An exhaust aftertreatment system connected to an internal combustion engine operative lean of stoichiometry includes first and second selective catalytic reactor devices. A preferred ratio of hydrocarbon:NOx to achieve a preferred concentration of ammonia immediately downstream of the first selective catalytic reactor device is determined. An ethanol-based reductant is dispensed upstream of the first selective catalytic reactor device.
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 The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of DE-FC26-02NT41218 awarded by the U.S. Department of Energy.