Optimizing Engine Combustion and Exhaust After treatment System for Passive Regeneration in Off-Highway Applications

The Bharat TREM V regulations in the off highway segment mandates use of Diesel Oxidation Catalyst (DOC) to reduce gaseous emissions and Diesel Particulate Filters (DPF) to trap solid particulates from engine exhaust. DPFs undergo regeneration, where trapped soot is burned, converting it into CO2 with ash as a byproduct. Regeneration can be active, using fuel injection to raise temperatures above 550°C, or passive, relying on NO2 formation at 300-400°C. Passive regeneration is preferred as a safer mode for both DPF health and longevity as well as reduction in fuel penalty and oil dilution. This paper highlights on the selection and optimization of combustion hardware and Exhaust Aftertreatment System to achieve the desired NO2 formation which is suitable for passive regeneration. Key considerations in engine hardware selection include the design of piston bowl, injector hole configuration to increase heat release rate and combustion temperature resulting in higher NOx/soot ratio. With respect to Exhaust Aftertreatment optimization, sizing, Cell density and material selection as well as PGM loading and ratio chemistry formulation of both DOC and DPF were taken into consideration. Further this paper also includes calibration strategies that optimize injection timing, rail pressure, and EGR variation to support passive regeneration through higher NOx formation. Passive regeneration rates were determined through pre- and post-soot gravimetric measurements of DPF. These measurements were further analyzed alongside accumulated soot mass rates under specific exhaust mass flow rates and temperature conditions. The soot mass balance results were validated over both legislation cycles NRSC and NRTC as well as simulated real life duty cycle - Low duty to heavy duty cycles on engine test bed. Additionally, efficacy of passive regeneration was tested and validated on key tractor applications.