In connection with the development of a method for analyzing indicator cards taken from high-speed compression-ignition engines, this investigation was undertaken to determine the average quantity of fuel discharged during each crank degree of injection period

Gerrish, Harold C

Voss, Fred

English

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TECHNICAL NOTES 
NATIONAL ADVISORY COEMITTEE FOR AERONAUTICS 
No . 373 
INVESTIGATIOr OF THE DISCEARG~ RATE OF A 
FUEL-I -J~CTION SYSTEi.i 
By Harold C. Gerrish and F~ed Voss 
Langley Hemorial Aeronautical Laboratory 
Washingtol. 
April, 1931 ., ,,,, &iriC 
ngt , D. C. 
11 
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NATIONAL ADVISO RY COMJ.i!ITTEE FOR AERONAUTICS 
TECHNICAL NOTE NO. 373 
INVESTIGATION OF THE DISCHARGE RATE OF A 
FUEL-INJECTIO N SYSTEl1 
By Harold O. Gerrish and Fred Voss 
Summary 
t , 
I n c9 nnec tion, with the development of a. method for analyz-
ing indicator ca rds taken from high-speed compression-igniti9il 
engines, . this investig?-tion was undertaken to determine the av-
erage quantity of fuel discharged during each crank degree of 
the i nj ection per iod. The fuel disc.1.1arged by a cam-operated 
pump and auto;natic inj ection valve was collect ed i n a rotating 
receiver. The weight of fuel discharbed per uni.t time was 
determined for various crank- angle positions over the entire 
injection period. 
The results show tha t 98 per cent of the fuel was dis~ 
charged during an interval of 25 degrees, whereas the duration 
of the period from the start to the stop of the fuel spray was 
68 degrees . The dur ation of t~e period as obtained in these 
tests checks wi th the r esults obtained with the o sc illo scope . 
During the 39 crank degrees after the start of injection and 
the 14 degre es before t t e stop of. injection only 3 per cent of 
the total we i ght of fuel is discharged . 
2 '· N~A.C . A . Technical Note No. 373 
The rat e of fuel injection oontinued to increase for 7 de-
grees after the pUE1P by-pass· valve opened . Calculations show 
that this interval is required for the pressure wave in the fuel 
to travel from the by-pass valve to the injection nozzle. 
Introduction 
The interpretation of indicator cards taken from compres-
sion-ignition engines is difficult because of the variation in 
the weight and heat contents of the mixture during the engine 
cycle due to the injection of the fuel. The interpretation 
requires, among other things, a knowledge not only of the time 
of start and cut-off of the fuel spray, but also of the rate of 
fuel injection. 
De Juhasz (Reference 1) developed an ap:paratus for'deter-
mining the rate of fuel discharge using a constant-pressure 
injection system. He utilized a stationary receiver located 
opposite a cam- actuated injection valve. Between the receiver 
and the valve was a rotating disk with a slot. By means of 
this apparatus De Juhasz obtained some valuabl e results on the 
angular rate of fuel discharge. He found that by increasing" 
the oil pressure the period of inj ection was increased and that 
the maximum rate occurs earlier in the period; and that the 
rate of discharge Was more unifoTl11 at higher camshaft speed and 
with smaller orifices. 
3 
The purpose of this i nve8ti~2ti~il was to det er~ine t~e rate 
of fuel d i 8charr.; e fr') :.1 a C1'L1-0-)era ten -pU;t1P 2..:10. au to:'ilH ti c i::1j ec-
tion valve for a con s t o....'YJ. t set tLr : ')! the fuel PU),;1:P c'Jntrols and 
8. s,!/eed of 750 revolutions ~er ,:1inut e , T~1e L1veeti r at ion 2.S 
conducted Rt the La:1g2.ey l:e:Jo ri8.l Aeronc:,utical Laborato r y of the 
:ational A~visory Oo~mit tee for ~eronButic s at Lanrley Field, Va . 
l!:ethod and A::-,paratus. 
The nethod ado~ted ~y the ffilthors of ~eter~inin~ the rRte of 
fuel di scharr;e diff ered fro::: tna t of De JUh2~S z in t'1a t 2 , ro ta ting 
receiver TI2r. e:!11Jloyed . T~is ··je t hoc. elLlin2~te'(l t~:.e rotatinr: disk 
and ")eri:ii tted a reduction in t'1e d i stance 'jetwee~1 the noz~le and 
the receiver . . he ~ethod was especiRlly ~~it~~l ~ ' for -fuei valve 
nozzles p roduc i nrr wi'de 'ang:_e or Y.1Ul tinle sDrays . 
The a')1Jaratu u eCi. :for det'er.1i ninr-" t ~1.e r ate of fuel disc~'larf-e 
i s shown i n Fi g:l~re J. . I t cons i sted 0: a fuel-i:1ject i') n syste:n , a 
rotating receive r 8,ssembl y , and a re701ution count er . 
The i nje c t ion syste:n consisted of a cC'lr.1-actuated fuel-injec-
tion pUl'JP , sU'r:)i)ly and di scharge line s , SW-Jply ta:1'{ , fuel cooler , 
i njection valve, pr~mary fuel ~w~~, ru1d pressure gauges . The in-
j ect ion ,?ur:11) was cla:-.1Ded to a '!Jlock whi c~ "as concentric 1:7i t h the 
flywheel ' s}1aft on vrhich was fixec~ t:1e variabl'e acceleration cam 
that actuated the pump . Levers which control t he time 0: closing 
and o'geni n[," of the pump by- pass valve are shown at t he tODof the 
pump . 
4 N.A.C.A . Technical Note No . 373 
A detail drawing of tll.e inj ection pump is sho'i'J11 in. Figure 
2. It differs from the pump as actually used only in having. 
micrometer screws for contl'olling the posi tion of the start and 
stop cams instead of levers. The start and stop cam blocks con-
trol the closing a-1d opening of the by-pass valve, thus chc:mgi~lg 
the time and period of inj ection. The shifting of the posi tion 
of the control blocks, comb ined wi th the vari ab le veloci ty cam.) 
varies tDe quantity and rate of fuel discharge. Figure 3 shows 
the p lunger di splac eme:nt plotted against crank angle. The tine 
of closing and opening of the pump by-pass valve as used during 
this investigation is also indicated . 
The injection valve used W2,S an automatic, spring-loaded 
valve (Fig . 40..). The nozzle used had seven orifices in one 
plane and is shown in detail in Fi~ure 4b. The injection tube 
was of steel, 1/8 inch insid e diameter a~1d 36 inches long. 
During this i:1vesti g2. t ion the valve opening pressure was 3,000 
pounds pe:t square inch; the maximum injection pressure during 
inj ection, 5,700 pounds per squ2.re i:t1C11; and t:1e p rim2.ry pump 
fuel pressure, 150 pounds per squo..re inc~1. 
The fuel used was 2. grade of Di ese l engine oil 11twing a 
specific gravity of 0.B47 and a Saybolt Universal viscosity of 
41 seconds at BOO F. Its temperature was kept at 800 F. by a 
water cooler. 
The rota tine; receiver assenbly consisted of a flywheel and 
a spray receiver. An electric motor was used to drive the fly-
N.A. O.A. Technical Note No . 373 5 
wheel at 750 revolutions per Binute by means of a leather belt. 
The flywheel and the receiver were surrounded by a loosely fit-
ted sheet- metal casing . The casing was connected to an exhaust-
er that removed the oil vapors and also the oil thrown off by 
the flywheel . In Fi§,'ure 1 the casing cover is rai"sed to show 
the location of the receiver . 
The duralumin receiver used is shown ' in Figure 5. The 
st:eel tip was designed to prevent the creeping' or ' spattering 'of 
oil into the orifice as the receiver passed through the fuel 
spray . The center line of the receiver was 7.00 inches from the 
' axis of rotation and the width of t he orifice was equal to 'the 
length oI a I-degree arc at this radius . The length of the ori-
fice ( 0 . 416 inch) was slightly greater than the widt11 of the 
spray when the dist ance b etween the receiver orifice and the in-
jection nozzle was 1/16 inch . During this investigation the 
clear'ance between the receiver and the injection nozzle Was 0 . 054 
inch. 
The test procedure was as follows: whe:n' the empty receiver 
was rotating at the des'ired sp eed and the prir.1ary oil pressure 
at the desired value, the spray was sta rted. by moving the control 
levers to the proper posi tion. Simultaneously wi th the r:lOving of 
th'ese levers, the stop watch and revolution counter were started. 
After a g iven number of injections, depending upon the part of 
the discharg~ period being investigated , the control levers WGre 
. ' 
moved to the stop position and the timing mechanism stopped. The 
6 N. A.C . A. Technical Note No . 373 
in'crease in the weight of the r eceiver was considered as the 
weight of fuel discharged. By changing tne angular position 
of the pump, othcr parts of the discharge :9criod were similarly 
investigated . 
The average quantity of fuel discharged per injection was 
determined by collecting in a bottle the fuel discharged from 
the inj ec.tion valve for a known nup.._ber of L1j cctions. Absorb-
ent cotton was placed between the injection valve and the bot-
tle neck to collect any vapors or spattered oil. 
An oscilloscope ( Reference 2) was used to determine the 
injection lag which is the time, or equivalent in crank degrees, 
between the closing of the pwnp by-pass valve and the start of 
the spray at the injection nozzle. 
Test Results and Discussion 
Table I, column 2, gives the average r ates of fuel dis-
charge for several observations for each point. This is the 
weight of fuel discharged by the injection systen per degree 
of crank angle for various intervals durinG the injection 
period. The rate curve (Fig . 6) was plotted fro~ thesc data . 
The devi ations from the average observations given in COlUi1111 
2 were less than ±2 per cent for all test points except four. 
Three of these were either at the start or stop of the injec-
tion period where the fuel collected was very small, even in 
1,000 i njections. The fourth point was near the peak of the 
N. A. C. A. Technical Note No. 373 7 
curve and th e deviation vvas +4 . 5 per ccnt fron t 21e averagc. Af-
ter the rat e o f inj ection curve was a,pproxLnately established, 
intermedi ate points w~r e t aken· and a sr.'looth curve could bc d r awn 
through a ll -the points obta ined, indi c a ting good reproducibility 
of th e data. 
The to tal weight of fue l discharged up to variou s points of 
the injection perio d i s g iven in Tab le I, column 3, and is p lo t -
ted as the weight curve i n Figure 6. This curve was derived fro['1 
the r a te curve by r.1 echanica l integl' 8.t ion . 
The avei' age quantity of fue l dischal'ged· according to tile 
.. 
bottle tests wa~ 0~000364 pound per injection, but that deter-
mined by int egrat ing the r ate curve was 0 . 000399 pound per in-
jection, an increaGe of 9.6 per c cnt over that collected i n tho 
bot t le. This error may be caused b~r oil vapor being draViTIl into 
the r eceiver by jet a ction, by the de terDination of the rate of 
discharge for too large an i nterval during the i llj ection perio d , 
or by a co mb i nat ion of both . 
Beca,use o:c t:1e high velocity ·of the fuel jet and the vis-
cosi ty of t:1e a ir surroundin8 the j ct , ('1,n excess quantity of 
fuel may have been drai'll1 i nto the receiver fron the spray within 
the c asinG . 
The i nterval of injection measured , as dctermined by the 
width of the orifice, affccts the r esi~l t s bec ause, as the intel'-
val increases , the fue l collected divided by tte interval would 
g ive atl. 2.verage value per crank degree t ;J.at, "'Theil plotted, mi ;'ht 
l 
8 N.A .C.A. Technioal Note.l o . . 373 
give a larger or smaller value than the instantaneous value . 
The value might be equal to the instantaneous value, depending 
upon the shape of the rate curve . It is advisable to make the 
width of the receiver orifice such that the quantities collected 
will more nearly approach instantaneous vB,lues instead of mean 
values. 
Figure 3 shows that the by-pass valve closed at 68 crank 
degrees before top center, while Figure 6 shows that the receiver 
was able to collect fuel at 34 crank degrees iJeiore top center 
and not earlier, although the quantity was ver~r small and does 
not show in the fi gure . The injection l ag is therefore 34 de-
grees, and checks exaotly the. lag as found by means of the 
oscilloscope. 
It will be noted in Figure 6 thL1,t the inj cction period is 
68 crank degr ees . However, from a practico..l vicv1Jpoint, the use-
ful injection perio d could not be cons idered to be more than 25 
crank degrees, because the results show that during the 29 crank 
degrees af ter the sturt of injection and the 14 degrees before 
the stop of injection only 2 per c0l1t of the total weight of 
fuel is discharged. 
The peak of t~e rate curvc in Figure 6 occurs at 10 degr ees 
after top c Emt cr, and according to Fi§,LJ.re 3 the by-pass valve 
opens at 3 degrees after top center. The adva~ce of the peak is 
due to t~le ti:i1e required for t~le pressure wave to trcwel from 
the by-pass valve to the injection valve nozzlc. This is in 
? A.C.A. Teoh!-lic1J.l ~~ote ~-o . 373 9 
agreement with the results shown by Rothrock (Reference 3). 
Oalculations show that if the bu l k r oc.ulus of elasticity E of 
the fuel oi 1 is taken as 284 ,000 pounds per s qua.re inch (Refer-
ence '4), then in the equat:i_on 
-/~ V - '" p 
wher e V is the 'ij\:!i-o ci ty of the pressure wave i n the fuol, 
the density, and g the [ ravit:ltional constant, the value of 
V is , 59,900 inches per second . Sinc o the lengtb of the oil 
path fro m the pump by- pass valve to the injection nozz le is 39 
inches, the advance of the peak of the r ate curve should be 
39 / 59]900 ,s,econds or ap~oroxirjat c ly 6 c l'a;:lk degrees ; vvhereas", it 
was 7 cr~nk degrees . 
Oonclusions 
Th ese tests wi th the rotating receiver showod that 98 per 
cent of the fuel was dischargec_ during an interval of 25 degrees , 
whereas, the durat i on of tile porio d f rOl:l the start to the stop 
of the fue l spray was 68 degrees . The duration of the period as 
obta ined in these t ests c~ecks with the results obtained with 
the oscilloscope . The results show that durine- the 29 cra:nk de-
gr ees after the star t of injection Rnd the 14 ~egrees before the 
stop of injection only 2 pCI' cent o f t~e total weisht of fuel is 
discharged, 
10 N.A.C . A. Technical Note No. 373 
T~e rat e of fuel injection continued to increas e for 7 de-
grees after the pump by-pa ss valve opencd . Calculations show 
tha t this interval is required for the pressure wave in the fuel 
to trav el froE1 the pump by-pass va lve to the inj ection nozzle_ 
Langley Memorial Aeronautical Lc_boratory, 
National Advisory Committee for Ae!'onautics , 
Langley Field, Va., April 6, 1931. 
1. De Juhasz, K. J. 
2. Hicks , Chester W. 
and 
Moore, Charles S. 
3. Rothrock, A. M. 
4. Hersey, Mayo D. 
References 
The Pennsylvania State College 
Bulletin, Vol. 22, No. 35, 
November, 1929 . 
Th e Determina tion of Several 
Spray Characteris tics of a 
Hi gh-Speed Oil Engine I njec-
tion System with an Oscillo-
scope.' N.A.C .A. Technical 
Note No. 298, 1928. 
Injection Lags in a Common-
Ra il Injection System . N.A.C.A . 
Technical Note No. 332, 1930. 
Viscosity of Diesel Eng ine 
Fu el Oil under Pressure . 
N.A . C.A . Technical Note No. 
315, 1929. 
N.A . C.A. Technical Note No . 373 11 
TABLE I 
To tal Wcigllt and Rat es of Fuel Inj 8c t ion 
Crank A-l-J' le Lt, ) Rate of Fuel To tal Weight of Fuel 
DischaTgcd , Dischargedj 
degrees lb. /dog . lb. 
B.T.C. 
10-6 -6 34 0 .00 x 0.0 x 10 
26 0.01 
18 0.04 
14 0.11 0.4 
12 0.25 
10 0.31 1.6 
8 0 . 81 
6 2 .12 6.0 
4 13.6 
2 10.55 28 . 8 
T.C. 14 . 99 54 . 4 
2 8S . 0 
4 20 . 84 127.6 
6 171. 2 
8 24 .47 218 . 4 
10 25.25 2 68 . 0 
11 25 .13 
12 23 . 48 317.6 
13 19.73 
14 15 .99 357.6 
15 11. 30 
16 5 .08 378.0 
17 3.14 
18 1. 84 390.0 
20 1.02 
22 394.4-
24 0.70 
26 0 . 63 397.2 
30 0.16 398.8 
34 0.06 399.4 
A.T.C. 
* Obtained by meohanica l integration. 
N.A.C.A. Techni cal Note No . 373 Fig.l 
Fig.l Fuel-injection apparatus. 
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Investigation of the Discharge Rate of a Fuel-injection System

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