Appendix 2

All but a tiny part of the carbon in the exhaust gas comes from the fuel, and all but a minimal part of this is manifest in the exhaust gas as CO₂. This is the basis for a system verification check based on CO₂ measurements. In the case of SI engines without control of excess air ratio λ or SI engines operating outside the range 0,97 ≤ λ ≤ 1,03, the procedure shall additionally include measurement of HC and CO.

The flow of carbon into the exhaust gas measurement systems is determined from the fuel flow rate. The flow of carbon at various sampling points in the emissions and particulate sampling systems is determined from the CO₂ (or CO₂, HC and CO) concentrations and gas flow rates at those points.

In this sense, the engine provides a known source of carbon flow, and observing the same carbon flow in the exhaust pipe and at the outlet of the partial flow PM sampling system verifies leak integrity and flow measurement accuracy. This check has the advantage that the components are operating under actual engine test conditions of temperature and flow.

Figure 7.1 shows the sampling points at which the carbon flows shall be checked. The specific equations for the carbon flows at each of the sample points are given in the following points.

The carbon mass flow rate into the engine q_{m Cf} [kg/s] for a fuel CHαOε shall be calculated by means of equation (7-150):

Where:

q_{m f}

fuel mass flow rate [kg/s]

The carbon mass flow rate in the exhaust pipe of the engine q_{m Ce} [kg/s] shall be determined from the raw CO₂ concentration and the exhaust gas mass flow rate by means of equation (7-151):

where:

c _CO2,r

wet CO₂ concentration in the raw exhaust gas [%]

c _CO2,a

wet CO₂ concentration in the ambient air [%]

q_{m ew}

exhaust gas mass flow rate on wet basis [kg/s]

M _e

molar mass of exhaust gas [g/mol]

If CO₂ is measured on a dry basis it shall be converted to a wet basis in accordance with point 2.1.3 or point 3.5.2.

As an alternative to performing the calculation solely based upon CO₂ in point 3.1, the carbon mass flow rate in the exhaust pipe of the engine q_{m Ce} [kg/s] shall be determined from the raw CO₂, HC and CO concentration and the exhaust gas mass flow rate by means of equation (7-152):

Where:

c _CO2,r

wet CO₂ concentration in the raw exhaust gas [%]

c _CO2,a

wet CO₂ concentration in the ambient air [%]

c _THC(C1),r

THC(C1) concentration in the raw exhaust gas [%]

c _THC(C1),a

THC(C1) concentration in the ambient air [%]

c _CO,r

wet CO concentration in the raw exhaust gas [%]

c _CO,a

wet CO concentration in the ambient air [%]

q_{m ew}

exhaust gas mass flow rate on wet basis [kg/s]

M _e

molar mass of exhaust gas [g/mol]

If CO₂ or CO are measured on a dry basis they shall be converted to a wet basis in accordance with point 2.1.3 or point 3.5.2.

For the partial flow dilution system, the splitting ratio also needs to be taken into account. The carbon flow rate in an equivalent dilution system q_{m Cp} [kg/s] (with equivalent meaning equivalent to a full flow system where the total flow is diluted) shall be determined from the dilute CO₂ concentration, the exhaust gas mass flow rate and the sample flow rate; the new equation (7-153) is identical to equation (7-151), being only supplemented by the dilution factor q_{m dew}/q_{m p}.

Where:

c _CO2,d

wet CO₂ concentration in the diluted exhaust gas at the outlet of the dilution tunnel [ %]

c _CO2,a

wet CO₂ concentration in the ambient air [ %]

q_{m dew}

diluted sample flow in the partial flow dilution system [kg/s]

q_{m ew}

exhaust gas mass flow rate on wet basis [kg/s]

q_{m p}

sample flow of exhaust gas into partial flow dilution system [kg/s]

M _e

molar mass of exhaust gas [g/mol]

If CO₂ is measured on a dry basis it shall be converted to a wet basis in accordance with point 2.1.3 or point 3.5.2.

For the partial flow dilution system, the splitting ratio also needs to be taken into account. As an alternative to performing the calculation solely based upon CO₂ in point 4.1, the carbon flow rate in an equivalent dilution system q_{m Cp} [kg/s] (with equivalent meaning equivalent to a full flow system where the total flow is diluted) shall be determined from the dilute CO₂, HC and CO concentrations, the exhaust gas mass flow rate and the sample flow rate; the new equation (7-154) is identical to equation (7-152), being only supplemented by the dilution factor q_{m dew}/q_{m p}.

Where:

c _CO2,d

wet CO₂ concentration in the diluted exhaust gas at the outlet of the dilution tunnel [%]

c _CO2,a

wet CO₂ concentration in the ambient air [%]

c _THC(C1),d

THC(C1) concentration in the diluted exhaust gas at the outlet of the dilution tunnel [%]

c _THC(C1),a

THC(C1) concentration in the ambient air [%]

c _CO,d

wet CO concentration in the diluted exhaust gas at the outlet of the dilution tunnel [%]

c _CO,a

wet CO concentration in the ambient air [%]

q_{m dew}

diluted sample flow in the partial flow dilution system [kg/s]

q_{m ew}

exhaust gas mass flow rate on wet basis [kg/s]

q_{m p}

sample flow of exhaust gas into partial flow dilution system [kg/s]

M _e

molar mass of exhaust gas [g/mol]

If CO₂ or CO are measured on a dry basis they shall be converted to a wet basis in accordance with point 2.1.3 or point 3.5.2 of this Annex.

The molar mass of the exhaust gas shall be calculated by means of equation (7-13) (see point 2.1.5.2.of this Annex).

Alternatively, the following exhaust gas molar masses may be used:

M _e (diesel)

28,9 g/mol

M _e (LPG)

28,6 g/mol

M _e (Natural gas/biomethane)

28,3 g/mol

M _e (Petrol)

29,0 g/mol