This study presents the influence of low-temperature heat release (LTHR) and high-temperature heat release (HTHR) on the combustion and particle number characteristics of the RCCI engine. The study investigates the relationship between the amount of LTHR, HTHR, and particle number emission characteristics. In this study, gasoline and methanol are used as low reactivity fuel (LRF), and diesel is used as a high reactivity fuel (HRF). The LRF is injected into the intake manifold using a port-fuel injection (PFI) strategy, and HRF is directly injected into the cylinder using a direct injection strategy. A particle sizer is used to measure particle emission in size ranging from 5 to 1000 nm. Firstly, the LTHR and HTHR are analyzed for different diesel injection timing (SOI) for RCCI operation. Later, the variation of particle emissions with LTHR and HTHR is characterized. Additionally, empirical correlations are developed to understand the relation between the LTHR and HTHR with particle emission. Two-staged auto-ignition of charge has been observed in RCCI combustion. Results depict that LTHR varies with diesel injection timing and the phasing of HTHR depends on the amount and location of LTHR. Results also showed that HTHR and LTHR significantly influence the formation of particle number concentration in RCCI combustion. The developed empirical correlation depicts a good correlation between diesel SOI and the ratio of HTHR to LTHR to estimate total particle number concentration.

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