Division 2.5.3: Subsonic venturi (SSV) - 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

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 (q_V _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} = \frac{q_{V SSV}}{\frac{A_{0}}{60} d_{2}^{V} p_{p} \sqrt{[\frac{1}{T_{in,V}} (r_{1,4286}^{p} - r_{1,7143}^{p}) (\frac{1}{1 - r_{4}^{D} r_{1,4286}^{p}})]}}

(7-73)

Where:

A ₀

collection of constants and units conversions $= 0,0056940 [\frac{m^{3}}{\min} \times \frac{K^{\frac{1}{2}}}{kPa} \times \frac{1}{{mm}^{2}}]$

q_V _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} \times 60 \times \frac{q_{V SSV}}{d_{V} \times μ}

(7-74)

with

μ = \frac{b \times T^{1,5}}{S + T}

(7-75)

Where:

A₁

collection of constants and units conversions = 27,43831 $[\frac{Kg}{m^{3}} \times \frac{\min}{s} \times \frac{mm}{m}]$

q_V _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 · K^0,5)]

S

110,4 (empirical constant) [K]

Because q_V _SSV is an input to the Re equation, the calculations shall be started with an initial guess for q_V _SSV or C _d of the calibration venturi, and repeated until q_V _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.

Division 2.5.3 Subsonic venturi (SSV)