[Code of Federal Regulations]
[Title 40, Volume 17]
[Revised as of July 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR86.119-90]
[Page 475-483]
TITLE 40--PROTECTION OF ENVIRONMENT
CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
PART 86_CONTROL OF EMISSIONS FROM NEW AND IN-USE HIGHWAY VEHICLES AND
ENGINES--Table of Contents
Subpart B_Emission Regulations for 1977 and Later Model Year New Light-
Sec. 86.119-90 CVS calibration.
The CVS is calibrated using an accurate flowmeter and restrictor
valve. Measurements of various parameters are made and related to flow
through the unit. Procedures used by EPA for both PDP and CFV are
outlined below. Other procedures yielding equivalent results may be used
if approved in advance by the Administrator. After the calibration curve
has been obtained,
[[Page 476]]
verification of the entire system can be performed by injecting a known
mass of gas into the system and comparing the mass indicated by the
system to the true mass injected. An indicated error does not
necessarily mean that the calibration is wrong, since other factors can
influence the accuracy of the system, e.g., analyzer calibration. A
verification procedure is found in paragraph (c) of this section.
(a) PDP calibrations. (1) The following calibration procedure
outlines the equipment, the test configuration, and the various
parameters which must be measured to establish the flow rate of the CVS
pump. All the parameters related to the pump are simultaneously measured
with the parameters related to a flowmeter which is connected in series
with the pump. The calculated flow rate ft\3\/min (at pump inlet
absolute pressure and temperature) can then be plotted versus a
correlation function which is the value on a specific combination of
pump parameters. The linear equation which relates the pump flow and the
correlation function is then determined. In the event that a CVS has a
multiple speed drive, a calibration for each range used must be
performed.
(2) This calibration procedure is based on the measurement of the
absolute values of the pump and flowmeter parameters that relate the
flow rate at each point. Three conditions must be maintained to assure
the accuracy and integrity of the calibration curve. First, the pump
pressures should be measured at taps on the pump rather than at the
external piping on the pump inlet and outlet. Pressure taps that are
mounted at the top center and bottom center of the pump drive headplate
are exposed to the actual pump cavity pressures, and therefore reflect
the absolute pressure differentials. Secondly, temperature stability
must be maintained during the calibration. The laminar flowmeter is
sensitive to inlet temperature oscillations which cause the data points
to be scattered. Gradual changes (2 [deg]F (1.1
[deg]C)) in temperature are acceptable as long as they occur over a
period of several minutes. Finally, all connections between the
flowmeter and the CVS pump must be absolutely void of any leakage.
(3) During an exhaust emission test the measurement of these same
pump parameters enables the user to calculate the flow rate from the
calibration equation.
(4) Connect a system as shown in Figure B90-8. Although particular
types of equipment are shown, other configurations that yield equivalent
results may be used if approved in advance by the Administrator. For the
system indicated, the following data with given accuracy are required:
Calibration Data Measurements
------------------------------------------------------------------------
Parameter Symbol Units Tolerances
------------------------------------------------------------------------
Barometric pressure (corrected). PB in. Hg 0.012
kPa)
Pressure drop across the LFE EDP in. H2O 0.001
kPa)
Air temperature at CVS pump PTI [deg]F( 2O (1.0 kPa)
that will yield a minimum of six data points for the total calibration.
Allow the system to stabilize for 3 minutes and repeat the data
acquisition.
(7) Data analysis:
(i) The air flow rate, Qs, at each test point is
calculated in standard cubic feet per minute from the flowmeter data
using the manufacturer's prescribed method.
(ii) The air flow rate is then converted to pump flow,
Vo, in cubic feet per revolution at absolute pump inlet
temperature and pressure:
[[Page 478]]
Vo = (Qs/n) x (Tp/528) x (29.92/
Pp)
Where:
(A) Vo = Pump flow ft\3\/rev (m\3\/rev) at Tp,
Pp.
(B) Qs = Meter air flow rate in standard cubic feet per
minute, standard conditions are 68 [deg]F, 29.92 in. Hg (20 [deg]C,
101.3 kPa).
(C) n = Pump speed in revolutions per minute.
(D)(1) Tp = Pump inlet temperature, [deg]R([deg]K) = PTI +
460.
(2) For SI units, Tp = PTI + 273.
(E)(l) Pp = Absolute pump inlet pressure, in. Hg. (kPa) =
PB - PPI (SP.GR./13.57).
(2) For SI units, Pp = PB - PPI.
Where:
(F) PB = barometric pressure, in. Hg. (kPa).
(G) PPI = Pump inlet depression, in. fluid (kPa).
(H) SP.GR. = Specific gravity of manometer fluid relative to water.
(iii) The correlation function at each test point is then calculated
from the calibration data:
[GRAPHIC] [TIFF OMITTED] TR06OC93.021
Where:
(A) Xo = correlation function.
(B) [Delta] Pp = the pressure differential from pump inlet to
pump outlet, in. Hg (kPa) = Pe - Pp.
(C)(1) Pe = Absolute pump outlet pressure, in Hg, (kPa) =
PB + PPO (SP.GR./13.57).
(2) For SI units, Pe = PB + PPO.
Where:
(D) PPO = Pressure head at pump outlet, in. fluid (kPa).
(iv) A linear least squares fit is performed to generate the calibration
equations which have the forms:
Vo = Do - M(Xo)
n = A - B([Delta] Pp)
Do, M, A, and B are the slope-intercept constants describing
lines.
(8) A CVS system that has multiple speeds should be calibrated on
each speed used. The calibration curves generated for the ranges will be
approximately parallel and the intercept values, Do, will
increase as the pump flow range decreases.
(9) If the calibration has been performed carefully, the calculated
values from the equation will be within 0.50
percent of the measured value of Vo. Values of M will vary
from one pump to another, but values of Do for pumps of the
same make, model, and range should agree within 3
percent of each other. Particulate influx from use will cause the pump
slip to decrease as reflected by lower values for M. Calibrations should
be performed at pump start-up and after major maintenance to assure the
stability of the pump slip rate. Analysis of mass injection data will
also reflect pump slip stability.
(b) CFV calibration. (1) Calibration of the CFV is based upon the
flow equation for a critical venturi. Gas flow is a function of inlet
pressure and temperature:
[GRAPHIC] [TIFF OMITTED] TR06OC93.022
Where:
(i) Qs=Flow.
(ii) Kv=Calibration coefficient.
(iii) P=Absolute pressure.
(iv) T=Absolute temperature.
The calibration procedure described below establishes the value of the
calibration coefficient at measured values of pressure, temperature and
air flow.
(2) The manufacturer's recommended procedure shall be followed for
calibrating electronic portions of the CFV.
(3) Measurements necessary for flow calibration are as follows:
Calibration Data Measurements
----------------------------------------------------------------------------------------------------------------
Parameter Symbol Units Tolerances
----------------------------------------------------------------------------------------------------------------
Barometric pressure (corrected)...... Pb................ Inches Hg (kPa)........ .01 in
Hg (.034 kPa)
Air temperature, flowmeter........... ETI............... [deg]F ([deg]C)........ .25[deg]F (.14[deg]C)
Pressure depression upstream of LFE.. EPI............... Inches H2O (kPa)....... .05 in
H2O (.012 kPa)
Pressure drop across LFE matrix...... EDP............... Inches H2O (kPa)....... .005
in H2O (.001
kPa)
Air flow............................. Qs................ Ft3/min. (m3/min,)..... .5 pct
[[Page 479]]
CFV inlet depression................. PPI............... Inches fluid (kPa)..... .13 in
fluid (.055 kPa)
CFV outlet pressure.................. PPO............... Inches Hg (kPa)........ 0.05
in. Hg (0.17 kPa)1
Temperature at venturi inlet......... Tv................ [deg]F ([deg]C)........ 0.5[deg]F (0.28[deg]C)
Specific gravity of manometer fluid Sp. Gr............
(1.75 oil).
----------------------------------------------------------------------------------------------------------------
1 Requirement begins August 20, 2001.
(4) Set up equipment as shown in Figure B90-9 and check for leaks.
Any leaks between the flow measuring device and the critical flow
venturi will seriously affect the accuracy of the calibration.
[[Page 480]]
[GRAPHIC] [TIFF OMITTED] TR06OC93.199
(5) Set the variable flow restrictor to the open position, start the
blower, and allow the system to stabilize. Record data from all
instruments.
(6) Vary the flow restrictor and make at least 8 readings across the
critical flow range of the venturi.
(7) Data analysis: The data recorded during the calibration are to
be used in the following calculations:
(i) The air flow rate, Qs, at each test point is
calculated in standard cubic feet per minute from the flow meter data
using the manufacturer's prescribed method.
(ii) Calculate values of the calibration coefficient for each test
point:
[[Page 481]]
[GRAPHIC] [TIFF OMITTED] TR06OC93.023
Where:
(A) Qs = Flow rate in standard cubic feet per minute,
standard conditions are 68 [deg]F 29.92 in. Hg (20 [deg]C, 101.3 kPa).
(B) Tv = Temperature at venturi inlet, [deg]R([deg]K).
(C)(1) Pv = Pressure at venturi inlet, mm Hg (kPa) =
PB - PPI (SP.GR./13.57).
(2) For SI units, Pv = PB - PPI.
Where:
(D) PPI = Venturi inlet pressure depression, in. fluid (kPa).
(E) SP.GR. = Specific gravity of manometer fluid, relative to water.
(iii) Plot Kv as a function of venturi inlet pressure.
For sonic flow Kv will have a relatively constant value. As
pressure decreases (vacuum increases), the venturi becomes unchoked and
Kv decreases. See Figure B90-10.
[[Page 482]]
[GRAPHIC] [TIFF OMITTED] TR06OC93.200
(iv) For a minimum of 8 points in the critical region calculate an
average Kv and the standard deviation.
(v) If the standard deviation exceeds 0.3 percent of the average
Kv take corrective action.
(8) Calculation of a parameter for monitoring sonic flow in the CFV
during exhaust emissions tests:
(i) Option 1. (A) CFV pressure ratio. Based upon the calibration
data selected to meet the criteria for paragraphs (d)(7) (iv) and (v) of
this section, in which Kv is constant, select the data values
associated with the calibration point with the lowest absolute venturi
[[Page 483]]
inlet pressure. With this set of calibration data, calculated the
following CFV pressure ratio limit, Prratio-lim:
[GRAPHIC] [TIFF OMITTED] TR18FE00.022
Where:
Pin-cal = Venturi inlet pressure (PPI in absolute pressure
units), and
Pout-cal = Venturi outlet pressure (PPO in absolute pressure
units), measured at the exit of the venturi diffuser outlet.
(B) The venturi pressure ratio (Prratio-i) during all
emissions tests must be less than, or equal to, the calibration pressure
ratio limit (Prratio-lim) derived from the CFV calibration
data, such that:
[GRAPHIC] [TIFF OMITTED] TR18FE00.023
Where:
Pin-i and Pout-i are the venturi inlet and outlet
pressures, in absolute pressure units, at each i-th interval during the
emissions test.
(ii) Option 2. Other methods: With prior Administrator approval, any
other method may be used that assure that the venturi operates at sonic
conditions during emissions tests, provided the method is based upon
sound engineering principles.
(c) CVS System Verification. The following ``gravimetric'' technique
can be used to verify that the CVS and analytical instruments can
accurately measure a mass of gas that has been injected into the system.
If the CVS and analytical system will be used only in the testing of
petroleum-fueled engines, the system verification may be performed using
either propane or carbon monoxide. If the CVS and analytical system will
be used with methanol-fueled vehicles as well as petroleum-fueled
vehicles, system verification performance check must include a methanol
check in addition to either the propane or carbon monoxide check.
(Verification can also be accomplished by constant flow metering using
critical flow orifice devices.)
(1) Obtain a small cylinder that has been charged with pure propane
or carbon monoxide gas (CAUTION--carbon monoxide is poisonous).
(2) Determine a reference cylinder weight to the nearest 0.01 grams.
(3) Operate the CVS in the normal manner and release a quantity of
pure propane or carbon monoxide into the system during the sampling
period (approximately 5 minutes).
(4) Following completion of step (3) in this paragraph (c) (if
methanol injection is required), continue to operate the CVS in the
normal manner and release a known quantity of pure methanol (in gaseous
form) into the system during the sampling period (approximately five
minutes). This step does not need to be performed with each
verification, provided that it is performed at least twice annually.
(5) The calculations of Sec. 86.144 are performed in the normal
way, except in the case of propane. The density of propane (17.30 g/
ft\3\/carbon atom (0.6109 kg/m\3\/carbon atom)) is used in place of the
density of exhaust hydrocarbons. In the case of carbon monoxide, the
density of 32.97 g/ft\3\ (1.164 kg/m\3\) is used. In the case of
methanol, the density of 37.71 g/ft\3\ (1.332 kg/m\3\) is used.
(6) The gravimetric mass is subtracted from the CVS measured mass
and then divided by the gravimetric mass to determine the percent
accuracy of the system.
(7) The cause for any discrepancy greater than 2 percent must be found and corrected. (For 1991-1995
calendar years, discrepancies greater than 2
percent are allowed for the methanol test, provided that they do not
exceed 8 percent for 1991 testing or 6 percent for 1992-1995 testing.)
[54 FR 14518, Apr. 11, 1989, as amended at 60 FR 34344, June 30, 1995;
62 FR 47121, Sept. 5, 1997; 63 FR 24448, May 4, 1998; 65 FR 8278, Feb.
18, 2000]