Fuel converter

From Memory Alpha, the free Star Trek reference

A fuel converter was a device used on the Delta Flyer during the Antarian Trans-stellar Rally to allow it to run on enriched deuterium, as required by the race's guidelines.

It was given to Tom Paris by another racer, Irina, as part of her plan to sabotage the race. Veridium isotopes leaked into the Flyer's warp core, causing the converter and the warp core to explode. (VOY: "Drive")