FIGURE A74-6.-Typical activated carbon trap (schematic). outlet tube of the collection traps to prevent ambient moisture from entering the trap. It is prepared by filling the empty drying tube with fresh desiccant using loose wad of glass wool to hold the desiccant in place. The desiccant is renewed when three-quarters spent, as indicated by color change. (iii) Collection tubing-stainless steel or aluminum, 16 inch ID, for connecting the collection traps to the fuel system vents. (iv) Polyvinyl chloride (vinyl) tubing-flexible tubing, 16 inch ID, for sealing butt-to-butt joints. (v) Laboratory tubing-airtight flexible tubing 16 inch ID, attached to the outlet end of the drying tubes to equalize collection system pressure. (vi) Clamps-hosecock, open side, for pinching off flexible tubing. (c) Weighing equipment. The balance and weights used shall be capable of determining the net weight of the activated carbon trap within an accuracy of +75 mg. (d) Temperature measuring equipment. (1) Temperature recorder-multichannel, variable speed, potentiometric, or substantially equivalent recorder with a temperature range of 50° F. to 100° F. and capable of either simultaneous or sequential recording of the ambient air and fuel temperatures within an accuracy of +1° F. (2) Fuel tank thermocouples—ironconstantan (type J) construction. (3) Other types of temperature sensing systems may be provided by the manufacturer if they record the information specified in subparagraph (1) of this paragraph with the required accuracy and if they are self-contained. Type J thermocouples are required for compatability with recording instruments used in Federal certification facilities. (e) Assembly and use of the activated carbon vapor collection system. (1) The prepared activated carbon trap, dried to constant weight, cooled to the ambient temperature and sealed with clamped sections of vinyl tubing is carefully weighed to the nearest 20 milligrams and the weight recorded as the "tare weight." (2) A drying tube is attached to the outlet tube and the clamp released, but not removed. A length of flexible tubing, for pressure equalization, is connected to the other end of the drying tube. (3) The inlet tube of the adsorption trap and external vent(s) of the fuel system will be connected by minimal lengths of stainless steel or aluminum tubing and short sections of vinyl tubing. Buttto-butt joints shall be made wherever possible and precautions taken against sharp bends in the connection lines, including any manifold systems employed to connect multiple vents to a single trap. (4) The clamp on the inlet tube of the trap shall be released but not removed. Care shall be exercised to prevent heating the vapor collection trap by radiant or conductive heat from the engine. (5) Upon completion of the collection sequence, the vinyl tubing sections on each arm of the collection trap shall be clamped tight and the collection system dismantled. (6) The sealed vapor collection trap shall be weighed carefully to the nearest 20 milligrams. This constitutes the "gross weight," which is appropriately recorded. The difference between the "gross weight" and "tare weight" represents the "net weight" for purposes of calculating the fuel vapor losses. (b) System or device tested (brief description). (c) Date and time of day for each part of the test schedule. (d) Instrument operator. (f) Vehicle: Make-Vehicle identification number-Model year-Transmission type-Odometer reading-Engine displacement-Engine family-Idle r.p.m.Fuel system-(fuel injection, nominal fuel tank capacity, fuel tank location, number of carburetors, number of carburetor barrels)-Inertia loading-Estimated curb weight-Actual road load horsepower at 50 m.p.h. and drive wheel tire pressure. (g) Dynamometer serial number and indicated road load power absorption at 50 m.p.h. an (h) All pertinent instrument information such as tuning-gain-serial number-detector number-range. As alternative, a reference to a vehicle test cell number may be used, with the advance approval of the Administrator, provided test cell calibration records show the pertinent instrument information. (i) Recorder charts: Identify zero, span, exhaust gas, and dilution air sample traces. (j) Test cell barometric pressure, ambient temperature, and humidity. (k) Fuel temperatures, as prescribed. (1) Pressure of the mixture of exhaust and dilution air entering the positive displacement pump, the pressure increase across the pump, and the temperature set point of the temperature control system. The sample temperature at the inlet to the pump may be measured, if desired, to verify that the temperature variations are within 5° F. of the set point. (m) The number of revolutions of the positive displacement pump accumulated while the test is in progress and exhaust flow samples are being collected. § 85.074-23 Analytical system calibration and sampling handling. (a) Calibrate the analytical assembly at least once every 30 days. Use the same flow rate as when analyzing samples. (1) Adjust analyzers to optimize performance. (2) Zero the hydrocarbon analyzer with zero grade air and the carbon monoxide and oxides of nitrogen analyzers with either zero grade air or nitrogen. The allowable zero gas impurity concentrations should not exceed 6 p.p.m. equivalent carbon response, 10 p.p.m. carbon monoxide and 1 p.p.m. nitric oxide. (3) Set the CO and CO, analyzer gains to give the desired range. Select the desired attenuation scale of the HC analyzer, set the capillary flow rate by adjusting the back pressure regulator, and adjust the electronic gain control, if provided, to give the desired range. Select the desired scale of the NO analyzer and adjust the phototube high voltage supply or amplifier gain to give the desired range. (4) Calibrate the HC analyzer with propane (air diluent) gases having nominal concentrations of 50 and 100 percent of full scale. Calibrate the CO analyzer with carbon monoxide (nitrogen diluent) gases having nominal concentrations equal to 10, 25, 40, 50, 60, 70, 85, and 100 percent of full scale. Calibrate the NO, analyzer with nitric oxide (nitrogen diluent) gases having nominal concentrations equal to 50 and 100 percent of full scale. The actual concentrations should be known to within ±2 percent of the true values. (5) Compare values obtained on the CO analyzer with previous calibration curves. Any significant change reflects some problem in the system. Locate and correct problem, and recalibrate. Use best judgment in selecting curves for data reduction. (6) NO, Converter Efficiency Determination: The apparatus described and .illustrated in Figure A 74-7 is to be used to determine the conversion efficiency of devices that convert NO, to NO. The following procedure is to be used for determining the values to be used in Equation (A). (i) Attach the NO/N2 supply (150-250 p.p.m.) at C2, the O, supply at C1 and the analyzer inlet connection to the efficiency detector at C3. If lower concentrations of NO are used, air may be used in place of O, to facilitate better control of the NO, generated during step (iv). (ii) With the efficiency detector variac off, place the NO. converter in bypass mode and close valve V3. Open valve MV2 until sufficient flow and stable readings are obtained at the analyzer. Zero and span the analyzer output to indicate the value of the NO concentration being used. Record this concentration. (iii) Open valve V3 (on/off flow control solenoid valve for O2) and adjust valve MV1 (O, supply metering valve) to blend enough O, to lower the NO concentration (ii) about 10 percent. Record this concentration. (iv) Turn on the ozonator and increase its supply voltage until the NO concentration of (lii) is reduced to about 20 percent om (ii). NO, is now being formed from the NO+O, reaction. There must always be at least 10 percent unreacted NO at this point. Record this concentration. (v) When a stable reading has been obtained from (iv), place the NOx converter in the convert mode. The analyzer will now indicate the total NO. concentration. Record this concentration. (vi) Turn off the ozonator and allow the analyzer reading to stabilize. The mixture NO+0, is still passing through the converter. This reading is the total NO, concentration of the dilute NO span gas used at step (iii). Record this concentration. (vii) Close valve V3. The NO concentration should be equal to or greater than the reading of (li) indicating whether the NO contains any NO,. Calculate the efficiency of the NO, converter by substituting the concentrations obtained during the test into Equation (A). % Eff.= (v) — (iv) × 100 percent (vi) — (iv) The efficiency of the converter should be greater than 90 percent. Adjusting the converter temperature may be needed to maximize the efficiency. Efficiency checks should be made on each analyzer range using an NO span gas concentration appropriate to the instrument range. (b) HC, CO, and NO, measurements: Allow a minimum of 20 minutes warmup for the HC analyzer and 2 hours for the CO and NO, analyzers. (Power is normally left on infrared and chemiluminescence analyzers; but when not in use, the chopper motor of the infrared analyzer is turned off and the phototube high voltage supply of the chemiluminescence analyzer is placed in the standby position.) The following sequence of operations should be performed in conjunction with each series of measurements: (1) Zero the analyzers. Obtain a stable zero on each amplifier meter and recorder. Recheck after test. (2) Introduce span gases and set the CO analyzer gain, the HC analyzer sample capillary flow rate and the NO, ana lyzer high voltage supply or amplifier gain to match the calibration curves. In order to avoid corrections, span and calibrate at the same flow rates used to analyze the test samples. Span gases should have concentrations equal to approximately 80 percent of full scale. If gain has shifted significantly on the CO analyzer, check tuning. If necessary, check calibration. Recheck after test. Show actual concentrations on chart. (3) Check zeroes; repeat the procedure in subparagraphs (1) and (2) of this paragraph if required. (4) Check flow rates and pressures. (5) Measure HC, CO, and NO, concentrations of samples. Prevent moisture from condensing in the sample collection bag. (6) Check zero and span points. (c) For the purposes of this paragraph, the term "zero grade air" includes artificial "air" consisting of a blend of nitrogen and oxygen with oxygen concentrations between 18 and 21 mole percent. § 85.074-24 Dynamometer test runs. (a) The vehicle shall be allowed to stand with engine turned off for a period of not less than 12 hours before the exhaust emission test, at an ambient temperature as specified in §§ 85.074-12 and 85.074-13. The vehicle shall be stored prior to the emission tests in such a manner that precipitation (e.g., rain or dew) does not occur on the vehicle. During the run the ambient temperature shall be between 68° F. and 86° F. For exhaust emission testing which is unrelated to fuel evaporative emission control, the ambient temperature requirement during storage shall be between 60° F. and 86° F. (b) The following steps shall be taken for each test: (1) Place drive wheels of vehicle on dynamometer without starting engine. (2) Start the cooling fan with the vehicle engine compartment cover open. (3) With the sample solenoid valves in the "dump" position, connect evacuated sample collection bags to the dilute exhaust sample and the dilution air sample line connectors. (4) Start the positive displacement pump (if not already on), the sample pumps and the temperature recorder. (The heat exchanger of the constant volume sampler should be preheated to its operating temperature before the test begins.) (5) Adjust the sample flow rates to the desired flow rate (minimum of 5 c.f.h.). (6) Attach the flexible exhaust tube to the vehicle tailpipe (s). (7) Simultaneously start the revolution counter for the positive displacement pump, position the sample solenoid valves to direct the sample flows into the bags, and start cranking the engine. (8) Fifteen seconds after the engine starts, place the transmission in gear. (9) Twenty seconds after the engine starts, begin the initial vehicle acceleration of the driving schedule. (10) Operate the vehicle according to the dynamometer driving schedule. (§ 85.074-14). (11) Five seconds after the last deceleration, simultaneously turn off the revolution counter and position the sample solenoid valve to the "dump" position. (12) Immediately after the end of the sample period turn off the cooling fan and close the engine compartment cover. (13) Immediately disconnect sample bags, transfer to analytical system and process samples according to § 85.074-23 as soon as practicable, and in no case longer than 10 minutes after the dynamometer run. (14) Disconnect the exhaust tube from the vehicle tailpipe(s) and remove vehicle from dynamometer. (15) The positive displacement pump may be turned off, if desired. § 85.074-25 Chart reading. (a) Determine the HC, CO, and NO, concentrations of the dilution air and dilute exhaust sample bags from the instrument deflection or recordings making use of appropriate calibration charts. (b) Determine the average dilute exhaust mixture temperature from the temperature recorder trace if a recorder is used. § 85.074-26 Calculations (exhaust emissions). The final reported test results shall be computed by use of the following formulae: (a) For light duty vehicles, excluding off-road utility vehicles: (1) Hydrocarbon mass: DensityHC-Density of hydrocarbons in the exhaust gas, assuming an average carbon to hydrogen ratio of 1:1.85, in grams per cubic foot at 68° F. and 760 mm. Hg pressure (16.33 gm./cu. ft.). IICeone Hydrocarbon concentration of the dilute exhaust sample minus hydrocarbon concentration of the dilution air sample in p.p.m. carbon equivalent i.e. equivalent propane X 3. COman Carbon monoxide emissions, in grams per vehicle mile. Densityco Density of carbon monoxide in grams per cubic foot at 68° F. and 760 mm. Hg pressure (32.97 gm./cu. ft.). = COcone Carbon monoxide concentration of the dilute exhaust sample minus the carbon monoxide concentration of the dilution air sample, in volume present. NOxman Oxides of nitrogen emissions in grams 'per vehicle mile. Density No2= Density of oxides of nitrogen in the exhaust gas assuming they are in the form of nitrogen oxide, in grams per cubic foot at 68° F. and 760 mm. Hg pressure (54.16 gm./cu. ft.). where: K NOxcone Oxides of nitrogen concentration of the dilute exhaust sample minus the oxides of nitrogen concentration of the dilution air sample, in p.p.m. = Vmiz Total dilute exhaust volume in cubic feet per mile, corrected to standard conditions (528° R and 760 mm. Hg). PB-Pi Vmiz KiXV.XNX 528° R 760 mm. HgX7.5 miles TD =0.09263. V. Volume of gas pumped by the positive displace- PB-Barometric pressure in mm. Hg. at the inlet to the positive displacement pump. T, Average temperature of dilute exhaust entering positive displacement pump during test while samples are being collected, in degrees Rankine. Ka-Humidity correction factor. (d) Example calculation of mass emissions values: Assume V,-0.265 cu. ft. per revolution; N=20,250 revolutions; R. 65%; PB-754 mm. Hg; Pa=22.225 mm. Hg; P=24 mm.; Hg; T,-550°R; HCcone-160 p.p.m. carbon equivalent; CO cone=0.09%; and NOzcenc=70 p.p.m. Then: H= Vaiz=(0.09263) (0.265) (20,250) (754–24) 659.8 cu. ft. per mile (550) |