U.S. patent number 3,699,814 [Application Number 05/233,082] was granted by the patent office on 1972-10-24 for gas sampler.
This patent grant is currently assigned to Philco-Ford Corporation. Invention is credited to Warren F. Kaufman.
United States Patent |
3,699,814 |
Kaufman |
October 24, 1972 |
GAS SAMPLER
Abstract
Apparatus for sampling gaseous exhaust emissions, on a constant
flow basis. A centrifugal type extractor pump is used to draw gas
through a critical flow venturi of predetermined flow rate. Exhaust
emissions are diluted with air and the critical flow venturi acts
as a constant volume flow device serving a metering function.
Samples are taken and collected continuously during the test run,
and are available to be analyzed for contaminants such for example
as hydrocarbon, carbon monoxide and oxides of nitrogen.
Inventors: |
Kaufman; Warren F. (Santa Ana,
CA) |
Assignee: |
Philco-Ford Corporation
(Philadelphia, PA)
|
Family
ID: |
22875816 |
Appl.
No.: |
05/233,082 |
Filed: |
March 9, 1972 |
Current U.S.
Class: |
73/863.11;
73/864.34 |
Current CPC
Class: |
G01N
1/24 (20130101); G01N 2001/244 (20130101) |
Current International
Class: |
G01N
1/24 (20060101); G01n 001/22 () |
Field of
Search: |
;73/421.5,23,27
;60/276 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hart; Douglas
Claims
I claim:
1. In apparatus for sampling the gaseous emissions of internal
combustion engines, for collection and analysis, a source of
diluent air adapted for connection with a conduit carrying the
exhaust of an engine, to produce a mixture of emissions and diluent
air, means for deriving samples of said mixture for analysis, and
means for regulating the flow of said mixture to maintain the flow
rate substantially constant, said last means comprising: a venturi
restriction having an inlet side and an expansion side, said inlet
side being coupled in the apparatus to receive said mixture; and
pump means coupled to the expansion side of said venturi
restriction and effective to draw the mixture therethrough, said
pump means being of capacity sufficient to insure that the venturi
restriction operates at conditions of critical gas flow throughout
test periods.
2. Apparatus in accordance with claim 1, and in which said means
for deriving samples includes hollow probe means of restricted
cross-section disposed in the stream of flowing mixture up-stream
of said venturi restriction, and receptacle means coupled to
receive the samples derived through said probe means.
3. Apparatus in accordance with claim 2, and further including
second hollow probe means of restricted cross-section disposed in
the stream of diluent air at a location to derive, for analysis,
samples of such air at a region upstream of the point of connection
of said conduit carrying the engine exhaust.
4. Apparatus in accordance with claim 1, and in which said pump
means is of the centrifugal type.
5. Apparatus in accordance with claim 1, and further characterized
by the inclusion of: means defining a plurality of flow paths
disposed in parallel, each including its own source of diluent air
and each adapted for connection to a separate engine; a plurality
of venturi restrictions each individual to a corresponding one of
said flow paths; and a single pump coupled in the system to draw
the mixture flowing in each flow path through the venturi
restriction included in that path.
6. Apparatus in accordance with claim 5, and in which said means
for deriving samples includes a plurality of probes of restricted
cross-section, each probe being disposed to sample the mixture
flowing in a corresponding one of said flow paths.
7. Apparatus in accordance with claim 1, and in which said means
for deriving samples is disposed in the region of said venturi
restriction and comprises: a conduit having a part disposed to
receive a small portion only of said mixture; a part defining in
said conduit an auxiliary venturi restriction; and means insuring
that said auxiliary venturi restriction operates at conditions of
critical gas flow during sampling.
8. Apparatus in accordance with claim 7, and further characterized
in that the ratio of the minimum cross-sectional areas of the two
venturi restrictions is solely determinative of the quantity of
flow through each.
9. In apparatus for sampling the gaseous emissions of internal
combustion engines, for collection and analysis, a source of
diluent air adapted for connection with a conduit carrying the
exhaust of an engine, to produce a mixture of emissions and diluent
air, means for deriving samples of said mixture for analysis, and
means for regulating the flow of said mixture to maintain the flow
rate substantially constant, said last means comprising: a venturi
restriction coupled in the apparatus to receive said mixture; and
pump means coupled to said venturi restriction and effective to
cause flow of the mixture therethrough, said pump means being of a
capacity sufficient to insure that the venturi restriction operates
at conditions of critical gas flow throughout test periods.
10. In apparatus for sampling the gaseous emissions of internal
combustion engines for analysis, means providing an inlet source of
diluent air, means coupling said source with a conduit carrying the
exhaust of an engine, to produce a mixture of emissions and diluent
air, conduit means through which said mixture passes and including
heat exchanger means effective to maintain the mixture at a
substantially constant temperature throughout a test period, means
coupled to said conduit means and effective to derive samples of
said mixture after passage through said heat exchanger means and to
collect said samples for analysis, and means for regulating the
flow of said mixture through said apparatus to maintain the flow
rate substantially constant, said last means comprising: means
defining a venturi restriction having an inlet side and an
expansion side, said inlet side being coupled to said conduit means
to receive the mixture flowing therethrough; and a centrifugal pump
coupled to the expansion side of said venturi restriction and
effective to draw the mixture therethrough, said centrifugal pump
being of capacity sufficient to insure that the venturi restriction
operates at conditions of critical gas flow throughout test
periods.
Description
BACKGROUND OF THE INVENTION
Standards have been set*(*See Section 1201, Chapter XII, Title 45
of the Code of Federal Regulations, as published in Federal
Register, Vol. 36, No. 128, Friday, July 2, 1971, at pages 12652 et
seq.) providing that exhaust emissions from 1973 and 1974 motor
vehicles shall not exceed specified values for certain
contaminants. For example the emissions may not exceed:
hydrocarbons -- 3.4 grams per vehicle mile; carbon monoxide -- 39.0
grams per vehicle mile; and oxides of nitrogen -- 3.0 grams per
vehicle mile.
The presence of such standards has made it imperative that the
exhaust emissions from vehicle engines be tested and analyzed to
determine the relative amounts of impurities therein. Much effort
has gone into the development of equipment for use in this field of
gas sampling and it is now known to pass gases from an internal
combustion engine through test apparatus at an accurately
controlled flow rate for purposes of determination, and analysis,
of the relative amounts of impurities. Since the engine is
"breathing" ambient air, and since such air is itself a source of
contaminants, care is taken that the analysis accurately reflects
the contaminants introduced by the engine only. The apparatus
currently available for sampling provides for introduction of
diluent air and combining of the same with the exhaust gases. A
proportional part of the diluted exhaust emissions is collected
continuously, for subsequent analysis, using a constant volume
(although variable dilution) sampler. A system which satisfies
these requirements, as set out by the Environmental Protection
Agency, is shown in diagrammatic form and described in the
identified portion of the Federal Register. (See also FIG. 1
hereof.)
The apparatus as illustrated and described utilizes a positive
displacement pump, specifically a Roots blower, to provide the
constant volume flow which is a prerequisite to successful
operation of the equipment. The volumetric flow rate is determined
as a function of the number of revolutions of the positive
displacement pump.
Apparatus of this kind is subject to a number of difficulties and
disadvantages among which are the following. Such equipment
customarily operates in what can be termed a hostile environment.
That is, the exhaust gases contain corrosive substances as well as
particulate matter. Such matter tends to build up within the
constant displacement pump, gradually diminishing the fine working
clearances and causing variation in displacement, and even pump
failure. Because of these problems periodic shutdowns of the
apparatus are necessary for maintenance and cleaning purposes. In
addition it has not been possible completely to eliminate leakage
across the pump, which is a function of gas temperature and
differential pressure. The leakage factor must be taken into
account in conducting tests with the equipment known heretofore,
and maintenance of this factor within predetermined limits requires
relatively frequent calibration tests of the positive displacement
pump, in order to insure continuing accuracy of flow measurement.
Further, it has been found that when such pumps are used in the
mentioned hostile environment pump damage results from the presence
of excessive heat as well as the corrosive elements referred to
above.
There is growing emphasis on turbine type engines and these engines
must also be subjected to exhaust testing. As can readily be
appreciated, a constant displacement pump system of the kind shown
and described in the Federal Register would have to be of enormous
proportions in order to deal with the output of such engines,
particularly when it is recognized that the pump also must handle
the dilution air admitted into the system.
SUMMARY OF THE INVENTION
I have discovered that all of the foregoing difficulties and
limitations can be eliminated in relatively simple manner by
utilizing a different constant flow device in place of the positive
displacement pump used heretofore. For this purpose I use a venturi
device in combination with a pump of capacity sufficient to insure
that the venturi operates at conditions of critical flow, that is,
under conditions such that gases reach sonic speed in the throat of
the venturi. It will be recognized by those skilled in the art that
the maximum gas velocity that can occur through the minimum area of
a flow channel is equal to the velocity of sound. As a coreelary it
has been recognized that the gas, by weight, reaches its maximum
flow rate when passing through the restriction under the sonic, or
critical, flow condition.
Since a venturi device operated in this way is inherently a
constant volume flow device, I subject the system to sufficient
pressure difference across the venturi to insure that the sonic
condition is reached and maintained throughout the test. For this
purpose I prefer to employ a simple centrifugal air pump, or
blower, coupled to the expansion side of the venturi and of
capacity sufficient to maintain critical flow of the mixture of
exhaust gases and diluent air through the venturi. If desired it is
possible, in accordance with the principles of my invention, to use
a plurality of constant flow venturi gas samplers in parallel, each
fed from a separate engine and preferably with a single centrifugal
pump or blower.
With the foregoing in mind it is the general objective of this
invention to provide improved sampling apparatus which will operate
in a predetermined range of flow and volume in an entirely reliable
and predictable manner, and with minimal deterioration of critical
components and virtual elimination of problems due to particulate
accumulation. More specifically, my improved apparatus operates
with such accuracy of flow measurement that deviations of only 1
percent in flow rate are currently achieved, and this with a
reduction of audible noise output and greatly prolonged life of the
equipment. It is possible to scale flow rates up or down relatively
easily, and I have built units which are rated at 100, 300 and 350
CFM (standard air).
The periodic calibration tests presently required on prior art
systems are not necessary with my apparatus and, in one embodiment,
temperature changes are no longer a limitation. Additionally,
variations in leakage rate are no longer of consequence. A very
important advantage of the improved system is that it is readily
usable in the sampling of exhaust emissions from turbine
engines.
In considering the nature and importance of the present
improvement, it is desirable to record that while the critical flow
characteristics of venturis have long been recognized, it has not
previously been known to utilize this characteristic to achieve the
advantages mentioned above. This fact is particularly significant
when it is borne in mind that in recent years great effort and
expense has been devoted to the production of emission sampling
equipment, and yet those engaged in these efforts have not advanced
the art beyond the system described in the Federal Register.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic illustration of the prior art exhaust gas
sampling system illustrated and described in the Federal
Register;
FIG. 2 is a perspective view of the actual hardware comprising a
sampling system constructed in accordance with the present
invention;
FIG. 3 is a diagrammatic view of the apparatus illustrated in FIG.
2;
FIG. 4 is a sectional view, on a larger scale, illustrating a
critical flow venturi of the type used in the apparatus illustrated
in FIGS. 2 and 3;
FIG. 5 is a diagrammatic view of a modified form of the invention
employing a plurality of constant flow of venturi devices arranged
in parallel; and
FIG. 6 is a perspective illustration of modified apparatus in which
a heat exchanger is not employed, and which apparatus is
particularly suited for testing gas emissions from turbine
engines.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is first made to FIG. 1, which illustrates the system
which presently satisfies the requirements of the Environmental
Protection Agency and which is illustrated in the Federal Register.
The apparatus of the present invention has elements in common with
this system. However, as will now be understood, it incorporates a
critical flow venturi and associated centrifugal blower in place of
the positive displacement pump appearing in FIG. 1.
In operation of the known apparatus shown in FIG. 1 the total
volumetric flow of exhaust gas, derived (throughout a simulated
driving cycle) from tail pipe adaptor 10, and from air introduced
through the dilution inlet 11, is metered by passing through a
positive displacement pump identified with that term and bearing
the reference numeral 12. Samples of the exhaust gas and diluent
air flow through suitable conduits and are collected in the bags or
receptacles shown, respectively, at 13 and 14. Filters are
introduced in the conduits where required, see for example the
three-part filter assembly 15 disposed in air inlet 11, and also
the filters appearing at 16 and 17 in the gas sampling lines which
are fed by probes 18 and 19. Three-way solenoid valves 20 and 21
direct sample streams either to their respective bags 14 or 13 or
to discard. Leak-tight fittings and suitable shut-off devices are
also employed, as are counter devices 22 and 23 which count the
revolutions of the constant displacement pump while tests are in
progress and samples are being collected.
In approved apparatus, incorporating as it does a constant
displacement pump, mixing of the entire stream of gas from an
internal combustion engine with a quantity of diluted air, insures
that a constant volume of the mixture will be translated through
the equipment during the entire test. It will be understood that
when a vehicle engine is under load, a larger portion of the
mixture will be exhaust gas. The approved equipment is so designed
that only a very small portion of the mixture is comprised of
contaminants. Small samples of the mixture are drawn off and
diverted to analyzing equipment (not shown). In such apparatus, as
long as flow through the equipment is maintained constant, the
proportion of gas drawn off will always be uniform. Since all of
the contaminants (after suitable correction for the atmospheric
conditions prevailing on the day of the test; see probe 18 and bag
14) can be assumed to come from the vehicle exhaust, sampling of a
constant fraction will permit calculation of the grams of
contaminant included in the entire stream of exhaust. As noted
above, a Roots blower has been used as the constant volume
displacement device, and counting the number of revolutions of the
pump or blower provides a direct indication of the quantity of
mixture displaced per unit of time. It is this blower which has the
limitations, and presents the difficulties, which my invention
overcomes.
In a system of the kind shown in FIG. 1 the inlet gas temperature
to the positive displacement pump 12 must be substantially
constant, in order that the pump may serve as a constant volume
metering device. A heat exchanger H is illustrated in FIG. 1, and
this heat exchanger, as is apparent from the legends appearing on
the drawing includes means for both heating and cooling the gases.
This exchanger, which need not be described in further detail
herein, meets the requirements of constant volume flow.
During an exhaust emission test, samples are collected in the
receptacles, or bags, 13 and 14, and analytical tests are made to
determine the hydrocarbon, carbon monoxide and oxides of nitrogen
mass emissions. In making such determinations use is made of
suitable analytical apparatus which is also shown diagrammatically
and described in the Regulations. Such analytical equipment need
not be illustrated or considered herein, since, per se, it forms no
part of the present invention.
Under the present standards a sample-collecting test is conducted
while simulating an average trip (e.g. 7.5 miles) in an urban area,
assuming a cold start. A proportionate part of the diluted gas
emissions is collected continuously for analysis, such
proportionate part being diluted with air to a constant volume.
For further and more detailed description of the system of FIG. 1,
and of the manner in which the apparatus thereof is controlled and
energized, reference should be had to the Federal Register which
includes a complete description of this system, including the
apparatus (not shown) for conducting gas analyses.
Apparatus of this kind, which as noted constitutes the present
standard, is subject to the difficulties and disadvantages set
forth above. In essence the present invention eliminates these
difficulties by separating the air metering function from the air
pumping function. This is done by utilizing a critical flow
venturi, for the metering function, in combination with a simple
and compact centrifugal blower. Apparatus of this improved type is
shown in FIGS. 2 and 3 now to be described. Later in this
specification reference will be made to FIG. 5, in which a
plurality, for example two, venturis are used in place of the
single venturi device of the apparatus shown in FIG. 3.
Referring first to FIG. 2, there is illustrated apparatus which has
yielded very good results. This apparatus is shown housed in a
cabinet 24 and comprises an inlet conduit 25 adapted for connection
to the exhaust pipe of an internal combustion engine (not shown).
Environmental air flows down through the stack 28 into a chamber
27, and thence upwardly through a conduit 26 to join the exhaust
gas inletted through 25. The combined gas and air pass through
conduit 29 into a separator 30. This separator is of known
centrifugal type and functions to remove from the air stream fine
particles which are introduced either through the conduit 25 or the
stack 28. After passing through the centrifugal separator the
mixture of gas and air moves through a conduit 31 and enters a heat
exchanger 32 which leads, through a passage 33, to a critical flow
venturi shown generally at 34. The heat exchanger is of a kind
shown diagrammatically in FIG. 1, and constitutes an element which
was hitherto essential to air sampling systems. As explained later
in this description, my invention also contemplates embodiments
which omit the heat exchanger. This is particularly important where
exhaust emissions from a turbine engine are to be sampled, since
the heat exchanger would be excessive in size.
The improved apparatus of FIG. 2 also includes a centrifugal blower
35 which is coupled, by a sleeve and clamp assembly shown at 36, to
the outlet or expansion side of the venturi device 34.
The system of FIG. 2 is shown diagrammatically in FIG. 3, which
latter figure bears reference numerals corresponding to those
appearing in FIG. 2. The centrifugal separator 30 is not
illustrated in FIG. 3, but it should be understood that such a
separator is preferably employed. It has the advantage of producing
an intimate mixture of particulate matter, exhaust gas and air. As
is the case with the positive displacement pump system of FIG. 1,
probes 18a and 18b are, respectively, disposed to sample the
diluent air and the mixture of exhaust and diluent air prior to
delivery of the samples to air bags, not shown. The blower 35 of
the system of FIG. 2 also appears in FIG. 3, and it is believed
that operation of the apparatus of this diagrammatic figure will
now be understood without further description. It should, however,
be recognized that a system in accordance with FIGS. 2 and 3 would
also include the filters, valving and gas collection
instrumentalities shown in the apparatus of FIG. 1, as well as the
necessary switching apparatus. The revolution counters of FIG. 1
are, of course not required in a system of the kind
diagrammatically represented in FIG. 3, since the system of the
latter figure, as well as the other embodiments of this invention,
employ a venturi device rather than a rotating positive
displacement pump.
Turning now to FIG. 4 there is seen an enlarged cross sectional
illustration of the venturi device 34. This device is specifically
designed to achieve a proper flow rate, in this case 300 CFM, when
operating under conditions of critical flow. The venturi is the
result of mathematical analysis and development tests which require
no treatment herein, since the nature thereof will be understood by
those skilled in the art, it only being necessary to specify the
desired rate (300 CFM at critical flow).
The length of the venturi along its axis, measured from the inlet
end at 37 to the outlet 38, which latter flares outwardly from the
expansion portion 39, is equal to 14.25 inches. The throat of the
venturi is defined by the narrow annular area represented in the
drawing at 40 and having a dimension parallel to the axis of the
venturi and equal to 0.100 inch. The inlet portion of the venturi
can be considered as being measured from the reference line 40a to
the plane of the inlet orifice 37 and is equal to 2.528 inches. The
flare angle of this inlet portion is 30.degree. with respect to the
axis of the venturi.
The expansion portion of the device extends from the reference line
40b to a lefthand line of reference shown at 41, a distance equal
to 9.062 inches and at a flare angle of 6.degree.. From the plane
of termination of the expansion portion of the venturi, i.e.
reference line 41, the device flares at an angle of
27.degree.9/minutes, with respect to the axis and terminates in the
exit orifice located in the plane shown at 38 in FIG. 4.
The venturi device is fabricated of suitable corrosion resistant
steel, and has a wall thickness of 0.25 inch. The tubing 33 which
extends into adjacency with the inlet of the venturi terminates in
a flanged portion 42 which confronts a similar portion 43, formed
on the venturi inlet. A circular clamp 44 serves to secure the two
flanges in confronting relation. At the opposite end of the venturi
device the flared outlet is provided with a circumferential flange
45 which is shaped and disposed to cooperate with a sleeve 46
forming a part of the housing of centrifugal blower 35. As
mentioned earlier in this description, a sleeve of resilient
material surrounds the portions 45 and 46 and is secured by
clamping structure 36.
As will be understood from the foregoing description, the venturi
34 serves as a means for metering the flow of gaseous mixture and
maintains the flow rate of said mixture within very close limits.
Since the mixture of exhaust gas and diluent air flows through the
venturi throughout a test, and because the pump means coupled to
the expansion side of the venturi restriction is of capacity
sufficient to insure that the restriction operates at conditions of
critical gas flow throughout any test period, the combined venturi
and pump operate, inherently, as a constant volume flow control
device.
FIG. 5 illustrates a modified embodiment of the invention in which
two systems of the kind illustrated in FIG. 3 are operated in
parallel, with common manifolding 47 adapted to receive the outflow
of two venturi devices 34a and 34b. A single blower 35a, or other
pressure reducing device, is coupled to the common manifold 47,
with provision for final exhausting of the output at 48. Such a
multiple system, which may include more than two venturi devices in
parallel, is adapted to receive gaseous input from several internal
combustion engines simultaneously, as is clear from the presence of
exhaust pipe connections 25a and 25b. The probes 18c and 18d would,
of course, be coupled with gas analyzer equipment (not shown).
In constant volume gas sampling, using embodiments of the kind
described thus far, the inlet gas temperature to the critical flow
venturi must be substantially constant. For this reason a heat
exchanger, which includes means for heating or cooling the gases,
has been provided and illustrated in the preceding embodiments.
An alternate approach, which provides a constant percentage sample
flow rate without the necessity of a heat exchanger, is illustrated
in FIG. 6. In common with the systems already described, the
mixture of exhaust gas and diluent air is fed to the inlet side of
a venturi 34' which is coupled to an excess capacity centrifugal
pump 35'. Gas samples are derived through a probe comprising a
small tube 19' which, in this embodiment, is provided with a
venturi restriction as appears at R. A small blower B is provided.
This blower is of sufficient capacity to maintain critical flow
within the venturi R. It can readily be demonstrated that the
quantity of flow taking place through the small venturi R, as a
percentage of the primary stream flow through venturi 34', is
constant and equal to the ratio of the areas of the two venturis.
Since the flow through each venturi is a function of the
temperature of the gas mixture, and since the same temperature
prevails at each venturi, no temperature compensation is necessary
and the ratio of the areas is solely determinative of the
respective flows. As will be understood, samples of gas derived
from the venturi R and the blower B would be fed to collection
equipment and suitable analyzing apparatus. Apparatus of this kind
is particularly useful in the testing of emissions from gas turbine
engines. The term "internal combustion," as used in the appended
claims, should be understood as including such engines within its
scope.
* * * * *