A . P . O L E S O N AND R IC H A R D W IE R E N o r t h e r n R e g io n a l R e s e a r c h L a b o r a to r y , U. S . D e p a r t m e n t o f A g r ic u ltu r e , Peoria, III.
T
H IS laboratory has been interested in th e possible utilization of agricultural residues as sources of producer gas in this country. A com prehensive laboratory investigation was made w ith tw o gas generators, from which certain results are draw n for use in this paper. A detailed account of these investigations will be published later. As a supplem ent to th e experim ental work, therm odynam ic calculations on tw o representative gaseous m ixtures are presented here in order fully to evaluate all the possibilities in th e use of such a fuel. These calculations enable one to predict tem perature, m axim um pressure, m ean effective pres
sure, work, an d therm al efficiency of these m ixtures when used as fuels in in tern al com bustion engines, as well as to m ake compari
sons w ith sim ilar d a ta obtained for octane (IS, 14, 26) and for alcohol {27).
A large am ount of work has been done on various fuels th a t m ay be used in portable gas generators, as evidenced by a volu
minous literatu re. An extensive bibliography on “Theory, De
sign, Fuels, Perform ance, U tilization, and Economics of Gas Producers” is available on application to th is laboratory. Woods (29) m ade tw o series of calculations of th e m axim um tem perature of com bustion of a producer gas m ixture having th e following composition: carbon dioxide, 2 % ; carbon monoxide, 31% ; m ethane, 0.5% ; hydrogen, 9.5% ; nitrogen, 57% . T his gas was m ixed w ith various proportions of air a t a fixed compression ratio of 6 to 1 and a t an in itial tem perature of 212° F . In his first series W oods took in to account only th e dissociation of w ater into hydrogen and oxygen, and of carbon dioxide into car
bon monoxide and oxygen; in th e second set of calculations th e form ation of nitric oxide was also included. F o r a theoretical m ixture th e m axim um tem perature of com bustion was 4627°
Ta b l eI. Eq u i l i b r i u m Co n c e n t r a t i o no f Di s s o c i a t i o n Pr o d u c t s, i n Mo l e Pe r Ce n t, a s a Fu n c t i o n o f Pr e s s u r e a n d
Ab s o l u t e Te m p e r a t u r e
.--- 3960° R .---—n , ---4680° R . C om po 3 1 2 .1 6 9 5 4 .7 1947.7 3 1 6 .7 6 9 6 4 .4 1 9 63.4
n e n t lb . / s q . in . lb. lb. lb. lb. lb.
NO 0 .1 2 8 0 .1 0 1 0 .0 9 4 0 .5 6 0 0 .4 4 5 0 .3 9 1
N j 7 5 .3 3 5 7 5 .4 1 6 7 5 .4 6 2 7 4 .3 1 0 7 4 .6 4 6 7 4 .8 2 2
O H 0 .1 2 9 0 .0 8 6 0 .0 7 0 0 .6 2 4 0 .4 2 6 0 .3 3 6
h 2 0 .0 3 8 0 .0 2 8 0 .0 2 1 0 .1 3 9 0 .1 0 4 0 .0 8 4
H 0 .0 0 3 0 .0 0 1 0 .0 0 1 0 .0 3 2 0 .0 1 6 0 .0 1 0
HjO 6 .3 7 0 6 .4 0 8 6 .4 2 7 5 .9 3 7 6 .1 0 4 6 .1 8 4
CO 0 .5 3 9 0 .3 9 7 0 .3 0 0 2 .2 4 3 1 .6 8 8 1 .377
CO* 17.264 1 7 .422 1 7 .5 2 8 1 5 .989 1 5 .3 6 8 1 6 .336
0 0 .0 0 3 0 .0 0 1 0 .0 0 1 0 .0 4 8 0 .0 2 2 0 .0 1 3
0 2 0 .191 0 .1 4 0 0 .0 9 6 0 .7 3 9 0 .5 6 0 0 .4 4 7
-5400° R C om po 3 2 6 .6 9 8 8 .4 2 0 0 3 .9
n en t lb. lb. lb.
N O 1.434 1.246 1 .115
N* 7 1 .9 7 7 7 2 .8 5 9 7 3 .3 0 9
O H 1.707 1 .250 1 .015
H*
H 0 .3 7 3
0 .2 1 0 0 .2 7 0 0 .1 0 2 0 .2 2 2
0 .0 6 6 (C om position a t 520° R .:
C 0 2l 2 % : CO. 3 0 % : H 2.
HiO 4 .9 0 9 5 .3 6 2 5 .5 7 9 1 0 % : CH*. 1% : N 2, 57% )
CO 5 .9 1 8 4 .5 0 2 3 .7 6 9
CO* 11.246 1 2 .8 4 8 13.672
0 0 .3 4 2 0 .1 6 9 0 .1 0 6
0 * 1 .8 8 4 1 .392 1.147
T h e c o m p o sitio n an d h e a ts o f c o m b u stio n o f producer g a s derived fro m variou s raw m a teria ls are given . A n o m o graph is p resen ted for c a lc u la tin g th e h e a ts o f c o m b u stio n o f producer gas m ix tu res c o n ta in in g h yd rogen , carbon m on oxid e, an d m e th a n e . T h e th eo retica l a ir-fu el ratios o f producer gas are com p ared w ith th o se o f o th e r fu e ls u sed in in te rn a l c o m b u stio n en g in e s, and a tte n tio n is called to th e ir im p o r ta n c e in c o n n e c tio n w ith carburetor d esig n . T h e h e a t o f c o m b u stio n o f a m ix tu re o f producer gas w ith th eo retica l air is con sid erab ly low er th a n th a t o f ga so lin e or a lco h o l; an d low er pow er o u tp u t m u s t be ex
pected from su ch a m ix tu re ru n u n d er id e n tica l co n d itio n s w ith th e liq u id fu e ls m e n tio n e d above. T h e th erm o d y n a m ic properties o f tw o ty p ica l producer gas m ix tu res are ca lcu la ted , an d th e r esu lts sh ow n o n ch a rts. A sa m p le ca lc u la tio n gives tem p era tu res an d pressu res a t various p o in ts o f th e O tto cy cle, as w ell as w ork, m ea n effective pressu re, a n d efficien cy. T h e effects o f com p ression ra tio an d in ta k e -m a n ifo ld pressu re o n m ea n effective pressure and th erm a l efficien cy are sh ow n by ch a rts. I t is p oin ted o u t th a t ex trem e com p ression ra tio s are n o t so p racticab le for a n O tto cycle e n g in e as a n in crease in m a n ifo ld pres
su re, sin c e a rela tiv ely low su p ercharge pressu re gives a power o u tp u t eq u iv a len t to th a t o f g a so lin e. I t w ou ld be possible to u se su ch a fu el in a D iesel gas en g in e.
Rankine by the first m ethod, and 4597° R. by th e second, a lowering of 30° R. due to th e nitric oxide reaction. M aking the same assum ptions, a tem perature of 4595° R ., alm ost identical w ith th e second of th e two figures, was obtained when th e d a ta for producer gas m ixture 2 (Table II) were used, although in this work th e form ation of atom ic hydrogen and oxygen, as well of OH, was also considered. This should tend to reduce th e tem perature still fu rth er; however, th e slight difference in com
position m ay, a t least in p a rt, account for th e discrepancy. T he im portance of dissociation a t high tem peratures and pressures is illustrated in T able I. Even though th e concentrations of some components m ay seem insignificant, these values, when m ulti
plied by th eir h eats of dissociation, m ake an appreciable contri
bution to th e internal energy of th e system.
T able I I gives th e average composition on a dry basis and th e h e at of combustion a t constant volume (w ater as vapor) of pro
ducer gas m ade from various fuels in portable gas generators as well as in a u n it designed in this laboratory.
I t should be understood th a t there are considerable variations of gas composition, depending on ty p e of generator, m oisture content of th e fuel or charge when w ater is added separately, and changing conditions w ithin the gas generator during combustion, as well as variations due to starting, acceleration, and speed of th e engine used in com bination w ith th e unit. Spiers and Giffen (23) m ade extensive tests on the perform ance of a converted gaso-6S3
654 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
T he therm odynam ic calculations were m ade sim ilarly to those previously m entioned (13,27). T h e perfect gas law has been assum ed to hold th ro u g h o u t th e calcula greater variatio n in composition of gas during operation th an , for instance, a good grade of charcoal. com bustion of a m ixture of fuel and air is of still greater interest, and in order to facilitate rapid calculation of th e h eat of combus
tion of any producer gas containing carbon monoxide, hydrogen, and m ethane as combustible constituents, th e following d a ta are cubic foot of theoretical air a t 60° F. is, therefore, (118.4/1.9996) = 59.2 B .t.u. per cubic foot. A sim ilar calculation for producer gas m ixture 2 indicates a value of 64.6 B .t.u. per cubic foot; th e cor
responding value for gasoline is 102 (2Ji). In actual practice, the above com puted values for th e heats of combustion will be some
w hat lower since th e gas is generally satu rated with w ater vapor a t th e exit tem perature of th e purifier.
T he large difference in th e theoretical air-fuel ratios by volume betw een producer gas and octane (gasoline) shown in T able I I I necessitates changes in carburetor design. L ichty (17) discussed th e fact th a t, for gasoline, m axim um power is obtained from a m ixture slightly richer th an th e one having th e correct air-fuel ratio. F or producer gas, however, maximum power is obtained from a m ixture containing from 92 to 98% of theoretical fuel (23).
Woods (28) found th a t th e “power m ixture stren g th curve for producer gas is of a sharply peaked n atu re” , an d fu rth er stated th a t “differences of th e order of * 10%, in the m ixture strength
On th e basis of th is equation, th e m aterial u n it chosen was th e theoretical w eight of fuel necessary to effect com
plete com bustion w ith one pound of air. T h e requisite am ounts for m ixtures 1 and 2 are, respectively, 0.878 and 0.847 pound of fuel per pound of air. T he above equation represents only th e stoichiom etric basis for our calcula
tions; actu ally th e com position of th e m ixture a fter th e various equilibria are “frozen” while th e gas is passing through th e exhaust system , does n o t inv alid ate our calculations. Two
July 1945 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 655
Tt
sis
3 0
-
25t o
-key: a + c - b B +E- D
o
-1-F igu re 1. N om ograp h for Low H ea t o f C o m b u stio n o f P rod ucer G as
and th e fraction of exhaust gas, / , re
m a in in g in th e cylinder. For fuel gas m ixture 2, in Figure 3 a t 520° R., H n is 69 B.t.u.
T he volume frac
tion of fuel gas mix
tu re in the cylinder is 1 — / = 0.959.
F or the exhaust gas i n F i g u r e 5 a t 2100° R , H , is 865 B . t . u . , a n d t h e volume fraction is / = 0.041. There
fore, H.i = 0.959 (69)+0.041(865) = 100.9 B .t.u.
F ind E, V, and m ixture tem pera
tu re T, correspond
ing to H.i on Fig
ure 3. V is deter
m ined by the point a t which lines for V a n d P ( 1 4 .7 pounds per square inch) m eet on the h o r i z o n t a l lin e drawn from a point c o rr e s p o n d in g to 100.9 B .t.u. on the scale for H,:
In t e r n a l En e r g y, To t a l. E = B .t.u. = algebraic sum of E , and th e contribution due to h eats of form ation involving hieh tem perature products of reaction (CO, H 2, OH, NO , H , O), from C 0 2, H 20 , 0 2, and N 2
En t h a l p y. H , = B .t.u ., defined by H , = E , + P V . A t 520°
R. its value is therefore equal to P V .
En t r o p y. S = B .t.u ./° R . F o r th e compression charts, zero entropy is assigned to all th e individual com ponents a t 520°
R . and 14.7 pounds p er square inch, since no chem ical reaction occurs. E n tro p y is defined by th e equation
Ei = 23 B .t.u.
Vi = 29.0 cu. ft.
Pi = 14.7 lb ./sq . in.
Ti = 589° R.
Co m p r e s s i o n. T he compression stroke is assumed to take place w ithout h eat exchange and therefore follows a line of con
s ta n t entropy. T he volume a t top dead center will be:
C T ir r p
Vi
7.0 29.0
7.0 4.14 cu. ft.
where P = p a rtial pressure of any com ponent
F or th e com bustion charts th e sam e equation holds; however, zero entropy is assigned only to C 0 2, H 20 , 0 2, a n d N 2 a t 520° R.
and 14.7 pounds per square inch, and th e en tro p y of each of the rem aining reactan ts is equal to its en tro p y of form ation.
C A L C U L A T I O N F O R G A S M I X T U R E 2
The compression charts are Figures 2 and 3; those represent
ing the equilibrium conditions after com bustion are Figures 4 and 5. F or illustrating th e use of these charts, th e following calcula
tion of an u n th ro ttled O tto cycle for gas m ixture 2 is given. The assumed initial conditions are:
Compression ratio = 7:1
In tak e tem p. T = 60° F . or 520° R.
In tak e pressure P = 14.7 lb ./sq . in.
Fraction / of exhaust gases rem aining in cylinder = 0.041 (checked a t end of calculation)
E xhaust tem p. T t = 2100° R. (also checked a t end)
In t a k e. Calculate H.i for intake conditions. T he enthalpy of the m ixture is the sum of th e enthalpies of th e fuel gas m ixture
Follow the constant entropy line from the intersection of Pi and Vi to V i and read P 2, T 2, and E ,t :
E,i = 252 B .t.u.
P 2 = 290 lb ./sq . in.
r 2 = 1238° R.
Co m b u s t i o n. This is assumed to take place a t constant volume—i.e., a t top dead center (Fs = F 2). Add E ,2 and E c to obtain E%. Ec m ust be m ultiplied by th e percentage of fresh fuel added, in this case 1 — 0.041 = 0.959.
E , = 252 + 0.959 (1667) = 1851 B.t.u.
On Figure 4 find P 3 and T } corresponding to volume of V3 ( - Vi — 4.14 cu. ft.):
Pi - 730 lb ./sq . in.
T 3 = 4485° R.
Ex p a n s i o n. Like compression, expansion is assumed to take place w ithout h eat exchange. Follow the constant entropy line of Figure 5 to Vt = Vi = 29.0 and read values of:
= 972 B .t.u.
P t = 67 lb ./sq . in.
T t = 2910° R.
Ex h a u s t. A s s u m e isentropic expansion w ith
in cylinder an d find:
P b - 14.7 Ib ./s q . in.
Vt = 100 cu. ft.
T b = 2100° R.
T he fraction / of exhaust gas volum e rem aining in th e cylinder can now be checked. A t a compres
sion ratio of 7 to 1 and a m ixture tem p eratu re T x of 589° R .,
^ 8 9 WO
3 2100 7
w hich agrees closely with th e value assum ed.
Wo r ko p Cy c l e. From th e preceding results we obtain:
w ork = (E z — E t) — (E'2 — Ei)
= (change of en
ergy during expansion) — ( c h a n g e of energy during com pression)
= (1851 - 972) - (252 - 23) = 650 B .t.u.
Ef f i c i e n c y o f Cy c l e. T he efficiency y is based on th e n e t h e a t of com
b u stion of th e fuel:
650
v = 0.959 X 1667 X 100
= 40.7%
Me a n Ef f e c t i v e Pr e s s u r e. T h e f o llo w in g e q uation is evolved:
w o rk m .e.p. =
V i - V 2 650 X 778 (29.0 - 4.14)144 141.3 lb ./s q . in.
T o avoid all possible mis
understanding, th e calcu
late d values in th is article are th e lim iting values obtainable u n d er th e as
s u m e d c o n d i t i o n s ; in actu al p ractice efficien
cies, m ean effective pres
sures, and pow er will b e m u c h lo w e r . T h e c o m p a r i s o n s m a d e
<N
July, 1945 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 657
N
«U 3
0
1
sOh X
+-•FN h
<<*<
0
•VB 3
£
V S
O
u
x
ce
Ue
w ith operating d a ta are therefore on a relative basis. In this connec
tion, it should be men
tioned th a t supercharg
ing or raising thq com
pression ratio m ay at times increase the over
all efficiency of an engine to such a degree th a t under these conditions the percentage increase in power o u tp u t will ap
pear to be greater than t h e o n e p r e d i c t e d theoretically.
Figure 6 shows the in
fluence of compression ratio on m ean effective p r e s s u r e , w o rk , a n d t h e r m a l e f f ic ie n c y . K uhne (IS), working w ith producer gas made from wood, states th at a 9 to 1 compression ratio will give a power ou tp u t of 80% of th a t obtainable from gasoline.
Assuming for his gasoline engine a c o m p re s s io n ratio of 7 to 1, the re
sults in Figure 7 indi
cate for octane (gasoline) a t atmospheric pressure a m ean effective pressure of 205 pounds per square inch; the m ean effective pressure for producer gas m ixture 2 a t a com
pression ratio of 9 to 1 (Figure 6) am ounts to 155 pounds per square inch. The ratio (155/- 205) = 75.6% agrees closely with the results obtained by Kuhne.
C O M P R E S S I O N R A T I O S
Compression ratios as high as 16.5 to 1 (23, 29) have been used in con
nection w ith producer gas; such extreme com
pression ratios, identical with those used in a Diesel engine, are of in
terest in connection with the recent development of Diesel gas engines (3, 11, 12, 18). Several m ethods have been pro
posed. The simplest is to c o n v e r t a D ie se l engine to a spark ignition engine by lowering the compression ratio of a standard Diesel to pos
sibly 10:1 and adding a
spark plug. T his can also be accom plished b y in
creasing th e compression ratio of a sta n d ard sp ark ignition engine, although this procedure m ay re
quire alm ost com plete re
building of th e engine since stiffer connecting rods, im proved bearings an d pistons, as well as changes in th e design of th e com bustion cham ber w ould be needed (7). T he necessity for changes such as stiffer connecting rods is given b y th e curve MEP/Pmax. in Figure 6.
A sim ple calculation^w ill
3 show th a t th e m axim um 1 pressures increase m uch
§ m ore rap id ly th a n th e
| m ean effective pressures, O an d it is th e high m axi-v m um pressure w hich p u ts 3 a severe stra in on an O tto
"jj cycle engine. How ever, 6* a ratio of 8 to 1 m ight be
*3 used w ith o u t m odification.
§ A far b e tte r process
ap-"B pears to be to compress a gas-air m ixture in a sta n d a rd D iesel engine and to ( j ignite th is m ix tu re b y
in-fa jection of varioUs am ounts
£ o f D ie s e l f u e l. E v e n
® though in some cases such
§ a gas-air m ixture will ig-2 n ite on compression, it
has been found desirable to inject a suitable liquid g fuel in order to stabilize
running conditions.
•c
I
T he use of producer gas in spark-ignition high- compression engines indi
cates th a t a t least some of its com ponents m u st have high octane num ber; how
ever, one of th e reviewers of th is p ap er suggested th a t th e presence of in ert gases has a tendency to reduce d etonation. T he A .S.T.M . M o to r M ethod value for m eth an e is 110 (9, 22). O ctane num ber is n o t a linear m easure of fuel q uality, n o r is th e s c a le p r o p e r l y defined above 100, b u t in a q uali
tativ e sense values above 100 are indicative of in
creased resistance tow ard knock which perm its an engine to be operated a t higher compression ratio s or supercharged. Several m ethods for extrapolating
i l ' H ‘A0M3N3 TTMMlLNI T » iO l
?8 rir
octane num bers have been proposed; however, none have so far been generally accepted. According to C o lw e ll ( 7 ) , G ra h a m E dgar believes th a t the difficulty of extending the octane num ber scale will be overcome in the near future, and th a t on the new scale the present 100 octane gasolines will have a value of 75 to 80. R e
cently it has been found (4, 18, 19) th a t high oc
tan e num bers and high compression ratios are no longer synonymous; in-
^ stead of the fuel, the
§ engines m ay become the tj principal variable. The JS h eat of combustion per
§ pound m ay ultim ately be-O come the sole criterion of
« fuels when turbine and jet 3 propulsion are considered.
« The A.S.T.M . M otor ft. M ethod value for carbon 'o monoxide is probably as
§ high as th a t for m ethane.
*3 The octane num ber for hydrogen appears to be g lower, which is indicated (3 by the observation of h Spiers and Giffen (S3)
th a t, w ith m ixtures of high h y d r o g e n c o n te n t, det-
§ onation was encountered jjj a t compression ratios of 10.5 to 1. Pure hydrogen y has been used successfully
a a t compression ratios as
¡3 high as 14 to 1 (1), and j j i t s e x c e p tio n a lly high speed of flame propaga
tion is undoubtedly re
sponsible for its interest
ing properties when em
ployed as fuel in internal combustion engines (1 ,6 , 8,20).
Therm al efficiency and m ean effective pressure are plotted against intake m anifold pressure a t a fixed compression ratio of 7 to 1 in Figure 7. An in
take m anifold pressure of som ewhat over 20 pounds per square inch absolute (not taking into account th e loss from running the supercharger) gives equal power o u tp u t w ith octane and alcohol. This checks closely w ith w hat has been found in actual practice by B randers (5), who stated th a t loss of power
659
•a
3 a
660 I N D U S T R I A L A N D E N G
F igu re 6. E ffect o f C o m p ressio n R a tio o n M ean E ffective P ressu re, W ork, an d T h erm a l E fficien cy
resulting from th e use of producer gas can be to tally com
pensated by a supercharging pressure of 6 pounds per square inch gage. In another instance (2) a six-cylinder engine w ith compres
sion ratio of 4.7 to 1 was ru n on gasoline and on producer gas, w ith and w ithout supercharging. T he results are given below as brake horsepower:
G asoline 86
G as w ith o u t s u p erch arg in g 47
G as w ith s u p erch arg in g a t 0.4 a tm . (5.9 lb ./s q . in.) 80 A dvantages of gaseous fuels in general are b e tte r distribution of charge and elim ination of th e engine-starting problem.
A C K N O W L E D G M E N T
We wish to express th an k s to M rs. M . E. H odler of th is labora
to ry for efficient help in assisting w ith th e calculations.
L I T E R A T U R E C I T E D (1) A nonym ous, Automobütech. Z ., 4 2 , 523 (1939).
(2) Ibid., 45, 71 (1942).
(3) A nonym ous, Gas Oil Power,33, 193 (1938).
(4) B ourdon, M . W ., Automotive and A viation I nth .,91, 26 (1944).
(5) B randers, H. A., Automotive In d .,84, 522 (1941).
(6) B ruckner, H o rst, and Lohr, H ans, Z . Ver. deut. Ing., 80, 1275 (1936).
(7) Colwell, A. T . , J . Soc. Automotive Engrs.,52, 1 (1944).
(8) E gerton, A. C ., S m ith, F. L., and Ubbelohde, A. R., Trans. Roy.
Soc. (London), 2 3 4 A , 462 (1935).
(9) Egloff, G u sta v , an d V an Arsdell, P . M ., J . In st. Petroleum Tech., 27, 121 (1941).
F igu re 7. E ffect o f I n ta k e M a n ifo ld P re ssu r e o n T h erm a l E fficien cy a n d M ea n E ffectiv e P re ssu r e a t
a F ixed C o m p ressio n R a tio
(10) G oldm an, Bosw orth, and Jones, N. C., J . In st. Fuel, 12, 103 (1939).
(11) G raham , J . J ., Gas Oil Power,33, A nn. T ech. R ev. N o., 20 (1938).
(12) Heidelberg, V ictor, U. S. P a te n t 1,858,824 (M ay 17, 1932).
(13) H ershey, R . L., E b e rh a rd t, J . E ., an d H o tte l, H . C ., J . Soc.
Automotive E ngrs.,39, 409 (1936) (includes list of references).
(14) H o ttel, H . C., an d E b e rh a rd t, J . E ., Chern. Rev., 21, 439 (1937).
(15) K ühne, G , Automobiltech. Z .,36, 265 (1933).
(16) Lewis, G . N ., an d R andall, M erle, “ T h erm o d y n am ics” , p. 102, N ew Y ork, M cG raw -H ill Book Co., 1923.
(17) L ichty, L. C., “ In te rn a l C om bustion E ngines” , p. 205, New Y ork, M cG raw -H ill Book Co., 1939.
(18) M ehler, M . J ., Motortech. Z ., 2, 101 (1940).
(19) M oloney, J . H „ Soc. of A utom obile E ngrs., T ra n sp o rta tio n <fc M aintenance M eeting, P o rtlan d , O reg., A ug., 1944.
(20) R icardo, H . R ., an d G lyde, H . S., “ H ighSpeed In te m a lC o m -b ustion E ngine” , p. 92, New Y ork, Interscience Pu-blishers, 1941.
(21) Schnürte, Adolf, Automobiltech. Z .,37, 300 (1934).
(22) S m ittenberg, J ., Hoog, H ., M oerbeek, B . H ., an d Z ijden, M . J . v d., J . In st. Petroleum Tech.,36, 294 (1940).
(23) Spiers, J . an d Giffen, E ., J . In st. Autom obile E ngrs., 1 1 ,17 (1942).
(24) T aylor, C. F ., an d T ay lo r, E . S., “ In te rn a l C om bustion E n g in e ", T ab le 6, p. 159, Scranton, P a ., In te rn . T ex tb o o k Co., 1938.
(25) T obler, J., Schweiz. Ver. Gas- u. W asserfach., M onats-B ull 20 143 (1940).
(26) Tsien, H . C., an d H o tte l, H . C., J . Aeronaut. S ei., 5, 203 (1938).
(27) W iebe, R ichard, et al., In d. En g. Chbm ., 34. 575 (1942) • 36 672 (1944).
(28) W oods, M . W ., E ngineer, 169, 448 (1940).
(29) Ib id 169, 468 (1940).