The key difference between CEV Stage IV and Stage 5 is the inclusion of after treatment system with the engine.
Engines with power rating up to 56kW will have Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF), while engines with power > 56kW will have Diesel Oxidation Catalyst (DOC) and Selective Catalytic Reduction Filter (SCRF) to meet the stringent requirements of PN (Particulate Number) and PM (Particulate Matter).
Aftertreatment oxidises harmful gases like unburnt hydrocarbon and carbon monoxide to less harmful gases & traps the soot (carbon) released from engine exhaust and emits cleaner emissions. Filtration is cleaned by a regeneration (Regen) process managed by an engine electronic control system.