Measurement of soot either by experiment or simulation normally giving in the form of mass (g) or mass concentration (g/m3). But common emission standards is given in g/km. So how to relate or convert these unit?
One car emits x grams pollutant per kilometer in a given traffic situation. So, a traffic volume of one car per hour on a one kilometer long road section gives a line source of x grams per hour. It is very straightforward, actually. To get to a concentration is a little more complex (initial concentration, dulition in atmospheric wind).
The link below may give you some pointers.
https://en.wikipedia.org/wiki/Atmospheric_dispersion_modeling
Thanks Ingo Riess, but that was the case for direct measurement from vehicle right? But if soot mass measured from in lab diesel engine, how to relate soot particles obtained with distance (km)?
The first question would be if you know whether it is the engine that is regulated or if is it regulated as part of a whole chassis? In most countries, there are vehicle categories (e.g., in the U.S., on-road motorcycles, light-duty vehicles and trucks under 8,500 lb. GVWR) that use chassis dynamometers (not engine testing) to demonstrate compliance with emissions standards over a proscribed vehicle speed vs time cycle for set distances (hence, g/km standards - mass of emissions divided by distance travelled). There are also engine categories (heavy-duty engines, nonroad engines, locomotives, marine engines) that rely on engine dynamometer testing (not chassis testing) to demonstrate compliance with emissions standards, but these do not report emissions in units of g/km. Instead, they use energy-specific units (e.g., g/kW-hr) with mass of emissions measured over a proscribed set of engine speed and torque conditions and then divided by the energy integrated over the cycle.
While it is technically possible to use hardware-in-the-loop (HIL) testing of an engine over a chassis cycle to simulate in-chassis operation, such efforts are only conducted as part of engineering development and are not part of official certified emissions results (U.S.) or type approval (EU). I have done HIL developmental testing in the past and can provide citations if necessary. I think it might be more likely that you will need to report emissions as g/kW-hr. If you are interested in the ISO engine dynamometer emissions calculations for Diesel engines, you should probably refer to ISO-8178. Diesel engine emissions calculations used in most of North America are a bit different and are posted online within the eCFR - search for U.S. Title 40 CFR Part 1065.
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