5.12.2 Dry/wet correction

When applying G _EXHW or V _EXHW, the measured concentration, if not already measured on a wet basis, shall be converted to a wet basis according to the following formulae.

conc(wet) = K_W·conc(dry)

(7)

5.12.2.1 For the raw exhaust gas:

(8)

(9)

(10)

with:

H _a	=	g water per kg dry air
R_a	=	relative humidity of the intake air, %
p _a	=	saturation vapour pressure of the intake air, kPa
p _B	=	total barometic pressure, kPa

Note Formulae using F _FH are simplified versions of those quoted in section 3.7 of appendix 6 of this Code (formulae (2-44) and (2-45)) which when applied give comparable results to those expected from the full formulae.

5.12.2.2 Alternatively:

(11)

5.12.2.3 For the intake air:

K_{W, a} = 1 - K_W2

(12)

5.12.2.4 Formula (8) shall be accepted as the definition of the fuel-specific factor F _FH. Defined this way, F _FH is a value for the water content of the exhaust in relationship to the fuel to air ratio.

5.12.2.5 Typical values for F _FH may be found in table 1 of appendix 6 of this Code. Table 1 of appendix 6 of this Code contains a list of F _FH values for different fuels. F _FH does not only depend on the fuel specifications, but also, to a lesser degree, on the fuel to air ratio of the engine.

5.12.2.6 Section 3.9 of appendix 6 of this Code contains formulae for calculating F _FH from the hydrogen content of the fuel and the fuel to air ratio.

5.12.2.7 Formula (8) considers the water from the combustion and from the intake air to be independent from each other and to be additive. Formula (2-45) in section 3.7 of appendix 6 of this Code shows that the two water terms are not additive. Formula (2-45) is the correct version but it is very complicated and, therefore, the more practical formulae (8) and (11) shall be used.