The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
During combustion in a diesel engine, an air/fuel mixture is delivered through an intake valve to cylinders and is compressed and combusted therein. After combustion, the piston forces the exhaust gas in the cylinders into an exhaust system. The exhaust gas may contain oxides of nitrogen (NOx) and carbon monoxide (CO).
Exhaust gas treatment systems may employ selective catalytic reduction (SCR) catalysts to reduce nitrogen oxides (NOx). A catalyst converts the NOx into nitrogen N2 and water H2O. Reductant may be added to the exhaust gas upstream from the SCR catalyst. For example only, the reductant may include anhydrous ammonia, aqueous ammonia or urea.
Exhaust systems with SCR catalysts are vulnerable to poor quality reductant. If a reductant tank has been filled with poor quality reductant, an exhaust diagnostic system will detect a low SCR conversion efficiency. In some vehicles, the engine control module may limit the speed of the vehicle and/or perform other remedial actions. The poor quality reductant should be replaced with higher quality reductant to correct the problem.