5.12 Calculation of the gaseous emissions
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Statutory Documents - IMO Publications and Documents - International Codes - NOx Technical Code (2008) - Technical Code on Control of Emission of Nitrogen Oxides from Marine Diesel Engines - Chapter 5 - Procedures for NOx emission measurements on a test bed - 5.12 Calculation of the gaseous emissions

5.12 Calculation of the gaseous emissions

  5.12.1 The final results for the test report shall be determined by following the steps in 5.12.2 to 5.12.6.

  5.12.2 Determination of the exhaust gas flow

  5.12.2.1 The exhaust gas flow rate (qmew ) shall be determined for each mode in accordance with one of the methods described in 5.5.2 to 5.5.4.

 5.12.3 Dry/wet correction

  5.12.3.1 If the emissions are not measured on a wet basis, the measured concentration shall be converted to a wet basis according to the following formulae:

cw = kw · cd (5)

  5.12.3.2 For the raw exhaust gas:

  • .1 Complete combustion where exhaust gas flow is to be determined in accordance with direct measurement method in 5.5.2 or air and fuel measurement method in 5.5.3 either of the following formulae shall be used:

  • or

  • with:

    Ha is the absolute humidity of intake air, in g water per kg dry air

  • Note: Ha may be derived from relative humidity measurement, dewpoint measurement, vapour pressure measurement or dry/wet bulb measurement using the generally accepted formulae.

  • where:

    pa = saturation vapour pressure of the intake air, kPa

  • with:

    ta = temperature of the intake air, °C; ta = Ta - 273.15
    pb = total barometric pressure, kPa
    pr = water vapour pressure after cooling bath of the analysis system, kPa
    pr = 0.76 kPa for cooling bath temperature 3°C

  • .2 Incomplete combustion, CO more than 100 ppm or HC more than 100 ppmC at one or more mode points, where exhaust gas flow is determined in accordance with direct measurement method 5.5.2, air and fuel measurement method 5.5.3 and in all cases where the carbon-balance method 5.5.4 is used – the following equation shall be used:

  • Note: The unit for the CO and CO2 concentrations in (11) and (13) is %.

  • with:

  • .3 The calculation shall be in accordance with paragraphs 5.12.3.1 to 5.12.3.2. However, qmf, WALF, WBET, WDEL, WEPS values shall be calculated in accordance with the following table:

    Factors in the formula (6) (7) (8)   Formula for factors
    qmf = qmf_G + qmf_L
    WALF =
    WBET =
    WDEL =
    WEPS =

  5.12.3.3 For the intake air:

  5.12.4 NOx correction for humidity and temperature

  5.12.4.1 As the NOX emission depends on ambient air conditions, the NOX concentration shall be corrected for ambient air temperature and humidity with the factors in accordance with 5.12.4.5, 5.12.4.6 or 5.12.4.7 as applicable.

  5.12.4.2 Other reference values for humidity instead of 10.71 g/kg at the reference temperature of 25°C shall not be used.

  5.12.4.3 Other correction formulae may be used if they can be justified, validated and are approved by the Administration.

  5.12.4.4 Water or steam injected into the charge air (air humidification) is considered an emission control device and shall therefore not be taken into account for humidity correction. Water that condensates in the charge cooler will change the humidity of the charge air and therefore shall be taken into account for humidity correction.

  5.12.4.5 For compression ignition engines:

 where:

  5.12.4.6 For compression ignition engines with intermediate air cooler the following alternative equation shall be used:

 where:

 To take the humidity in the charge air into account, the following consideration is added:

 where:

 However if Ha ≥ HSC, then HSC shall be used in place of Ha in formula (17) or (17a).

5.12.4.7 For engines to be tested with gas fuel only:

khd = 0.6272 + 44.030 ✕ 10-3 ✕ Ha - 0.862 ✕ 10-3 ✕ Ha2 (17a)

where:

Ha is the humidity of the intake air at the inlet to the air filter in g water per kg dry air.

 5.12.5 Calculation of the emission mass flow rates

  5.12.5.1 The emission mass flow rate of the respective component in the raw exhaust gas for each mode shall be calculated in accordance with 5.12.5.2 from the measured concentration as obtained in accordance with 5.11.1, the applicable u gas value from table 5 and the exhaust gas mass flow rate in accordance with 5.5.

Table 5 Coefficient ugas and fuel-specific parameters for raw exhaust gas

Gas NOX CO HC CO2 O2
pgas kg/m3 2.053 1.250 footnote 1.9636 1.4277
  pe footnote Coefficient ugas footnote
Liquid fuelfootnote 1.2943 0.001586 0.000966 0.000479 0.001517 0.001103
Rapeseed Methyl Ester 1.2950 0.001585 0.000965 0.000536 0.001516 0.001102
Methanol 1.2610 0.001628 0.000991 0.001133 0.001557 0.001132
Ethanol 1.2757 0.001609 0.000980 0.000805 0.001539 0.001119
Natural gas 1.2661 0.001621 0.000987 0.000558 0.001551 0.001128
Propane 1.2805 0.001603 0.000976 0.000512 0.001533 0.001115
Butane 1.2832 0.001600 0.000974 0.000505 0.001530 0.001113
  Values for u given in table 5 are based on ideal gas properties.
In multiple fuel type operation, the u gas value used shall be determined from the values applicable to those fuels in the table set out above proportioned in accordance with the fuel ratio used."

 Values for u given in table 5 are based on ideal gas properties.

  5.12.5.2 The following formulae shall be applied:

qmgas = ugas · cgas · qmew · khd (for NOx) (18)
   
qmgas = ugas · cgas · qmew (for other gasses) (18a)

 Where:

qmgas = emission mass flow rate of individual gas, g/h
ugas = ratio between density of exhaust component and density of exhaust gas, see table 5
cgas = concentration of the respective component in the raw exhaust gas, ppm, wet
qmew = exhaust mass flow, kg/h, wet
khd = NOx humidity correction factor

  Note: In the case of CO2 and O2 measurement, the concentration will normally be reported in terms of %. With regard to the application of formula 18a, these concentrations will need to be expressed in ppm. 1.0 % = 10000 ppm.

  5.12.5.3 For the calculation of NOx, the humidity correction factor khd as determined according to 5.12.4 shall be used.

  5.12.5.4 The measured concentration shall be converted to a wet basis according to 5.12.3 if not already measured on a wet basis.

 5.12.6 Calculation of the specific emission

  5.12.6.1 The emission shall be calculated for all individual components in accordance with the following:

  • 1.

 where:

  • 2.

 and

  5.12.6.2 The weighting factors and the number of modes (n) used in the above calculation shall be according to the provisions of 3.2.

  5.12.6.3 The resulting average weighted NOx emission value for the engine as determined by formula (19) shall then be compared to the applicable emission limit given in regulation 13 to determine if the engine is in compliance.

Parent topic: Chapter 5 - Procedures for NOx emission measurements on a test bed
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