Investigation on Combustion Stability, Unregulated and Particle Emissions in RCCI Engine

This study experimentally investigates the combustion stability in RCCI engines along with the gaseous (regulated and unregulated) and particle emissions. Multifractal analysis is used to characterize the cyclic combustion variations in the combustion parameters (such as IMEP, CA₅₀, and THR). This analysis aims to investigate the multifractal characteristics of the RCCI combustion mode near the misfiring limit. The investigation is carried out on a modified single-cylinder diesel engine to operate in RCCI combustion mode.The RCCI combustion mode is tested for different diesel injection timing (SOI) at fixed engine speed (1500rpm) and load (1.5 bar BMEP). The particle number characteristics and gaseous emissions are measured using a differential mobility spectrometer (DMS500) and Fourier Transform Infrared Spectroscopy (FTIR) along with Flame Ionizing Detector (FID), respectively. The results indicate that the NO_x emissions decrease with advanced SOI while the Total Hydro-Carbon (THC) emission increases. The result shows that advanced SOI decreases the formation of propylene (C₃H₆), ethylene (C₂H₄), 1-3 butadiene (C₄H₆), and methane (CH₄). However, formaldehyde (HCHO) emission increased with advanced SOI. The emission of the total particle number (PN) and nucleation mode particles (NMPs) decreased with advanced diesel SOI. Multi-Fractal Detrended Fluctuation Analysis (MFDFA) demonstrated a positive correlation between diesel SOI and the level of multifractality. It is found that the time series of combustion parameters exhibits large fluctuations at smaller time scales, while small fluctuations are detected at higher time scales.