been stressed by several workers. Garner ( 8 ) , in 1928, wrote: The study of r a d i a t i o n f r o m flames is in the embryonic stage of d e v e l o p m e n t . I t shows promise, however, of becoming a knowledge, highly specialized which willb rpalnacyh an of important part in the elucidat'ionof the mechanism of the processes of combustion occurring in flames. I n the following year, Robertson e
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STEELE,Bureau of Standards, Washington, D.
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This is the first of a series of papers describing a n investigation of infra-& radialion from the cylinder of a n Otto cycle engine delivering power. The radiation Passes through a Jluorite window, f o r which thirty-one positions are available, each gicing a view of a small depth of charge in a direction approsimute~yperpendicular to flame travel. A system of surface-silcered mirrors focuses the radiation, first on the slit Of a droboscope (open f o r 2" of crank angle) and ,finally on a sensitive single-juncfion antimony-bismulh tacuum thermocouple. The e. m. f. generated is measured on a specially mounted Thomson galvanometer* show the on radiation of a red glass jilter, variation in engine operating conditions, and change of window position, benzole being used as fuel.
called black body a t a temperature of 2200' c.7 plotted to a wave-length s c a l e , and a t this temperature less than per cent of the total energy appears in the combined visible and ultra-violet r e g i o n s . (The distribution of the various c l a s s e s of electromagnetic waves throughout the whole scale of wave lengths is indicated in Figure 1.) T h e unbroken curve gives a typical spectral energy distribution from an flame ( 2 ); the part corresponds closely to the dotted black body curve, quent deviations being discussed in a later paragraph. There are f o u r t y p e s of receiving apparatus available for the measurement of i n f r a - r e d radiation-namely, the Bolometer, the Radiometer, the Radiomicrometer, and the thermopile. Each type can claim special advantages (and possesses certain disadvantages), but from the combined points of view of adaptability, flexibility, and rapidity of observation, a single-junction thermopile (thermocouple) was chosen for this investigation. I n the literature only one reference to work in any way similar was discovered. Midgley and McCarty (10) in 1924 measured radiation from the cylinder of a 0.75-km. Delcolight engine using a single quartz window in the engine head, a stroboscope open for 20" of crank angle, and a thermopile and galvanometer.
(12) reported:
the radiation from flames is in the
invisible part of the spectrum and mainly in the infra-red, there
THETVIXDOW For infra-red work, quartz is not suitable for use as a window. Referring again to the unbroken curve in Figure 1, the maximum a t 1.2 p is due to incandescent carbon (which too 80
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FIGURE 1. ACETYLENE FLAME AND BLACK BODYRADIATION (2)
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is here a wide field of work in clearing up the mystery of flame, and the same is true as regards the phenomena of explosion of
both gaseous and solid explosives.
"Infra-red radiation" is the name given to the radiant energy emitted by a body when heated below incandescence. If the temperature is increased and the body becomes luminous, the greater part of the radiant energy is still t o be found in the infra-red region. I n Figure 1 the dotted curve represents the distribution of energy radiated from a so-
OF QUARTZ(SiOn), FLUORITE (CaFd, FIGURE 2. TRANSMISSION ROCKSALT(NaCl), AND SYLVITE (KCl) (4)
approximates black body radiation), that a t 4.4p to a characteristic emission band in the spectrum of. carbon dioxide, that a t 2.75 p to combined radiation from carbon dioxide and water vapor; beyond 5 p (not shown), maxima in the
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April, 1933
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FIGURE 3. DIAGRAM OF .kPP.4R.4TUS A.
B. C.
Engine head a. Exhaust valve b. Inlet valve c . Piston 0 Window positions Detail of fluorite window a . Nickel plug b. Fluorite c. Rubber-asbestos washers Transite screen and shutter
emission spectrum of Jvater vapor occur a t 5.3 p , 6.4 p , 6 . i 5 p , and 7.2 p. Incandescent carbon, carbon dioxide, and water vapor are all present in an engine cylinder and may therefore be expected to emit their characteristic bands. Figure 2 (4) shows spectral transmission curves of quartz, fluorite, rock salt, and sylvite; for the thickness required i n this work, quartz cuts out all of the most important carbon dioxide band at 4.4 p, as well as the smaller bands due to water vapor on wave lengths greater than 5 p. Consequently, the choice of window material for use in the present investigation narrowed down to fluorite, rock salt, and sylvite, fluorite being selected on account of its superior mechanical characteristics. A single-cylinder four-cycle engine having a bore of 3.75 inches (9.53 cm.) and a stroke of 4 inches (10.2 cm.) was used in these experiments, and a variety of heads, designed for work on flame movement (9), mas al-ailable; the one used is shown diagrammatically in Figure 3A. It is important that each window give a view of a small depth of charge in a direction perpendicular to the motion of the flame. The fluorite windows were cut from polished plates 8 mm. thick. I n Figure 3B, a represents a nickel plug, and b the fluorite window in position bet-iveen washers shown a t c. The nickel plug was designed with the idea of damping out as far as possible the pressure waves to which the fluorite was subjected and also of preventing actual contact of the flame and window; nickel was chosen on account of its high thermal conductivity. The washers were made from a rub-
D. Long-focus concave mirror E. F G:
Plane mirror Stroboscope hase-changing device below Detail of st;o%oscope disks H . Short-focus concave mirror K. Thermocouple box T. Rock salt windows t . Thermojunction 1. Magnifying lens s. Shutter
ber-asbestos compound, two being used both below and above the fluorite, and the whole arrangement was rendered gastight by the screwed plug shown in Figure 3B. It was found that the assembly had to be but little more than fingertight, the procedure being to rotate the engine by motor, screw down the plug until leakage from the cylinder ceased, and then back off a fraction of a turn. Using this technic a window would last many hours of running, and, except when excessively rich mixtures were used in the engine, deposition of carbon was negligible. A window free from cleavage planes would last many weeks (occasionally being removed and cleaned with a little rouge), and only one window disintegrated while the engine was running. The diameter of the cylindrical passage through which the engine radiation passed was slightly greater than 3 mm.
THE OPTICALSYSTEM About 2 cm. above the engine head and shielding it coinpletely mas a transite (asbestos compound) screen, shown in Figures 3C and 4. A small hole in this came directly above the window in use (the screen was movable), and an electromagnetically operated shutter (also movable) was provided, enabling zero and radiation readings to be taken alternately. The screen was cooled by the draught from a fan so placed that air was blown continuously between it and the engine head.
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(t,u crirrespond to t l i e c r u s section US tlie pencil oE iiicideut rays) which was covered by a rock salt window to exclude ilraagiits. The target US tho tliermocoiiplc was less than 2 111111. square, and in order to Eacilitate focusing, a Iiole (wliich wold lie closed by a shutter) was made in the back of the box and a niagnifyirig lens rnounted hetween it and tlie target. 111 Figure 3K rock salt windows are shown at 7 : tlie thrnnojunctioii at 2, the magnifying lens at 1, and the sliritter at 8. Tlie box, painted inside and out with optical
black and aloininum paint, respectively, was loosoly packed with cotton wadding, and its shape permitted a small angle to be maintained hetween the rays incident on and reflected from mirror li THE h ACKNO WLBDGMENT Tlie writer wishes to acknowledge his debt to H . C. Ijickinson, chief of the Heat arid Power Division of the
H u r e s u of StiLirilttrds, for permission to xork at the b u r e a u on this problem, and to W. W. Coblentz ?or advice asid assistauce. At t h e Johns llopkini University (where the writer holds a C o m m u n w e a l t h Fund Fellaaslrip) he acknowledges similar iiidchtedncss to A. H. I'fund a n d D o n a l d N . A u d r c w s . The work wa8 performed in tlie Aotornot i v e L a b o r a t o r y o? t h e Ihreau of Stamlsrda i n collaboration witith C. F. Marsin, dr., the a p p a r a t u s b e i n g assembled and operated with the lielp of A. Wharton and C. H. Roeoeder. Thanks are due W. W. Cohlente for permission to reproduce Figure 1 (2) and Figure 2 (4).
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(iioni. cobicntz; cQmegieinst. Wosiiinyioni'ah., 97, (lii Cohlentr, Stair, and Iioguo, Bar. Blimrlards 1. Research. 7, 728 (1931). (7) 1)iokinson and Nen~all.Nntl. Adviaory Chmm. Aeronaut.. N I . P ~ . (.$)
107 (IWI).
IXD,EN(;. Cnnr.. 20, 1008 (IO'Rj. Marvin aiicl nest, Natl. Advisorg Cornm. Acronuiit.. Repl. 399
(8)Garner.
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(1931).
a d McC'uty, J . Soc. kilomoliae BILL 14, 1112 (1924). (11) Rtm"iiis ami Taylor, "Infra-Red Analysis of Moloculnr Structime," p. 135. Unirersiry Press. Cernbridgo. Englnnd, and Macniillan. N e w York, 1CJ28. (12) Itobertmn, Hnflurc, 123,915 (1929).
(13) Steole, I h i d . , 128, 1x3 (1931). ltscmvm November 2 6 , 1932. The substance of thin vwrr mas presented under
