Understanding the combustion mode transition from CDC to RCCI and RCCI to CDC – An experimental approach

•Understanding the combustion mode transition is essential to implement RCCI in commercial vehicles studied in this work.•A dual fuel control algorithm and calibrated parameter maps have been developed for smooth CDC to RCCI and RCCI to CDC mode transition.•The engine combustion, performance, and emissions trends during the mode transition were studied.•Compared to CDC mode, increased brake thermal efficiency and reduction in CO2 were obtained in RCCI mode.•CO2 reduction with increased efficiency of ICEs set the path for development of ultra-high efficiency ICEs and to tackle the challenges in pure electrification goals. This article presents an experimental understanding of combustion mode transition from conventional diesel combustion (CDC) mode to reactivity-controlled compression ignition (RCCI) combustion mode. In the current study the variations in combustion, performance, and emissions during the mode transition were investigated and accordingly a dual fuel control algorithm for achieving smooth transition between CDC and RCCI combustion modes was developed. Experimental data are presented for CDC with diesel and RCCI with Gasoline/Diesel at 1600 rev/min, 25 N.m torque only, considering the data size and ease of understanding the mode transition. Nine steps have been adopted to switch from CDC to RCCI combustion mode. The operating variables such as number of diesel injections, injected diesel mass between the injections, gasoline energy fraction, diesel start of injection, and exhaust gas recirculation (EGR) flow rate have been altered to switch from CDC to RCCI. Changes in combustion, performance, and emissions have been recorded and analyzed at each operating variable to determine the optimal path for smooth combustion mode transition. A similar approach has been extended to medium and high loads to obtain the optimal path. Finally, all the optimal paths have been collated to develop calibrated maps for operating the chosen test engine from CDC to RCCI and RCCI to CDC modes smoothly.