Optimized Exhaust After-Treatment System Solution for Indian Heavy Duty City Bus Application - The Challenges Involved and the Right Approach to Meet Future BS VI Emission Legislations and Real World Driving Emissions 2019-26-0139

The vehicular pollution and emission levels are alarmingly increasing in India. The metro and urban cities are worst hit by the gaseous and particulate emissions produced by internal combustion engine powered vehicles. Following the trend from other developed countries, Government of India (GOI) has decided to migrate from existing BS IV legislation directly to BS VI legislation from April 2020 all across India. This migration in emission legislation took almost 10 years to be implemented in European Union (EU) countries. However, for India, the targeted implementation time is just 3 years, making it an uphill challenge for all the vehicle manufacturers. City bus is one such applications, which run mostly within the city and currently are powered by conventional Diesel engines. The vehicle manufacturers should focus on finding an optimized solution for meeting the future emission legislation in true sense. This calls for meeting the emission limits with not only the legislative engine dynamometer cycles but also considering the real world driving cycle (RDE) in their solution.

The study presented here involves finding the optimized solution for engine and exhaust after-treatment system (EATS) for the city bus application to meet future BS VI emission regulations. The focus was to not only meet the emission specific drive cycles like WHTC & WHSC, but also evaluate and optimize the solution for real world driving emission cycle (RDE). Although it should be noted, that there is no direct regulation for heavy-duty commercial vehicle with RDE cycles as compared to the light duty Diesel segment, but the vehicle manufacturers have to ensure that the system performance with respect to emission in worst-case real life scenario is always protected and achieve a reasonable Conformity Factor (CF). For this study, a RDE cycle specifically for city bus application has been developed in Mumbai city, capturing the real driving scenario in typical metro Indian cities, with many start stops and low vehicle velocity operations. With such a vehicle duty cycle, typical Selective Catalyst Reduction (SCR) based solution for these heavy-duty application will be impacted with delayed light-off and lower conversion efficiencies. Different heating strategies like late post injections, variable valve timing, intake throttling, hydro carbon dozer, electric heated catalysts etc. has been also analyzed in the presented study. Different EATS layouts involving DOC, DPF, SCR etc. have been simulated and optimized with respect to system performance and total fluid consumption (Fuel and AdBlue) to arrive at the best solution for this segment. FEV has an internally developed mean value based simulation platform to optimize the complete powertrain along with the EATS. This simulation tool has been used to simulate the different engine dynamometer based emission cycles and the selected RDE cycle with different EATS layouts and heating strategies. In addition, as part of this study to achieve in-cylinder emission reduction, the engine level modifications needed for the current BS IV engines has also be detailed and analyzed. This will also provide an insight into any new engine developments for this segment by the manufactures.

This study provide the Indian manufacturers a direction to meet the future stringent emission legislation for the city bus application (heavy commercial segment) not only for meeting the mandated emission specific cycles on engine dynamometer but also with the real life driving cycle (RDE). The study achieves system optimization in terms of real life emission, system cost and fluid consumption reduction, which will be very critical and deciding factor for improving the manufacturer’s presence into the Indian market in future.