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NATIONAL ADVISORY COMMITTEE 
FOR AERONAUTICS 



REPORT No. 714 

AN APPARATUS FOR MEASURING RATES OF 
DISCHARGE OF A FUEL-INJECTION 

SYSTEM 

By FRANCIS J. DUtEE 




1941 



For saJe by the Superintendent of Documents, Washington, D. C. - -- -- -- -- -- -- -- -- -- -- - Price 10 cents 



w 

m 
I 



S 

Sic 

G 

b 

c 

A 

V 

L 
D 
D 0 
V< 



AERONAUTIC SYMBOLS 
1. FUNDAMENTAL AND DERIVED UNITS 





Symbol 


Metric 


Unit 


Abbrevia- 
tion 


Length _ _ 


I 
t 

F 


meter _ _ 


m 

s 

kg 


Time 


second _ 


Force 


weight of 1 kilogram 


Power. 


P 
V 


horsepower (metric) 




Speed _ 


f kilometers per hour 

\ meters per second _ _ 


kph 

mps 



English 



Unit 



foot (or mile) 

second (or hour)_ 
weight of 1 pound 

horsepower 

miles per hour 

feet per second 



Abbrevia- 
tion 



ft (or mi) 
sec (or hr) 
lb 



hp 

mph 

fps 



2. GENERAL SYMBOLS 



Weight =mg 

Standard acceleration of gravity =9.80665 m/s 2 
or 32.1740 ft/sec 2 

Mass=— 

Moment of inertia =mk 2 . (Indicate axis of 

radius of gyration k by proper subscript.) 
Coefficient of viscosity 



v Kinematic viscosity 
p Density (mass per unit volume) 
Standard density of dry air, 0.12497 kg-m 



and 760 mm; or 0.002378 lb-ft -4 sec 2 
Specific weight of " standard' ' air, 
0.07651 lb/cu ft 



s 2 at 15° C 
1.2255 kg/m 3 or 



3. AERODYNAMIC SYMBOLS 



Area 

Area of wing 
Gap 
Span 
Chord 

Aspect ratio, ^ 
True air speed 
Dynamic pressure, 



Lift, absolute coefficient CV=-o 

qS 



Drag, absolute coefficient C D = 



D 

qS 



Profile drag, absolute coefficient ^Do^^g 



Induced drag, absolute coefficient C Di = ^ 
Parasite drag, absolute coefficient Cd p = ~§ 
C Cross-wind force, absolute coefficient C c = 



i u Angle of setting of wings (relative to thrust line) 
i t Angle of stabilizer setting (relative to thrust 
line) 

Q Resultant moment 

6 Resultant angular velocity 

VI 

R Reynolds number, p — where I is a linear dimen- 

sion (e.g., for an airfoil of 1.0 ft chord, 100 mph, 
standard pressure at 15° C, the corresponding 
Reynolds number is 935,400; or for an airfoil 
of 1.0 m chord, 100 mps, the corresponding 
Reynolds number is 6,865,000) 

a Angle of attack 

e Angle of downwash 

oq Angle of attack, infinite aspect ratio 

a t Angle of attack, induced 

a 3 Angle of attack, absolute (measured from zero- 
lift position) 

7 Flight-path angle 



qS 



REPORT No. 714 



AN APPARATUS FOR MEASURING RATES OF DISCHARGE 
OF A FUEL-INJECTION SYSTEM 

By FRANCIS J. DUTEE 
Langley Memorial Aeronautical Laboratory 



i 



NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 



HEADQUARTERS, NAVY BUILDING, WASHINGTON, D. C. 



Created by act of Congress approved March 3, 1015, for the supervision and direction of the scientific study of the problems 
of flight (U. s. Code, Title 50, Sec. 151), lis membership was increased to 15 by act approved March 2, 191*9. The members are 
appointed by the President, and serve as such without compensation. 



Vannkvar IUisii. Sc. I >.. Chairman, 

Washington, D. < \ 
Geobge J. Mead, Sc. P., Vice Chairman, 

Washington, D. C. 
Charles G. Abbot, Sc. D., 

Secretary, Smithsonian Institution. 
Henry H. Arnold, Major General, United States Army. 

Deputy Chief of Staff, Chief of the Air Corps, War 
Department. 

George H. Brett, Major General, United States Army, 
Acting Chief of the Air Corps, War Department. 

LYM AN J. P.KKiGS, I'll. P., 

Director, National Bureau of Standards. 
Donald H. Connolly, B. S., 

Administrator of Civil Aeronautics. 



Rom R l B. I ►ohbrty, M. S., 

Pittsburgh, Pa. 
Robert H. Hinckley, A. B., 

Assistant Secretary of Commerce. 
Jerome C. Hunsaker, Sc. D., 

( Cambridge, Mass. 
Sydney M. Kbaus, Captain, United States Navy, 

Bureau Of Aeronautics, Navy Department. 
Francis W. Reichelderfkr, Sc. D., 

Chief, United States Weather Bureau. 
John H. Towers, Rear Admiral, United State s Navy, 

Chief, Bureau of Aeronautics, Navy Department 
Edward W miner, Sc. D., 

Washington, D. C. 
Orville Wright, Sc. D., 

Dayton, Ohio. 



GEORGE W. Lewis, Director of Aeronautical Research S. PAXIL Johnston, Coordinator of Research 

John F. Victory, Secretary 
Henry J. E. Reid, Wnffineer-in-Charge, Langley Manorial Aeronautical Laboratory, T.anyh y Field, Va. 
Smith J. DeFrance, Engineer-in-Charge, Ames Aeronautical Laboratory, Moffeti Field, Calif. 



TECHNICAL COMMITTEES 

AERODYNAMICS aircraft structures 

power plants for aircraft aircraft accidents 

AIRCRAFT MATERIALS INVENTIONS AND DESIGNS 

Coordination of Research Needs of Military and Ciril Aviation 

Preparation of Research Programs 
Allocation of Problems 
Prevention of Duplication 
Consideration of Inventions 

LANGLEY MEMORIAL AERONAUTICAL LABORATORY AMES AERONAUTICAL LABORATORY 

LANGLEY field, va. moffett field, calif. 

Conduct, under unified control, for all agencies, of scientific research on the fundamental problems of flight. 

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WASHINGTON, D. C. 

Collection, classification, compilation, and dissemination of 
scientific and technical information on aeronautics 



REPORT No. 714 



AN APPARATUS FOR MEASURING RATES OF DISCHARGE 
OF A FUEL-INJECTION SYSTEM 



By Fr \xcis J. Di im 



SUMMARY 

A portabh apparatus for rapidly determining rates of 
discharge of a fuel-injection system is described. Satis- 
factory operation of this apparatus with injection-pump 
speeds up to 2400 rpm was obtained. Hate-oj -discharge 
tests were made with several cam-plunger-valve injection 
systems with long injection tubes. A check valve de- 
signed to reduce secondary discharges vjas tested. This 
check valve was operated with injection-pump speeds up 
to 2400 rpm without the occurrence of large secondary 
discharges. 

Comparable performance tests on the two-stroke-cycle 
compression-ignition engine wen madt with low fuel- 
injection rati and with thi highest injection rate obtained. 
Thi maximum gross brake mean effective pressure was in- 
ert used 7.6 percent, and thi minimum gross brake specific 
fuel consumption was decreased 6.2 percent by changing 
from the lower to the Mgher injection rate. 

INTRODUCTION 

Experimental work on the effect of fuel-injection 
characteristics upon the performance of compression- 
ignition engines has in the past been limited principally 
lo consideration of the injection period. Data in ref- 
erence l show thai a short injection period is desir- 
able from considerations of power output and fuel 
economy. A knowledge of the quantitative rate of 

discharge for all conditions of operation of the injec- 
tion system is needed in order that the effects of the 

rate of injection on engine performance may be fully 
invest igated. 

Injection systems that have long discharge periods 
accompanied by large secondary injections are undesir- 
able because they result in late burning, smoky exhaust, 
and a relatively high specific fuel consumption. These 
injection characteristics occur at high engine speeds or 
high throttle settings. 

Apparatus that have been used for the determination 
of injection characteristics include: inject ion- valve- 
stem lift indicators, pressure indicators of the cathode- 
ray oscillograph type, and the slotted-disk type of 
rate-of-discharge apparatus described in reference 2. 
References 2 and 3 show the rate-of-discharge character- 
istics of some cam-plunger-valve injection systems using 
long injection tubes for pump speeds up to 1000 rpm. 

320842—41 



An apparatus that gives a quick and an accurate 
measurement of the rate of discharge has been designed 
by the NACA and is described in this report. Mr. 
George T. Hemmeter, formerly on the Committee 
staff, aided in the conception and the preliminary design 
of the apparatus. Rate-of-discharge data are included 
to show the reproducibility of test results. A pump 
check valve that reduces secondary discharges was 
tested with two different cam outlines and with pump 
speeds from 1250 to 2400 rpm. The performance data 
obtained with this check valve are presented together 
with comparable data obtained with a Bosch check 
valve. Some data are included to show the effect of 
rate of injection upon the performance of a two-stroke- 
cycle compression-ignition engine at a speed of 1800 
rpm. The work was done in 1937 and 1939 at Langley 
Field. Va. 

APPARATUS 
RATE-OF-DISCHARGE APPARATUS 

Description.- The rate-of-discharge apparatus used 
in these tests is a portable unit designed for use in 
conjunction with the NACA universal test engine and 
an electric dynamometer. It consists essentially of a 
high-speed rotary fuel receiver and an adjustable 
mounting bracket for the injection valve. During 
rate-of-discharge tests, the engine is motored by means 
of the elect lie dynamometer. Figure 1 is a photograph 
of the apparatus connected to the test engine and the 
injection pump. The rotor is gear-driven by a power 
take-off from the water-pump shaft of the test engine. 
It is designed for safe operation with a maximum 
engine crankshaft speed of 3000 rpm (rotor speed of 
5000 rpm) and inject ion pump speeds of 1500 and 3000 
rpm on four- and two-stroke-cycle engines, respectively. 

Seventy receiver compartments extend around the 
upper periphery of the rotor shown in figure 2. These 
compartments are connected by drilled fuel passage- 
ways to glass lubes that serve as fuel reservoirs. Each 
ejass tube has an internal capacity of 0.390 cubic inch 
and is graduated in increments of 0.003 cubic inch. 
These tubes are mounted in retaining grooves milled in 
the periphery of the forged aluminum-alloy rotor. The 

Calibration markings on the tubes are exposed to view 

through slots in the outer circumference of the rotor 

1 



2 



KEI'OKT NO. 71 I 



NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 




Figure t. — Rate-of-discharge apparatus and test equipment. 




Figure 2. — Rate-of-discharge apparatus, sectional diagram. 



The sides of each receiver are formed by two vanes 
so spaced thai the receiver will collect fuel during* a 1° 
rotation of the engine crankshaft. The centers of 
adjacent receivers have an angular spacing about the 
center of the rotor of 5°, equivalent to a 3° rotation of 
the engine crankshaft. The receiver compartments 
are divided into three sections, two of which contain 
receivers and one which contains 24 receivers. These 
sections are separated from each other by three equal 
spacings on the circumference of such a width that 
angular rotation of the rotor between centers of ad- 
jacent receivers is 8°20', which ts equivalent to a 5° 
rotation of the engine crankshaft. One of these 
spa.cings is shown at A in figure 3. 

Dining operation the fuel is discharged from the 
injection valve, is collected in the receivers, and is 
transmitted by centrifugal force into the glass tubes. 
Fuel thai is discharged between the receivers is wasted. 
After ;i tesl run the volume of fuel collected in each 
tube can be quickly observed and recorded. 




Figure 3.— Rotor assembly, view showing vanes and receiver compartments. 



APPARATUS FOH MEASURING RATES OF DISCHARGE OF A FUEL-INJECTION" SYSTEM 



At the beginning of each test run bhe injection start 
is synchronized with the receiver sections by means of a 
Stroborama in such a manner that any single discharge 
is completed within a single sect ion of receivers. Succes- 
sive discharges occur alternately within the three sec- 
tions owing to the fact that the rotor revolves at a 
speed 1% times the speed of the engine crankshaft. The 
receiver compartments of any section are 1° out of 
phase with the compartments of either of the other two 
sections. Each section provides data for rate of dis- 
charge to define the curve every :]° of the engine crank- 
shaft, and the data from the three sections can be 

correlated to define the curve every 1°. Each section 
of receivers collects approximately the same weight of 
fuel, and thus satisfactory balance of the rotor is 

maintained throughout the test run. 

The rotor may be started and stopped by a friction 
clutch provided in the apparatus. This clutch includes 
a positive engagement mechanism by w hich the angular 

position of the rotor can be adjusted and locked in the 

proper phase relation with the injection-pump shaft. 

Operation. — The amount of fuel discharged during 
each test run was adjusted to such a value that the 
maximum quantity of fuel collected by any one of the 
glass tubes filled the tube within the limits of 70 to 100 
percent of its capacity. The number of fuel discharges 
during elach test run was thus necessarily varied approxi- 
mately inversely with the maximum rate of discharge of 
the injection system. In figure 4, for example, each 
Curve represents an average of at least 1(>4() discharges. 
A fuel scale that automatically weighed a predeter- 
mined amount of fuel controlled a solenoid-operated 
Stop watch and revolution counter. The injection- 
pump throttle was manually opened at the beginning 
of each test run and closed at the end of each test run. 
The apparatus operated satisfactorily at the highest 
test speed of 2400 rpm. Operation at higher speeds 
appeared feasible. No difficulty was experienced from 
vibration originating within the apparatus. 

After the test equipment had been completely as- 
sembled, a test run for any one condition of speed and 
throttle setting could be made in 8 minutes. This 
operation included starting, synchronizing, operating 
the injection system, stopping, recording data, and 
draining and sealing the glass t ubes for another test run. 

Reproducibility and accuracy. — A large number of 
preliminary rate-of-discharge tests were made with the 
apparatus to calibrate the equipment and develop a 
satisfactory method of operation. Figure 4 shows the 
reproducibility obtained in four sets of rate-of-discharge 
data taken with comparable injection-system condi- 
tions. In 44 rate-of-discharge tests with various con- 
ditions of pump speed and throttle setting, the greatest 
discrepancy between the average fuel (piantity per 
injection as determined by the rate-of-discharge 
apparatus and as determined by the fuel scale was 4 
percent. No error could be detected in the period of 



discharge abjudicated by the rate-of-discharge appara- 
tus from observation of the fuel sprays with the aid of a 
Stroborama. 

The best, results were obtained with the apparatus 
when injection nozzles having all orifices in a single 
vertical plane were used. The operating clearance 
between the injection nozzle and the edge of the 
receiver vanes was found to have no effect on the 
accuracy of the rate-of-discharge data for clearances 
less than 0.060 inch. A clearance of 0-050 inch was 
used in these tests. Tests with an injection valve 
delivering a cone-type spray indicated some sacrifice 
inaccuracy because the tip of the valve was so shaped 



.3 



. / 

















1 1 
Pump 


\ 1 
Fuel 


















K 




speed, 


quant i) 

- t ht 1 s- i //~~ 1 


V 
















N 




— rpm — 
o 10/3 




4.18^10 


e — 

-4 




















□ 

A 


971 
967 


3.99 
4.16 






















V 


963 






3.9. 


















1 






































































.0 






























C 




































aire 


d a 


ver 


age 
























































































































0 
































c 








o 
































































H 




1 




















I 


V 












































A 




















2^ 




w>° 




Ar. • ■ 


> 


O 





0 4 8 12 16 20 24 2d 



Pump deq 

Figure 4.— Comparison of rate-of-discharge data for quadruplicate test runs. Pump 
and check valve, Bosch; cam 1; plunger diameter, 0.394 inch; injection-valve open- 
ing pressure, 3500 pounds per square inch; orifice area, 0.0O0S05 square inch. 

that it could not be run close enough to the receiver 
vanes to obtain the necessary minimum clearance. 

INJECTION PUMPS 

Three different Bosch pumps were used in these 
tests: a one-cylinder unit with a 0. 394-inch diameter 
plunger; a two-cylinder unit with ;i 0.394-inch diameter 
plunger and both cams in phase; and a six-cylinder 
unit with a 0.354-inch diameter plunger and cam- 
phased ()()° apart. Unless otherwise specified, all 
data from mult [Cylinder pumps are for only one cylinder. 

Plunger-lift curves for the two different cams investi- 
gated are shown in figure 5. These curves were plotted 
from the manufacturer's specifications. Fuel-displace- 
ment curves based on the plunger-lift curves/of figure 5 
are shown in figure i\. ( "ha rael erist ies of the bypass- 



4 



REPORT NO. 714 — NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 



port flow area arc shown in figure 7. The data for 
this figure were calculated from the dimensions of the 
pump plungers and the pump cylinders used. The 
same curve is applicable to all pump units tested. The 
rate of opening of the bypass port is dependent upon 
this curve and the plunger-lift curves. 



PUMP CHECK VALVES 



Figure 8 (a) shows the Bosch check valve. The 
valve is constructed with a fluted guide and a lapped 



in the injection tube. 

Figure 8 (b) shows an NACA design of a chec 
valve. Fuel flows through the ball check valve dur- 
ing delivery. Residual pressure in the injection tube 
can be adjusted to any desired value by changing the 
spring tension on the pressure-release valve. The 
valve was adjusted to open at 1000 pounds per square 
inch in these tests. The release of pressure waves 
from the injection tube into the inlet chamber of the 
injection pump set up pressure waves in the primary 



b 



.0/2 



.0/0 



o 

a 
i 



.008 



006 



004 



002 

















































Com 

: 
































2 
































































































































J 


































/ 
































'For 


t c/c 


yses 











































100 110 120 130 MO 150 160 '70 

Pump deg 

Figure 5— Plunger lift curves. Cam position for maximum lift, 180°. 



130 

























































































/ 






























/ 






























/ 






























r 






























/ 






























7 






























/- 























































































































.02 .04 .06 .08 .10 .12 .14 

Plunger movement after start of port opening, in. 

Figure 7.— Characteristics of the bypass-port flow area. 



.16 



5x/0 




0 10 20 30 40 

Camshaft position after ports close, deg 

Figure 6.— Fuel-displacement curves for various combina- 
tions of cam outline and plunger diameter. 



shoulder. Delivery does not begin until fuel pressure 
from the pump forces the valve upward far enough for 
the lapped shoulder to clear the seat. At the end of 
the discharge the lapped shoulder returns to its lowest 
position and partly releases the pressure in the in j ec- 
tion tube for the purpose of preventing dribble. No 
further discharge from the injection valve can take 
place except as the result of pressure-wave phenomena 



fuel system that adversely affected the charging of the 
pump cylinders and caused a variation of fuel quantity 
delivered per injection. Even charging of the pump 
cylinders was obtained by placing two surge chambers 
in the inlet and the outlet primary fuel lines to damp 
out the pressure waves. The chambers were placed 
close to opposite sides of the injection pump. Each 
chamber had an internal capacity of 140 cubic inches. 



APPARATUS FOR MEASURING RATES OF DISCHARGE OF A FUEL-INJECTION SYSTEM 



5 




(a) Bosch design. (b) NACA design. 



Figure 8.— Pump check valves. 



Unless otherwise noted in the text, the following 
equipment and conditions were held constant through- 
out the rate-of-discharge tests: 

1. Injection pump: plunger diameter, 0.394 inch 

2. Injection tube: steel; inside diameter, 0.125 inch; 
outside diameter, 0.25 inch; single tube from pump 
outlet to injection valve 

3. Injection valve: NACA injection valve 13; dif- 
ferential area type; sectional diagram shown in refer- 
ence 4 

4. Injection nozzles: multiple-orifice type; all orifices 
in same plane; characteristics appear in table I 

5. Fuel: Diesel oil; 0.83 specific gravity at 68° F; 
41 seconds Saybolt Universal viscosity at 80° F; G2 
cetane number 

TABLE I 
NOZZLE CHARACTERISTICS 



Orifice arrange- 
ment 


Total orifice 
area (sq in.) 


Orifice diameter 
(in.) 


m- A 


0. 000GG1 


fA =0.023 
-|Bi= .012 
[B 2 = .013 


B 

/eo° 

\60° A 
B 


0. 000605 


/A =0.023 
\B = .011 




0. 000868 


fA =0.016 
\B = .010 
[C = .014 


— "A 

V^§T^A 
C on B 


0. 000895 


fA =0.020 
\B = .011 
lC = .007 



Rate-of-discharge tests were run for all conditions 
listed in table II. All rate-of-discharge data and curves 



that show the weight of fuel discharged were plotted 
against pump degrees. 

TABLE II 
RATE-OF-DISCHARGE TESTS 



Variable test 
condition 



Fuel quantity. 

Do 

Do 

Do 

Injection system 



1250 
1250 
1250 
2100 

1800 



2. 80-4. 54 
2. 80-4. 32 
2. 02 J. 35 
1.01 1.01 

4. 07 



0. 301 
.394 
.394 
.394 
f .301 
I .354 



Single.. 
...do.... 
...do.... 
...do.... 

/Y 

\Single.. 



Bosch... 

..do 

NACA.. 
...do..... 

...do 



0.001 Mis 
.OOOSfIS 

Mis 

.000(105 
( .000150 1 
I .000605 



> 



3500 
3500 
351)0 

3000 
3000 



TEST ENGINE 



The single-cylinder, water-cooled, two-stroke-cycle 
compression-ignition engine described in reference 5 was 
used in the engine performance tests. The 4% by 7- 
inch cylinder admits air through circular inlet ports at 
the bottom of the cylinder and exhausts tlnmigh four 
poppet valves in the cylinder head. 

The following engine conditions were maintained 
constant during these tests: 

1. Compression ratio based on swept volume, 13.7 

2. Valve and port timing (deg A. T. C): exhaust 
opens, 91; exhaust closes, 223; inlet opens, 129; inlet 
closes, 231 

3. Inlet-port dimensions: height, 1 inch; diameter of 
ports, % inch; number of ports, 63; entry angle, 56° 
to radial; cylinder-liner thickness at port band, % 6 inch 

4. Maximum cylinder pressure: 1000 pounds per 
square inch. Engine-performance tests were made with 
the following injection systems: Bosch pump with one 
0.354-inch-diameter cylinder connected to a single in- 
jection valve; Bosch two-cylinder pump having both 
cams in phase, with Y-tube connection to a single- 
injection valve 



6 



KKPOKT NO. 7 I 1 



—NATIONAL ADVISOR? COMMITTEE FOB AERONAUTICS 



( \>mparable engine-performance tests were made with 
two different rates of fuel injection obtained by the use 
of the two different fuel-injection systems. The effect 
of fuel quantity on engine performance for both injec- 
tion systems was determined with an engine speed of 



of the fuel. More complete information on this 
phenomenon is given in reference 6. A brief description 
of the action is as follows: Pressure waves, which are 
originally set up by the plunger, travel through the 
fuel in the injection tube at the rate of approximately 




10 20 
Pump deg 

Figure 9.— Discharge characteristics with Bosch 
check valve and cam 1. Pump speed, 1250 rpni; 
injection-tube length, 31 inches; injection-valve 
opening pressure, 3500 pounds per square inch; 
orifice area, 0.0008*58 square inch. 




10 20 
Pump deg 

Figure 10— Discharge characteristics with Bosch check 
valve and cam 2. Pump sj)eed, 1250 rpm; injection-tube 
length, 31 inches; injection-valve opening pressure, 3500 
pounds per square inch; orifice area, 0.000868 square inch. 




10 20 
Pump deg 

Figure 11.— Discharge characteristics with NAC A 
check valve and cam 2. Pump speed, 1250 rpm; 
injection-tube length, 31 inches; injection-valve 
owning pressure, 3500 pounds per square inch; 
orifice area, o. nooses square inch. 



1800 rpm and a scavenging-air pressure of 20 inches of 
mercury. 

RESULTS AND DISCUSSION 

RATE OF DISCHARGE 

Effect of pump check valve. — A considerable number 
of injection-valve stem-lift diagrams of injection systems 
equipped with the Bosch check valve, with a plain ball 
check valve, and with no check valve are shown in 
reference 3. In the present tests a critical rate of 
plunger motion was found above which secondary dis- 
charges occurred. (See figs. 9 and 10.) The secondary 
discharges resulted from fuel pressure waves in the 
injection tube caused by the elasticity and the inertia 



:)().()()() inches per second. When the pressure wave 
reaches the injection nozzle, any energy of the wave 
that is not dissipated in discharge of fuel through the 
orifice is reflected toward the pump. The back-rushing 
wave after reaching the pump plunger is reflected and 
again traverses the tube toward the inject ion valve. A 
conventional type of pump check valve such as the 
Bosch cheek valve, which prevents return of find from 
the injection tube to the pump cylinder after cut-off, 
will completely relied residual pressure waves in the 
injection tube. If these waves are of sufficient inten- 
sity, they will open the injection valve repeatedly and 
cause secondary discharges to occur. These pressure 



APPARATUS FOR MEASURING RATES OF DISCHARGE OF A FUEL-INJECTION SYSTEM 



7 



waves are dissipated by the release of fuel in the 
secondary discharges, and the discharges cease when 
the pressure waves are no longer great enough to open 
the injection valve. 

The NACA check valve was designed to reduce 
secondary injections and yei maintain a residual pres- 
sure in the injection tube. Pressure waves reflected 
from the injection valve, are partly dissipated at the 
pump end of the injection tube by the release of fuel 
through I lie pressure-release valve, the plunger barrel, 




10 



40 



ao 30 

Pump deg 

FIGURE 12.— Effect of fuel quantity on discharge characteristics at a pump speed of 
2400 rpm. Check valve, NACA; cam 1; injection-tube length, 44 inches; injection- 
valve opening pressure, 3000 pounds per square inch; orifice area, 0.000005 square 
inch. 

and the bypass port into the primary fuel chamber. 
It was found that a maximum residual pressure equal 
to one-third of the injection-valve opening pressure 
could be maintained with this check valve without 
excessive secondary discharges. The data of figure 11 
were taken with an injection system using the XACA 
check valve and are comparable with the data of figure 
10 for the Bosch check valve. The NACA check valve 
was used with pump speeds up to 2400 rpm without 
large secondary discharges. (See fig. 12.) Inasmuch 
as difficulty was experienced in obtaining an even 
charging of the pump cylinders when us'mg this check 



valve, a word of caution in regard to its use is advisable 
Sullieient pump inlet-chamber capacity is necessary to 
damp out pressure waves or they will cause large 
variations in fuel quantity w ith change of pump speed 

or slight unevenness of fuel quantity at constant pump 

speed. 

ENG1 N I : I * I : R F ORMANCE 

Figure 14 shows a comparison of the performance of 
the two-stroke-cycle compression-ignition engine for the 

two injection systems for which rate-of-discharge data 




20 30 
Pump deg 

Figure 13.— Comparison of injection characteristics for two arrangements of the 
injection system at a pump speed of 1*00 rpm. Check valve, NACA; cam [; 
injection-valve opening pressure, 3000 pounds per square inch. Injection-tube 
lengths: plunger to Y, 0.5 inches; plunger to orifice, 44 inches. 

are shown in figure 13. The injection nozzles were of 
comparable design except for the total discharge-orifice 
area. (See table I for characteristics.) The Larger 

orifice area was used with the two-cylinder injection 
pump to allow injection of a full-load fuel quantity 
without exceeding tin* safe delivery pressure of the 
injection pump. The higher rate of injection gave an 

increase of 7.6 percent in maximum gross brake mean 
effective pressure and a reduction of 6.2 percent in the 
minimum gross brake specific fuel consumption from 

that obtained with the lower injection rate. The 

injection advance angle was 2° to 4° less with the 



8 



REPORT NO. 714 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 



higher rate of injection, which indicates that the rate 
of pressure rise in the combustion chamber was greater. 
The lesser fuel consumption with the higher rate of 
injection was due to the burning of a greater percentage 
of fuel in the early part of the stroke where the expan- 
sion ratio is high. These data indicate that an improve- 
ment in engine performance can be expected by 



180 



160 
&I40 



X 

1 1 00 

IP 

^ 80 
60 




60 

:« 40 



%20 

CD 



O T 




o One pump cylinder connected 

' to one injection valve-, plunger 

diameter, 0.354 in ; orifice 
- area, 0. 000605 sq in. A V- 



• Two pump cylinders with Y-tube 
— connected to one in jection 

value-, cams operated in phase 
_ plunger diameter, 0. 394 in. -, 

orifice area, 0. 000661 sq in. 



2 3 4 5x10 - A 6 

Fuel quantity, lb /cycle 

Figure 14.— Comparative effect of rate of fuel injection on the performance of a two- 
stroke-cycle compression-ignition engine obtained with two different injection 
systems. Engine speed, 1800 rpm; check valve, NACA; injection-valve opening 
pressure, 3000 pounds per square inch. Injection-tube lengths: plunger to Y, 6.5 
inches; plunger to orifice. 41 inches. 

increasing the maximum rate of injection and shortening 
the injection period. 

Changing from the lower to the higher rate of fuel 
displacement in this case caused a change in the shape 
of the rate-of-discharge curve that tended to make it 
conform more nearly with the desired rate-of-in ject ion 
curve. It is believed that the rate-of-in jection curve 
should increase as a function of the rati' of volume 



change in the engine cylinder to a maximum value and 
then return instantaneously to zero. Further tests 
will he made to determine the correctness of this 
assumption. 

CONCLUSIONS 

1. The rate-of-discharge apparatus used in these 
tests consistently reproduced its own average data for 
repeated test conditions within ±4 percent. Satis- 
factory operation was obtained with pump speeds up 
to 2400 rpm; satisfactory operation with higher speed 
w as indicated. 

2. Secondary discharges were practically eliminated 
at all operating conditions by use of a combination 
check valve and pressure-release device. 

3. Engine performance improved with increased rate 
of injection and decreased injection period, 



Langley Memorial Aebonaxttical Laboratory, 
National Advisory Committee for Aeronautics, 
Langley Field, Va., March 24, 1941. 

REFERENCES 

1. Spanogle, J. A., and Moore, C. S.: Performance of a Com- 

pression-Ignition Engine with a Precombustion Chamber 
Having High- Velocity Air Flow. T. N. No. 396, NACA, 
1931. 

2. Gelalles, A. G., and Marsh, E. T.: Rates of Fuel Discharge 

as Affected by the Design of Fuel-Injection Systems for 
Internal-Combustion Engines. Rep. No. 433, NACA, 
1932. 

3. Rothrock, A. M., and Marsh, E. T.: Distribution and Regu- 

larity of Injection from a Multicylinder Fuel-Injection 
Pump. Rep. No. 533, NACA, 1935. 

4. Rothrock, A. M., and Marsh, E. T.: Effect of Viscosity on 

Fuel Leakage between Lapped Plungers and Sleeves and 
on the Discharge from a Pump-Injection System. Rep. 
No. 477, NACA, 1934. 

5. Spanogle, J. A., and Whitney, E. G.: A Description and 

Test Results of a Spark-Ignition and a Compression- 
Ignition 2-Stroke-Cycle Engine. Rep. No. 495, NACA, 
1934. 

6. Rothrock, A. M.: Bydraulics of Fuel Injection Pumps 

for Compression-Ignition Engines. Rep. No. 396, NACA, 
1931. 



U. S. GOVFRNMKNT PRINTING OFFICE: I9il 




Y 

Z 

Positive directions of axes and angles (forces and moments) are shown by arrows 



Axis 




Moment about axis 


Angle 


Velocities 


Designation 


Sym- 
bol 


Force 
(parallel 
to axis) 
symbol 


Designation 


Sym- 
bol 


Positive 
direction 


Designa- 
tion 


Sym- 
bol 


Linear 
(compo- 
nent along 
axis) 


Angular 


Longitudinal 


X 


X 


Rolling 

Pitching 

Yawing 


L 


Y >Z 


Roll 


4 

0 


u 

V 

w 


V 


Lateral _ _ _ 


Y 


Y 


M 
N 


Z — >x 


Pitch 

Yaw 


Normal. _ 


Z 


Z 


X >Y 




Q 






4> 


r 



Absolute coefficients of moment 

^ l ~qbS Cm ~qcS Cn ~^bS 

(rolling) (pitching) (yawing) 



Angle of set of control surface (relative to neutral 
position), 5. (Indicate surface by proper subscript.) 



Diameter 
Geometric pitch 
Pitch ratio 
Inflow velocity 
Slipstream velocity 



d, 

z>> 

P/D, 

V, 

V„ 

T, 
Q, 



1 hp. = 76.04 kg-m/s=550 ft-lb./sec. 
1 metric horsepower =1.01 32 hp. 
1 m.p.h. =0.4470 m.p.s. 
1 m.p.s.=2.2369 m.p.h. 



4. PROPELLER SYMBOLS 

Power, absolute coefficient C P - 





P, 








V, 


T 


n, 






Q 




1 pn 2 D s 





4 



Speed-power coefficient =- 

Efficiency 
Kevolutions per second, r.p.s. 

Effective helix angle — tan" l ( ^ ^ ^ 



5. NUMERICAL RELATIONS 



1 lb. =0.4536 kg. 

1 kg=2.2046 lb. 

1 mi. = l,609.35 m=5,280 ft. 

1 m=3.2808 ft.