AC 76-01
Technical Support Report for Regulatory Action
Alternative Derivations of the Standards for T5
(Supersonic Transport) Class Gas Turbine Aircraft Engines
January, 1976
Notice
Technical support reports for regulatory action do not necessarilv
represent the final EPA decision on regulatory issues. They are intended
to present a technical analysis of an issue and recommendations resulting
from the assumptions and constraints of that analysis. Agency policy
considerations or data received subsequent to the date of release of
this report may alter the recommendations reached. Readers are cautioned
to seek the latest analysis from EPA before using the information contained
herein.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management
U.S. Environmental Protection Agency
-------
Abstract
This document contains five alternative approaches to the development
of standards for emissions from T5 class (supersonic transport) aircraft
engines. Four of these approaches attempt to comply with EPA's earlier
stated intention to set standards that "will represent the same level of
emissions reduction from current supersonic aircraft, through application
of the same types of combustor design technology, as will be required of
subsonic aircraft,..." (Preamble to Aircraft Standards, FR Vol. 38, No.
136 19088). Three of these approaches are found faulty by not imposing
on the T5 class "the same types of combustor design technology, as will
be required of subsonic aircraft." The fourth approach satisfactorily
imposes the implementation of a common, acceptable technology. A fifth
approach is investigated which attempts to set standards which are com-
patible with the constraint of requiring compliance in 1979 or shortly
thereafter.
Prepared by:
Approved by:
Alii!
Richard W. Hunt, SDSB
W. Houtman, Program
Manager, Aircraft
Approved by:
Charles Gray, Chief
SB
iCTD
P. DeKany", Directo/,
Distribution:
-------
Introduction and Summary
At the time of promulgation of the aircraft emissions regulations,
EPA established a separate class of engines to include only those engines
that were intended for supersonic flight. This was done because of the
realization that the special characteristics of supersonic flight required
an engine design that would have a large fuel penalty at low speed which
would, in turn, produce large emissions. EPA further stated its intent
in the preamble to the aircraft regulations to set standards for the T5
class that "will represent the same level of emissions reduction from
current supersonic aircraft, through application of the same types of
combustor design technology, as will be required of subsonic aircraft,
though the absolute hydrocarbon and carbon monoxide levels will be
several times higher". (FR Vol. 38, No. 136, 19088)
This report first analyses four approaches which attempt to establish
standards for both newly manufactured and newly certified engines which
are based upon an equivalent technology between the two classes. One
approach is found to satisfactorily comply with EPA's earlier stated
intent to establish standards for the T5 class based upon the application
of the same combustor technology in both the T5 and T2 classes.
A brief analysis of the lead time necessary to implement this
technology is included in the report as Appendix B. This analysis shows
that the sophisticated technology that is characteristic of the solutions
to the T2 class emissions problem cannot be incorporated into newly
manufactured T5 class engines (in particular, the Olympus 593) until
1982. This delay of three years from the original 1979 deadline (for
newly manufactured engines) in the Notice of Proposal Rulemaking (FR
Vol. 39, No. 141, P26653, 1974) would severely compromise the usefulness
of the standards if the total production of these aircraft does not
exceed forty or fifty aircraft as most or all of the aircraft would have
been built by the time the standards went into effect. In that event
the newly manufactured engine standards, despite their stringency, do
not accomplish any useful air quality gain.
The primary reason for this long leadtime is that without the
benefit of a fixed goal (standards) the manufacturers have been directing
their efforts for newly manufactured engines (NME) towards the development
of a simple and inexpensive, but relatively effective fix (insofar as
hydrocarbons and carbon monoxide are concerned). The technology involved
in this does not in any way approach the sophistication of the best
concepts being pursued for T2 class engines which are very effective in
controlling all three gaseous pollutants, hydrocarbons (HC), carbon
monoxide (CO), and oxides of nitrogen (NOx). As a consequence, the
manufacturers would be forced to start all over again if the NME standard
were based upon the equivalent technology criterion.
The report then examines an alternative approach which is to
consider promulgating NME standards consistent with that development
already being pursued by the manufacturers. Because this work has
-------
-2-
always been directed towards the T5 engine and because it involves
simple modifications which result in easier optimization, simple tooling
changes, and simple qualifications, it is likely to be available by 1979
or 1980. This would then result in air quality benefit despite the
lessening of the standards for newly manufactured engines because they
would affect some aircraft even if the total production run were as few
as forty or fifty. The standards for newly certified engines (NCE)
would be those found to be consistent with the equivalent technology
criterion and would be therefore the most rigorous that can be satisfied
through adoption of the best technology expected for those engines.
This is the approach that is recommended.
Discussion
I. Issue of Equivalent Technology
The T5 class (supersonic commercial transport aircraft) was created
in recognition of the special characteristics of supersonic flight which
create significant problems in the development of an engine for such
aircraft which is both economically acceptable and clean enough to meet
the T2 class (subsonic commercial transport aircraft) emissions standards
as promulgated in 40 CFR part 87.
The special characteristics which give rise to the emissions problem
of supersonic transports (SST) can be seen in the following discussion.
The standard used to describe aircraft engine emissions may be interpreted
as comprised of two multiplicative terms, one representative of the
combustor performance (in terms of mass of pollutant per mass of fuel),
and the other descriptive of the fuel consumption efficiency of the
engine (in terms of mass of fuel per level of useful output), both terms
being weighted over the prescribed landing-takeoff cycle;
standard = (combustor performance) x (fuel consumption
performance)
or
standard = mass of pollutant x mass of fuel
mass of fuel useful output
= (Emissions Index or "El") x (Specific Fuel
Consumption or "SFC")
or, simply,
, , mass of pollutant (called "EPAP")
standard = j:c-
useful output
Compliance with the standard can thus be approached in two ways,
(1) by improvement of the combustor performance, and (2) by improvement
of the fuel consumption efficiency at lower speeds. The latter approach
-------
-3-
is accomplished principally by modification of the thermodynamic cycle
of the engine, that is, modification of the compressor pressure ratio
and the fan bypass ratio, and in the T5 class, especially, the degree of
afterburning.
However, high speed flight (supersonic, especially) conditions
require additional considerations for optimal fuel economy. The optimum
thermodynamic cycle for an engine is a function of the aircraft's cruise
speed, its aerodynamic efficiency, and its mission (design range) such
that the cycles that promote high speed fuel efficiency are generally at
odds with those that promote low speed fuel efficiency. The following
brief discussion will expand upon this. The overall efficiency of the
engine (the ratio of the useful power to the rate of energy input into
the engine through the fuel, can be written as
ex °° °° Thrust x flight velocity
o fQ heat release rate
where
U = average velocity of the exhaust gases
U = flight speed
fQ = heat release rate of the fuel (a constant at the design
point of the engine)
This efficiency is zero at a zero flight speed (no useful power is being
developed), zero again at U = U (thrust has gone to zero), and a
maximum at U^ = U /2. At high subsonic speeds, optimum efficiency is
achieved through the use of a large fan which produces a low exhaust
velocity (U ). Further, at low subsonic speeds, a propeller is used
(turboprop) which produces a very low exhaust velocity thereby keeping
the efficiency high. For supersonic speeds, on the otherhand, the U
produced by a large fan is too low compared to the flight speed (U^) to
give high efficiency. In fact, if U^ > U , the thrust of the engine
goes to zero because, roughly,
Thrust = Ma (U - U )
ex °°
(Ma = air mass flow rate through engine)
This, of course, is the reason that the efficiency goes to zero also at
this point (U = U ). It is therefore imperative that at supersonic
speeds, the exhaust velocity (U ) be increased. This is done by reducing
See, e.g., "Mechanics and Thermodynamics of Propulsion," by P.G. Hill
and C. Ro Peterson, Addison-Wesley, 1965, pp. 143-145.
-------
-4-
the fan size (perhaps to zero, a pure turbojet) and relying instead upon
the hot core flow for thrust where U is much greater. This is the
primary reason for reducing or eliminating a fan for supersonic flight.
Secondarily, the size and weight of the fan offer large drag penalties
at flight speeds in excess of Mach 1.
The second significant thermodynamic problem at high speed is that
as the ram compression heats the air in addition to the compressor
heating, the point would be reached that the air entering the combustor
is already at the maximum allowable turbine inlet temperature, thereby
permitting no fuel to be added. It is necessary, therefore, to reduce
the amount of compression from the compressor to reduce the combustor
inlet temperature enough to permit proper energy addition from the fuel.
The disparity between the high and low speed design conditions
becomes greater as the spread between the high speed and the low speed
widens: For supersonic flight the loss of high speed efficiency with the
use of a subsonic cycle (high pressure ratio, high bypass ratio) is of
such a magnitude (at best, a JT9D engine operating at Mach 2 is only 56%
as efficient in terms of specific fuel consumption as an Olympus 593
engine designed specifically for Mach 2; this large and heavy engine
would also cause aerodynamic problems) that there is little room for
compromise and, the high speed cruise condition wherein the bulk of the
fuel is consumed essentially dictates the engine design. On the other
hand, the use of a good supersonic cycle (moderate pressure ratio, low
or no bypass ratio) performs with mediocre efficiency at low subsonic
speeds (at take-off, with afterburner, the efficiency of the SST is one-
fourth the efficiency of a B-747) as encountered at or near the airport.
This high fuel consumption contributes directly to the high emissions
levels of this aircraft. For this reason there is considerable advantage
to the variable cycle engine concept which is at this time only in early
stages of exploration.
Without the existence in the near future of a variable cycle engine
(VCE), a SST engine is necessarily constrained to optimize its engine
cycle at or very near its cruise condition. Improvements in its emissions
then can be realized only through improvements in its combustor emissions
performance. In view of the low speed fuel consumption penalty experienced
by SST engines (when compared with subsonic engines), such improvements
in the combustor performance would have to be much greater than that
necessary for subsonic engines if both supersonic and subsonic engines
had to meet the same standard. ' This would imply the use of a much more
sophisticated control technology on the part of the SST engine.
There is, however, one critical factor which weighs against the
imposition of too sophisticated an emission control technology for the
T5 class: There is a practical limit to which one can go in utilizing
advanced technology in an existing system (speaking now of the standards
for newly manufactured engines) . Radical innovations may not mate well
with the existing system, causing degradation in performance or major
renovation of large parts of the engine. Such radical advances in
emissions technology belong more reasonably in totally new engines or
engines for which major features are being redesigned. This is the
intent behind the separate standards for newly certified engines.
-------
-5-
The philosophy first considered is to determine the SST standards
based upon the application of a common, available and acceptable com-
bustion system technology applicable to all large engines. This satis-
fies the requirement of the technical limitations imposed by the systems.
This philosophy is also expounded in the preamble to the T5 class NPRM:
"These standards will represent the same level of emissions
reduction from current supersonic aircraft, though application of
the same types of combustor design technology, as will be required
of subsonic aircraft, though the absolute hydrocarbon and carbon
monoxide levels will be several times higher ...."
There remains then, the question of what standards for the T5 class
best represent the "application of the same types of combustor design
technology." There are four readily identifiable strategies for computing
standards for the T5 which are based on some sense of equivalency.
These will be discussed individually below.
Alternative I
Set T5 standards identical to the T2 standards.
This approach assumes the argument that the two types of aircraft,
commercial subsonic and supersonic, perform the same function, are
directly competitive, and hence ought to meet the same standards.
Referring to 40 CFR part 87.21 (d) and (e), the standards are then:
EPAP mass of pollutant *
useful out
HC CO NOx
NME** 0.8 4.3 3.0
NCE*** 0.4 3.0 3.0
* pounds of pollutant per 1000 pounds-thrust x hours per
LTD cycle LTO = Landing-Takeoff)
** Newly Manufactured Engines - date of implementation discussed
in Appendix B.
*** Newly Certified Engines - date of implementation discussed in
Appendix B.
TABLE I
However, this approach totally fails to recognize the existence of
the T5 class. The issue of fuel consumption and combustor performance
differences between the T2 and T5 classes are ignored entirely. It is
therefore, technically unacceptable from the start.
-------
-6-
Alternative II
- Require the same Emission Indices (Ibs. of pollutant/1000 Ibs. of
fuel) for supersonic engine combustors as are expected to be found in
future subsonic engines and set the T5 standards accordingly, accounting
for the increased fuel consumption characteristics of the SST type
engines that result from the requisite thermodynamic cycle. Add after-
burner contribution separately.
By this approach, for the main burner,
EI(T5) = EI(T2)
The bars over the values indicate values averaged over the LTOf/cycle.
Then, as the standard can be written as
EPAP = El x SFC,
the T5 standards would be
EPAP(T5) = EPAP(T2) x -
EI(T2) SFC(T2)
or, because of the equality indicated by equation (1),
EPAP (T5) = EPAP (T2) x SFC(T5)
SFC(T2)
The LTD weighted SFC will differ from engine to engine, being a
function of individual engine characteristics (e.g., idle speed) and the
thermodynamic cycle of the engine (i.e., pressure ratio and bypass
ratio), and can be represented approximately by an empirical expression
valid for a large range of turbine engines (offered by Rolls Royce),
..
v '
_ _
(LTD cycle) 0.47 + 0.039 x PR + 0.19 x BR
where
BR = Bypass ratio, PR = Pressure ratio.
Considering the JT9D as representative of modern T2 class engines,
having BR = 5.2 and PR = 22.3, and taking the Olympus 593 as the T5
class engine, having BR = 0 (a pure turbojet) and PR = 15, the T5 SFC
will be 2.20 times the value of the T2 SFC. It is worth reiterating
here the discussion at the beginning that the cycle differences between
the T5 class which lead to this SFC problem are fundamental to the
design goals of the two classes: One engine (T2) is optimized for
subsonic cruise, the other (T5) supersonic cruise. If the EPAP value
for 'each of the three gaseous pollutants of the T2 standard is then
multiplied by 2.20, a T5 standard results. That is, the T2 1979 and
-------
-7-
1981 standards are
EPAP (T2)
HC CO NOx
1979 (NME) 0.8 4.3 3.0
1981 (NCE) 0.4 3.0 3.0
which when multiplied by 2.20 gives for the T5 class:
EPAP (T5) (less afterburner contribution)
HC CO NOx
NME* 1.8 9.5 6.6
NCE* 0.9 6.6 6.6
*Date of implementation discussed in Appendix B.
TABLE II
However, this calculation has not yet considered the contribution
of the afterburner to the emissions. The afterburner is separate from
the functioning of the main combustor and therefore must be considered
separately.
A certain degree of afterburner (20%) has been assumed for both the
1979 and 1981 standards which is based upon the present Olympus/Concorde
System. Without considerable advances in the propulsion system (e.g.,
variable cycle engine) or in the airframe (e.g., swing wing) such after-
burning is reasonable even for the newly certificated engine standards.
SNECMA has indicated that the present Olympus 593 afterburner has a
combustion efficiency of 98% and that expected improvements should bring
this to 99.0% which would be applicable to the newly manufactured engine
(NME) standards. A combustion efficiency of 99.5% is believed possible
for newly certified engines (NCE) although there has been little technical
development for an efficiency above 99..0% at this point. A combustion
efficiency less than 100% results in a mixture of hydrocarbons (HC) and
carbon monoxide (CO) in the exhaust. The afterburner apparently does
not contribute to the formation of NOx because of the leaner burning
(less elevated temperatures), lower pressures, and shorter residence
times.
Figure 1 (at the back) shows that for any given combustion efficiency
a wide range of EC/CO ratios can exist. However, as the data show,
there is a reasonably well defined mean. As the entrance conditions to
an afterburner are quite hot and partially depleted of oxygen, the CO/EC
ratio will be higher than that for a main burner at the same combustion
efficiency. The afterburner points used in this analysis and shown on
figure 1 reflect this fact. Rolls Royce's own recommendation assumed a
-------
-8-
CO/HC ratio of 9.2 (see Alternative V). For afterburners in newly
manufactured engines (n = 99.0%), a CO/HC ratio of 9.0 was chosen as
being most probable. From the circular point on the figure on the n =
99.0% line the emission indices are seen to be 3.4 and 30.4 for HC and
CO respectively (CO/HC = 9.0) in Ibs. per 1000 Ibs. of fuel for the
afterburner. For the Olympus 593, the afterburner fuel flow rate is
22,000 Ibs. per hour for a duration of 1.2 minutes. The total emissions
from the afterburner are then
El x M.. , x time
fuel
or
, . , , 22,000 1.2
Mass of HC = 3.4 x j-- x -~
= 1.50 Ibs.
and
Mass of CO = 30.4 x 2??°°° x ^
1,UUU ou
= 13.4 Ibs.
The total impulse of the engine over the LTO cycle (that is, the useful
output referred to in the denominator of the expression for the standard)
for the Olympus 593 is 3002 Ib-thrust x hours. (Note: the total impulse
of the engine, not simply the impulse due to the afterburner operation
must be used here so that these terms and the EPAP values found in Table
II can be added). Dividing the mass of each pollutant by the total
impulse x 10 gives the afterburner contribution to the EPAP. The same
procedure is followed for NCE but with an afterburner combustion efficiency
of 99.5% and a CO/HC ratio of 15. The afterburner contribution is:
Afterburner AEPAP (NME and NCE)
HC CO NOx
NME 0.5 ' 4.5 0
NCE 0.2 2.5 0
TABLE III
These AEPAP values for the afterburner must be added to the EPAP values
calculated for the main burner only given in table II. The T5 class
standards, then, by this procedure are
-------
-9-
EPAP (T5)
HC CO NOx
NME 2.3 14.0 6.6
NCE 1.1 9.1 6.6
TABLE IV
This method, however, must also be rejected as the supposition of
technological equivalence of combustor performance between subsonic and
supersonic engines cannot be defended in spite of the equating of the
Emission Indices. Emission Indices are generally considered to be
descriptive of the sophistication of the emission control technique
employed on a particular engine. However, the simple comparison of the
Emissions Indices found in two different systems is not adequate to make
a genuine comparison of the relative merits of the different technologies.
The reason for this is that operating conditions as well as technical
design affect the pollutant production. If two identical combustors
(thereby eliminating technology and size effects) are run at two different
operating conditions as reflected primarily by the combustor inlet
pressure for the same fuel-air ratio (to simulate the same engine power
setting), that combustor which is run at the higher pressure will exhibit
lower HC and CO Emission Indicies, but higher NOx Emission Indices. The
reason for this is that at higher inlet pressures (and the correspondingly
higher inlet temperatures): (1) the greater temperature and pressure
increase the chemical reaction rate of hydrocarbon combustion, (2) the
greater temperature leads to better fuel evaporation, and (3) the greater
pressure drop across the combustor leads to better mixing. These factors
reduce the pollutants that result from inefficient combustion, namely HC
and CO. On the other hand, the greater temperature and pressure increase
that reaction rate of NOx which leads to greater NOx formation.
In the case at hand, therefore, it may be expected that despite the
application of equivalent combustor technology, the lower inlet pressure
of the SST engine (and the correspondingly lower inlet temperature)
would make it more difficult to achieve a combustion efficiency at each
power setting comparable to that found in a typical modern high pressure
ratio subsonic turbofan (e.g., the Olympus 593 has a pressure ratio of
15, the JT9D, 22). A lower combustion efficiency would mean higher
levels of HC and CO (as expressed by the Emissions Index) in the Olympus
593. However, the Olympus 593 has a fairly lengthy combustor residence
time at low power compared with other engines. This would allow it to
better consume the HC and CO left as a result of the lower combustor
pressure. While combustor size (and hence residence time) may be considered
an emissions control technique for newly certified engines, ?t cannot be
so construed for newly manufactured engines as the geometries of such
engines are fairly well fixed. Hence, on one hand, the SST has an
operating cycle (pressure ratio) that lends itself to poor HC and CO
-------
-ID-
emissions, but on the other hand, its corabustor size is favorable to
good HC and CO emissions. Requiring equal Emissions Indices for HC and
CO between the T2 and the T5 class will not in itself result in equivalent
technology.
As far as NOx emissions are concerned, the lower pressure ratio of
the engine will contribute to low NOx production and the imposition of
equal Emissions Indices for NOx between the two classes is patently
favorable to the SST class.
Alternative III
Apply the percentage reductions to the T5 baseline EPAPs that have
been demonstrated or are expected to be demonstrated in the near future
in other engine applications.
ts
The following emissions reductions have been demonstrated or are
expected to be demonstrated shortly in typical modern subsonic engines
(newly manufactured engines):
EPAP (T2 NME)
Production HC CO NOx
JT9D 4.8 13.8 5.7
CF6-6 3.4 10.0 7.2
CF6-50 4.3 10.8 7.7
Average 4.2 11.5 6.9
Expected (No water) 0.8 4.3 3.8
% Reduction 80% 60% 55%
These reductions, if not already demonstrated, are expected on the basis
of development work, both in-house and public, which is now nearing
completion. Typical of this work is the NASA Experimental Clean Combustor
Program.
For newly certified engines, the following reductions are antici-
pated:
EPAP,(T2 NCE)
HC CO NOx
Average Production 4.2 11.5 6.9
Expected 0.4 3.0 3.8
% Reduction 90% 75% 55%
Support for the anticipated reductions for newly certified engines comes
largely from EPA Report No. 1168-1, Assessment of Aircraft Emission
Control Technology and from the present subsonic engine standards for
newly certified engines which reflect these anticipated reductions.
-------
-11-
Applying these percentage reductions to the baseline Olympus 593,
taken as representative of the T5 class engines, gives
EPAP(T5)
HC ' CO NOx
Baseline (main
burner only) 15.2 57.1 8.8
% reduction 80% 60% 55%
NME standard 3.4 22.8 4.0
% reduction 90% 75% 55%
NCE 1.5 14.3 4.0
TABLE V
As with Method 2, however, the afterburner contribution which is
not present in the T2 class must be considered separately. This contri-
bution is given in Table III and is discussed in detail in Section 2.
Adding the EPAP values from that table to Table V, gives
EPAP(T5)
HC CO NOx
NME* 3.9 27.3 4.0
NCE* 1.7 16.8 4.0
*Date of implementation discussed in Appendix B.
TABLE VI
This method should be rejected, however, because implicit in this
procedure is the assumption that the two baselines (subsonic and supersonic)
represent equal emissions technology levels. If this is not true and
the baseline of either group is founded upon a combustion system technology
different from that represented by the other group's baseline, then
simple application of percentage reductions would preserve that inequality
of technology in the standards set for the T5 class based upon that
procedure.
Furthermore, there is no assurance that changes in emission tech-
nology are adequately represented by percentage reductions in emissions.
That is, if a certain advance in technology yields some percentage
reduction in emissions from a representative engine of one group (e.g.,
subsonic), there is no assurance that this technology, if applied in a
representative engine of another class which has markedly different
operating environment (e.g., supersonic), will yield the same percentage
reduction. Standards based upon this procedure may then implicitly
generate a condition of inequality of technical demands on the combustors
between subsonic and supersonic engines.
-------
-12-
Alternative IV
Identify the best demonstrated or anticipated emissions control
technology that would be applicable to the T5 class, determine its
emissions performance (i.e., its Emission Indices) when operating in an
SST engine type environment (i.e., inlet pressure, air loading parameter,
etc.), account for the increased fuel consumption per unit output (specific
fuel consumption) due to the SST type thermodynamic cycle (i.e., pressure
ratio, bypass ratio) and set the standards accordingly. Add afterburner
contribution separately.
This description of the procedure warrants further explanation.
The four steps are, in order,
(a) Identify the best emissions control technology, demonstrated
or anticipated in any engine (as measured by the Emissions Indices of
the combustor subject to the particular operating conditions of the
engine), which is applicable to the T5 class.
(b) Determine the emissions performance of that technology concept
subject to the particular operating conditions of the representative T5
engine (as measured by the Emissions Indices).
(c) Determine the fuel consumption characteristic of the representa-
tive SST engine.
(d) Compute the emissions performance of the basic T5 engine using
(b) and (c) (as measured by the EPAP). Add the afterburner contribution
separately.
Each step is relatively straightforward and is discussed in detail
below.
(a) Identify the best emissions control technology (demonstrated
or anticipated).
HC and CO
There is considerable work being done now in support of low emissions
in all the classifications of engines for which regulations exist. The
work involving the large, commercial subsonic engines is most relevant
to the T5 class as the corabustor technology is generally transferable.
The major efforts here are those programs being conducted by the manu-
facturers and through the NASA Experimental Clean Combustor Program.
To identify the best available technology, it is insufficient
merely to specify the Emissions Indices experienced by test hardware.
Emissions Indices for all pollutants are functions not only of the
technology incoporated into the design, but also of the operating condi-
tions. This point was alluded to in earlier discussions of the first and
second method of calculation and must be analysed further here.
-------
-13-
Emissions of hydrocarbons and CO reflect incomplete combustion
generally at low power, an off design point. This incomplete combustion
occurs because the operating conditions of the combustor (temperature,
pressure, and residence time) are not conducive to good combustion. The
inlet temperature is too low and the air flow rate too low for good fuel
preparation (atomization and evaporation), the pressure drop across the
combustor is too low for good turbulent mixing of the fuel and air, and
the combustor temperature and pressure are too low for rapid chemical
reaction (especially CO -> C09). The ability of the combustor to perform
well can be described by one of several so-called "air-loading parameters",
all of which are empirical and equally good here. The one chosen for
use here was offered by Rolls-Royce Corporation in its response to the
T5 class NPRM. It is
fl (air loading parameter) = a
P1'8 V f (T)
where
f(T) - 10(0-°°143T)/3.72
V = combustor volume (ft )
P = combustor pressure (atm.)
M = air mass flow rate (Ibs/sec)
a
T = combustion inlet temperature ([K)
Smaller values of fi are more favorable to good combustion and hence
lower emissions of HC and CO. The value of ti experienced may depend on
several factors: (1) power setting (the higher the power setting, the
lower the air loading parameter), (2) engine design (a higher pressure
ratio engine will have a proportionally lower £2 at all power settings),
and (3) combustor design (a larger combustor volume would have a lower
air loading parameter). Except for the secondary effect of ambient
temperature, the combustor inlet temperature is directly related to the
compressor pressure ratio and hence is not an independent variable.
The emissions performance of a combustor can be correlated with the
value of the air loading parameter (with some scatter), as shown in
Figure 2. In the figure, the emissions performance is measured by the
combustion inefficiency (1-n) which is computable from the Emissions
Indices:
1-n = [ 0.875 EI(HC) + .2322 EI(CO)]x 10~3
where EI(HC) is in terms of CH,. This correlation holds true for all
engines of comparable emissions technology and thus it is a measure of
that technology.
-------
-14-
While the correlation line of Figure 2 shows the emissions performance
for the present day technology, a new correlation line is necessary to
measure the performance of an advanced emissions technology. Such a
line would be below the present technology line and is shown schematically
below:
Present
A
Advanced
f f
i-n
n
Figure 3 shows the new technology line (labeled "NME") that is-emerging
as a result of the studies and programs currently underway. This line
represents the upper bound of the performance achieved by actual combustor
rig tests of the NASA - General Electric double-annular combustor, the
present configuration of which has been designed for the CF6-50. It is
this demonstrated technology, then, that shall form the basis of the T5
standards calculated here, at least for newly manufactured engines.
Also, shown on Figure 3 is the anticipated technology line applicable
to newly certified engines (labeled "NCE"). This is quite advanced
technology and, as such, it has not been demonstrated. It is based upon
projections of the technology should be applicable to both in the 1980
decade. This technology should be applicable to both subsonic and
supersonic engines and is reflected in the T2 standards for newly certi-
ficated engines. The EPAP values of the T2 standards for newly certifi-
cated engines can be correlated with Emission Indices values and hence
combustion inefficiency by properly accounting for engine effects (SFC)
and pollutant formation characteristics (i.e., the vast bulk of HC and
CO are formed at idle, generally 95-99%). This is discussed in detail
in Appendix A.
NOx
NOx production (El) is closely correlated with combustor inlet
temperature for all conventional modern combustors (see Figure 4)
according to the work of Lipfert. An advance in NOx control technology
may be expected to lower this curve. Improvements at low power will not
be as significant as at high power because the greater combustion
efficiency at low power (resulting from efforts to reduce HC and CO
emissions) will increase the idle temperature (and, therefore, the NOx
production rate) enough to largely offset the low NOx characteristics of
the combustor. The NOx situation is shown below schematically.
-------
-15-
EI(NOx)
Present
Advanced
The demonstrated technology for NOx reduction shown in Figure 5 is
that which has been surpassed in rig tests in support of subsonic engine
emissions reduction. It does not rely on water injection at high power,
but relies, rather, on combustor design (lean burning).
Unlike the HC and CO situation, there is no technology line drawn
for newly certified engines (NCE) for in parallel with the T2 class
standards, the maximum identifiable control of NOx is established in
this approach in the newly manufactured engine standards.
(b) Determine the emissions performance expected of the T5 class
engine.
This follows quite readily from the results of step (a). For both
CO and HC on one hand, and NOx on the other, not only has the emissions
performance of the new combustors been identified, but technology lines
have been established (Figs 3 and 5). To find the emissions performance
of this low emissions technology when applied to SST engines, it is only
necessary to identify the operating points of that engine on the abscissa
of Figs 3 and 5 and record the associated combustion efficiency and
Emissions Index for NOx. To determine the Emissions Indices for HC and
CO from the combustion efficiency, refer to Fig 1. The set of Emissions
Indices for a given combustion efficiency is not unique (although the
converse is) so the most probable relationship, which is also shown on
the figure, should be taken.
It is necessary to identify properly the operating points of the T5
class engine. For HC and CO emissions, the operating point is determined
by the air loading parameter as discussed earlier. This parameter is to
a limited degree an independent variable. That is, given the engine
cycle (present ratio) and size (air mass flowrate), the designer is at
liberty to select the combustor volume V so as to reduce ft and thereby
improve the emissions performance. However, this freedom is limited by
other performance constraints on V, such as altitude relight. Hence,
within a band of considerable scatter, the fl limits of a given engine
are determined by the pressure ratio of the compressor (Figure 6). For
-------
-16-
the Olympus 593 in particular, the present idle value of the air loading
parameter, ft = 1.6, may be taken as representative of what will be found
in future versions of it and in new T5 engines (although it should be
expected that the designer will take full advantage of what leeway he
has in the selection of fi to reduce emissions).
Reading the combustion efficiency values from the "demonstrated
technology" lines for newly manufactured engine (NME) and certified
engines (NCE) from Figure 3 and the corresponding Emissions Index values
from Figure 1 gives the following results for each of the flight modes
of an SST engine:
T5 Class
Newly Manufactured Newly Certificated
»s
Mode HC CO HC CO
Idle 3.8 19.5 2.1 13.5
Takeoff* - 0.5
Climbout - 1.0
Descent 1.3 10.0 0.6 6.0
Approach 0.2 3.0 0.1 2.0
* Main Burner only
TABLE VII
For NOx emissions, the operating point is determined by the combustor
inlet temperature which for standard day sea level conditions is essen-
tially a unique function of the compressor pressure ratio by
T_ (combustor inlet temperature) = T , . . x
3 ambient
comp
+ 1
where n = compressor adiabatic efficiency which for large compressors
will lie between 0.7 and 0.9, depending on the spread between the design
point and the operating point in question. For the Olympus 593 (maximum
pressure ratio equal 15), the operating points are shown in Fig 5. The
Emissions Indices for the NOx at the various power settings of the LTO
cycle are, from 'Figure 5,
-------
-17-
T5 Class
Mode EI(NOx)
Idle 2.1
Takeoff 8.2
Clitnbout 6.8
Descent 3.1
Approach 4.6
TABLE VIII
(c) Determine the fuel consumption characteristic of the represen-
tative SST engine.
This information has been given to EPA by Rolls Royce, the manu-
facturer:
Olympus 593
Mode Thrust Fuel flowrate SFC Time in Mode (min.)
Idle 1,800 2,500 1.39 26
Takeoff* 32,000 28,000 0.88 1.2
Afterburner** 6,500 22,000 3.88 1.2
Climbout 25,000 20,000 0.80 2.0
Descent 5,800 5,200 0.90 1.2
Approach 13,100 10,000 0.76 2.3
* main burner only
** on during takeoff
TABLE IX
(d) Compute the emissions performance of the basic engine.
For each pollutant the EPAP can be calculated as follows from the
known quantities:
total pollutant formation per LTO cycle
(total impulse per LTO cycle/1000)
= EPAP , , + EPAP . ,
main burner afterburner
or
- t°tal pollutant formation by main burner
- (total impulse/1000)
total pollutant formation by afterburning
(total impulse/1000)
-------
-18-
The total impulse is given by
E Thrust x time
where the thrust and time values are given in Table IX. For the Olympus
593, the total impulse is 3002 pound thrust x hours. The numerator of
the first term of the EPAP expression, EPAP main burner, is given by
M
£
modes*
El x
fuel x time (hours)
1000
(* takeoff values exclude the afterburner)
Table X summarizes the results for the computation of the numerator. The
appropriate Emissions Indices are taken from Tables VII and VIII.
Newly Manufactured Engines (NME)
Mode
Idle
Takeoff*
Climbout
bescent
Approach
Fuel flowrate
2,500 Ibs/hr
28,000
20,000
5,200
10,000
Emissions Index
Time in Mode
26 rain
1.2
2.0
1.2
2.3
HC
3.8
0
0
1.3
0.2
CO
19.5
0
1.0
10.0
3.0
NOx
2.1
8.2
6.8
3.1
4.6
Mass per Mode
HC
4.11
0
0
0.14
0.08
CO
21.12
0.28
0.28
1.04
1.15
NOx
2.28
4.59
4.59
0.32
1.76
Total 4.33 23.87 13.48
Newly Certified Engines (NCE)
Mode
Idle
Takeoff*
Climbout
Descent
Approach
Fuel flowrate
2,500 Ibs/hr
28,000
20,000
5,200
10,000
Emissions Index
Time in Mode
26 min
1.2
2.0
1.2
2.3
HC
2.1
0
0
0.6
0.1
CO
13.5
0
0
6.0
2.0
NOx
2.1
8.2
6.8
3.1
4.6
Mass per Mode
HC
2.28
0
0
0.06
0.04
CO
14.63
0
0
0.62
0.77
NOx
2.28
4.49
4.53
0.32
1.76
Total 2.38 16.02 13.48
* Main burner only
TABLE X
-------
-19-
From the total pollutant formation by the main burner given in
Table X, division by the total impluse/1000 or 3.002 gives the EPAP
values for the main burner (Table XI):
EPAP (Main Burner)
HC CO ' NOx NOx + 10%
NME S1.4 8.0 4.5 5.0
NCE 0.8 5.3 4.5 5.0
TABLE XI
Although the calculated NOx EPAP value is 4.5, a 10% margin has
been added to account for certain anomolies in the NOx production charac-
teristics of these low HC and CO combustors. At lower power settings
(approach and below), the fuel staging which generally is employed in
such combustors is operating only on the primary injectors in order to
give a hotter flame to consume the HC and CO. This has the effect of
increasing the emissions index for NOx at those lower power settings,
thus distorting the shape of the technology line (Figure 5). This
effect has been examined in CF6-50 case and is roughly 10% of the EPAP
value.
The afterburner contribution must now be added to get the total
EPAP. This contribution is given in Table III. The total EPAPs and
therefore the standards as calculated by this method are:
T5 Class
EPAP
Implementation
HC CO NOx Date*
NME 1.9 12.5 5.0 January, 1982
NCE 1.0 7.8 5.0 January, 1984
* Date of implementation derived and discussed in Appendix B.
TABLE XII
This approach is considered to be the most technically acceptable
in that it takes demonstrated or anticipated combustor technology directly
and computes its performance in the T5 situation. For the standards for
newly manufactured engines (NME), in particular, the presence of demonstrated
technology virtually ensures compliance. Furthermore, this approach
readily satisfies the earlier criterion set by EPA that the T5 standards
"will respresent the same level of emissions reduction from current
supersonic aircraft, through application of the same types of combustor
design technology, as will be required of subsonic aircraft,..." (Preamble
to Aircraft Standards, FR Vol. 38, No. 136 19088).
-------
II. Issue of Expeditious Promulgation of Standards for Newly Manu-
factured Engines
Alternative V
Set the standards for newly manufactured engines equal to the values
recommended by Rolls Royce and set the standards for newly certified engines
equal to those values calculated by alternative IV.
As is discussed in Appendix B, the most expeditious approach to
controlling the T5 class is to set the T5 standards to be compatible
with the development work currently underway by the manufacturers.
According to Rolls Royce, one of the two members of the Olympus 593
consortium, its effort has been directed at the following goals which
are applicable to their engine (the newly manufactured engine category):
EPAP
HC CO NOx
NME 3.9 30.1 9.0
A comparison with the production engine
EPAP
HC CO NOx
Production 16.2 66.5 8.8
shows that Rolls Royce is seeking a reduction in HC and CO, but not in
NOx. In fact, they are allowing themselves a slight increase in the NOx
emissions which makes the job of reducing HC and CO emissions that much
easier.
Rolls Royce set its HC and CO goals in a manner similar to the
calculation of method 3 using, however, not the average reduction of the
main representative T2 engines, but only the JT9D. Their calculation
proceeded as follows.
JT9D
CO HC
Current EPAP 11.3 3.0
1979 T2 standards 4.3 0.8
Reduction required 62% 73%
-------
-21-
Olympus 593
Current EPAP 58 15.4 (Main Burner)
Reduction 62% 73%
Goals 22.1 4.1
AEPAP 5.5 0.6 (Afterburner)
EPAP Goal 27.6 4.7
Adjusted EPAP* 30.1 3.9
*This increase in the CO level and decrease in the HC level is
recommended over that of the initial calculation as it accounts for the
decrease in the HC/CO ratio as combustion efficiency is improved (see
Figure 1).
Technically this approach suffers the same drawbacks as method 3 with
the additional inconsistency that NOx is not treated in the same manner
as the other pollutants. Pragmatically, though, this approach would
permit standards to be implemented as soon as possible and certainly it
is not open to criticism as being unreasonably stringent as Rolls Royce
itself recommends these standards.
The fact that Rolls Royce has not been pursuing NOx reduction is
worthy of further comment. Their approach to setting goals for HC and
CO emissions is certainly not the best as is discussed in method 3 (an
approach similar to the Rolls Royce calculation), but it does offer a
justifiable rationale. However, the failure to set a NOx goal in the
same fashion demonstrates that Rolls Royce in the absence of promulgated
standards elected to take the far simpler approach and not pursue the
NOx problem.
For newly certified engines there is currently no development
underway for such engines which would conflict with the imposition of
the most rigorous standards now judged to be technically feasible (NCE
standards by alternative IV). The use of this set of standards has the
advantage of imposing the greatest control on the second generation of
SSTs which would be built only if the class were a commercial success.
These later aircraft would be built in larger numbers so that strong
control would be much more important.
The set of standards by this approach are then,
EPAP
Implementation
HC CO NOx Date*
NME 3.9 30.1 9.0 January, 1980
NCE 1.0 7.8 5.0 January, 1984
* Date of implementation derived and discussed in Appendix B.
-------
Recommendation
Method one is rejected because it does not recognize the existence
of the T5 class at all which is contrary to EPA's stated intent.
Method two is rejected because there is no rationale for imposing
equal Emissions Indices in order to force a common technology between
the classes. This method fails to recognize that even the best combustor
would be affected by the operating conditions characteristic of each
engine type.
Method three adopts an acceptable point of view, but may be overly
stringent or lenient if the baseline values upon which the percentage
reductions are imposed reflect a technology which is already advanced
or, alternatively, is obsolete.
Method four carries out its calculations directly referring to the
technology available and how well it will perform in the SST environment,
as well as accounting for SST fuel consumption characteristics. This is
the preferred approach from a technical point of view. Method four,
however, can result in an essentially uncontrolled SST fleet because
control could not be achieved until January, 1982 at which time the
fleet, if produced in only limited numbers, would escape any control.
Method five results in control of SST emissions at the earliest
possible date (January 1, 1980) while retaining the strictest possible
standards for subsequent generations of SST's. It is thus recommended.
-------
o
CJ
^'
M
w
Most Probable Ratio (Main
Burner)
Afterburner
Data Points
1.5% Combustion Inefficiency
10
EI(HC) as CH4
Figure 1
15
20
i
NJ
UJ
I
-------
-24-
10
.01
Production Engines
D
Q
a
a)
H
o
H
01
C
M
o
H
4-1
tn
I
.001
.0001
.01
O CF6-50
O CF6-6D
© CFM-56
D JT9D-7
a JT3D-7
@ JT8D-17
A JT15D
<>TFE-731
£> Olympus-593
.10
Air Loading Parameter
1.0
Ib
10.
ft - sec
Figure 2
-------
-25-
.10
.01
a
g
6
o
H
U
OT
3
"I
O
u
.001
.0001
Production
NME
NCE
.01
.10
1.0
10.0
Air Loading Parameter
Ib
ft -sec
Figure 3
-------
-26-
o
o
o
W
HJ
10
to
.0
9
8
7
5
4
1
60
0. ,
Zr
yG 0
aE*
/6
/
x\
I_J
D
ffi
^
/
O
a or
X'
O CF6-50
3CF6-6D
© CFNI 56
D JT9D-7
OH JT3D-7
0JT8D-17
£) Olympus 5
'/
.,
.3
0 800 1000 1200 1400 1600
Compressor Discharge Temperature " °R
Figure 4
-------
-27-
o
o
o
x
o
53
Present Da\^ Technology
Best Demonstrated Technology
Olympus 593 (producdion)
600
800 1000 1200
Compressor Discharge Temperature " °R
Figure 5
1400
1600
-------
-28-
O
Q)
W
I
O
U
IM
VJ
CD
4J
QJ
s
n)
K
rt
C^
to
C
H
13
rt
O
^
M
H
<
3-
fO
1
1-
O CF6-50
3 CF6-6D
© CFM-56
D JT9D-7
E3 JT8D-17
Q RB-211
fil Pegasus
A JT15D
<>TFE-731
QM 45H
£j Olympus 593
O
D
10 15
Rated Pressure Ratio
20
25
30
Figure 6
-------
-29-
Appendix A
Calculation of Anticipated Future Combustor Performance
The T2 class standards for newly certified engines are based upon
the existence of an emissions control technology that should be common
to both supersonic and subsonic engines. In order to derive T5 standards
that reflect this commonality, it is necessary to correct the EPAP
values in the T2 standards (NCE) to their respective Emissions Indices
in order to compute the combustion inefficiency for Figure 2.
For a modern T2 class engine the great bulk of the hydrocarbon and
CO is produced during the idle mode (see Table below); hence, to a
good approximation it is sufficient to consider the total hydrocarbons
and CO to be a result of incomplete combustion of the mass of fuel
consumed at idle only.
Mode
Idle
Takeoff
Climbout
Approach
HC(lbs)
19.5
0
0
0.39
CO(lbs)
54.6
.20
.41
3.27
% of Total
94.6
0.2
0.5
4.7
Total 19.89 58.48 100
Emissions for JT9D-7(T2 class)
Roughly, then, .
- Total Emissions (HC or CO)
-
or uw j-uxc , -_* fuel consumed at idle/1000)
where
Total Emissions (HC or CO) Idle = (EPAP Anticipated x Total
impulse over LTO cycle/1000)
so that
El (HC or CO) Idle = Anticipated EPAP x Total Impulse over LTO
cycle/Mass of fuel consumed at idle
For subsonic newly manufactured engines, the following EPAP values
are expected:
HC CO
NME(T2) 0.8 4.3
and for subsonic newly certified engines,
HC CO
NCE(T2) 0.4 3.0
-------
-30-
Thesc values agree with the percent reductions listed in the discussion
df Alternative III.
The CF6-50 may be taken as a representative subsonic engine in order
to establish the expected technology lines. For this engines,
total impulse over LTO cycle = 3868 Ib-thrust x hrs.
mass of fuel consumed at idle (26 min) = 528 Ibs.
Thus, the Els and the combustion inefficiency can be calculated for NME
and NCE to give
ET(HC) El(CO) 1-n «
NME 5.9 31.5 1.24% 2.18
NCE 2.9 22.0 0.77% 2.18
where the air loading parameter for the CF6-50 is included so that the point
can be fixed in figure 3. The technology lines are then drawn perpendicular
to the production engine technology line. This last step may be opti-
mistic at the high power points (small fi), however, as these points con-
tribute little, if anything to the total HC and CO EPAP calculations,
the point is moot.
-------
-31-
Appendix B
Implementation Data^~
Introduction
This appendix presents an analysis of the leadtimes necessary to
implement the two most acceptable alternatives discussed in the main text.
The first analysis here examines the leadtime for Alternative IV which
is considered the most acceptable from a strictly technical point of
view (It establishes T5 standards that require the use of the best
technology thought to be available).
The second analysis examines the leadtime for Alternative V which is
the recommended approach because, as the analysis shows, it can be im-
plemented sooner. An early date of effectiveness is desirable because of
the liklihood that only a small fleet (less than 60) of SSTs Will be built.
More control can then be achieved by early enforcement.
Method Four
Method four represents the technically most stringent standards
that can reasonably be imposed on the T5 class. From that point of view
it is the preferred approach. The question then must be answered: At
what date can these standards go into effect?
The NME standards calculated by method four are based upon the
application of oombustor technology already demonstrated in rig tests in
the United States. The time necessary to implement that technology into
production depends on the accomplishment of the tasks listed below in
the graph. The EPA estimates of the time required to complete these
tasks are derived from the times involved in the NASA Experimental Clean
Combustor Program, Phases II and III, communications with General Electric
and Pratt and Whitney Aircraft, EPA experience with smoke reduction programs,
and explanations in EPA Report No. 1168-1, "Assessment of Aircraft Emission
Control Technology", September 1971. The NASA program times are concerned
with the demonstration of the technology in rig and engine prototype tests,
while the manufacturer and EPA times are concerned with engine certification,
checkout, and production preparation times. Some foreshortening of the
General Electric time estimates has been assumed and the differences are
noted herein.
The tasks are described as follows:
1. Combustor demonstration in rig test. The requisite technology
has already been successfully demonstrated in rig tests in the United
States as part of the NASA Experimental Clean Combustor Program (ECCP).
The operating environment of the tests simulated subsonic engine operating
conditions and the geometries were scaled to specify subsonic engines.
While that technology is transferable to other engines and other operating
-------
-32-
0 1 '2 (years) 3456
1. Combustor
demonstration
in rig test
2. Engine
demonstration
3. Production
design and
procurement
4. Engine
testing
5. Flight
testing
6. Qualification
7. Service
Evaluation
Production
,v
\\
\\
\\
\\
(1
\\
N\
\\
N\
\\'
\\
A
K\
\\
k\
(i
\\
>
c
V
)(
\
3)
NV
,v
sV
\v
sV
Xs
(
\l
Nv
),
V
c
\
c
(2
),
V
:2)
0,
3)
\^
(3
(
,(
V
)
4)
4).
V
*
(5
s
1
(1) NASA ECCP
(2) GE communication
(3) EPA Report No. 1168-1
(4) P&WA communication
(5) Comparison with other service evaluation programs
* Start of this task advanced 3 months
** Start of this task advanced 6 months
-------
-33-
conditions, nonetheless, it must be verified and refined in rig tests
prior to engine testing so that the effectiveness of the scheme to
control emissions in that application can be proven. Rig testing also
permits extensive optimization of the system for safety and reliability.
It further permits simulated altitude performance testing (including
relight) which otherwise would be very costly in engine tests in altitude
chambers, if possible at all. The time allotted for this task is 15
months and is chosen because it is identical to that of Phase II of the
NASA ECCP wherein similar work was done.
2. Engine Demonstration. Engine demonstration is necessary first
to verify that the combustor, which was optimized in the rig tests,
operates satisfactorily in the full engine and second to design the
necessary fuel control system to achieve that satisfactory performance.
Satisfactory performance here means (1) acceptable steady state performance
as evidenced by specific fuel consumption within production specification
and acceptable turbine inlet temperature profile and (2) acceptable
transient performance as evidenced by acceleration/deceleration times
within FAA requirements with sufficient surge margin. The time allotted
for this effort is again 15 months and is identical to that of Phase III
of the NASA ECCP wherein similar work is being accomplished.
3. Production Design. This task involves the design and manufacturer
(in limited numbers) of all the engine parts modified by the low emissions
system and the associated tooling. Such engine parts may include, in
addition to the combustor liner itself, the inner and outer casing,
diffuser, struts, fuel control, nozzles.
Manufacturing includes the necessary tooling as well as the limited
production to supply engines for static and flight testing, qualification,
and service evaluation. As reported in EPA Report No. 1168-1, September
1971 and by General Electric in a separate communication this exercise
should take a little over 1 1/2 years, much of which can overlap the
engine demonstration period as the final configuration is finally identified,
thereby requiring only four additional months until engine testing can
begin.
4. Engine Testing. This activity involves endurance and cyclic
testing necessary first to generate an adequate safety record for later
flight testing and engine qualification and second to develop a main-
tenance and reliability record for airline service. This is a continuous
effort throughout the service life of the engine, but only eight months
are necessary before sufficient time is accumulated to begin flight
tests. General Electric suggested that about fourteen months be given
to ground testing before flight testing begins. Through a more intensive
test schedule this can be shortened to eight months, saving six.
5. Flight Testing. This is done primarily to investigate engine
performance at altitude. It is usually done on a corporate owned
experimental aircraft or an available military aircraft neither of which
are subject to the FAA requirements of certification. Included in the
-------
-34-
engine performance criteria arc- thrust, specific fuel consumption,
relight, and transient behavior. Environmental factors such as icing,
etc., may be investigated as necessary. General Electric and Pratt and
Whitney generally allocate about six months to flight testing prior to
start of qualification.
6. Qualification. This step involves obtaining the necessary type
certificate, supplemental type certificate, or engineering approval for
the low emissions engine. The amount of effort involved here is largely
dependent upon the type of certification necessary. In any case, FAA
certification here involves mostly paperwork as a large part of the
necessary testing has already been done. Following the recommendation
of the manufacturers, six months is delegated to this task.
7. Service Evaluation. Once an engine has the necessary FAA
certification or approval, it is, strictly speaking, available for
public use. Nonetheless, another stage of testing, that of service
evaluation, has developed as a matter of industry policy prior to full
production. The procedure in service evaluation is to have a limited
number of engines installed on fleet aircraft (one per plane) for a long
enough period of time to judge their performance, reliability, and
maintainability in actual airline use. While reliability may be considered
a safety issue (the FAA considers service evaluation a vital supplement
to its own required testing for certification), it is intended primarily
to prove the economics of the engine in service. The length of time of
the service evaluation depends upon the rate at which flight time and
landing-takeoff cycles are accumulated in service and the extent to
which the new system differs from the old (an exotic system will be
scrutinized more thoroughly for reliability). A system which has had a
history of difficulty in development will command a longer service
evaluation.
General Electric has indicated that a one year service evaluation
would be adequate for its engines. This is a fairly short time, giving
a high time of perhaps 3500 hours and 1400 cycles. This is supported
also by EPA Report No. 1168-1, referenced earlier. However, it should
be pointed out that some service evalutions take longer, for instance
the JT3D and JT8D smoke retrofit programs took 1 and 1/2 to 2 years to
complete. However, both represented attempts to install advanced
technology in quite mature engines (canannular combustors) and both
experienced a history of development problems.
Totally then (steps 1 through 7), 4-1/2 years should be sufficient
to implement the demonstrated technology into a production T5 class
engine. In comparison, the staff of Rolls Royce, Derby Division (not
involved in the T5 class) suggested a six year leadtime is necessary
from the definition of a concept (rig test) to production (steps 2
through 7). This analysis calls for 4-1/4 years and an analysis based
upon General Electric's unmodified estimates calls for 5 years for the
same set of tasks (steps 2 through 7).
-------
-35-
A 5-1/2 year leadtime from July 1976- would mean that the T5 standards
for newly manufactured engines (by Alternative IV) would go into effect
January 1, 1982. Following the patterns set by the T2 class standards,
a two year interval from the implementation of the standards for newly
manufactured engines to the standards for newly certificated engines
would establish the advanced standards on January 1, 1984. Further
extension of the deadline for newly certificated engines is not warranted
in this case as these standards (Alternative IV) do not presume the
development of a variable cycle engine which may be some distance in the
future.
Method Five
For newly manufactured engines, this method is nothing more than
Rolls Royce's own target values which, in November 1974, they felt
confident in meeting by January 1, 1979. While it is possible that they
and their partner, SNECMA, have been continuing to pursue development
directed towards their original target, it may well be that because of
the roughly one year delay in the promulgation of the standards, Rolls
Royce and SNECMA have been delaying further work pending redefinition of
their goals. If this is the case, then a one year delay is likely to be
necessary.
Their concepts for both the main burner and the afterburner have
been identified and, at least for the main burner, demonstrated in an
engine (the status of the afterburner is not known). This fact, coupled
with the fact that the burner changes involved are sufficiently minor
that only a minimal qualification effort is necessary, supports the
notion that the low emissions engine may be ready by January 1, ]979 and
certainly by January 1, 1980.
As the NCE standards for method 5 are nothing more than those of
method 4, it follows that the implementation date aimed at above for
method 4 is adequate, namely, January 1, 1984. An alternative approach
which gives essentially the same date is to first presume that most
development work for newly certified engines will be done for the T2
class and that for a newly certified T5 engine the necessary technology
will have to be transferred, an activity which involves rig verification
and refinement and engine demonstration. Such activities closely follow
the work done in Phases II and III of the current NASA Experimental
Clean Combustor Program. That work requires 30 months or 2 1/2 years to
account for unforseen difficulties in the technology transfer, then it
may be concluded that implementation of the T5 standards for newly
certified engines would be about three years behind that for the T2
class, giving again January 1, 1984 (adding three years to January 1,
1981, the implementation date for the T2 standards for newly certified
engines).
------- |