[Code of Federal Regulations]
[Title 40, Volume 30]
[Revised as of July 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR1065.110]
[Page 654-657]
TITLE 40--PROTECTION OF ENVIRONMENT
CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
PART 1065_TEST PROCEDURES AND EQUIPMENT--Table of Contents
Subpart B_Equipment and Analyzers
Sec. 1065.110 Exhaust gas sampling system; spark-ignition (SI) engines.
(a) General. The exhaust gas sampling system described in this
section is designed to measure the true mass of gaseous emissions in the
exhaust of SI engines. (If the standard-setting part requires
determination of THCE or NMHCE for your engine, then see subpart I of
this part for additional requirements.) Under the constant-volume
sampler (CVS) concept, you must measure the total volume of the mixture
of exhaust and dilution air and collect a continuously proportioned
volume of sample for analysis. You must control flow rates so that the
ratio of sample flow to CVS flow remains constant. You then determine
the mass emissions from the sample concentration and total flow over the
test period.
(1) Do not let the CVS or dilution air inlet system artificially
lower exhaust system backpressure. To verify proper backpressures,
measure pressure in the raw exhaust immediately upstream of the inlet to
the CVS. Continuously measure and compare the static pressure of the raw
exhaust observed during a transient cycle--with and without the CVS
operating. Static pressure measured with the CVS system operating must
remain within 5 inches of water (1.2 kPa) of the
static pressure measured when disconnected from the CVS, at identical
moments in the test cycle. (Note: We will use sampling systems that can
maintain the static pressure to within 1 inch of
water (0.25 kPa) if your written request shows that this closer
tolerance is necessary.) This requirement serves as a design
specification for the CVS/dilution air inlet system, and should be
performed as often as good engineering practice dictates (for example,
after installing an uncharacterized CVS, adding an unknown inlet
restriction on the dilution air, or otherwise altering the system).
(2) The system for measuring temperature (sensors and readout) must
have an accuracy and precision of 3.4[deg] F
(1.9[deg] C). The temperature measuring system for
a CVS without a heat exchanger must respond within 1.50 seconds to 62.5
percent of a temperature change (as measured in hot silicone oil). For a
CVS with a heat exchanger, there is no specific requirement for response
time.
(3) The system for measuring pressure (sensors and readout) must
have an accuracy and precision of 3 mm Hg (0.4
kPa).
(4) The flow capacity of the CVS must be large enough to keep water
from condensing in the system. You may dehumidify the dilution air
before it enters the CVS. You also may heat or cool the air if three
conditions exist:
(i) The air (or air plus exhaust gas) temperature does not exceed
250[deg] F (121[deg] C).
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(ii) You calculate the CVS flow rate necessary to prevent water
condensation based on the lowest temperature in the CVS before sampling.
(We recommend insulating the CVS system when you use heated dilution
air.)
(iii) The dilution ratio is high enough to prevent condensation in
bag samples as they cool to room temperature.
(5) Bags for collecting dilution air and exhaust samples must be big
enough for samples to flow freely.
(6) The general CVS sample system consists of a dilution air filter
(optional) and mixing assembly, cyclone particulate separator
(optional), a sample line for the bag sample or other sample lines a
dilution tunnel, and associated valves and sensors for pressure and
temperature. Except for the system to sample hydrocarbons from two-
stroke engines, the temperature of the sample lines must be more than
3[deg] C above the mixture's maximum dew point and less than 121[deg] C.
We recommend maintaining them at 113 8[deg] C.
For the hydrocarbon sampling system with two-stroke engines, the
temperature of the sample lines should be maintained at 191 11[deg] C. A general schematic of the SI sampling
system is shown in Figure 1065.110-1, which follows:
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(b) Steady-state testing. Constant proportional sampling is required
throughout transient testing, but is not required throughout steady-
state testing.
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Steady-state testing requires that you draw a proportional sample for
each test mode, but you may sample in different proportions for
different test modes, as long as you know the ratio of the sample flow
to total flow during each test mode. This allowance means that you may
use simpler flow control systems for steady-state testing than are shown
in Figure 1065.110-1 of this section.
(c) Configuration variations. Since various configurations can
produce equivalent results, you need not conform exactly to the drawings
in this subpart. You may use other components--such as instruments,
valves, solenoids, pumps and switches--to provide more information and
coordinate the components' functions. Based on good engineering
judgment, you may exclude other components that are not needed to
maintain accuracy on some systems.
(d) CFV-CVS component description. The flow characteristics of a
Critical-Flow Venturi, Constant-Volume Sampler (CFV-CVS) are governed by
the principles of fluid dynamics associated with critical flow. The CFV
system is commonly called a constant-volume system (CVS) even though the
mass flow varies. More properly, they are constant-proportion sampling
systems, because small CFVs in each of the sample lines maintains
proportional sampling while temperatures vary. This CFV maintains the
mixture's flow rate at choked flow, which is inversely proportional to
the square root of the gas temperature, and the system computes the
actual flow rate continuously. Because pressures and temperatures are
the same at all venturi inlets, the sample volume is proportional to the
total volume. The CFV-CVS sample system uses critical flow venturis for
the bag sample or other sample lines (these are shown in the figure as
flow control valves) and a critical flow venturi for the dilution
tunnel. All venturis must be maintained at the same temperature.
(e) EFC-CVS component description. The electronic flow control-CVS
(EFC-CVS) system for sampling is identical to the CFV system described
in paragraph (b) of this section, except that it adds electronic flow
controllers (instead of sampling venturis), a subsonic venturi and an
electronic flow controller for the CVS (instead of the critical flow
venturi), metering valves, and separate flow meters (optional) to
totalize sample flow volumes. The EFC sample system must conform to the
following requirements:
(1) The system must meet all the requirements in paragraph (b) of
this section.
(2) The ratio of sample flow to CVS flow must not vary by more than
5 percent from the test's setpoint.
(3) Sample flow totalizers must meet the accuracy specifications in
Sec. 1065.150. You may obtain total volumes from the flow controllers,
with our advance approval, if you can show they meet these accuracies.
(f) Component description, PDP-CVS. The positive-displacement pump-
CVS (PDP-CVS) system for sampling is identical to the CFV system
described in paragraph (b) of this section, except for the following
changes:
(1) Include a heat exchanger.
(2) Use positive-displacement pumps for the CVS flow and sampling-
system flow. You do not need sampling venturis or a venturi for the
dilution tunnel. All pumps must operate at a constant flow rate.
(3) All pumps must operate at a nominally constant temperature.
Maintain the gas mixture's temperature--measured at a point just ahead
of the positive-displacement pump (and after the heat exchanger for the
main CVS pump)--within 10[deg] F (5.6[deg] C) of the average operating temperature
observed during the test. (You may estimate the average operating
temperature from the temperatures observed during similar tests.) The
system for measuring temperature (sensors and readout) must have an
accuracy and precision of 3.4[deg] F (1.9[deg] C),
and response time consistent with good engineering judgment.
(g) Mixed systems. You may combine elements of paragraphs (d), (e),
and (f) consistent with good engineering judgment. For example, you may
control the CVS flow rate using a CFV, and control sample flow rates
using electronic flow controllers.
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