The digital electronic engine control (DEEC) system installed on an F100 engine in an F-15 aircraft was tested. The DEEC system incorporates a closed-loop air start feature in which the fuel flow is modulated to achieve the desired rate of compressor acceleration. With this logic the DEEC equipped F100 engine can achieve air starts over a larger envelope. The DEEC air start logic, the test program conducted on the F-15, and its results are described

Burcham, F. W., Jr.

English

NASA Technical Reports Server

I-- 
Paper 8 
AIRSTART PERFORMANCE OF A DIGITAL ELECTRONIC 
ENGINE CONTROL SYSTEM ON AN FlOO ENGINE 
Frank W. Burcham, Jr. 
NASA Ames Research Center 
Dryden Flight Research Facility 
Edwards, California 
SUMMARY 
The ability to achieve reliable and rapid airstarts is an important feature of an 
engine. Engine shutdowns may occur as a result of nonrecoverable stalls or over- 
temperatures. The airstart logic in the engine control system meters fuel to the 
combustor to achieve combustor light off, and then to accelerate the compressor. If 
the fuel flow is too high, the compressor will stall, resulting in a hot start. If 
the fuel flow is too low, the compressor will not accelerate, resulting in a hung 
start. The allowable fuel flow range between the hot start and the hung start may be 
very small, particularly for turbofan engines. Most engine control systems have an 
open-loop airstart system in which the fuel flow is preprogrammed as a function of 
time. Due to the normal variations between engines, the control system tolerances, 
and differences in fuel characteristics, these airstarts are not always successful. 
The NASA Ames Research Center's Dryden Flight Research Facility (DFRF) has 
recently tested the digital electronic engine control (DEEC) system installed on an 
FlOO engine in an F-15 airplane. The DEEC incorporates a closed-loop airstart fea- 
ture, in which the fuel flow is modulated to achieve the desired rate of compres- 
sor acceleration. With this logic, the DEEC-equipped FlOO engine is capable of 
achieving airstarts over a larger envelope. This paper describes the DEEC airstart 
logic, the test program conducted on the F-15, and the results. 
127 
https://ntrs.nasa.gov/search.jsp?R=19860015879 2020-03-20T15:28:26+00:00Z
AIRSTART LOGIC 
In the event of an engine shutdown or flameout, the DEEC monitors several param- 
eters to ensure a successful airstart. A simplified block diagram of DEEC airstart 
logic is given in the following figure. An open-loop fuel scheduling routine is used 
until the burner "light" (fuel mixture ignition) is indicated by a rise in the fan 
turbine inlet temperature (FTIT) signal. Once the burner light has been detected by 
the DEEC, fuel flow (WF) and the compressor bleed control switches to the closed-loop 
logic shown in the figure. This logic attempts to maintain a desired core rotor 
speed (N2) rate by varying fuel flow. The desired N2 rate is a function of fan inlet 
static pressure (PS2), fan inlet total temperature (TT2), and N2. If the fuel flow 
is too high, the compressor will stall, resulting in a hot start. If the fuel flow 
is too low, the available energy will not be sufficient to overcome the losses in the 
engine and the accessory power drain, resulting in a hung start. The DEEC airstart 
logic maintains the optimal N2 rate subject to a bias if FTIT exceeds a limit of 
approximately 760' C. The minimum fuel flow set by a stop in the fuel metering valve 
is approximately 115 kglhr. The compressor bleeds are held open until 56 percent N2 
is attained. 
The jet fuel starter (JFS) may also be used to assist in airstarts. The JFS is 
an auxiliary power unit that may be connected to the N2 rotor via a gearbox. It is 
normally used for ground starting and may also be used for airstarts below 6100 m. 
For JFS-assisted airstarts, the DEEC uses a higher scheduled N2 rate and a higher 
FTIT limit. 
DEEC Airstart Logic 
COMPRESSOR 
START BLEED 
DFRF83-538 
PS2 
M- 
N.2 aN'2 FTIT 
SCHEDULES TO FUEL FLOH BIAS 
128 
SPOOLDOWN AIRSTART AT 250 KNOTS 
The next figure is a time history of a DEEC 40-percent spooldown airstart at an 
airspeed of 250 knots and an altitude of 9100 m, which also illustrates the use of 
closed-loop airstart logic. The power lever angle (PLA) was moved to the on/off 
position to shut down the engine at time (t) = 10 sec. Immediately after shutdown 
there was a corresponding drop in core speed (N2), fan turbine inlet temperature 
(FTIT), and fuel flow to the engine. The pilot initiated the ignition sequence by 
moving the throttle up over the idle detent to the idle power setting at t = 22 set 
as the core rpm reached 40 percent. At this point the fuel flow began at the minimum 
value of 115 kg/hr. At t = 31 set, the fuel mixture was ignited (light) as noted by 
the increase in FTIT. The DEEC closed-loop logic modulated the fuel flow to achieve 
the desired rate of acceleration of the engine core. N2 increased uniformly to 
t= 45 set, then increased more rapidly. Idle speed was reached at t = 77 sec. FTIT 
varied between 450' C and 520' C during the airstart. The time required for the ail- 
start, defined as the difference between idle and pressurization times, was 55 sec. 
129 
DEEC Airstart DFRF83.532 
WF, 
kq/hr 
FTIT, 
OC 
40 Percent Spooldown 
250 Knots 
r SHUTDOWN ;/--PRESSURIZ.ATIOt /- IDLE 
500 - - LIGHT 
0 
,J4- 
I 
1ono - 
- 
0  I I I 
80 
N2 , 
percerl t 
60 
40 
20 
0 4-i--- fin - 
I 
PLA, 
dw 
4n = 
I I I I 
130 
AIRSTART AT 200 KNOTS AT 9250 METERS 
Airstarts at lower airspeeds took longer, 
inlet flow and lower burner pressures. 
due to the reduced energy of the 
The figure below shows a 40-percent spool- 
down airstart at an airspeed of 200 knots and an altitude of 9250 m. Shutdown time 
was t = 12 set, pressurization at t = 23 set, light at t = 32 set, and idle at 
t= 108 sec. Airstart time was 86 sec. The FTIT reached 600' C at t = 38 set, with 
the fuel flow on the minimum flow stop. 
DEEC Airstart 
40 Percent Spooldown 
200 Knots 
DFRF83.530 
I /-PRESSURIZATIQN IDLE 7 
60 
N2. 
per-c en t 40 
20 
80 
PLA. 
deq 
40 
40 60 80 100 120 
t, set 
131 
AIRSTART AT 200 KNOTS AT 4600 METERS 
A DEEC 40-percent spooldown airstart at 200 knots, at an altitude of 4600 m, 
is shown below. Shutdown occurred at t = 9 set, pressurization at t = 15 set 
and light at t = 23 sec. Following the light, the N2 continued to decrease for 
10 set as fuel flow was increased. At t = 40 set, a positive N2 rate was achieved 
and fuel flow was cut back as FTIT reached 600' C. In the time between t = 50 set 
and 70 set, oscillations in N2, FTIT, and WF occurred indicating that the gains in 
the closed-loop control logic were slightly high. The airstart continued and idle 
was reached at t = 104 set, for an airstart time from pressurization to idle 
(T) = 89 set, slightly longer than the 86 set time from the previous figure at the 
higher altitude but a similar airspeed. 
DEEC Airstart 
40 Percent Spooldown 
200 Knots 
l- SHUTDOVN 
PRESSURIZATION 
,-LIGHT 
IIF, 
kg/hr 
I I I I I 
0 
1000 -
FTIT, 
OC 
N2, 
percent 
80 - 
PLA, 
deg 40 - 
1 <, I I I I 
DFRF83-531 
I 
120 0 20 40 60 80 100 
t, set 
132 
JFS-ASSISTED AIRSTARTS 
For more rapid airstarts at altitudes below 6100 m, the jet fuel starter was 
used for assisted airstarts. The figure below shows a time history of a JFS-assisted 
airstart at calibrated airspeed (VC) = 255 knots at an altitude of 6100 m. Shutdown 
occurred at t = 11 set and the JFS was engaged at t = 33 -set at an N2 of 25 percent. 
The N2 increased as a result of the JFS assist and stabilized at N2 = 32 percent. The 
pressurization was delayed for this test until stable JFS motoring speed was observed 
at t = 68 sec. After the light at t = 79 set, N2 increased rapidly and idle was 
achieved at t = 106 set for an airstart time of 38 sec. 
DFRF88533 
DEEC JFS Airstart 
255 Knots 
SHUTDOWN JFS DISENGAGEMENT 
r 
500 - /JFS ENGAGEMENT 
LIGHT 
WF, 
kg/h- o 
PRESSURIZATI'IN 
-l 
I I I 
1000 
FTIT, 
500 
OC 
60 
N2, 
percent 40 
PLA, 
deg 40 
I 1 I 
40 60 
t. set 
f 
133 
JFS-ASSISTED AIRSTART AT 210 KNOTS 
A JFS-assisted airstart at a lower speed of VC = 210 knots and at an altitude of 
6100 m.is shown below. Shutdown occurred at t = 14 set, JFS engage at t = 34 set, 
pressurization at t = 36 set, and light at t = 46 sec. The N2 rate was reduced to 
nearly zero at t = 65 set prior to JFS disengage. Following the JFS disengage an 
increase in N2 rate occurred. The airstart was completed at t = 83 set, for an air- 
start time of 47 sec. 
All JFS-assisted airstarts attempted were successful from VC = 400 knots to 
200 knots over a wide range of altitudes. 
DFRF83-534 
DEEC JFS Airstart 
210 Knots 
WF , 
kg/h- 
FTIT, 
cc 
N2, 
percent 
PLA, 
deg 
500 
0 
80 
0 
80 
40 
- .IFS ENGAGEMENT 
0 20 4n 60 80 100 
t, set 
134 
__--_.. _ .._ _ .__ ,.. __ _. -. _..--.~_ 
I::- 
SUMMARY OF AIRSTART TIMES 
Airstart times - T - for the DEEC airstarts are shown in the figure below for the 
40-percent spooldown airstarts, for the 25-percent spooldown airstarts, and for JFS- 
assisted airstarts. Airstart times for the 40-percent spooldown airstarts were 
approximately 50 set at VC = 250 knots, 85 set at VC = 200 knots, and up to 192 set 
at VC = 175 knots. For the 25-percent spooldown airstarts, times were approximately 
65 set at VC = 250 knots, and from 97 set to 135 set at airspeeds of 205 knots to 
210 knots. It is clear that airstarts at VC = 200 knots are only marginally SUC- 
cessful, due to the long start times. 
EFFECT OF AIRSPEED 
AND ALTITUDE ON AIRSTART TIMES 
DFRF 62-260 
130 - 
ALTITUDE, ft 
120 - 
90 - 
AIRSTART TIME, 
set 80 - 
70 - 25 % SPOOLDOWN 
80 - 
30 
150 175 200 225 250 275 300 325 350 
AIRSPEED, kts 
135 
I I III ll11 I lllllll llllll llllll llllIIll III 
HUNG AIRSTART 
At airspeeds below 200 knots, most of the spooldown airstarts were unsuccessful. 
The unsuccessful airstarts were mostly hung starts in which the N2 either decreased 
or did not increase. A typical example of a hung start, shown in the figure below, 
is a 25-percent spooldown airstart attempt at VC = 180 knots at an altitude of 7600 m. 
Following the light, N2 increased very slowly to 28 percent and then stabilized. The 
fuel flow remained on the minimum flow stop; FTIT initially exceeded 600' C and then 
slowly decreased. 
DEEC Hung Airstart 
DFRF63.535 
25 Percent Spooldown 
180 Knots 
/- SHLlTDO!JN 
PRESSURIZATION 
500 -- LIGHT 
WF, 
kg/hr 
FTIT, 
OC 
80 
60 
N2, 
percent 
40 
20 
L 
t, set 
136 
HOT START 
Only one hot start occurred in the airstart test; it is shown in the figure 
below. It was a 40-percent spooldown air-start attempt at VC = 160 knots at 7600 m. 
Following the burner light at t = 35 set, N2 continued to decrease, while FTIT 
increased rapidly, even with the fuel flow at the minimum value, indicating a stalled 
compressor condition. When the FTIT reached the maximum allowable value of 800' C, 
the pilot shut down the engine. 
DEEC Hot Start 
DFRF63-536 
40 Percent Spooldown 
160 Knots 
r 
SHUTDO!IN 
PRESSURIZATION 
500 
WF, 
ka/hr k- 
LIGHT 
f 
SHUTDOWN 
0 
1c)oo 
FTIT, 
OC 
500 
pK 
1( 
I 
0 
80 - 
60 - 
N2, 
percent 40 - 
2. -\;, 
0 
80 
PLA, 
deq 
40 - 
I 
0- 
I 
20 40 60 
t, set 
137 
I Ill1 II llllll ll lll IIIII I I I 
SUMMARY OF AIRSTART SUCCESS 
A summary of the DEEC spooldown airstart success is shown in the figure below. 
All DEEC airstarts at and above 200 knots were successful, both for 25-percent and 
40-percent spooldown airstarts. This capability represented a 50-knot to loo-knot 
improvement over the standard FlOO engine handbook limit. 
DEEC SPOOLDOWN AIRSTARTS DFRFW270a 
40x103 
30 
ALTITUDE, 2. 
FT 
0 
- 
n - A’RSTART AT 40% 
u - A’RSTART AT 25% 
OPEN SYMBOL - SUCCESSFUL 
SOLID SYMBOL - UNSUCCESSFUL 
- 
FlOO LIMIT 
I I 
.2 .4 .6 .6 1.0 
MACH NUMBER 
N2 
N2 
138 
II 
CONCLUDING REMARKS 
The summary of the DEEC airstart capability of an FlOO engine equipped with 
a DEEC is shown below. 
logic was very effective. 
The DEEC airstart capability with the closed-loop control 
All airstarts at 200 knots and above were successful, a 
50-knot to loo-knot improvement over the standard FlOO engine. Airstart times for 
spooldown airstarts ranged from 50 set to 70 set at 250 knots to.80 set to 130 set at 
200 knots. All JFS-assisted airstarts were successful at airspeeds between 170 knots 
and 400 knots. At speeds below 200 knots, most of the airstarts were unsuccessful, 
as expected, due to hung starts. 
Summary DFRF83437e 
DEEC closed-loop airstart logic effective 
All airstarts at airspeeds of 200 knots or greater were 
successful, 50 to 100 knot improvement over 
standard FIOO 
Airstart times between 50 to 70 set at 250 knots and 
80 to 130 set at 200 knots 
All JFS-assisted airstarts were successful 
Unsuccessful starts at airspeeds of 175 knots 
and below, as expected 
139 


Airstart performance of a digital electronic engine control system on an F100 engine

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server