Experimental study on morphology, nanostructure and oxidation reactivity of particles in diesel engine with exhaust gas recirculation (EGR) burned with different alternative fuels

Abstract

Experiments were conducted at a diesel engine with exhaust gas recirculation (EGR), and the particulates produced by the combustion of Fischer-Tropsch (F-T) diesel, biodiesel as well as diesel were collected. The influences of fuel characteristics upon the morphology, nanostructure and oxidation reactivity of particles were explored by high-resolution transmission electron microscope (HRTEM), Raman spectroscopy (RS) and thermogravimetry (TGA). The results show that compared with diesel, F-T diesel particulates possess smaller fractal dimension (Df) and fringe tortuosity (Tf), lower the area ratio of D1 peak to G peak (AD1/AG) and half peak width of D1 peak (D1-FWHM), longer fringe length (La), shorter separation distance (d), higher oxidation characteristic temperature and apparent reactive energy (Ea), while biodiesel particulates exhibit the opposite features. Among the samples, F-T diesel particulates display the highest graphitization degree and the lowest oxidation reactivity, biodiesel particulates present the most disorderly nanostructure and are more easily oxidized. The application of EGR increases the agglomeration degree, reduces the graphitization degree and oxidation characteristic temperature, and enhances the oxidation reactivity of particulate. Compared with the particulates collected without EGR, the Ea of FT diesel, biodiesel, and diesel particulates are reduced by 36.7%, 41.2%, and 37.5% as the EGR rate is 30%.