90.408 Pre-test procedures.§ 90.408 Pre-test procedures.
(a) Engine service accumulation and stabilization procedure. Use the service accumulation procedure determined by the manufacturer for exhaust emission stabilizing of an engine, consistent with good engineering practice (see § 90.118).
(1) The manufacturer determines, for each engine family, the number of hours at which the engine exhaust emission control system combination is stabilized for emission testing. However, this stabilization procedure may not exceed 12 hours. The manufacturer must maintain, and provide to the Administrator upon request, a record of the rationale used in making this determination. If the manufacturer can document that at some time prior to the full 12 hour service accumulation period the engine emissions are decreasing for the remainder of the 12 hours, the service accumulation may be completed at that time. The manufacturer may elect to accumulate 12 hours on each test engine within an engine family without making this determination.
(2) During service accumulation, the fuel and lubricants specified in § 90.308 must be used.
(3) Engine maintenance during service accumulation is allowed only in accordance with § 90.118.
(b) Engine pre-test preparation. (1) Drain and charge the fuel tank(s) with the specified test fuel (see § 90.308(b)) to 50 percent of the tank's nominal capacity. If an external fuel tank is used, the engine fuel inlet system pressure must be typical of what the engine will see in use.
(2) An evaluation of the effects of test measurement systems on engine emissions shall be conducted using good engineering judgment to ensure that such test systems do not significantly impact exhaust emissions from the engine. For example, this would require evaluation of all types of emission sampling systems, and of fuel- and air-flow measurement systems for raw sampling. This can be accomplished by operating the engine at the highest engine torque value that will be encountered on the test cycle before and after such test systems are installed to ensure that the impact on measured torque is less than 5 percent. This may also be accomplished by measuring air-to-fuel ratio using a zirconia universal exhaust gas oxygen (UEGO) sensor to ensure that the impact on measured air-to-fuel ratio is less than 5 percent at the highest engine torque value that will be encountered on the test cycle before and after such test systems are installed. The impact of air- and fuel-flow measurement systems may be evaluated based on an engineering analysis of the impact of the change in pressure induced on air-intake pressure and fuel supply pressure by these measurement systems. While this would typically be done before testing, it may also be done as a post-test verification.
(c) Analyzer pre-test procedures. (1) If necessary, warm up and stabilize the analyzer(s) before calibrations are performed.
(2) Replace or clean the filter elements and then leak check the system as required by § 90.324(a). If necessary, allow the heated sample line, filters, and pumps to reach operating temperature.
(3) Perform the following system checks:
(i) If necessary, check the sample-line temperature. Heated FID sample line temperature must be maintained between 110 °C and 230 °C; a heated NOX sample line temperature must be maintained between 60 °C and 230 °C.
(ii) Check that the system response time has been accounted for prior to sample collection data recording.
(iii) A HC hang-up check is permitted (see § 90.413(e)).
(4) Check analyzer zero and span before and after each test at a minimum. Further, check analyzer zero and span any time a range change is made or at the maximum demonstrated time span for stability for each analyzer used.
(d) Check system flow rates and pressures and reset, if necessary.[60 FR 34598, July 3, 1995, as amended at 65 FR 24312, Apr. 25, 2000; 70 FR 40449, July 13, 2005]