Division 3.6.1 Emission mass calculation and background correctionF1

United Kingdom

The calculation of gaseous emissions mass m _gas [g/test] as a function of molar emissions flow rates shall be calculated as follows:

(a)

Continuous sampling, varying flow rate, shall be calculated by means of equation (7-106):

m_{gas} = \frac{1}{f} \times M_{gas} \times \sum_{i = 1}^{N} ṅ_{exhi} \times X_{gasi}

[see equation (7-106)]

Where:

M _gas

generic emission molar mass [g/mol]

ṅ _exhi

instantaneous exhaust gas molar flow rate on a wet basis [mol/s]

x _gasi

instantaneous generic gas molar concentration on a wet basis [mol/mol]

data sampling rate [Hz]

number of measurements [-]

(b)

Continuous sampling, constant flow rate, shall be calculated by means of equation (7-107):

m_{gas} = M_{gas} \times ṅ_{exh} \times {\bar{x}}_{gas} \times Δ t

[see equation (7-107)]

Where:

M _gas

generic emission molar mass [g/mol]

ṅ _exh

exhaust gas molar flow rate on a wet basis [mol/s]

{\bar{x}}_{gas}

mean gaseous emission molar fraction on a wet basis [mol/mol]

Δ t

time duration of test interval

(c)

Batch sampling, regardless the flow rate is varying or constant, shall be calculated by means of equation (7-108):

m_{gas} = \frac{1}{f} \times M_{gas} \times {\bar{x}}_{gas} \sum_{i = 1}^{N} ṅ_{exhi}

[see equation (7-108)]

Where:

M _gas

generic emission molar mass [g/mol]

ṅ _exhi

instantaneous exhaust gas molar flow rate on a wet basis [mol/s]

{\bar{x}}_{gas}

mean gaseous emission molar fraction on a wet basis [mol/mol]

data sampling rate [Hz]

number of measurements [-]

(d)

In case of diluted exhaust gas calculated values for mass of the pollutants shall be corrected by subtracting the mass of background emissions, due to dilution air:

(i)

Firstly, the molar flow rate of dilution air n _airdil [mol/s] shall be determined over the test interval. This may be a measured quantity or a quantity calculated from the diluted exhaust gas flow and the flow-weighted mean fraction of dilution air in diluted exhaust gas, ${\bar{x}}_{dil ∕ exh}$ ;
(ii)

The total flow of dilution air n _airdil [mol] shall be multiplied by the mean concentration of background emission. This may be a time-weighted mean or a flow-weighted mean (e.g., a proportionally sampled background). The product of n _airdil and the mean concentration of a background emission is the total amount of a background emission;
(iii)

If the result is a molar quantity, it shall be converted to a mass of the background emission m _bkgnd [g] by multiplying it by emission molar mass, M _gas [g/mol];
(iv)

Total background mass shall be subtracted from total mass to correct for background emissions;
(v)

The total flow of dilution air may be determined by a direct flow measurement. In this case, the total mass of background shall be calculated, using the dilution air flow, n _airdil . The background mass shall be subtracted from the total mass. The result shall be used in brake-specific emission calculations;
(vi)

The total flow of dilution air may be determined from the total flow of diluted exhaust gas and a chemical balance of the fuel, intake air, and exhaust gas as described in point 3.4. In this case, the total mass of background shall be calculated, using the total flow of diluted exhaust gas, n _dexh . Then this result shall be multiplied by the flow-weighted mean fraction of dilution air in diluted exhaust gas, ${\bar{x}}_{dil ∕ exh}$ .

Considering the two cases (v) and (vi), equations (7-115) and (7-116) shall be used:

$m_{bkgnd} = M_{gas} \times x_{gasdil} \times n_{airdil}$ ή $m_{bkgnd} = M_{gas} \times {\bar{x}}_{dil ∕ exh} \times {\bar{x}}_{bkgnd} \times n_{dexh}$	(7-115)
m _gascor = m _gas – m _bkgnd	(7-116)

where:

m _gas

total mass of the gaseous emission [g]

m _bkgnd

total background masses [g]

m _gascor

mass of gas corrected for background emissions [g]

M _gas

molecular mass of generic gaseous emission [g/mol]

x _gasdil

gaseous emission concentration in dilution air [mol/mol]

n _airdil

dilution air molar flow [mol]

{\bar{x}}_{dil ∕ exh}

flow-weighted mean fraction of dilution air in diluted exhaust gas [mol/mol]

{\bar{x}}_{bkgnd}

gas fraction of background [mol/mol]

n _dexh

total flow of diluted exhaust gas [mol]

Division 3.6.1 Emission mass calculation and background correctionF1

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