Nitrogen dioxide generation diagnostic for a diesel after-treatment system

A vehicle comprising:

• a diesel engine configured to propel the vehicle;
• an after-treatment (AT) system having a diesel oxidation catalyst (DOC) arranged downstream of the engine and configured to generate the NO2 and a selective catalytic reduction (SCR) catalyst arranged downstream of the DOC and configured to convert oxides of nitrogen (NOX) into diatomic nitrogen (N2) and water (H2O) with the aid of the generated NO2;
• an exhaust manifold configured to receive the exhaust gas flow from the engine;
• a turbocharger connected to the exhaust manifold and configured to pass the exhaust gas flow from the exhaust manifold into the AT system;
• and
• a controller configured to:
• regulate injection of a reductant into the exhaust gas flow at a location in the AT system downstream of the DOC and upstream of the SCR catalyst;
• monitor temperature of the exhaust gas flow at the SCR catalyst inlet during transient engine operation;
• detect a concentration of NOX at the inlet of the DOC and a concentration of NOX at the outlet of the SCR catalyst as the engine continues transient operation and the temperature of the exhaust gas flow at the SCR catalyst inlet is in a predetermined range;
• determine a conversion efficiency of NOX by the SCR catalyst using the detected concentrations of NOX at the inlet of the DOC and at the outlet of the SCR catalyst;
• and
• assess whether the NO2 generation efficiency in the AT system is at or above a threshold NO2 generation efficiency by comparing the determined conversion efficiency of NOX with a threshold conversion efficiency of NOX.

A method of assessing nitrogen dioxide (NO2) generation efficiency in a diesel engine after-treatment (AT) system, the method comprising:

• passing the exhaust gas flow from the engine into the AT system, wherein the AT system includes a diesel oxidation catalyst (DOC) arranged downstream of the engine and configured to generate the NO2, and a selective catalytic reduction (SCR) catalyst arranged downstream of the DOC and configured to convert oxides of nitrogen (NOX) into diatomic nitrogen (N2) and water (H2O) with the aid of the generated NO2;
• injecting a reductant into the exhaust gas flow at a location in the AT system downstream of the DOC and upstream of the SCR catalyst;
• monitoring temperature of the exhaust gas flow at the SCR catalyst inlet during transient engine operation;
• detecting a concentration of NOX at the inlet of the DOC and a concentration of NOX at the outlet of the SCR catalyst as the engine continues transient operation and the temperature of the exhaust gas flow at the SCR catalyst inlet is in a predetermined range;
• determining a conversion efficiency of NOX by the SCR catalyst using the detected concentrations of NOX at the inlet of the DOC and at the outlet of the SCR catalyst;
• and
• assessing whether the NO2 generation efficiency in the AT system is at or above a threshold NO2 generation efficiency by comparing the determined conversion efficiency of NOX with a threshold conversion efficiency of NOX.