In situ spatial soot and temperature distributions were investigated experimentally for B20 (20% v/v butanol and balance mineral diesel blend) vis-a-vis mineral diesel using endoscopic visualization technique. Endoscope captured the in-cylinder combustion images in a production-grade direct injection compression ignition (DICI) engine at varying engine operating conditions. A comparative combustion data analysis using pressure-crank angle history and the captured endoscopic images was performed. An attempt was made to correlate the results of these two experimental investigations. Combustion duration (CD) obtained from the endoscopic images was relatively longer than the CD calculated from the thermodynamic analysis. Most research on soot and NOx emitted from the engine using a raw exhaust gas emission analyzer provides bulk, time-averaged, and cycle-averaged information about the pollutant formation. This investigation is unique wherein the spatial or time-resolved soot and NOx formation (Via spatial temperature distribution) are evaluated. The findings of this study support the research finding available in the open literature using an emission analyzer. This study and the technique therein on the deployment of engine endoscopy as an emerging optical technique is potentially useful to original automotive manufacturers (OEMs) in designing more efficient engines, capable of meeting upcoming stringent emission norms.