1065.376—Chiller NO2 penetration.
(a) Scope and frequency.
If you use a chiller to dry a sample upstream of a NOX measurement instrument, but you don't use an NO[=E T=8052]2-to-NO converter upstream of the chiller, you must perform this verification for chiller NO[=E T=8052]2 penetration. Perform this verification after initial installation and after major maintenance.
(b) Measurement principles.
A chiller removes water, which can otherwise interfere with a NOX measurement. However, liquid water remaining in an improperly designed chiller can remove NO[=E T=8052]2 from the sample. If a chiller is used without an NO[=E T=8052]2-to-NO converter upstream, it could remove NO[=E T=8052]2 from the sample prior NOX measurement.
(c) System requirements.
A chiller must allow for measuring at least 95% of the total NO[=E T=8052]2 at the maximum expected concentration of NO[=E T=8052]2.
(1) Instrument setup.
Follow the analyzer and chiller manufacturers' start-up and operating instructions. Adjust the analyzer and chiller as needed to optimize performance.
(2) Equipment setup and data collection.
(i)
Zero and span the total NOX gas analyzer(s) as you would before emission testing.
(ii)
Select an NO[=E T=8052]2 calibration gas, balance gas of dry air, that has an NO[=E T=8052]2 concentration within ±5% of the maximum NO[=E T=8052]2 concentration expected during testing.
(iii)
Overflow this calibration gas at the gas sampling system's probe or overflow fitting. Allow for stabilization of the total NOX response, accounting only for transport delays and instrument response.
(vi)
Next saturate the sampling system by overflowing a dewpoint generator's output, set at a dewpoint of 50 °C, to the gas sampling system's probe or overflow fitting. Sample the dewpoint generator's output through the sampling system and chiller for at least 10 minutes until the chiller is expected to be removing a constant rate of water.
(vii)
Immediately switch back to overflowing the NO[=E T=8052]2 calibration gas used to establish x
NOxref. Allow for stabilization of the total NOX response, accounting only for transport delays and instrument response. Calculate the mean of 30 seconds of recorded total NOX data and record this value as x
NOxmeas.
(viii)
Correct x
NOxmeas to x
NOxdry based upon the residual water vapor that passed through the chiller at the chiller's outlet temperature and pressure.
(3) Performance evaluation.
If x
NOxdry is less than 95% of x
NOxref, repair or replace the chiller.
(1)
You may omit this verification if you can show by engineering analysis that for your NOX sampling system and your emission calculations procedures, the chiller always affects your brake-specific NOX emission results by less than 0.5% of the applicable NOX standard.
(2)
You may use a chiller that you determine does not meet this verification, as long as you try to correct the problem and the measurement deficiency does not adversely affect your ability to show that engines comply with all applicable emission standards.