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PROCEDURE FOR DYNAMOMETER ROAD HORSE
POWER CALIBRATION This appendix describes the method for determining the road horsepower absorbed by a chassis dynamometer. The measured absorbed road horsepower includes the dynamometer friction as well as the power absorbed by the power absorption unit. The dynamometer is driven above the test speed range. The device used to drive the dynamometer is then disengaged from the dynamometer and the roll(s) is allowed to coast down. The kinetic energy of the system is dissipated by the dynamometer friction and absorption unit. This method neglects the variations in roll bearing friction due to the drive axle weight of the vehicle. The difference in coast down time of the free (rear) roll relative to the drive (front) roll may be neglected in the case of dynamometers with paired rolls.
These procedures shall be followed:
1. Devise a method to determine the speed of the drive roll if not already measured. A fifth wheel, revolution pickup or other suitable means may be used.
2. Place a vehicle on the dynamometer or devise another method of driving the dynamometer.
3. Engage inertia flywheel for the most common vehicle weight class for which the dynamometer is used.
4. Drive dynamometer up to 50 m.p.h.
7. Disengage the device used to drive the dynamometer.
8. Record the time for the dynamometer drive roll to coast down from 55 m.p.h. to 45 m.p.h.
9. Adjust the power absorption unit to a different level.
14. Once the road load horsepower at 50 m.p.h. is known for a vehicle, it may be tested on other dynamometers using a similar calibration.
APPENDIX III The following calibration procedure outlines the equipment, the test setup configuration, and the various parameters which must be measured to establish the flow rate of the constant volume sampler pump. All the parameters related to the pump are simultaneously measured with the parameters related to a flowmeter which is connected in series with the pump. The calculated flow rate (ft3/rev u pump inlet absolute pressure and temperature) can then be plotted versus a correlation function which is the value of a specific combination of pump parameters. The linear equation which relates the pump flow and the correlation function is then determined. In the event that a CVS has a multiple speed drive, a calibration for each range should be performed.
This calibration procedure is based on the measurement of the absolute values of the pump and flowmeter parameters that relate the flow rate at each point. Three conditions must be maintained to assure the accuracy and integrity of the calibration curve. First, the pump pressures should be measured at taps on the pump rather than at the external piping on the pump inlet and outlet. Pressure taps that are mounted at the top and bottom center of the pump drive headplate are exposed to the actual pump cavity pressures, and therefore reflect the absolute pressure differentials. Secondly, temperature stability must be maintained during the calibration. The laminar flowmeter is sensitive to inlet temperature oscillations which cause the data points to be scattered. Gradual changes (+ 2°F) in temperature are acceptable as long as they occur over a period of several minutes. Finally, all connections between the flowmeter and the CVS pump must be absolutely void of any leakage.
During a CVS emissions test the measurement of these same pump parameters enables the user to calculate the flow rate from the calibration equation,
After the calibration curve has been obtained, a verification test of the entire system can be performed by Injecting a known mass of gas into the system and comparing the mass indicated by the system to the true mass injected. An indicated error does not necessarily mean that the calibration is
wrong, since other factors can influence the accuracy of the system. Equipment:
The following list of equipment will be needed to perform this calibration procedure. Figure 1 illustrates a typical equipment arrangement used for calibration. All of the equipment involved should conform to the range and accuracy as specified in Figure 1. Equipment List:
1. LFE--Laminar Flowmeter
6. Temperature Indicator with type J Thermocouples
7. A variable flow restrictor with appropriate piping to connect the CVS pump and LFE.
After the system has been connected as shown in Figure 1, set the variable restrictor in the wide open position and run the CVS pump for twenty minutes. Record the calibration data.
APPENDIX IV DURABILITY DRIVING SCHEDULE The schedule consists basically of 11 laps of 3.7 mile course. The basic vehicle speed for each lap is listed below:
70 During each of the first nine laps there are 4 stops with 15 second idle. Normal accelerations and decelerations are used. In addition, there are 5 light decelerations each lap from the base speed to 20 m.p.h. followed by light accelerations to the base speed.
The 10th lap is run at a constant speed of 55 m.p.h.
The 11th lap is begun with a wide open throttle acceleration from stop to 70 m.p.h. A normal deceleration to idle followed by a second wide open throttle acceleration occurs at the midpoint of the lap.
*Note: The fluid level in the manometer tube should stabilize before the reading is made and the elapsed time for revolution counting should be greater than 120 seconds.
Reset the restrictor valve to a more re- fully, the calculated Vo values from the equastricted condition in an increment of pumption will be within +.50% of the measured inlet depression (aout 4' H2O) that will value of Vo. Values of M will vary from one yield a minimum of six data points for the pump to another, but values of Do for pumps total calibration.
of the same make, model, and range should Allow the system to stabilize for 3 minutes agree within +3% of each other. Particulate and repeat the data acquisition.
inaux from use will cause the pump slip to
decrease as reflected by lower values for M. Data Analysis:
Calibrations should be performed at 0, 50, 100, The data recorded during the calibration
200, 400, etc. hours of pump operation to asare to be used in the following calculations.
sure the stability of the pump slip rate. 1. The air flow rate at each test point is
Analysis of mass injection data will also recalculated in standard cubic feet per minute
flect pump slip stability. (Qs) from the flowmeter data using the man
CVS System Verification: ufacturer's prescribed method.
2. The air flow rate is then converted to The following technique can be used to pump flow, Vo, in cubic feet per revolution verify that the CVS and analytical instruat absolute pump inlet temperature and ments can accurately measure a mass of gas pressure.
that has been injected into the system.
1. Obtain a small cylinder that has been Vo= 5 * 530 * P,
charged with pure propane or carbon Where:
monoxide gas (caution-carbon monoxide is QS=Meter air flow rate in standard cubic feet per minute
poisonous !). Critical flow orifice devices can (flowmeter standard conditions are 70°F. 29.92
also be used for constant flow metering. "Hg). n=Pump speed in revolutions per minute.
2. Determine a reference cylinder weight to P = Absolute pump inlet pressure, in ("Hg).
the nearest 0.01 gram. P;=PB-PPI (SP.GR./13.57), To=PTI+460.
3. Operate the CVS in the normal manner 3. The correlation function at each test point is then and release a quantity of pure propane or calculated from the calibration data, as follows:
carbon monoxide into the system during the sampling period.
4. The calculations of $ 85.074–26 are perWhere:
formed in the normal way except, in the case AP,= The pressure differential from pumpinlet to pump of propane, the density of propane (17.30 outlet, in ("Hg). AP= P.-P.
grams/cu. ft./carbon atom) is used in place PE=Absolute pump outlet pressure P.-Pk+PPO (SP.GR./13.57).
of the density of exhaust hydrocarbons. In
the case of carbon monoxide, the density of See $ 85.074-26 for other definitions.
32.97 grams/cu. ft. is used. 4. A linear least squares fit is performed
5. The gravimetric mass is subtracted from to generate the calibration equations which
the CVS measured mass and then divided by have the forms
the gravimetric mass to determine the perVo=Do-M(Xo)
cent accuracy of the system. n=A-B(AP)
6. The cause for any discrepancy greater Do, M, A, and B are the slope-intercept than +2% should be found and corrected. constants describing the lines.
The following list of parametric errors may A CVS system that has multiple speeds assist the operator in locating the cause of should be callbrated on each speed used. The large errors. calibration curves generated for the ranges Positive Error (Indication is higher than will be approximately parallel and the inter true value): cept values, Do, will increase as the pump 1. Calculated V. is greater than actual Vo. flow range decreases.
a. Original calibration in error. If the calibration has been performed care- 2. Pump inlet temperature recorder is
reading low. A 6° F. discrepancy will give a 1% error.
3. Pump inlet pressure indicator is reading high. A 3.5 in. H20 high reading will give 1% error.
4. Background concentration reading is too low. Check analyzer zero. Check leakage at floor inlet.
5. Analyzer is reading high. Check span.
6. Barometer reading is in error (too high). Barometric pressure reading should be gravity and temperature corrected.
7. Revolution counter is reading high (Check pump speed and counters.)
8. Mixture is stratified causing the sample to be higher than the average concentration in the mixture. Negative Error (Indication is lower than true value):
1. Calculated V, is less than actual Vo. a. Original calibration in error.
b. Pump clearances decreased due to influx of some surface adherent material. Recalibration may be needed.
2. Pump inlet temperature recorder is reading high.
3. Pump inlet pressure indicator is reading low.
4. Background concentration reading is too high.
5. Analyzer is reading low. 6. Barometer reading is in error (too low). 7. Revolution counter is reading low.
8. There is a leak into the sampling system. Pressure check the lines and fittings on the intake side of sample transfer pumps on both the CVS and analyzer console.