Absorption Spectra of Gaseous Charges in a Gasoline Engine
P
IZEVIOUS experirrieirts An apparatus is described that photographs carried out wit,h an engine absorption spectra of the gases within an in( f - 5 ) e s t a b l i s h e d the ternal-combustion engine running u.nder it.? own follon.ing pertinent facts about A number oJ typical spectra taken power. rngine knock: (1) knocking and inserted on opposite sides of the under various engine conditions and with several rionkirocking combustion differ combust,ion chamber. T h e s e iu tlic nature of the last part of different fuels is presented. The absorption windows were 6.1 em. long and the burn; (2) a knocking ex1.8 cm. high and could readily be spectra show that under some engine conditions plosion is characterized by the removcd for cleaning. Figure 2 in the .fuel-air iniztures chenzical changes occur includes a plan view of the comrapid rate with which the flame busrion elir~mbershowing the relaprior to injlummation. Such changes are sprcads through the last part of tive positions of t,he windows, greater in degree or different in nature in knockthe charge and hy the accoinvalves, piston, and spark p l u g . pan ying rapid pressure rise in the The engine had a fixed compresing than in nonknocking combustion. The sion ratio of 5.2 to 1. cornbustion chamber:. (3) . . spou. facts established by this work support the idea The carburetion svst,em eontaneous i g n i t i o n s o m e t i m e s that knock is due to spontaneous ignition ahead s i s t e d of a Venturi-and a jet occurs ahead of the flame fronts ahichcould be connected t,o&her of /he norniuljlume fronts. as the knock begins; (4) the of two f l o a t bowls hy m e a n s eiriission of the CH and C , bands, of B two-wav vnlve. This mnde which are characteristic of most hwir(icarbon flames. is much it possible to change fuels without stopping the engine. A thermocouple was susponded in the intake pipe at % position such that the temperature of the fuel-air mixture could be estimaied just before it entered the engine. As shown in Figure I, the engine WYBSfilbd with a stnhoscopic shutter consisting of a disk and slot rotated in B verlicrrl plaric at can-shsft speed. By proper adjustment of the disk wit.h respect to its drive shaft, a selected portion of the ctmrge located between the t.wo vindows could bo oxamined a t :my desired crank-shttit angle. OPTICALSYSTEM.The arrangement of tho optical system is shovim in Figure 2. It consisted essentially of three lenses which, togellrer nith the source, were mount,ed upon at1 optical bench that WRS supported from the spectrograph so t,hst ttrc syst,em could be shift.ed as a unit irom one sect,ion of tho eoi11bustion chamber to another. The source, U,w i ~ slocated a t the principal focus of lens Li, and the light passed through the eriginc i n a parallel beam. The lens h formed an image of the source in the plane of the stroboscopic disk, S , and the lens La formed a second image 011 t.he slit of the spectrograph. The disphmgmnis, Diand Os,close to the engine windows, served to limit the region trayversed by t.he light, beam. The rectangular apertures in these diaphragms were 0.62 cm. wide and 1.27 om. hid>,arid for this tween the unburned charges in work they wer;
