Investigation of Combustion Stability in an RCCI Engine Using Recurrence Analysis of Cylinder Pressure Data

The Reactivity Control Compression Ignition (RCCI) engine, with its dual fuel system and coordinated injection strategy, offers superior emission control and fuel efficiency compared to conventional diesel engines. However, cyclic variations leading to engine combustion instability poses a significant challenge to their development and commercialization. In this study, statistical (COV and Histogram) and nonlinear dynamic (Recurrence Plot and its Quantification) analysis techniques are applied on the time-series data obtained from a single-cylinder diesel engine modified to operate in CNG-Diesel RCCI mode. The engine, while advancing the main injection timing (SOI-2), is tested under various operating conditions, including different engine loads, direct injection mass ratios (DIMR) and port fuel injection (PFI) masses, to help identify the configurations with better temporal correlations and deterministic traits. Such configurations hold potential for control strategy implementation. Through this study it is found that the engine operates in RCCI mode primarily at intermediate to advanced SOI-2 timings. After comparing RQA results of IMEP, Pmax, and CA50; IMEP is determined to be ideal for recurrence analysis. Ultimately, the configuration with a 70-30 DIMR at higher load and higher PFI mass demonstrates superior deterministic traits compared to the other test cases.