I've finished designing rolling stock for this. I can now reveal (drum roll please):
The Irish Fertiliser Industries ammonia train!
This highly recognisable and sometimes controversial train transported ammonia between IFI's three factories at Marino Point, Arklow, and Belfast. I owe my Irishness to IFI, as my parents moved here in 1990 when my dad took a job at Marino Point, so when I wanted to build some kind of Irish Rail diesel locomotive, ammonia seemed a fitting cargo.
Here's a closer look at one of the tankers. Notably, this is the first time I've ever found the Lego colour "bright light orange" useful - it looks just right for the stripe. Supposedly the chassis was dark green but these things were constantly so dirty that it's hard to verify that from photos. Depending on part availability I might change all the white to tan - it would be a better representation of the dirty white tankers!
And here's a barrier wagon - these carried water which acted as a defence against spillages of the highly flammable ammonia in the event of a derailment. These also never showed their nice dark green paint jobs. I might change the colour to black, especially if sourcing the dark green parts is too expensive or awkward (I'm looking at you,
inverted radar dish).
I doubt I'll ever go so far as to build FOUR tankers, but it would probably look strange with any less than three, so when it comes to building this in the brick it is going to be a monstrous undertaking, given that it will also require two barrier wagons.