Characterization of deposits formed on diesel injectors in field test and from thermal oxidative degradation of n-hexadecane in a laboratory reactor

Solid deposits from commercially available high-pressure diesel injectors (HPDI) were analyzed to study the solid deposition from diesel fuel during engine operation. The structural and chemical properties of injector deposits were compared to those formed from the thermal oxidative stressing of a diesel fuel range model compound, n-hexadecane at 160°C and 450 psi for 2.5 h in a flow reactor. Both deposits consist of polyaromatic compounds (PAH) with oxygen moieties. The similarities in structure and composition of the injector deposits and n-hexadecane deposits suggest that laboratory experiments can simulate thermal oxidative degradation of diesel in commercial injectors. The formation of PAH from n-hexadecane showed that aromatization of straight chain alkanes and polycondensation of aromatic rings was possible at temperatures as low as 160°C in the presence of oxygen. A mechanism for an oxygen-assisted aromatization of cylcoalkanes is proposed

The Deconvolution of the Thermal, Dilution, and Chemical Effects of Exhaust Gas Recirculation (EGR) on the Reactivity of Engine and Flame Soot

In a recent paper, we demonstrated that the exhaust gas recirculation (EGR) enhanced the oxidative reactivity of diesel engine soot. In this paper, we show that simulated EGR, via carbon dioxide (CO2) addition to the intake air to an engine at concentrations of 0, 2, 4, and 8 vol.% and to the oxidizer stream of an ethylene diffusion flame at concentrations of 0, 5, and 10 vol.%, affects the reactivity of the soot in the same manner as actual EGR. Motivated by this fact, post-flame ethylene soot was produced from a co-flow laminar diffusion flame to better understand the mechanism by which the CO2 affects soot reactivity. This objective was accomplished by successfully isolating and examining the thermal, dilution, and chemical effects of the CO2 on soot reactivity. These three effects account for 45%, 35%, and 20% of the total reactivity of soot respectively, with the thermal effect being the most important factor governing the soot reactivity. The results showed that all of these effects account for a measurable increase in soot reactivity

Thermal analysis of mineral soils before and after oxidation with sodium hypochlorite

The nature of recalcitrant organic carbon (OC) in soil is a matter of great debate and various chemical treatments exist for its isolation. We compared calorimetric properties from silt+clay fractions of eight mineral soils by means of DSC before and after chemical oxidation with sodium hypochlorite (NaOCl) to find out, whether recalcitrance of soil organic matter against chemical oxidation coincides with its thermal stability. NaOCl oxidized around 75% of the OC, which corresponded well to a mean loss in heat of reaction of 80%. Peak temperatures and 50% burnoff temperatures did not change systematically after oxidation showing that the thermal stability of NaOCl residues was similar to that of untreated samples. Three samples revealed peaks at >520°C after oxidation indicative for the presence of pyrogenic carbon