Effect of dimethyl carbonate on the micromorphology and structure of combustion particles from diesel engines

Particulate matter emitted by internal combustion engines is one of the main sources of air pollution. Oxygenated fuels can partially replace diesel fuel in combustion and reduce the emission level, especially the particulate matter emitted by diesel engines. In this paper, the emitted particles from the combustion of dimethyl carbonate (DMC)/diesel blends with different blending ratios were collected, and the effects of DMC on the morphology of the diesel particles were analyzed via scanning electron microscopy and small-angle X-ray scattering (SAXS) with a synchrotron radiation source. By studying the small-angle scattering intensity, particle size distribution, fractal dimension, and interface thickness of DMC/diesel combustion particles, the effects of DMC on the degree of agglomeration of particles, particle size distribution, and surface roughness were investigated. The results showed that as the DMC blending ratio increased, the radius of gyration of the particles decreased, the particle size of the primary carbon particles formed by combustion decreased, and the particle size distribution became narrower. With increasing DMC blending ratio, the electron density differences in the particles gradually decreased, the statistical average distance between the particles decreased, the fractal dimension increased, the degree of agglomeration increased, and the structural arrangement was more compact. SAXS analysis revealed that the combustion particles exhibited surface fractal characteristics at a wide angle range and exhibited mass fractal characteristics at a small angle range. The surface fractal dimension and mass fractal dimension of the particles were both higher than those of diesel particles, indicating that the surface roughness, irregularity, and degree of agglomeration of the particles all increased.