# Commission Delegated Regulation (EU) 2017/654 of 19 December 2016 supplementing Regulation (EU) 2016/1628 of the European Parliament and of the Council with regard to technical and general requirements relating to emission limits and type-approval for internal combustion engines for non-road mobile machinery, Division 2.5.3: Subsonic venturi (SSV)

Extent: E+W+S+N.I.

Calibration of the SSV is based upon the flow equation for a subsonic venturi. Gas flow is a function of inlet pressure and temperature, pressure drop between the SSV inlet and throat, as shown in equation (7-40).
The airflow rate (qV SSV) at each restriction setting (minimum 16 settings) shall be calculated in standard m3/s from the flowmeter data using the manufacturer's prescribed method. The discharge coefficient shall be calculated from the calibration data for each setting by means of equation (7-73):
C d = q V SSV A 0 60 d 2 V p p 1 T in,V r 1,4286 p − r 1,7143 p 1 1 − r 4 D r 1,4286 p
(7-73)
Where:
A 0 collection of constants and units conversions = 0,0056940 m 3 min × K 1 2 kPa × 1 mm 2
qV SSV air flow rate at standard conditions (101,325 kPa, 273,15 K) [m3/s]
T in,V temperature at the venturi inlet [K]
d V diameter of the SSV throat [mm]
r p ratio of the SSV throat to inlet absolute static pressure = 1 – Δp/p p [-]
r D ratio of the SSV throat diameter, d V, to the inlet pipe inner diameter D [-]
To determine the range of subsonic flow, C d shall be plotted as a function of Reynolds number Re, at the SSV throat. The Re at the SSV throat shall be calculated by means of equation (7-74):
R e = A 1 × 60 × q V SSV d V × μ
(7-74)
with
μ = b × T 1,5 S + T
(7-75)
Where:
A1 collection of constants and units conversions = 27,43831 Kg m 3 × min s × mm m
qV SSV air flow rate at standard conditions (101,325 kPa, 273,15 K) [m3/s]
d V diameter of the SSV throat [mm]
μ absolute or dynamic viscosity of the gas [kg/(m · s)]
b 1,458 × 106 (empirical constant) [kg/(m · s · K0,5)]
S 110,4 (empirical constant) [K]
Because qV SSV is an input to the Re equation, the calculations shall be started with an initial guess for qV SSV or C d of the calibration venturi, and repeated until qV SSV converges. The convergence method shall be accurate to 0,1 % of point or better.
For a minimum of sixteen points in the region of subsonic flow, the calculated values of C d from the resulting calibration curve fit equation shall be within ± 0,5 % of the measured C d for each calibration point.

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Source: https://www.legislation.gov.uk/eur/2017/654/annex/VII/division/2/division/2.5/division/2.5.3 (the official version)
Page: https://openlegislation.uk/eu-regulation-2017-654/annex-VII/division-2/division-2.5/division-2.5.3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.