Patent ID: 8273315

Claim:
A method of operating an emission control system coupled to an exhaust passage of an engine, comprising: injecting an amount of reductant upstream of a first monolithic cylindrical substrate having a plurality of channels of radially varying cell density, the radial variation including inner channels with a higher cell density and outer channels with a lower cell density, the injected amount of reductant flowing unobstructedly from an injector into the first substrate without use of a mixer; flowing exhaust gas through the first substrate to mix the exhaust gas with the injected reductant; and flowing the mixed exhaust gas over an SCR catalytic washcoat to catalytically convert a component of the mixed exhaust gas, wherein the channels are along a length of the first substrate, and wherein the channels are rotated progressively along a lateral axis along the length of the first substrate, a twist angle of the rotation varying exponentially as a function of a distance from an inlet of the first substrate.