(4) Set up equipment as shown in Figure 6 in appendix A to subpart and eliminate leaks. (Leaks between the flow measuring devices and the critical flow venturi will seriously affect the accuracy of the calibration.)

(5) Set the variable flow restrictor to the open position, start the blower, and allow the system to stabilize. Record data from all instruments.

(6) Vary the flow restrictor and make at least eight readings across the critical flow range of the venturi.

(7) Data analysis. The data recorded during the calibration are to be used in the following calculations:

(i) The air flow rate (designated as Q.) at each test point is calculated in standard cubic feet per minute from the flow meter data using the manufacturer's prescribed method.

(ii) Calculate values of the calibration coefficient for each test point:

PPI Venturi inlet pressure depression, (kPa).

(iii) Plot K, as a function of venturi inlet pressure. For choked flow, K, will have a relatively constant value. As pressure decreases (vacuum increases), the venturi becomes unchoked and K, decreases. (See Figure 7 in appendix A to this subpart.)

(iv) For a minimum of eight points in the critical region calculate an average K, and the standard deviation.

(v) If the standard deviation exceeds 0.3 percent of the average K,, take corrective action.

(e) CVS system verification. The following "gravimetric" technique can be used to verify that the CVS and analytical instruments can accurately measure a mass of gas that has been injected into the system. (Verification can also be accomplished by constant flow metering using critical flow orifice devices.)

(1) Obtain a small cylinder that has been charged with 99.5 percent or greater propane or carbon monoxide gas (Caution-carbon monoxide is poisonous).

(2) Determine a reference cylinder weight to the nearest 0.01 grams.

(3) Operate the CVS in the normal manner and release a quantity of pure propane into the system during the sampling period (approximately 5 minutes).

HC. Hydrocarbon concentration of the dilute exhaust bag sample or, for diesel heat exchanger systems, average hydrocarbon concentration of the dilute exhaust sample as calculated from the integrated HC traces, in ppm carbon equivalent. For flow compensated sample systems (HC.) is the instantaneous concentration.

HC Hydrocarbon concentration of the dilution air as measured, in ppm carbon equivalent.

(2) For oxides of nitrogen equations: NOXmass Oxides of nitrogen emissions, in grams per test mode.

Density NO2 = Density of oxides of ni

trogen is 1.913 kg/m3, assuming they are in the form of nitrogen dioxide, at 20 °C and 101.3 kPa pres

sure.

NOXconc = Oxides of nitrogen concentration of the dilute exhaust sample corrected for background, in ppm:

NOX conc=NOX - NOx 1
(1-DF)

Where:

NOxe Oxides of nitrogen concentration of the dilute exhaust bag sample as measured, in ppm. For flow compensated sample systems (NOxe) is the instantaneous concentration.

NOxa Oxides of nitrogen concentration of the dilute air as measured, in ppm.

(3) For carbon monoxide equations: Comass-Carbon monoxide emissions,

grams per test mode. Density co-Density of carbon monoxide (1.164 kg/m3 at 20 °C and 101.3 kPa pressure).

sel, a

R=Relative humidity of the engine in

take air, in percent.

Pa-Saturated vapor pressure (kPa) at the engine intake air dry bulb temperature.

PB-Barometric pressure (kPa). (e) The final reported brake-specific fuel consumption (BSFC) shall be computed by use of the following formula:

40 CFR Ch. I (7-1-95 Edition)

M=mass of fuel in grams, used by the engine during a mode kW-hr-total kilowatts integrated with respect to time for a mode

(f) The mass of fuel for the mode is determined from mass fuel flow measurements made during the mode, or from the following equation:

Where: