Raman Spectroscopy of Diesel and Gasoline Engine-Out Soot Using Different Laser Power

TL;DR

This study uses Raman spectroscopy with varying laser power to analyze soot from diesel and gasoline engines, revealing differences in oxidation reactivity and carbon structure.

Contribution

It introduces a MATLAB-based curve fitting method with DOE to accurately analyze Raman spectra of engine soot samples at different laser powers.

Findings

High laser power causes soot oxidation, increasing D/G ratio.

Diesel soot shows higher amorphous/graphitic ratio than gasoline soot.

Raman spectra indicate diesel soot has higher oxidation reactivity.

Abstract

We studied engine-out soot samples collected from a heavy-duty direct-injection diesel engine and a port-fuel injection gasoline spark-ignition engine. The two types of soot samples were characterized using Raman spectroscopy with different laser power. A Matlab program using least-square-method with trust-region-reflective algorithm was developed for curve fitting. We used a DOE (design of experiments) method to avoid local convergence. This method was used for two-band fitting and three-band fitting. The fitting results were used to determine the intensity ratio of D and G Raman bands. We find that high laser power may cause oxidation of soot samples, which gives higher D/G intensity ratio. Diesel soot has consistently higher amorphous/graphitic carbon ratio and thus higher oxidation reactivity, in comparison to gasoline soot, which is revealed by the higher D/G intensity ratio in Raman spectra measured under the same laser power.