Adjustment of the dilution ratio. The dilution air must be set such that the temperature of the diluted exhaust gas measured immediately prior to the primary filter must not exceed 325 K (52°C) at any mode. The dilution ratio (q) must not be less than 4. For systems that use CO2 or NOx concentration measurement for dilution ratio control, the CO2 or NOx content of the dilution air must be measured at the beginning and at the end of each test. The pre- and post test background CO2 or NOx concentration measurements of the dilution air must be within 100 ppm or 5 ppm of each other, respectively.
Adjustment of the dilution ratio. The particulate sampling system shall be started and running on bypass for the single filter method (optional for the multiple filter method). The particulate background level of the dilution air may be determined by passing dilution air through the particulate filters. If filtered dilution air is used, one measurement may be done at any time prior to, during, or after the test. If the dilution air is not filtered, measurements at a minimum of three points, after the starting, before the stopping, and at a point near the middle of the cycle, are required, and the values averaged. The dilution air shall be set to obtain a maximum filter face temperature of 325K (52 °C) or less at each mode. The total dilution ratio shall not be less than four. For the single filter method, the sample mass flow rate through the filter shall be maintained at a constant proportion of the dilute exhaust mass flow rate for full flow systems for all modes. This mass ratio shall be within ± 5 per cent, except for the first 10 seconds of each mode for systems without bypass capability. For partial flow dilution systems with single filter method, the mass flow rate through the filter shall be constant within ± 5 per cent during each mode, except for the first 10 seconds of each mode for systems without bypass capability. For CO2 or NOx concentration controlled systems, the CO2 or NOx content of the dilution air must be measured at the beginning and at the end of each test. The pre- and post-test background CO2 or NOx concentration measurements of the dilution air must be within 100 ppm or 5 ppm of each other, respectively. When using a dilute exhaust gas analysis system, the relevant background concentrations shall be determined by sampling dilution air into a sampling bag over the complete test sequence. Continuous (non bag) background concentration may be taken at the minimum of three points, at the beginning, at the end, and a point near the middle of the cycle and averaged. At the manufacturer’s request background measurements may be omitted.
