Directive 2005/55/EC of the European Parliament and of the Council of 28 September 2005 on the approximation of the laws of the Member States relating to the measures to be taken against the emission of gaseous and particulate pollutants from compression-ignition engines for use in vehicles, and the emission of gaseous pollutants from positive-ignition engines fuelled with natural gas or liquefied petroleum gas for use in vehicles (Text with EEA relevance) (repealed) (c. 55)

ANNEX III U.K. TEST PROCEDURE

Appendix 5 CALIBRATION PROCEDURE

2. CALIBRATION OF THE CVS-SYSTEM U.K.

2.3. Calibration of the Critical Flow Venturi (CFV) U.K.

Calibration of the CFV is based upon the flow equation for a critical venturi. Gas flow is a function of inlet pressure and temperature, as shown below:

where,

K_v

=

calibration coefficient

p_A

=

absolute pressure at venturi inlet, kPa

T

=

temperature at venturi inlet, K

2.3.1. Data analysis U.K.

The air flowrate (Q_s) at each restriction setting (minimum eight settings) shall be calculated in standard m³/min from the flowmeter data using the manufacturer's prescribed method. The calibration coefficient shall be calculated from the calibration data for each setting as follows:

where,

Q_s

=

air flow rate at standard conditions (101,3 kPa, 273 K), m³/s

T

=

temperature at the venturi inlet, K

p_A

=

absolute pressure at venturi inlet, kPa

To determine the range of critical flow, K_v shall be plotted as a function of venturi inlet pressure. For critical (choked) flow, K_v will have a relatively constant value. As pressure decreases (vacuum increases), the venturi becomes unchoked and K_v decreases, which indicates that the CFV is operated outside the permissible range.

For a minimum of eight points in the region of critical flow, the average K_v and the standard deviation shall be calculated. The standard deviation shall not exceed ± 0,3 % of the average K_V.