Exhaust volume measurement device
View Patent ↗A vehicle exhaust measurement system is provided includes that a conduit having a conduit inlet and a conduit outlet. A make-up air tube is connected to and is in fluid communication with the conduit inlet. The make-up air tube provides make-up air for mixing an exhaust gas. A mixed gas tube is connected to and is in fluid communication with the conduit outlet. The mixed gas tube conveys a mixture of make-up air and exhaust gas to analysis equipment. In the preferred embodiment, the exhaust gas tube extends through an outer wall of the conduit. A mixing plate is arranged in either the conduit or the mixed gas tube with the exhaust gas tube extending to a position adjacent to the mixing plate. The exhaust gas tube conveys the exhaust gas to the mixing plate to mix the exhaust gas and the make-up air at the mixing plate. A correction factor may be applied to the measurements taken by a differential pressure based fluid flow measurement device such as a smooth approach orifice (SAO) to provide an adjusted flow of measurement at the flow measurement device to correct for the pressure pulsations. The correction factor is calculated based upon the intensity of the pulsations of the differential pressure signal, which indicates the flow through the SAO.
1. A method of correcting an exhaust flow measurement in a vehicle exhaust measurement system comprising the steps of:
a) measuring a pressure differential across a head type flow measurement device indicative of a magnitude of exhaust gas flow pressure pulsations;
b) determining a frequency of the exhaust gas pressure pulsations;
c) calculating a correction factor based upon the magnitude and the frequency of the exhaust gas pressure pulsations; and
d) applying the correction factor to measurements taken by the flow measurement device to provide an adjusted flow measurement at the flow measurement device.
2. A method of correcting an exhaust flow measurement in a vehicle exhaust measurement system comprising the steps of:
a) measuring a pressure differential across a head type flow measurement device indicative of a magnitude of exhaust gas flow pressure pulsations, wherein the flow measurement device is a smooth approach orifice measuring make-up air;
b) determining a frequency of the exhaust gas pressure pulsations;
c) calculating a correction factor based upon the magnitude and the frequency of the exhaust gas pressure pulsations; and
d) applying the correction factor to measurements taken by the flow measurement device to provide an adjusted flow measurement at the flow measurement device.
3. The method according to claim 2 , wherein the flow measurement device includes a differential pressure sensor fluidly connected to the smooth approach orifice at a throat location and an inlet location.
4. The method according to claim 3 , wherein the correction factor is applied to a flow determined from the smooth approach orifice.
5. The method according to claim 1 , wherein the correction factor is a function of pulsation intensity.
6. The method according to claim 5 , wherein the pulsation intensity is a function of magnitude and frequency of the exhaust gas pulsations.
7. The method according to claim 5 , wherein pulsation intensity I p is represented by the equation:
I
p
=
Δ
P
σ
Δ
P
μ
·
c
*
(
c
*
+
10.64
·
f
4
·
Δ
x
)
,
wherein
c
*
=
c
-
Q
min
π
ϕ
in
2
4
,
c is speed of sound, ΔP μ is filtered frequency signal, ΔP σ is the magnitude, f is the frequency, Δx is distance between pressure transducer taps at flow measurement device, Q air is volumetric make-up air flow, and d th is throat diameter of the flow measurement device.
8. The method according to claim 7 , wherein the correction factor F p (I p ) is represented by the equation:
F
p
(
I
p
)
=
1
2
·
π
·
∫
0
2
x
(
I
p
·
sin
(
θ
)
+
1
)
ⅆ
θ
.
9. The method according to claim 7 , wherein , ΔP μ is a cutoff frequency at approximately half of a minimum frequency of the exhaust gas pressure pulsations.
10. The method according to claim 5 , wherein the pulsation intensity is a function of the ratio of a filtered frequency and the magnitude.
11. The method according to claim 10 , wherein the filtered frequency is a cutoff frequency at approximately half of a minimum frequency of the exhaust gas pressure pulsations.
12. A method of correcting an exhaust flow measurement in a vehicle exhaust measurement system comprising the steps of:
a) providing a first and second venturi;
b) measuring a pressure differential across one of the venturis, the pressure differential indicative of a magnitude of exhaust gas flow pressure pulsations;
c) determining a frequency of the exhaust gas pressure pulsations;
d) calculating a correction factor based upon the magnitude and the frequency of the exhaust gas pressure pulsations; and
e) applying the correction factor to measurements taken by one of the venturis to provide an adjusted flow measurement.
13. The method according to claim 12 , wherein the first and second venturis respectively are subsonic an sonic venturis, step b) performed at the subsonic venturi.
14. The method according to claim 13 , wherein the subsonic venturi is a smooth approach orifice.
15. The method according to claim 13 , wherein step e) is performed according to the equation:
Q ex =Q CFV −F p ( I p (Δ P μ, ΔP σ, f ))· Q air ,
wherein Q ex is exhaust flow, Q CFV is flow through the sonic venturi, F p is the correction factor, I p is pulsation intensity, ΔP μ is filtered frequency signal, ΔP σ is the magnitude, f is the frequency, and Q air is make-up air flow through the subsonic venturi.
16. The method according to claim 15 , wherein, ΔP μ is a cutoff frequency at approximately half of a minimum frequency of the exhaust gas pressure pulsations.
17. The method according to claim 15 , wherein the pulsation intensity is a function of the ratio of a filtered frequency and the magnitude.
18. The method according to claim 17 , wherein the filtered frequency is a cutoff frequency at approximately half of a minimum frequency of the exhaust gas pressure pulsations.