Currently, ORTS (and in the past, MSTS) assumes that all particle emissions are emanating from an orifice that is perfectly round. However, this is not always the case. In particular, diesel locomotive exhaust stacks/ports are often oblong or rectangular in shape. Case in point:
This is the TrainArtisan BNSF SD40-2 that came with the MSTS version 1.2 update, as seen in ORTS. As you can see, even though the physical exhaust stack on the model is clearly rectangular when viewed from overhead, the emitters still assume that the stack is round, resulting in a very thin exhaust plume.
My solution is to specify size dimensions for the emitter on 2 or more axes. So, instead of this:
Effects ( DieselSpecialEffects ( comment ( the format of these little blocks is as follow: offset.x offset.y offset.z normal.x normal.y normal.z width in metres defining the offset from the shape pivot point where steam / smoke should appear, the direction it should go and the width of the nozzle ) Exhaust1 ( 0.0 4.738 1.485 0 1 0 0.1 ) ) )
...the code would be this:
Effects ( DieselSpecialEffects ( comment ( the format of these little blocks is as follow: offset.x offset.y offset.z normal.x normal.y normal.z size.x size.y size.z defining the offset from the shape pivot point where steam / smoke should appear, the direction it should go and the size of the nozzle on each axis ) Exhaust1 ( 0.0 4.738 1.485 0 1 0 0.74 0 0.1 ) ) )