Cost Effective Pathways toward Highly Efficient and Ultra-Clean CI Engines, Part I: Combustion System Optimization

Following global trends of increasingly stringent greenhouse gas (GHG) and criteria pollutant regulations, India will likely introduce within the next decade equivalent Bharat Stage (BS) regulations for Diesel engines requiring simultaneous reduction in CO2 emissions and up to 90% reduction in NOx emission from current BS-VI levels. Consequently, automakers are likely to face tremendous challenges in meeting such emission reduction requirements while maintaining performance and vehicle total cost of ownership (TCO), especially in the Indian market, which has experienced significant tightening of emission regulation during the past decade. Therefore, it is conceivable that cost effective approaches for improving existing diesel engines platforms for future regulations would be of high strategic importance for automakers. In this first of a two-part article, cost effective means of improving the combustion process in a Diesel engine to reduce engine-out emissions, specifically of NOx and smoke, are discussed in detail. The primary focus is on the co-optimization of fuel injector and piston bowl design to improve air utilization and hence reduce net soot formation. Additionally, novel dilute combustion strategies driven by geometry guided fuel-air mixing aided by tailored multi-lip piston bowl design are presented to suppress in-cylinder NOx formation. Both modelling and experimental data are provided to aid the discussion and demonstrate the potential for engine out NOx as low as 1 g/kW.h and smoke below 0.2 FSN with peak injection pressure of 1800 bar, achievable only by implement component level changes such as piston bowl design and injector nozzle configuration. Finally, the cost-to-performance trade-off of several combustion strategies is presented to discuss application-specific consideration for diesel engines – namely light-duty and heavy-duty.