Despite the trend in increased prosperity, the Indian automotive market, which is traditionally dominated by highly cost-oriented producion, is very sensitive to the price of fuels and vehicles. Due to these very specific market demands, the U-LCV (ultra-light commercial vehicle) segment with single cylinder natural aspirated Diesel engines (typical sub 650 cc displacement) is gaining immense popularity in the recent years. By moving to 2016, with the announcement of leapfrogging directly to Bharat Stage VI (BS VI) emission legislation in India, and in addition to the mandatory application of Diesel particle filters (DPF), there will be a need to implement effective NOx aftertreament systems.
Due to the very low power-to-weight ratio of these particular applications, the engine operation takes place under full load conditions in a significant portion of the test cycle. These lead to further challenges in terms of high engine-out NOx emissions and non-optimum temperature window for efficient operation of NOx aftertreatment devices.
In the state-of-the-art calibration processes, the aftertreatment system is considered separately from the calibration of the thermodynamics. This conventional approach makes it more challenging to achieve a simultaneous optimization of the fuel consumption and the tailpipe emissions under transient operating conditions. To meet this goal, the SimEx powertrain simulation tool from FEV enables a simultaneous optimization of the multiple sub-systems considering engine thermodynamics, controls, transmission system, gear shifting strategy and exhaust gas aftertreatment.
In the 1st phase of the research study presented here, the base engine was optimized in terms of friction reduction and cylinder volume right-sizing to enable sufficient EGR rates even at full load to achieve lower engine out NOx without compromising the fuel economy and performance. In the 2nd phase of the study, different configurations of NOx aftertreatment concepts were analysed. The results indicate that an improved engine design with single stage LNT (lean NOx trap) system i.e. “LNT + cDPF” can bring the tailpipe NOx into the BS VI window, but without sufficient engineering margins. However, a two stage LNT i.e. “LNT + cDPF + LNT” due to its improved behavior also ensures sufficient engineering margins. Finally, the BS VI capability of all the engine concepts was also investigated with a SCR coated DPF (SDPF) based system, which showed lowest tailpipe emissions due to its improved conversion behavior in a wide temperature window. A final selection of the aftertreament strategy will depend significantly on the application specific boundary conditions (i.e. base engine technology, performance, robustness, costs etc.). Overall, this integrated simulation approach supports efficient frontloading strategies and allows the cumulative optimization of the total system configuration meeting the stringent tailpipe legislation and fuel economy targets with the lowest total cost of ownership.