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With India achieving the BSVI milestone, the diesel particulate filter (DPF) has become an imperative component of a modern diesel engine. A DPF system is a device designed to trap soot from exhaust gas of the diesel engine and demands periodic regeneration events to oxidize the accumulated soot particles. The regeneration event is triggered either based on the soot mass limit of the filter or the delta pressure across it. For a Heavy Duty Diesel Engine (HDDE), pressure difference across the DPF is not usually reliable as the size of the DPF is large enough compared to the DPF used ina passenger vehicle diesel engine. Also, the pressure difference across DPF is a function of exhaust mass flow and thus it makes it difficult to make an accurate call for active regeneration. This demands for a very accurate soot estimation model and it plays a vital role in a successful regeneration event.

Selective Catalytic Reduction has established itself to significantly reduce NOx emissions from diesel engines. Typically, in this technology, aqueous urea solution is injected into hot exhaust stream which chemically decomposes to form ammonia and then reacts with NOx to form safe byproducts as H2O and N2 over the catalyst surface. However, incomplete thermal decomposition of urea not only reduces the NOx conversion efficiency and increases the ammonia slip, but also leads to the formation of solid crystals that adversely affect the performance of the system by increasing the back pressure and lowering the overall fuel economy. The present study discusses about the main reasons that lead to crystal formation in a vanadium based SCR system on a six cylinder 5.6l diesel engine and also design considerations of decomposition tube that affect the formation of crystals and ways to mitigate them.