Brake Specific NOx
The ratio of the rate at which oxides of nitrogen leave the engine exhaust manifold to the brake horsepower.
EURO V NOx emissions for heavy duty vehicles have a limit set at 2g/kWh.
In general engine load does not have a big effect on the brake-specific NOx emission rates for diesel engines vehicles. At low engine speeds nearly all of the energy is released in the pre-mixed stage.
As the load increases the pre-mix remains roughly constant while diffusion burning increases linearly. NOx production is proportional to fuel consumption. Thus brake specific NOx emissions are constant as NOx emissions increase with power.
Leslie L. Sloss, "Nitrogen Oxides Control Technology Fact Book" Noyes Data Corporation