Automotive manufacturers are facing increased pressure to meet more stringent emissions legislation and new legislative driving cycles. One technology that has the potential to meet future legislation is Low Temperature Combustion (LTC), which has the potential to significantly reduce NOx over conventional diesel combustion. Most studies reported in the literature evaluating this technology only change 'one-factor-at-a-time' at steady state conditions. This paper addresses these issues and presents a methodology utilising DoE analysis to optimise a validated multi-fidelity engine simulation for LTC over a transient cycle (WLTP) which makes the results more applicable to real world driving conditions. A validated simulation for a 2.4-litre compression ignition engine was developed in Ricardo WAVE. To increase the fidelity of the model, empirical data such as 3D scans of the inlet geometry were included. The simulation was validated against experimental engine emissions and performance data. A characterization study using a full factorial DoE was performed on the whole engine simulation to minimise vehicle emissions using LTC. The vehicle simulation was tested against the WLTP and the response of the emissions for different levels of exhaust gas recirculation (EGR), pilot start of injection (SOI) and main SOI timings and pilot injection duration were recorded. The results of the optimization showed that over the WLTP the NOx emissions decreased by approximately 85 % with an EGR of 47.5 %, retarding the pilot SOI and main SOI maps with 1 CAD compared to the default maps and increasing the pilot injection duration by 200 microseconds. NOx emissions were reduced by approximately 18 % with the use of 12 % EGR without exceeding the Euro 4 CO emissions limit. Further increase in EGR percentage significantly increased the CO emissions.
Van Niekerk, A. S., Kay, P. J., Drew, B., & Larsen, N. (2019). Optimisation of low temperature combustion technology, for future drive cycles, using a factorial design of experiments