Another thing that popped into my mind about not only steam engine emitters, but diesel and rolling stock FX emitters as well. Currently, the parameters for FX emitters in ORTS assume the outlet the effect is emanating from is perfectly round, and only one "radius" parameter is given. However, this is not always the case, as the outlets for steam/smoke/exhaust/etc., can be any shape--oblong, square, or rectangular.
Obviously, here in the United States, most if not all steam locomotive smokestacks are round in overhead views, but diesel exhaust stacks/ports are usually oblong, rectangular or square. On the other hand, some steam locomotives in the UK and Europe have oblong stacks (or funnels, chimneys or whatever term you wish to use), such as the famous Giesl ejectors.
Also, an improvement to safety valve emitters: In ORTS it is possible to define multiple safety valve emitters, just like in the real world, but the problem is that, contrary to reality, they all turn on and off at the same time. In the real world each safety valve is set to go off at successively higher pressures, exemplified by
49 CFR Part 230, section 230.48, paragraph A...:
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"Every boiler shall be equipped with at least two safety relief valves, suitable for the service intended, that are capable of preventing an accumulation of pressure greater than 6 percent above the MAWP (Maximum Allowable Working Pressure) under any conditions of service. An FRA inspector may require verification of sufficient safety valve relieving capacity."
...and section 230.49, paragraph B.:
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"At least one safety relief valve shall be set to open at a pressure not exceeding the MAWP. Safety relief valves shall be set to open at pressures not exceeding 6 psi above the MAWP."
So finding a way to specify the number of safety valves on a locomotive, their steam usage rates, and the pressures each one is to go off at would be beneficial.