91.409 Engine dynamometer test run.§ 91.409 Engine dynamometer test run.
(a) Engine and dynamometer start-up.
(1) Only adjustments in accordance with § 91.118 may be made to the test engine prior to starting a test.
(2) If necessary, warm up the dynamometer as recommended by the dynamometer manufacturer ore good engineering practice.
(3) At the manufacturer's option, the engine can be run with the throttle in a fixed position or by using the engine's governor (if the engine is manufactured with a governor). In either case, the engine speed and load must meet the requirements specified in paragraph (b)(12) of this section.
(b) Each test consists of the following:
(1) Record the general test data as specified in § 91.405.
(2) Precondition the engine in the following manner;
(i) Operate the engine at idle for 2 to 3 minutes;
(ii) Operate the engine at a power greater than or equal to 50 percent power at the rated speed for 5 to 7 minutes;
(iii) Operate the engine at rated speed and maximum power for 25 to 30 minutes;
(iv) Option. For four-stroke engines, where appropriate, it is permitted to precondition the engine at rated speed and maximum power until the oil and water temperatures are stabilized. The temperatures are defined as stabilized if they are maintained within 2 percent of point for 2 minutes. The engine must be operated a minimum of 10 minutes for this option. This optional procedure may be substituted for step in paragraphs (b)(2)(iii) of this section;
(v) Option. If the engine has been operating on service accumulation for a minimum of 40 minutes, the service accumulation may be substituted for steps in paragraphs (b)(2) (i) through (iii) of this section.
(3) Record all pre-test data specified in § 91.405(c).
(4) Start the test cycle (see § 91.410) within 10 minutes of the completion of the steps required by paragraph (b)(2) of this section.
(5) During the first mode calculate the torque corresponding to 71.6, 46.5, and 25.3 percent of the maximum observed torque for the rated speed (see Table 2 in appendix A of this subpart).
(6) Once engine speed and load are set for a mode, run the engine for a sufficient period of time to achieve thermal stability. At the manufacturers option, determine and document the appropriate criterion for thermal stability for each engine family.
(7) Record all modal data specified in § 91.405(e) for a minimum time period of the last two minutes of each mode. Longer averaging periods are acceptable, but the data averaged must be from a continuous time period. The duration of time during which this data is recorded is referred to as the “sampling period.” The data collected during the sampling period is used for modal emission calculations.
(8) Continuously record the analyzer's response to the exhaust gas during the sampling period.
(9) Modes may be repeated.
(10) If a delay of more than one hour occurs between the end of one mode and the beginning of another mode, the test is void and must be restarted as described at paragraph (b)(1) of this section.
(11) The engine speed and load must be maintained within the requirements of § 91.410 during the sampling period for each mode. If this requirement is not met, the mode is void and must be restarted.
(12) If at any time during a mode, the test equipment malfunctions or the specifications in § 91.410 can not be met, the test is void, and must be aborted. Corrective action should be taken and the test restarted.
(13) Fuel flow and air flow during the idle condition may be determined just prior to or immediately following the dynamometer sequence, if longer times are required for accurate measurements. If the dilute sampling method (Constant Volume Sampling) is used, neither fuel flow nor air flow measurements are required.
(c) Exhaust gas measurements. (1) Measure HC, CO, CO2, and NOX concentration in the exhaust sample.
(2) Each analyzer range that may be used during a test segment must have the zero and span responses recorded prior to the start of the test. Only the range(s) used to measure the emissions during the test is required to have its zero and span recorded after the completion of the test. Depending on the stability of each individual analyzer, more frequent zero checks or spans between modes may be necessary.
(3) It is permitted to change filter elements between test segments.
(4) A leak check is permitted between modes.
(5) A hang-up check is permitted between modes (see § 91.413).
(6) If, during the emission measurement portion of a mode, the value of the gauges downstream of the NDIR analyzer(s) G3 or G4 (See Figure 1 in appendix B of subpart D of this part) differs by more than ±0.5 kPa, the mode is void.