Impacts of fuels on Ag/Al $_{2}$ O $_{3}$ SCR catalyst in diesel engines

Poku, Robert (2023). Impacts of fuels on Ag/Al $_{2}$ O $_{3}$ SCR catalyst in diesel engines. University of Birmingham. Ph.D.

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Abstract

The combustion of propane and NH $_{3}$ in diesel engines on low load operation, produces high level of unburnt THC and NH $_{3}$ emissions. Taking advantage of the increased THC and NH $_{3}$ levels in the exhaust, the NOx reduction activities of a Ag/Al $_{2}$ O $_{3}$ SCR catalyst was investigated.

Impacts of diesel fuel injection timing on the combustion, performance and emissions of a diesel engine running on diesel-propane dual fuelling system were studied. Advanced injection timing was found to improve the combustion performance at low engine load operation. The higher in-cylinder pressure and temperature due to advanced injection timing improved the combustion of the in-cylinder fuel-air mixture.

The effects of NH $_{3}$ with additionally added H $_{2}$ (mimicking engine operation with NH $_{3}$ addition) on the NOx reduction activity over Ag/Al $_{2}$ O $_{3}$ catalyst were investigated in a diesel engine in the presence of low concentrations of HC reductant using a DOC+SCR aftertreatment configuration. It was found that although, part of the exhaust HC was involved in HC-SCR of NOx, the introduction of H $_{2}$ and NH $_{3}$ mixture provided the catalyst with additional reductant that supported the removal of NOx at the exhaust.

Subsequently, under diesel-propane fuelling system, where 25% of diesel fuel was replaced with low carbon fuel (i.e., propane), higher concentration of HC reductant and NO $_{2}$ were made available for the SCR Ag/Al $_{2}$ O $_{3}$ catalyst in the presence and absence of H $_{2}$ and NH $_{3}$ mixture. Although, significant amount of CO and THC escaped the catalyst unconverted, NOx conversion efficiency was enhanced. This study shows that the high level of NH $_{3}$ and THC emissions in the exhaust can be beneficial to the SCR aftertreatment system.