91.408 Pre-test procedures.§ 91.408 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 § 91.117).
(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 § 91.308 must be used.
(3) Engine maintenance during service accumulation is allowed only in accordance with § 91.117.
(b) Engine pre-test preparation. (1) Drain and charge the fuel tank(s) with the specified test fuel (see § 91.308) 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) Operate the engine on the dynamometer measuring the fuel consumption (fuel consumption required only for raw gas sampling method) and torque before and after the emission sampling equipment is installed, including the sample probe, using mode 1 from Table 2 in appendix A of this subpart. The emission sampling equipment may not significantly affect the operational characteristics of the engine (typically, the results should agree within five percent).
(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 vacuum leak check the system per § 91.324(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 hang-up check is permitted.
(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.