Stringent space constraints for on and off highway vehicles require compact exhaust aftertreatment system packaging to meet both EPA 2010 and final Tier 4 emission regulations. Development and validation of a compact diesel fuel vaporization and mixing system is the focus of this work. The fuel vaporization and mixing system is comprised of a fuel dosing system, catalytic monolith and mechanical mixer. A fuel reformer, lean NOx trap (LNT), diesel particulate filter (DPF) and a selective catalytic reduction (SCR) catalysts are positioned downstream of the fuel vaporizer system. A 44% reduction in total fuel vaporization / mixing path length was achieved using an optimized injection chamber, catalytic monolith and mixing element. Reformer outlet temperature results confirm that reformer inlet fuel vapor uniformity targets meet design specifications. Similarly, the fuel reformer efficiency using the fuel vaporizer met the design targets within the compact packaging envelope.