Appendix
General Design Specifications for Heavy Duty Vehicle Analytical
Instruments.
I. Measurement accuracy:
A. All emission analyzers: Listed are suggested ranges for all
emission analyzers. Select the appropriate ranges and number of ranges
for each analyzer. The analyzers must operate between 20 percent and
95 percent of full-scale value for non-linear instruments (20 to 100
percent for linear analyzers) during the measurement of the emissions
for each mode. The exceptions to the lower limit of this operating
rule are:
(I) The analyzer response may be less than 20 percent
of full-scale if the full-scale value is 120 ppm (or ppm
C) or less.
(2) The analyzers response may be less than 20 percent of
full-scale if the emissions from the engine are irratic and
the integrated chart-deflection value is greater than 20
percent of full-scale.
C3) The^analyzer response may be less than 20 percent of
full-scale during the initial part of the CT mode provided
that the integrated chart-deflection value is greater than
20 percent of full-scale.
The magnitude of full-scale value of the suggested ranges
may vary somewhat to suit instrument characteristics or to facilitate
data collection.
Suggested Ranges Instrument Accuracy
0-10. ppm or ppm C 5 percent of full-scale
0-40. ppm or ppm C 2 percent of full-scale
0-100. ppm or ppm C 1 percent of full-scale
0-400. ppm or ppm C 1 percent of full-scale
0-1000. ppm or ppm C 1 percent of full-scale
0-4000. ppm or ppm C 1 percent of full-scale
0-10000. ppm or ppm C 1 percent of full-scale
0-40000. ppm or ppm C 1 percent of full-scale
0-10.00 percent 1 percent of full-scale
0-15.00 percent 1 percent of full-scale
0-20.00 percent 1 percent of full-scale
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B. The dynamometer test stand and other instruments for measurement
of power output shall be accurate to within + 2 percent of full-scale
at all power settings.
C. The fuel flow measurement instrumentation shall have a minimum
accuracy of 1 percent of full-scale for each range used. Fuel flow
measurements may not be used as official values if the readings are
below 20 percent of full scale value unless the point accuracy has
an error of less than 5 percent.
II. NDIR instruments: Nondispersive infrared (NDIR) analyzers shall
be used for the continuous monitoring of carbon monoxide and carbon
dioxide.
A. Analyzer description: The NDIR instruments operate on the
principle of differential energy absorption from parallel beams of
infrared energy. The energy is transmitted to a differential detector
through parallel cells, one containing a reference gas, and the other,
sample gas. The detector, charged with the component to be measured,
transduces the optical signal to an electrical signal. The electrical
signal thus generated is amplified and continuously recorded.
B. Analyzer specification:
Response time (pnuematic)>"-15 percent of full-scale in 0.5
seconds or less.
Response time (electrical)—95 percent of full-scale in
0.5 seconds or less.
Noise—KL percent of full scale on most sensitive range.
Repeatability—t-l_ percent of full scale.
Zero drift—Less than +1 percent of full-scale in 2 hours
on all ranges.
Span drift-—Less than +1 percent of full-scale in 2 hours
on all ranges.
Cell Temperature—Minimum 50°C maintained within 4^ 2°C.
C. Cell length: All NDIR instruments shall be equipped with
cells of sufficient length to accurately measure the exhaust con-
centrations encountered during the test. (See I A.) Range changes
shall be accomplished either by the use of stacked sample cells
or changes in the electronic circuitry, or both.
D, Zero supression: Various techniques of zero supression may be used
to increase readability. Note, that by supressin& the zero response, the
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readability of the emission response is increased, but accuracy of
this response expressed as a percent of full-scale value does not
change.
III. Total hydrocarbon analyzer:
A. Analyzer description: The measurement of total hydrocarbon
is to be made by an analyzer using a flame ionization detector (FID) .
With this type detector an ionization current proportional to the mass
rate of hydrocarbon entering a hydrogen flame is measured by an electro-
meter amplifier and continuously recorded.
The analyzer shall be fitted with a constant-temperature oven
housing the detector and sample-handling components. It shall maintain
temperature within Hh 2°C of the set point.
The detector and sample-handling components shall be suitable
for continuous operation at temperatures to 200°C.
B. Analyzer specification:
Response time (pneumatic) — 15 percent of full-scale in .5
seconds or less.**
Response time (electrical)— 95 percent of full scale in 0.5
seconds or less.
—f-l^ percent of full scale on most sensitive range.
Repeatability — +1 percent of full scale.
Zero drift — Less than +1 perecent of full scale in 2 hours
on all ranges.
Span drift' — Less than +1 perecnt of full scale in 2 hours
on all ranges.
Linearity — Response with propane in air shall be linear
within +_ 2 percent.
C. Detector response optimization:
0-1 Follow manufacturers instructions for instrument
start-up and basic operating adjustments.
(a) The fuel shall contain 40 + 1% hydrogen. The
balance shall be helium. The mixture shall contain
less than 2 ppm C hydrocarbon.
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(b) The air shall contain 21 +_ 1% oxygen. Compressed
"hydrocarbon-free" grade of atmospheric air meets the
oxygen-concentration requirements.• The air shall contain
less than 2 ppm C hydrocarbon.
. C2) Set the oven temperature 5°C hotter than the required
sample-line.temperature. Allow at least one-half hour after
the oven has reached temperature for the system to equilibrate.
(3) Peak the detector: With the fuel and air set at the
manufacturer's settings, introduce a mixture of propane in
air to the detector. The propane concentration should be
approximately 80 ppm C + 20 ppm C. Determine the response
at a given fuel flow from the difference between the span-
gas response and the zero-gas response. Incrementally adjust
the fuel flow above and below the manufacturer's specification.
Record the span and zero response at these fuel flows. A
plot of the difference between the span and zero response versus
fuel flow will be similar to the one shown in Fig III-l. Ad-
just the fuel flow-rate to the rich side of the curve, as shown.
This is an initial flow-rate setting and may riot be the final
optimized-flow-rate.
•*
(4) Oxygen effect: check the response of the detector with
various concentrations of oxygen in the sample. Conduct this
test with the oven temperature set as required by step III B (2).
The initial fuel flow shall be the same as that determined by
step III B (3).
(a) Zero the analyzer with hydrocarbon-free air. Introduce
nitrogen (N2) zero-gas. The response to the nitrogen zero-
gas must be less than 0.5 percent of full-scale value of
the lowest anticipated range.
(b) The following blends of calibration gases shall be used
to determine the effect of oxygen (02) in the sample.
Calibration-Gas 0? concentration Balance
Propane 21% N2
Propane 15% N2
Propane 10% No
Propane 5% N2
Propane 0% N2
The oxygen-concentration blend-tolerance is + 1%
(i.e. 10 + 1% means 9% to 11%). The analysis of the oxygen-
concentration must be within + 1% of the absolute con-
centration-value. The calibration-gas concentration should
be about 80 ppm C + 20 ppm C and must be known within + 1%
of the absolute concentration-value.
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Detector
Response
Optimum
Fuel Flow
Figure III - I
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(c) Calibrate the analyzer with the calibration
mixture containing 21% oxygen.
(d) Introduce the calibration mixtures containing
the 15, 10, 5 and 0 percent oxygen to the detector
in sequence. Record the response to each of the
mixtures.
(e) Recheck the zero response. If it has changed,
repeat the test.
(f) Calculate the oxygen interference (% C^j) for
the 15, 10, 5, and 0 percent oxygen-mixtures by
equation III-l.
CII1-1) % 021 ~ Bx - Analyzer Response (ppm C)
Bx
where
Bx = hydrocarbon concentration of the oxygen-
interference cylinders (15%, 10%, 5% and 0%)
ClII"^) Analyzer Response =
[hydrocarbon concentration (ppm C) in the 21% mixture](100) (% of Full-Scale ana-
% of full-scale analyzer response due to 21% mixture lyzer response due to Bx)
(g) If the oxygen interference for the 15, 10, and 5 per-
cent oxygen mixtures is less than + 2% and less than +2.5%
for the zero percent oxygen mixture, then no oxygen-
interference correction-factor need be used.
(h) If the oxygen interference is greater than the
specifications, incrementally adjust the air flow above
and below the manufacturer's specifications, and repeat
subparagraphs (c) through (g) of step III C (4).
(j) If the oxygen interference is still greater than
the specifications, repair or replace the detector.
(5) Linearity:
(a) With the fuel flow, air flow, and sample flow adjusted
to meet the oxygen interference specification, the instrument
linearity shall be checked for the ranges covering the range
of analysis using propane-in-air with nominal concentrations
of 30, 60, and 90 percent of full-scale of each range. The
deviation of a best-fit curve from a least-squares best-fit
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straight line should not exceed 2 percent of the value
at any point. If this specification is met, concentra-
tion values may be calculated by use of single calibration
factor.
Note, by varying the air, fuel, and sample flow-rates
within the boundaries of the oxygen interference specifica-
tions, the analyzer may produce a more linear response. If
the deviation exceeds 2 percent at any point, concentration
values shall be calculated from a calibration curve prepared
during this alignment procedure (III C (5)).
(b) With the exception of any possible changes required by
subparagraph (6) of III C, the flow-rate, air flow-rate,
and sample flow-rate are defined as "optimized" at this
point.
(6) Initially, and within every 180 days thereafter, make
a comparison of response to the different classes of compounds
using (individually) propylene, toluene, n-hexane, and propane,
each at 20 to 50 ppm C concentration in air. If the response
to propylene, toluene, or n-hexane differs by more than 5 percent
from the response to propane, check instrument operating para-
meters. Reducing sample flow rate generally improves uniformity
of response.
iy. Oxides of Nitrogen (NOx) Analyzer:
A. Analyzer description: The method of measuring total oxides of
nitrogen consists of two distinct operations. First the nitrogen dioxide
(N02) in the sample is converted to an equivalent.amount of nitric oxide
(NO). Next this amount of (NO) is added to the NO that was already in
the sample. This total amount of NO is then measured by the chemilumine-
scence method.
(1) N0£ •* NO Converter: There are at least two methods of con-
venting N0£ to NO. The most frequently used methods employ either
a thermal-conversion principle of a combination of thermal-con-
version and catalytic-conversion. In order to meet the sample
response-times required, it is usually necessary to employ a
high flow-rate converter. The governing criterion for the
converter is that it must have a minimum conversion efficiency
of 90% when converting N02 -»• NO.
(2) Chemiluminescence Reaction Chamber: The chemiluminescence
method utilizes the principle that nitric oxide (NO) reacts with
ozone (03) to give nitrogen dioxide (N0£) and oxygen (02). Approxi-
mately 10 percent of the N02 is electronically excited. The transi-
tion of excited NOn to the ground state yields a light emission
(600-2600 nanometer region at low pressures). The detectable
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region of this emission depends on the PM-tube/optical filter
being u:;ed in the detector. The intensity'of this emission
is proportional to the mass flow rate of NO into the reactor.
The light emission can be measured utilizing a photomultiplier
tube and associated electronics.
B. Analyzer specifications: Specifications for the oxides of
nitrogen analysis system are:
Response time (pneumatic)—15 percent of full-scale in 1.5
seconds or less.
Response time (electrical)-—95 percent of full-scale in 0.5
seconds of less.
Noises-Less than 1 percent of full-scale.
Repeatability—+1 percent of full-scale.
Zero drift—Less than +1 percent of full-scale in 2 hours.
Span drift—Less than +1 percent of full-scale in 2 hours.
Linearity—Linear to within +2 percent of full-scale on all
ranges.
C. System optimization:
0-1 Follow manufacturer's instructions for instrument start-up
and basic operating adjustments.
(2) N02 -»• NO Converter Check: The apparatus described and
illustrated in Figure IV-1 is to be used to determine the
conversion efficiency of devices that convert NOx to NO. The
following procedure is to be used for determining the values
to be used in Equation IV-1.
(a) Attach the NO/N2 supply (150-250 ppm) at C2, the 02
supply at Cl and the.analyzer inlet connection to the
efficiency detector at C3. If lower concentrations of
NO are used, air may be used in place of 02 to facilitate
better control of the N02 genernated during step (d).
(b) With the efficiency detector variac off, place the
NOx converter in bypass mode and close valve VS.. Open
valve NV2 until sufficient flow and stable readings are
obtained at the analyzer. Zero and span the analyzer
output to indicate the value of the NO concentration
being used. Record this concentration.
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(c). Open valve V3 (on/off flow control solenoid valve
for Oo) and adjust valve MV1 (02 supply metering valve)
to blend enough Oo to lower the NO concentration (b)
about 10 percent, Record this concentration.
Cd) Turn on the ozonator and increase its supply voltage
until the NO concentration of (c) is reduced to about
20 percent of (b). NO,, is now being formed from the NO +
Oo reaction. There must always be at least 10 percent un-
reacted NO at this point. Record this concentration.
Ce) When a stable reading has been obtained from (d),
place the NOx converter in the convert mode. The analyzer
will now indicate the total NOx concentration. Record
this concentration.
6
(f) Turn off the ozonator and, allow the analyzer reading
to stabilize. The mixture NO + 02 is still passing through
the converter. This reading is the total NOx concentration
of the dilute NO span gas used at step (c). Record this
concentration.
(g) Close valve V3. The NO concentration should be equal
to or greater than the reading of (b) indicating whether
the NO contains any M^. Calculate the efficiency of the
NOx converter by substituting the concentrations obtained
during the test into Equation (IV-1).
CIV-1) % Eff. = [(e) - (f)]
1 + I(c) - (d)] x 100%
The efficiency of the converter should be greater than 90
percent. Adjusting the converter temperature may be needed
to maximize the efficiency. Although steps (b) and (g)
are not used in the calculations, their values should be
recorded to complete the data set for the test sequence.
This procedure does not depend on the amount of N02 in the
span gas nor the equivalence of flows in the by-pass and
converter modes. However, to be consistent with good
operating practice, flows should be nominally the.same,
and the N0£ concentration should be less than 5% of the
NOx span concentration. Efficiency checks shall be made
weekly.
Ch) If the converter does not meet the conversion-ef-
ficiency specifications, repair or replace the unit.
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(3) Carbon Dioxide (C02) and carbon monoxide interference
check:
(a) Calibrate the NOx analyzer on the lowest anticipated
range that may be used during testing.
(b) Introduce (separately) blends of C02/N0x and CO/NOx
(diluent N2) to the analysis system. The CC>2 and CO
concentrations should be approximately equal to the highest
concentration that may be measured during testing. The
NOx concentration should be similar to the concentration
used in step a). Record the response.
(c) Recheck calibration. If it has shifted, recalibrate
and rerun the interference test.
(d) The difference between the NOx response with the
interference gases and the calculated NOx response must
not be greater than + 2 percent. The calculated response
is based on the calibration curve (Step (c)) and the in-
terference-bottle NOx concentration.
(e) The interference from C02 and CO in this checking
procedure must be less than 2 percent.
(4) Linearity:
(a) With the operating parameters adjusted to meet the
converter efficiency check and the interference checks,
the instrument linearity shall be checked for the ranges
of analysis using NO in N2 at nominal concentrations of
30, 60, and 90 percent of full-scale of each range. The
deviation of a best-fit curve from a least-squares best-fit
straight line should not exceed 2 percent of the value
at any point. If this specification is met, concentration
values may be calculated by use of a single calibration
factor. If the deviation exceeds 2 percent at any point,
concentration values shall be calculated from a calibration
curve prepared during this alignment procedure (IV C (4)).
(b) The operating parameters are defined as "optimized" at
this point.
V. Humidity Calculations:
A. The specific humidity (H) is.defined by equation (V-l).
(V-l) H = K Pv
BARO - Pv
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where
EA.\0 = barometric pressure (Pa)
Pv = partial pressure of water vapor (Pa)
'(18.01534 LB. of H20) (18.01534 gm of H20)
LB. Mx'le gm Mole
K= : -• = .6219
(28.967 LB. of Dry Air) (28.967 gm of Dry Air)
LB, Mole gm Mole
units of H = LB. of H20 = gm of H20
LB. of Dry Air gm of Dry Air
B. The partial pressure of water vapor may be determined in
two manners:
(1) A dew point device may be used. In that case:
Pv = P™, = staturation vapor pressure of water at
theDew-Point temperature, (Pa)
(2) A wet-bulb, dry-bulb method may be used. In that
case "Ferrels equation" (eq. (V-2)) is used.
(V-2) P = Pra -(3.67)(10)-* (BARO)(tdb - twh)Itwb + 1539]
1571
Pyg and (BARO) must have the same units
where
t,, = Dry bulb temperature (°F)
fcwb = Wet bulb temperature (°F)
C. The saturated vapor pressure of water at the wet-bulb temperature
(Prrg) is defined by equation (V-3) (Ref. Wexler and Greenspan, equation
(23), National Bureau of Standards).
(V-3) PWB = (e) IB In T^ + Z F T ^
1=0
where
^WB = is in Pascals (Pa)
TWB = Wet~bulb temperature (*K)
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B - -12.150799
F0 = -8.49922(10)3
FT = -7.4231865(10)3
F2 = 96.1635147
F3 = 2.4917646(10)~2
F4 = -1.3160119(10)-5
F5 = -1.1460454 CIO)"8
F6 = 2.1701289(10)-11
Fy = -3.610258(10)-15
F8 = 3.8504519(10)~18
F9 = -1.4317(10)-21
D. The saturate vapor pressure of water at the dry-bulb temperature
(Pj)j>) is found (if required) by using dry-bulb absolute-temperature (°K)
in equation (V-3).
E, The percent of relative humidity (RH) (if required) is defined
by equation (V-4).
CV-4) RH = P^ (100)
PDB
C6) The water-vapor volume-concentration of the engine intake
air (Y) is defined by equation (V-5):
CV-5) Y = (H) (Mair) = Pv
BARO-PV
where
Mair = Molecular weight of air = 28.967
= Molecular weight of water = 18.01534
VI. Airflow Measurement: There are many different methods of measuring
airflow to Diesel and gasoline engines. The method used should have a turn-
down ratio large enough to accurately measure the airflow over the engine
operating range during the test. Preferred measurement techniques include
measurement by a laminar flow device or a vortex shedding device. Other
techniques may be used; however, the overall measurement accuracy should
be +1 percent of full-scale value of the measurement device.
(1) Engine System: When measuring inlet air, various engines
systems may have additions or subtractions of small quantities
of air downstream of the airflow measuring device. An example
of air addition would be an air injection system (i.el air pump).
An example of air subtraction would be compressor bleed-air that
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is used to operate an intercooler fan on a turbocharged
engine. This bleed-air is normally vented to the atmosphere
and does not pass through the engine. In determining the (f/a)
ratio for the required calculations, use the following conventions:
(a) Wet to Dry conversion factor (Kw): When calculating
the (f/a) ratio to be used in determining Kw, use only the
airflow entering the combustion chamber. This may require
substraction-of bleed-air, etc. from the measured airflow.
(b) Fuel/Air ratio comparison: When comparing measured (f/a)
ratio to an emissions calculated (f/a) ratio the5 measured
airflow (in terms of mass) is the total mass of air entering
the exhaust pipe. This may include additions of air mass to
the exhaust pipe by an air injection system.
(2) Corrections to the measured air mass-flow-rate: When an engine
system incorporates devices that add or substract air mass as deter-
mined by VI (1) , determine the air mass from these devices by one
of the following methods:
(a) Measure the air mass-flow from the device during each
operating mode.
(b) Determine that the air mass-flow for each mode from
the device is typical for many system applications. Then
the device flow-rate for each mode may be generally applied.
(c) Under certain circumstances, such as turbomachinery,
theorectical calculations that predict the device mass flow-
rate during each mode may be used.
(3) Gasoline fueled engine systems: When measuring air flow-rate
of a gasoline engine, special care must be taken in the areas of
flow distribution, velocity profiles, and pressure drop to the engine
system:
(a) Flow distribution: The air-cleaner is considered part
of the engine system. Flow distribution should be considered •
as flow distribution to the air .cleaner. A plenum chamber
of sufficient volume is recommended to insure uniform distri-
bution to the engine.
(b) Velocity profile: The velocity profile is considered
the velocity profile to the air cleaner. The shape of the
plenum chamber and the entrance to the plenum chamber in-
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fluence the velocity distribution. The desired condition
is a uniform velocity - profile with .a velocity between 3.3
to 13.2 metres per second (10 to 40 feet per second delivering
air to the air cleaner.
(c) Pressure drop: During the measurement process of air
flow, the velocity at the point of measurement is usually
quite high, i.e. as high as 61 metres/sec (200 ft/sec). In
order to slow this velocity down to the desired velocity
range in the plenum chamber without incurring additional
pressure-losses, it is recommended that a diffusser be used
between the air-flow measurement device and the plenum chamber.
In any case, the pressure drop (from atmospheric pressure)
at the inlet to the air cleaner should not be more than 1.74
kPa (7.0 in H-O) .
(d) Vents: Devices like PCV valves that vent to the air
cleaner, should continue to be vented to the air cleaner.
Devices that vent to the atmosphere as some carburetor float
vents, governors, etc. should vent to the plenum chamber.
(e) Hot air: Engine inlet air temperature: Due to the
preconditioning schedule, ambient soak, and subsequent warm-
up idle, the first test-sequence should not be considered
a cold test-sequence. Therefore, considering current under-
hood-temperatures on a 20°C (68°F) to 30°C (86°F) day, devices
that provide hot air to the carburetor are defined as non-
functional during the test sequence. Use the following conven-
tion in determining the inlet air temperature to the engine:
(A) Ducted Ambient-Air: On engines that use ducted
ambient-air to the carburetor, the hot-air device should
be non-functional during the test sequence. The engine
should induct ambient air at 20°C (68°F) to 30°C (86°F).
(B) Under-Hood Air: On engines that induct air under
the hood, the hot air device (if used) will be non-
functional during the test sequence. The engine should
induct air at a typical under hood temperature that would
occur on a 20°C (68°F) to 30°C (86°F) day. The manu-
facturer should specify and substantiate the under hood
intake air temperature.
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