40 CFR 89.419 - Dilute gaseous exhaust sampling and analytical system description.
(a)General. The exhaust gas sampling system described in this section is designed to measure the true mass of gaseous emissions in the exhaust of petroleum-fueled nonroad compression-ignition engines. This system utilizes the CVS concept (described in 40 CFR part 1065, subparts A and B) of measuring mass emissions of HC, CO, and CO2. A continuously integrated system is required for HC and NOX measurement and is allowed for all CO and CO2 measurements. The mass of gaseous emissions is determined from the sample concentration and total flow over the test period. As an option, the measurement of total fuel mass consumed over a cycle may be substituted for the exhaust measurement of CO2. General requirements are as follows:
(1) This sampling system requires the use of a PDP-CVS and a heat exchanger or a CFV-CVS with either a heat exchanger or electronic flow compensation. Figure 2 in appendix A to this subpart is a schematic drawing of the PDP-CVS system. Figure 3 in appendix A to this subpart is a schematic drawing of the CFV-CVS system.
(i) The HFID sample must be taken directly from the diluted exhaust stream through a heated probe and integrated continuously over the test cycle. Unless compensation for varying flow is made, the HFID must be used with a constant flow system to ensure a representative sample.
(ii) The heated probe shall be located in the primary dilution tunnel and far enough downstream of the mixing chamber to ensure a uniform sample distribution across the CVS duct at the point of sampling.
(3) The CO and CO2 analytical system requires:
(ii) Continuously integrated measurement of diluted CO and CO2 meeting the minimum requirements and technical specifications contained in paragraph (b)(4) of this section. Unless compensation for varying flow is made, a constant flow system must be used to ensure a representative sample.
(4) The NOX analytical system requires a continuously integrated measurement of diluted NOX meeting the minimum requirements and technical specifications contained in paragraph (b)(4) of this section. Unless compensation for varying flow is made, a constant flow system must be used to ensure a representative sample.
(5) Since various configurations can produce equivalent results, exact conformance with these drawings is not required. Additional components such as instruments, valves, solenoids, pumps, and switches may be used to provide additional information and coordinate the functions of the component systems. Other components, such as snubbers, which are not needed to maintain accuracy on some systems, may be excluded if their exclusion is based upon good engineering judgment.
(b)Component description. The components necessary for exhaust sampling shall meet the following requirements:
(1)Exhaust dilution system. The PDP-CVS shall conform to all of the requirements listed for the exhaust gas PDP-CVS in 40 CFR part 1065. The CFV-CVS shall conform to all the requirements listed for the exhaust gas CFV-CVS in 40 CFR part 1065. In addition, the CVS must conform to the following requirements:
(i) The flow capacity of the CVS must be sufficient to maintain the diluted exhaust stream at or below the temperature required for the measurement of hydrocarbon emissions noted in the following paragraph and to prevent condensation of water at any point in the dilution tunnel.
(ii) The flow capacity of the CVS must be sufficient to maintain the diluted exhaust stream in the primary dilution tunnel at a temperature of 191 °C or less at the sampling zone for hydrocarbon measurement and as required to prevent condensation at any point in the dilution tunnel. Gaseous emission samples may be taken directly from this sampling point.
(iii) For the CFV-CVS, either a heat exchanger or electronic flow compensation is required (see Figure 3 in appendix A to this subpart).
(iv) For the CFV-CVS when a heat exchanger is used, the gas mixture temperature, measured at a point immediately ahead of the critical flow venturi, shall be within ±11 °C) of the average operating temperature observed during the test with the simultaneous requirement that condensation does not occur. The temperature measuring system (sensors and readout) shall have an accuracy and precision of ±2 °C. For systems utilizing a flow compensator to maintain proportional flow, the requirement for maintaining constant temperature is not necessary.
(v) The primary dilution air shall have a temperature of 25 °C ±5 °C.
(2)Continuous HC measurement system.
(i) The continuous HC sample system (as shown in Figure 2 or 3 in appendix A to this subpart) uses an “overflow” zero and span system. In this type of system, excess zero or span gas spills out of the probe when zero and span checks of the analyzer are made. The “overflow” system may also be used to calibrate the HC analyzer according to 40 CFR part 1065, subpart F, although this is not required.
(ii) No other analyzers may draw a sample from the continuous HC sample probe, line or system, unless a common sample pump is used for all analyzers and the sample line system design reflects good engineering practice.
(iii) The overflow gas flow rates into the sample line shall be at least 105 percent of the sample system flow rate.
(iv) The overflow gases shall enter the heated sample line as close as practical to the outside surface of the CVS duct or dilution tunnel.
(v) The continuous HC sampling system shall consist of a probe (which must raise the sample to the specified temperature) and, where used, a sample transfer system (which must maintain the specified temperature). The continuous hydrocarbon sampling system (exclusive of the probe) shall:
(A) Maintain a wall temperature of 191 °C ±11 °C as measured at every separately controlled heated component (that is, filters, heated line sections), using permanent thermocouples located at each of the separate components.
(B) Have a wall temperature of 191 °C ±11 °C over its entire length. The temperature of the system shall be demonstrated by profiling the thermal characteristics of the system where possible at initial installation and after any major maintenance performed on the system. The profiling shall be accomplished using the insertion thermocouple probing technique. The system temperature will be monitored continuously during testing at the locations and temperature described in 40 CFR 1065.145.
(C) Maintain a gas temperature of 191 °C ±11 °C immediately before the heated filter and HFID. These gas temperatures will be determined by a temperature sensor located immediately upstream of each component.
(vi) The continuous hydrocarbon sampling probe shall:
(A) Be defined as the first 25 cm to 76 cm of the continuous hydrocarbon sampling system.
(B) Have a 0.48 cm minimum inside diameter.
(C) Be installed in the primary dilution tunnel at a point where the dilution air and exhaust are well mixed (that is, approximately 10 tunnel diameters downstream of the point where the exhaust enters the dilution tunnel).
(D) Be sufficiently distant (radially) from other probes and the tunnel wall so as to be free from the influence of any wakes or eddies.
(E) Increase the gas stream temperature to 191 °C ±11 °C at the exit of the probe. The ability of the probe to accomplish this shall be demonstrated using the insertion thermocouple technique at initial installation and after any major maintenance. Compliance with the temperature specification shall be demonstrated by continuously recording during each test the temperature of either the gas stream or the wall of the sample probe at its terminus.
(vii) The response time of the continuous measurement system shall be no greater than:
(A) 1.5 seconds from an instantaneous step change at the port entrance to the analyzer to within 90 percent of the step change.
(B) 20 seconds from an instantaneous step change at the entrance to the sample probe or overflow span gas port to within 90 percent of the step change. Analysis system response time shall be coordinated with CVS flow fluctuations and sampling time/test cycle offsets if necessary.
(C) For the purpose of verification of response times, the step change shall be at least 60 percent of full-scale chart deflection.
(3)Primary dilution tunnel.
(i) The primary dilution tunnel shall be:
(A) Small enough in diameter to cause turbulent flow (Reynolds Number greater than 4000) and of sufficient length to cause complete mixing of the exhaust and dilution air;
(B) At least 46 cm in diameter; (engines below 110 kW may use a dilution tunnel that is 20 cm in diameter or larger)
(C) Constructed of electrically conductive material which does not react with the exhaust components; and
(D) Electrically grounded.
(ii) The temperature of the diluted exhaust stream inside of the primary dilution tunnel shall be sufficient to prevent water condensation.
(iii) The engine exhaust shall be directed downstream at the point where it is introduced into the primary dilution tunnel.
(4)Continuously integrated NOX. CO, and CO2measurement systems.
(i) The sample probe shall:
(A) Be in the same plane as the continuous HC probe, but shall be sufficiently distant (radially) from other probes and the tunnel wall so as to be free from the influences of any wakes or eddies.
(B) Heated and insulated over the entire length, to prevent water condensation, to a minimum temperature of 55 °C. Sample gas temperature immediately before the first filter in the system shall be at least 55 °C.
(C) Alternative NOX measurement techniques outlined in 40 CFR part 1065, subpart D, are not permitted for NOX measurement in this subpart.
(D) All analytical gases must conform to the specifications of § 89.312.
(E) Any range on a linear analyzer below 155 ppm must have and use a calibration curve conforming to § 89.310.
(iii) The chart deflections or voltage output of analyzers with non-linear calibration curves shall be converted to concentration values by the calibration curve(s) specified in § 89.313 before flow correction (if used) and subsequent integration takes place.