Gold, Harold

Straight, David M

English

NASA Technical Reports Server

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RM No . E8C08 
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RESEARCH MEMORANDUM 
A FUEL-DISTRIBUTION CONTROL FOR GAS-TURBINE ENGINES 
By Harold Gold and David M. Straight 
Flight Propulsion Research Laboratory 
Cleveland, Ohio 
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A:.Jr.'J ttY Cn .... C .rE 1977 
D T8 12-14-53 T.C.F. 
NATIONAL ADVISORY COMMITTEE 
FOR AERONAUTICS 
WASHINGTO 
June 14, 1948 ,------
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https://ntrs.nasa.gov/search.jsp?R=19930085433 2020-06-17T14:53:54+00:00Z
NACA RM No. ESCOS CONFIDENTIAL 
NATIONAL ADVISORY COMMITI'EE FOR AERONAUTICS 
RESEARCH MEMORANDUM 
A FUEL-DISTRIBUTION CONTROL FOR 
GAS-TURBINE ENGINES 
By Harold Gold and David M. Straight 
SUMMARY 
The principle of operation of a device to control the distri-
bution of fuel to any number of discharge nozzles of a gas-turbine 
engine is presented. A description of an experimental model of the 
device and the results of a bench investigation are presented. This 
device controlled the flow to four discharge nozzles within 2 per-
cent of perfect distribution over a wide range of fuel flow and was 
unaffected by uneven discharge-nozzle pressures. 
INTRODUCTION 
In current gas-turbine engines the fuel is pumped into a mani-
fold from which it flows to the various atomizing nozzles. If the 
fuel manifold is large and symmetrical, the effect of fluid friction 
is negligible and fuel reaches all the discharge nozzles at the same 
static pressure. If all the nozzles have the same area and equal 
coefficients at all flows, the flow through the discharge nozzles 
will at all times be equal. The complexity imposed on the nozzle 
by the need for a well-atomized discharge, however, makes the equal-
izing of fuel flow through the nozzles over a wide range of fuel 
flows extremely difficult. With the relatively low pressures used 
in some current gas-turbine-engine fuel manifolds at low flows, 
differences in nozzle elevations and inertia forces markedly affect 
the fuel distribution. In addition, the malfunctioning of one 
nozzle can greatly disturb the fuel flow to the other nozzles. By 
means of the distribution-control method described, these effects 
can be entirely overcome. 
In the course of investigation at the NACA Cleveland labor-
atory of methods to obtain uniform fuel sprays in gas-turbine 
engines, a fuel-distribution control was developed that presents 
a possible means for obtaining improved and more consistent 
fuel distribution in gas-turbine engines than can be obtained with 
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2 CONFIDEWfIAL NACA RM No. ESC08 
the use of the manifold system. The principle of operation of the 
fuel-distribution control, a description of the experimental model 
used in the investigation, and the results of the bench investigation 
are presented. 
PRINCIPLE OF OPERATION 
Control method. - If matched metering jets were placed upstream 
of the discharge nozzles in each branch of a fuel manifold, the 
static pressure of the fuel on the ups~ream side of the jets would 
be equal in each branch, but the downstream static pressure would 
be affected by the discharge nozzle and the fuel distribution would 
not be improved. If, however, automatic valves were placed between 
the metering jets and the discharge nozzles to maintain equal static 
pressures on the downstream side of the metering jets in each branch, 
t he distribution would be controlled by the metering jets and would 
be unaffected by the discharge nozzles. Such a system, schematically 
shown in figure 1, is the basis of the fuel-distribution control 
developed during this investigation. 
Control mechanism. - A schematic diagram of the fuel-distribution 
control is presented in figure 2. Fuel is delivered to this control 
under pressure from a pressure-type metering control (not shown). The 
fuel flows through the inlet :and fills the manifold passage. From the 
manifold passage the fuel flows into the individual manifold branches 
and through the branch metering Jets and the downstream pressure-
regulating valves to the individual branch discharge nozzles. Fuel 
also flows from the manifold passage into the pilot branch, through 
the pilot metering Jet and the pilot regulator jet, to the pilot 
di scharge nozzle. 
By means of the pressure-equalizing passage, the static pres-
sures in the individual chambers A are maintained equal. The 
cont rol diaphragms that separate chambers A and B position the 
downstream pressure-regulating valves until the pressures in cham-
bers B are equal to the pressures in chambers A. 
If t he branch discharge-nozzle pressures are equal to the 
pilot discharge-nozzle pressure, the stati c-pressure drop across 
each of t he downstream pressure-regulati ng valves wi l l be equal 
to the stat ic-pressure drop across the pilot regulator jet. The 
open area of the valves will then be proportional to t he area of 
the pilot regulator jet and this area will remain fixed at all 
fuel f lows. If any one branch discharge-nozzle pressure should 
rise above the pilot discharge-nozzle pressure, the downstream 
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NACA RM No. E8C08 CONFIDENTIAL 3 
pressure-regulating valve in the branch supplying that nozzle would 
have a reduced static-pressure drop and would move to a position of 
larger opening. If any one branch discharge-nozzle pressure should 
fall below the pilot discharge-nozzle pressure, the reverse would 
occur. In either case the static-pressure drop acrose the branch 
metering jet remains equal to the drop across the pilot metering 
jet and the fuel distribution is undisturbed. 
The pilot discharge nozzle can supply fuel to the engine in 
the same manner as the branch discharge nozzles. Because of the 
dependence of the entire system, however, on the flow in the pilot 
branch, it may be advisable to return the pilot flow to the fuel 
tank as indicated in figure 2. 
EXPERIMENTAL MODEL, APPARATUS, AND PROCEDURE 
Experimental model. - A photograph of the experimental model 
of the four-branch fuel-distribution control used in the bench 
investigation Is shown in figure 3. The control diaphragms are 
mounted on four faces of a cube. In operation, the control is so 
mounted that the control diaphragms are each in a vertical plane, 
which eliminates the effect of the valve-plug weight on the pres-
sure in chaI!l.ber B. Other arrangements can be used but the weight 
of the plugs must always be made to act in the same direction on 
all the valves. The pilot metering and regulator jets are in a 
separate hOUSing, which is not shown in figure 3. 
Matching of metering jets. - The metering Jets used in the 
experimental model were drilled and then placed in a Navy-type 
orifice comparator. (See reference 1.) While in the comparator, 
the four jets were matched by polishing with crocus cloth. After 
the jets were matched on the comparator, a flow check was made 
with naphtha. The results of the flow check (fig. 4) show that 
the four jets, which were matched in the comparator, give nearly 
the same flows over a wide range of metering heads. 
Bench apparatus. - The apparatus used with the experimental 
model of the fuel-distribution control is schematically shown in 
figure 5 and photographically shown in figure 6. Total fuel flow 
to the fuel-distribution control was measured with a rotameter 
having a range of 200 to 2000 pounds per hour. The fuel flowing 
in each branch passed through a rotameter having a range of 40 to 
200 pounds per hour. Above a total fuel flow of 800 pounds per 
hour, therefore, only the total-flow rotameter could be used. 
From the branch rotameters the fuel was discharged through four 
CONFIDENTIAL 
4 CONFIDENTIAL NACA RM No. E8C08 
diaphragm-operated, spring-loaded nozzles. One of the four noz41es 
was vented to a variable-pressure air line in order that its dis-
charge pressure could be varied . A well-type mercury manometer was 
used to measure the discharge-nozzle pressure. 
The four branch rotameters were calibrated in series after 
installation on the bench apparatus. The calibration was recorded 
by plotting the float position of each rotameter in millimeters 
against the fuel flow in pounds per hour as indicated by one of 
the four rotameters. The fuel flow through the pilot branch was 
measured with a rotameter having a range of 3 to 25 pounds per hour. 
The pressure drop across each of the metering jets was 
mea.sured with a 100-inch naphtha manometer. Each chamber B was 
connected to one tube of a bank of four tubes that was arranged 
as shown in figure 5. The differences in the level of the fuel 
in the four tubes indicated the differences in static pressure in 
the four chambers B and thereby the accuracy with which the down-
stream pressure-regulating valves were functioning. 
The fuel was naphtha having a specific gravity of 0.74 at 
a temperature of 700 F. 
RESULTS AND DISCUSSION 
Discharge-nozzle calibration. - The r1ischarge nozzles that 
were used in the bench runs on the experimental model were first 
operated on a manifold to determine the ability of the nozzles to 
distribute the fuel equally. The results of this calibration, which 
are shown in figure 7, indicate a maximum deviation of 30 percent from 
, perfect distribution. 
Performance of experimental model. - The bench performance of the 
experimental model of the fuel-distribution control is shown in fig-
ure 8. In the range of total fuel flow from 180 to 300 pounds per 
hour, the deviation of any branch flow from perfect distribution was 
no greater than 2 percent. Above a total fuel flow of 320 pounds 
per hour, the deviation was less t han 1 percent. Although branch~ 
rotameter ranges limited the maximum recorded branch fuel flow, use 
of the total-flow rotameter alone extended the total -fuel-flow range 
to the limit of 1260 pounds per hour imposed by the bench apparatus. 
Comparison of the pressures in chambers B indicated that the same 
accuracy of control was maintained over this additional range. Com-
parison of the results shown in figures 7 and 8 clearly indicates 
the marked improvement that can be obtained with this type of auto-
matic fuel-distribution control. 
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NACA RM No. E8C08 CONFIDENTIAL 5 
In order to demonstrate the ability of the experimental model 
to compensate for uneven nozzle pressures, the discharge pressure 
of one of the four nozzles was varied from 3 to 13.8 inches of 
mercury gage while the three others were kept at an approximately 
constant pressure of 11.3 inches of mercury gage. The flow through 
the control was kept constant at 370 pounds per hour. The results 
of this run, which are given in figure 9, show that the branch fuel 
flow remained constant within 3 percent over the entire range of 
nozzle pressures from 3 to 13.3 inches of mercury gage. Above a 
pressure of 13.3 inches of mercu~ gage, the downstream pressure-
regulating valve in that branch began to lose control. The fuel-
distribution control can be made to compensate for a much wider 
range of uneven nozzle pressures at any pressure level by altering 
the dimensions of the downstream pressure-regulating valve and the 
size of the pilot regUlator jet. 
SUMMARY OF RESULTS 
A study of an experimental model of a fuel-distribution control 
for gas-turbine engines gave the following results: 
1. The experimental model oontrolled the fuel flow to four 
unmatched discharge nozzles within +2 percent of perfect distri-
bution at a total flow of 180 to 1260 pounds per hour. 
2. The experimental model maintained the fuel flow through 
a discharge nozzle within 3 percent of a constant value while the 
discharge-nozzle pressure was varied from 3 to 13.3 inches of 
mercury gage. 
Flight Propulsion Research Laboratory, 
National Advisory Committee for AeronautiCS, 
Cleveland, Ohio. 
REFERENCE 
1. Anon.: Instruction Manual D-3217 for Operation of Orifice 
Comparator - Navy Type Model III, Bureau of Aeronautics. 
Instruction Manual D-3217, The Mariam Instr. Co. (Cleveland), 
Jan. 10, 1944. 
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6 CONFIDENTIAL NACA RM No. ESCOS 
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Figure I. - Schematic diagram of control elements in apparatus for main-
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Figure 6. - Photograph of apparatus used with experimental model of fuel-
distribution control. 
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total fuel flow, 370 pounds per hour. 
CONFIDENTIAL 
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A Fuel-distribution Control for Gas-turbine Engines

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