In 2008 the city of London, England, implemented its Low Emission Zone (LEZ) program, to improve air quality by targeting action on older, higher polluting diesel vehicles such as lorries and buses. In the first phase of the program, Euro 2 vehicles operating in the city center required upgrade to Euro 3 emission


Diesel particulate matter required reduction by 33% to 46%, depending on the engine model, in order to achieve an emissions upgrade from Euro 2 to Euro 3. The LEZ certification program included emissions testing of the diesel emission retrofit package under the FIGE duty cycle and assessment of a deterioration factor. The retrofit package needed to be easy to install, maintenance free, and cost effective for older vehicles.


DCL collaborated with its local partner in London, KleenAir Systems UK, to design, test and market a flow-through diesel particulate filter (DPF) for LEZ certification and easy retrofit on a variety of vehicles. DCL supplied the flow-through DPF substrate elements and KleenAir Systems developed the muffler packaging. The flow-through DPF was shown to achieve over 46% conversion efficiency in Euro 2 vehicles and received Transport for London Low Emissions Certification. The flow-through DPF design was a passive system that provided low back-pressure and operated maintenance free under low exhaust temperatures typical of urban center driving cycles. Two thousand units were successfully installed and operated under the program.