Locations of TWC and DPF in Automotive Exhaust After-treatment Systems

The TWC (Three-Way Catalytic Converter) is used in gasoline vehicles, while the DPF (Diesel Particulate Filter) is used in diesel vehicles; they differ in system placement and serve completely different functions.

TWC: Gaseous pollutant purifier for gasoline vehicles

Location: After the exhaust manifold (close-coupled); some models also feature a secondary under-floor TWC.

Function: Simultaneously purifies three types of gaseous pollutants—CO, HC, and NOx—with a conversion efficiency of ≥95%.

Key requirements: Air-fuel ratio (λ) ≈ 1; operating temperature of 250–900°C.

DPF: Particulate matter trap for diesel vehicles

Location: After the DOC and either before or after the SCR.

Function: Captures carbon particulates (PM) with an efficiency of ≥90%. Accumulated soot requires high-temperature regeneration (550–650°C) to burn off deposits.

Substrate type: Wall-flow honeycomb ceramic (channels are alternately plugged).

Comparison of Location and Function

Comprehensive Layout for Diesel Vehicles

Modern diesel vehicle exhaust systems utilize a multi-stage series configuration: DOC → DPF → SCR → ASC (regarding the placement of the DPF relative to the SCR, the specific design determines whether it comes before or after the SCR).

Summary

The differences between TWC and DPF can be summarized as follows: TWC treats gaseous pollutants (CO, HC, NOx) from gasoline vehicles and is located at the front of the exhaust system; DPF captures solid particulate matter from diesel vehicles, is positioned in the middle-to-rear section, and requires periodic regeneration. Gasoline vehicles primarily rely on TWC, whereas diesel vehicles require a multi-stage combination of DOC, DPF, and SCR; the two systems target different pollutants associated with their respective fuel types.