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Diesel engine will remain relevant even in the net-zero carbon society due to its high torque and high thermal efficiency characteristics. Inversed-delta injection rate shaping Diesel spray has been proven to increase Diesel engine thermal efficiency further. Although enhancement of heat release due to large scale vortices growth and development in the unstable inversed-delta-injected Diesel spray flame was observed, its impact on combustion duration reduction is much lesser than anticipated. In this study, apparent heat release rate derived from pressure history will be compared with the simultaneous high-speed images of OH* chemiluminescence and laser Schlieren; all the data were previously acquired in a constant volume combustion chamber CVCC experiment using a TAIZAC (TAndem Injector Zapping ACtivation) injector. MATLAB-based codes were employed for the flow velocity field turbulence intensity and the fuelair mixture spatiotemporal distributions analysis using Flame Imaging Velocimetry (FIV) analysis and Musculus-Kattke 1D model, respectively. Inversed-delta injection rate shaping exhibits enhancement of heat release throughout the diffusion combustion phase compared to that of conventional rectangle injection. Large scale vortices effect seems to be dominant factor in enhancing the heat release and OH* intensity in the inversed-delta injection rate shaping at the earlier stage of diffusion combustion phase. At the later stage, effects of high turbulence intensity coincide with fuel-air mixture availability at the spray tail marks by a larger OH* reacting area seems to be more pronounced in enhancing heat release rate for the inversed-delta injection. Regardless of the detected vortex and fuel-air mixture at the spray tail during the late combustion phase, no apparent OH* signal is observed in both injection cases suggesting that the mixture might be overly lean. [ABSTRACT FROM AUTHOR]