Emission Spectra of Engine Flames GERALDR/I. RASSWEILER
LLOYDWITHROW General Motors Research Laboratories, Detroit, Mich.
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HE work d e s c r i b e d in effort made to compare this with The separate spectrographic studies of flame this paper is one phase the action of engine flames on fronts and afterglows in a gasoline engine haze of a general investigathe same materials. been extended into the ultra-violet. I t has been tion of the mechanism of engine It was also previously shown shown that OH molecules are present in both combustion being carried on in (26) that, in knocking combusflame fronts and afterglows. Further comparithis laboratory with a variety of tion, there is a decrease in the tools, such as the sampling valve i n t e n s i t i e s of the CH and Cz sons have been made between spectra of engine and (24), the c o m b u s t i o n camera bands in the detonating zoneburner flames. B y using a n improved technic, (2.9, the electrical pressure inthat is, in that portion of the spectra of knocking and nonknocking combustion d i c a t o r ( I S ) , a n d the spectrocombustion chamber where the hate been obtained simultaneously on one specgraph. It consists essentially of last part of the c h a r g e b u r n s trogram, and thereby a number of uncertainties a continuation of the previously and where the knock is initiated. reported studies of the spectra To improve t h i s c o m p a r i s o n involz*ed in the precious comparisons of spectra emitted by various fuels burning of spectra of flames in and out qf these two types of combustion have been elimiin the gasoline engine and in open of the detonating zone in knocknated. A discussion of the relationship of this air (25). The results obtained ing and nonknocking c o m b u s work to combustion studies of other workers is inby use of the spectrograph are of t i o n , a r e d u c e d image of the cluded. singular importance in the study l o n g window i n the-engine of combustion, because s u c h was focused along the length emission spectra yield information about the intermediate of the spectrograph slit. Thus, on a single plate, engine reaction products that are formed in the flames themselves, spectra FF-ere simultaneously recorded from flames in and out and it is hoped that such information may assist materially in of the detonating zone, and increased confidence can be the final determination of the course of the combustion placed in the data obtained. reactions. A few of the spectra taken in the more recent stages of this The work described herein had three objectives: first, to investigation are reproduced and discussed herein and an effort extend the earlier observations into the ultra-violet; second, is made to relate the work to studies of combustion by other to make a detailed comparison between flames in and out of workers. the engine; and third, to eliminate some of the uncertainties APPARATUS AND PROCEDURE that entered into the earlier comparisons of spectra of knocking and nonknocking combustion. Since the data reproduced herein include spectra taken with The extension of the work into the ultra-violet is of impor- each of three spectrographs, a short description of the instrutance because this spectral region contains the well-known ments is given. The one was a glass spectrograph which “water bands” emitted by OH free radicals. The ultra- could be fitted with either one of two cameras, and was violet emission from the gasoline engine has been studied described in an earlier paper ($5). The second was a small previously by Clark and his eo-workers (5, 6, 7 ) , but, as was Gaertneroquartz instrument. Its range extended from 1850 pointed out in the earlier paper @6), their apparatus was so arranged that they could not study separately the light from t o 7000 A,, the length of the spectrum keing about 70 mm. the flame fronts and afterglows. This separate study has been The ddspersion varied f;om around 32 A. per millimeter a t carried out in the ultra-violet, using a method quite similar 2500 A. to ahout 230 A. per millimeter a t 4500 A., which to that employed in the visible region and previously de- made this instrument unsuitable for work in the visible region, but fairly serviceable in the ultra-violet. A curved platescribed. In their previous paper (26) the writers presented data holder was substituted for the flat one with which the instruwhich showed that, when hydrocarbon fuels are burned in the ment was originally equipped in order that a larger portion of engine, the flame front and afterglow spectra in the visible the spectrum could be brought into focus at one time. The region are emitted by different molecules. Furthermore third was a Bausch and Lomb 2820 quartz spectrograph. the visible spectra of flame fronts of hydrocarbon fuels burn- This gave comoparatively large dispersion (7 A. per mi!iing under nonknocking conditions were shown to resemble meter at 2500 A.) and the whole range, 7000 to 2100 A., quite closely those emitted from the inner cone of a non- was in focus on one plate. It was well suited for the study luminous flame produced in an ordinary burner with illuminat- of flames outside the engine, but it was not used for engine ing gas and air, Since, by means of their flame separators, spectra. The single-cylinder ell-head engine equipped with a long Smithells and Ingle (22) and others hare collected a considerable amount of information about the chemical processes that quartz window extending the full length of the combustion take place in the various cones of ordinary Bunsen burner chamber has been described in previous papers (93, 64). A flames, it was of utmost importance to carry this comparison stroboscopic disk was rotated a t crank-shaft speeds in a between the spectra of flames in and out of the engine as far as horizontal plane above the engine in such a manner that the possible. To complete this analogy, the spectrum of the slot in the disk passed along the window in a direction opposite outer cone of a Bunsen burner flame has been compared with to the motion of the flames. The spectrograph was mounted that of the afterglow radiation coming from an engine. above the engine with its collimator axis vertical, and an exThe action of an illuminating gas-oxygen flame on tetraethyl- ternal lens attached to the collimator focused the light from lead and iron carbonyl has also been investigated, and an the engine window on the spectrograph slit. 528
1.
2. 8.
Bunsrri burner Bensene in engine Inobctanc in engine
4.
Gasoline
iii
enpitie
6. Hydrown afterglow i n engine B. Hydrogen in eiigine: no disk
2. n r r ~ : . F,,,, ~r. REcoRns OF i l V , > S O
