All of non-road diesel engines over 19 kW in North America are required to reduce further Nitrogen Oxides (NOx) and Particulate Matter (PM) to meet US EPA emissions regulation. Especially, it is necessary to reduce PM emission up to one-tenth as conventional. In addition to improve combustion in engine, it is needed to add exhaust gas after-treatment device to reduce PM emission.It is necessary for diesel engine with exhaust gas after-treatment device, to have Diesel Particulate Filter (DPF) regeneration system, which burns periodically PM in DPF. Generally, DPF regeneration is implemented by using post injection with common rail system. However, post injection is not available in small diesel engine which has mechanical injection system and IDI combustion system instead of common rail system. As an alternative way, an original fuel reformer technique is introduced for DPF regeneration. Fuel reformer is located in the upper exhaust gas flow of DPF, and works independently from fuel injection system of engine. Consequently this system realizes DPF regeneration that can be used in various kinds of injection and combustion systems.This paper introduces techniques to meet US EPA Tier4 emissions regulations with the small diesel engine without common rail system.