1.DETERMINATION OF THE GASEOUS EMISSIONS
1.1.Introduction
Section 1.2 and Figures 7 and 8 contain detailed descriptions of the recommended sampling and analysing systems. Since various configurations can produce equivalent results, exact conformance with Figures 7 and 8 is not required. Additional components such as instruments, valves, solenoids, pumps, and switches may be used to provide additional information and co-ordinate the functions of the component systems. Other components which are not needed to maintain the accuracy on some systems, may be excluded if their exclusion is based upon good engineering judgement.
1.2.Description of the analytical system
An analytical system for the determination of the gaseous emissions in the raw (Figure 7, ESC only) or diluted (Figure 8, ETC and ESC) exhaust gas is described based on the use of:
HFID analyser for the measurement of hydrocarbons;
NDIR analysers for the measurement of carbon monoxide and carbon dioxide;
HCLD or equivalent analyser for the measurement of the oxides of nitrogen.
The sample for all components may be taken with one sampling probe or with two sampling probes located in close proximity and internally split to the different analysers. Care must be taken that no condensation of exhaust components (including water and sulphuric acid) occurs at any point of the analytical system.
1.2.1.Components of Figures 7 and 8
EP Exhaust pipe
Exhaust gas sampling probe (Figure 7 only)
A stainless steel straight closed end multi-hole probe is recommended. The inside diameter shall not be greater than the inside diameter of the sampling line. The wall thickness of the probe shall not be greater than 1 mm. There shall be a minimum of three holes in three different radial planes sized to sample approximately the same flow. The probe must extend across at least 80 % of the diameter of the exhaust pipe. One or two sampling probes may be used.
SP2 Diluted exhaust gas HC sampling probe (Figure 8 only)
The probe shall:
be defined as the first 254 mm to 762 mm of the heated sampling line HSL1;
have a 5 mm minimum inside diameter;
be installed in the dilution tunnel DT (see Section 2.3, Figure 20) at a point where the dilution air and exhaust gas are well mixed (i.e. approximately 10 tunnel diameters downstream of the point where the exhaust enters the dilution tunnel);
be sufficiently distant (radially) from other probes and the tunnel wall so as to be free from the influence of any wakes or eddies;
be heated so as to increase the gas stream temperature to 463 K ± 10 K (190 °C ± 10 °C) at the exit of the probe.
SP3 Diluted exhaust gas CO, CO2, NOx sampling probe (Figure 8 only)
The probe shall:
be in the same plane as SP2;
be sufficiently distant (radially) from other probes and the tunnel wall so as to be free from the influence of any wakes or eddies;
be heated and insulated over its entire length to a minimum temperature of 328 K (55 °C) to prevent water condensation.
HSL1 Heated sampling line
The sampling line provides a gas sample from a single probe to the split point(s) and the HC analyser.
The sampling line shall:
have a 5 mm minimum and a 13,5 mm maximum inside diameter;
be made of stainless steel or PTFE;
maintain a wall temperature of 463 K ± 10 K (190 °C ± 10 °C) as measured at every separately controlled heated section, if the temperature of the exhaust gas at the sampling probe is equal to or below 463 K (190 °C);
maintain a wall temperature greater than 453 K (180 °C), if the temperature of the exhaust gas at the sampling probe is above 463 K (190 °C);
maintain a gas temperature of 463 K ± 10 K (190 °C ± 10 °C) immediately before the heated filter F2 and the HFID.
HSL2 Heated NOx sampling line
The sampling line shall:
maintain a wall temperature of 328 K to 473 K (55 °C to 200 °C), up to the converter C when using a cooling bath B, and up to the analyser when a cooling bath B is not used,
be made of stainless steel or PTFE.
SL Sampling line for CO and CO2
The line shall be made of PTFE or stainless steel. It may be heated or unheated.
BK Background bag (optional; Figure 8 only)
For the sampling of the background concentrations.
BG Sample bag (optional; Figure 8 CO and CO2 only)
For the sampling of the sample concentrations.
F1 Heated pre-filter (optional)
The temperature shall be the same as HSL1.
F2 Heated filter
The filter shall extract any solid particles from the gas sample prior to the analyser. The temperature shall be the same as HSL1. The filter shall be changed as needed.
P Heated sampling pump
The pump shall be heated to the temperature of HSL1.
HC
Heated flame ionisation detector (HFID) for the determination of the hydrocarbons. The temperature shall be kept at 453 K to 473 K (180 °C to 200 °C).
CO, CO2
NDIR analysers for the determination of carbon monoxide and carbon dioxide (optional for the determination of the dilution ratio for PT measurement).
NO
CLD or HCLD analyser for the determination of the oxides of nitrogen. If a HCLD is used it shall be kept at a temperature of 328 K to 473 K (55 °C to 200 °C).
C Converter
A converter shall be used for the catalytic reduction of NO2 to NO prior to analysis in the CLD or HCLD.
B Cooling bath (optional)
To cool and condense water from the exhaust sample. The bath shall be maintained at a temperature of 273 K to 277 K (0 °C to 4 °C) by ice or refrigeration. It is optional if the analyser is free from water vapour interference as determined in Annex III, Appendix 5, Sections 1.9.1 and 1.9.2. If water is removed by condensation, the sample gas temperature or dew point shall be monitored either within the water trap or downstream. The sample gas temperature or dew point must not exceed 280 K (7 °C). Chemical dryers are not allowed for removing water from the sample.
T1, T2, T3 Temperature sensor
To monitor the temperature of the gas stream.
T4 Temperature sensor
To monitor the temperature of the NO2-NO converter.
T5 Temperature sensor
To monitor the temperature of the cooling bath.
G1, G2, G3 Pressure gauge
To measure the pressure in the sampling lines.
R1, R2 Pressure regulator
To control the pressure of the air and the fuel, respectively, for the HFID.
R3, R4, R5 Pressure regulator
To control the pressure in the sampling lines and the flow to the analysers.
FL1, FL2, FL3 Flowmeter
To monitor the sample by-pass flow rate.
FL4 to FL6 Flowmeter (optional)
To monitor the flow rate through the analysers.
V1 to V5 Selector valve
Suitable valving for selecting sample, span gas or zero gas flow to the analysers.
V6, V7 Solenoid valve
To by-pass the NO2-NO converter.
V8 Needle valve
To balance the flow through the NO2-NO converter C and the by-pass.
V9, V10 Needle valve
To regulate the flows to the analysers.
V11, V12 Toggle valve (optional)
To drain the condensate from the bath B.
1.3.NMHC analysis (NG fuelled gas engines only)
1.3.1.Gas chromatographic method (GC, Figure 9)
When using the GC method, a small measured volume of a sample is injected onto an analytical column through which it is swept by an inert carrier gas. The column separates various components according to their boiling points so that they elute from the column at different times. They then pass through a detector which gives an electrical signal that depends on their concentration. Since it is not a continuous analysis technique, it can only be used in conjunction with the bag sampling method as described in Annex III, Appendix 4, Section 3.4.2.
For NMHC an automated GC with a FID shall be used. The exhaust gas shall be sampled into a sampling bag from which a part shall be taken and injected into the GC. The sample is separated into two parts (CH4/Air/CO and NMHC/CO2/H2O) on the Porapak column. The molecular sieve column separates CH4 from the air and CO before passing it to the FID where its concentration is measured. A complete cycle from injection of one sample to injection of a second can be made in 30 s. To determine NMHC, the CH4 concentration shall be subtracted from the total HC concentration (see Annex III, Appendix 2, Section 4.3.1).
Figure 9 shows a typical GC assembled to routinely determine CH4. Other GC methods can also be used based on good engineering judgement.
Components of Figure 9
PC Porapak column
Porapak N, 180/300 μm (50/80 mesh), 610 mm length × 2,16 mm ID shall be used and conditioned at least 12 h at 423 K (150 °C) with carrier gas prior to initial use.
MSC Molecular sieve column
Type 13X, 250/350 μm (45/60 mesh), 1 220 mm length × 2,16 mm ID shall be used and conditioned at least 12 h at 423 K (150 °C) with carrier gas prior to initial use.
OV Oven
To maintain columns and valves at stable temperature for analyser operation, and to condition the columns at 423 K (150 °C).
SLP Sample loop
A sufficient length of stainless steel tubing to obtain approximately 1 cm3 volume.
P Pump
To bring the sample to the gas chromatograph.
D Dryer
A dryer containing a molecular sieve shall be used to remove water and other contaminants which might be present in the carrier gas.
HC
Flame ionisation detector (FID) to measure the concentration of methane.
V1 Sample injection valve
To inject the sample taken from the sampling bag via SL of Figure 8. It shall be low dead volume, gas tight, and heatable to 423 K (150 C).
V3 Selector valve
To select span gas, sample, or no flow.
V2, V4, V5, V6, V7, V8 Needle valve
To set the flows in the system.
R1, R2, R3 Pressure regulator
To control the flows of the fuel (= carrier gas), the sample, and the air, respectively.
FC Flow capillary
To control the rate of air flow to the FID.
G1, G2, G3 Pressure gauge
To control the flows of the fuel (= carrier gas), the sample, and the air, respectively.
F1, F2, F3, F4, F5 Filter
Sintered metal filters to prevent grit from entering the pump or the instrument.
FL1
To measure the sample by-pass flow rate.
1.3.2.Non-methane cutter method (NMC, Figure 10)
The cutter oxidises all hydrocarbons except CH4 to CO2 and H2O, so that by passing the sample through the NMC only CH4 is detected by the FID. If bag sampling is used, a flow diverter system shall be installed at SL (see Section 1.2, Figure 8) with which the flow can be alternatively passed through or around the cutter according to the upper part of Figure 10. For NMHC measurement, both values (HC and CH4) shall be observed on the FID and recorded. If the integration method is used, an NMC in line with a second FID shall be installed parallel to the regular FID into HSL1 (see Section 1.2, Figure 8) according to the lower part of Figure 10. For NMHC measurement, the values of the two FID's (HC and CH4) shall be observed and recorded.
The cutter shall be characterised at or above 600 K (327 °C) prior to test work with respect to its catalytic effect on CH4 and C2H6 at H2O values representative of exhaust stream conditions. The dewpoint and O2 level of the sampled exhaust stream must be known. The relative response of the FID to CH4 must be recorded (see Annex III, Appendix 5, Section 1.8.2).
Components of Figure 10
NMC Non-methane cutter
To oxidise all hydrocarbons except methane.
HC
Heated flame ionisation detector (HFID) to measure the HC and CH4 concentrations. The temperature shall be kept at 453 K to 473 K (180 °C to 200 °C).
V1 Selector valve
To select sample, zero and span gas. V1 is identical with V2 of Figure 8.
V2, V3 Solenoid valve
To by-pass the NMC.
V4 Needle valve
To balance the flow through the NMC and the by-pass.
R1 Pressure regulator
To control the pressure in the sampling line and the flow to the HFID. R1 is identical with R3 of Figure 8.
FL1 Flowmeter
To measure the sample by-pass flow rate. FL1 is identical with FL1 of Figure 8.