Step 1: Ask which locomotives even produce an exhaust to worry about.
Battery and trolley wire locomotives are both electric, they draw power from a battery or overhead wire and have no internal combustion process at all, so there is no exhaust gas stream for them to treat in the first place.
Step 2: Consider the steam locomotive briefly.
A steam locomotive does burn fuel, but it does so in an external firebox producing large volumes of smoke, heat and steam rather than a compact, hot exhaust stream from an engine, and this makes steam locomotives generally unsuitable and rare underground regardless of exhaust treatment, so it is not the locomotive type this question is describing.
Step 3: Focus on the diesel locomotive's exhaust hazards.
A diesel locomotive's internal combustion engine produces a hot exhaust stream that can carry sparks and contains toxic gases such as carbon monoxide and oxides of nitrogen. Used underground, especially in a coal mine, that hot spark laden exhaust is a double danger, it could ignite flammable gas and it could poison the air miners breathe.
Step 4: Connect the two named fittings to these two dangers.
A flame trap is fitted onto the exhaust manifold to quench any sparks or flame before they leave the pipe, preventing gas ignition, while an exhaust conditioner box, usually a water bath scrubber, cools the hot gases and helps dissolve out some of the noxious components. Because only a diesel locomotive generates this kind of exhaust needing both treatments, it is the locomotive type fitted with an exhaust conditioner box and flame trap arrangement.
\[ \boxed{\text{Diesel locomotive}} \]