With the new exhaust customisation options, it feels like smoke has been rather left out. The following parameters might help the smoke effects feel as up to snuff as the exhaust.
Intensity/Opacity controls how thick or wispy the smoke looks. Imagine it being like how the thickness is affected by throttle. This parameter would allow smoke to be visible on H2(l)/O2(l) engines if one so chooses.
Drag controls how quickly the smoke’s surface velocity decelerates.
Size is a set of two numbers which clamp the minimum and maximum size of the smoke particles, a set akin to the expansion clamping on the exhaust.
Lifetime controls how quickly smoke particles decay. Max functioning value is perhaps double the current lifetime.
Tip Colour introduces a gradient to the smoke similar to the exhaust.
Colour, visibility, and speed can all remain.