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This work studied the evolution of in-cylinder polycyclic aromatic hydrocarbons (PAHs) in a diesel engine fueled with n -heptane, and explored the effects of adding toluene to n -heptane on in-cylinder PAHs. In-cylinder PAHs were sampled in a direct injection diesel engine using a total cylinder sampling system. PAHs were analyzed by gas chromatography–mass spectrometry with programmed temperature vaporization in the solvent vent mode. For n -heptane, the mass of total in-cylinder PAHs ( Σ M PAHs ) increased in premixed and late diffusion combustion phases, and decreased in early diffusion and late combustion phases. Among the 16 PAHs detected, Naphthalene (Nap) was the most abundant. PAHs with two benzene rings and one five-membered ring, such as Acenaphthylene, Acenaphthene and Fluorene, were also plentiful, implying that PAHs with five-membered ring could play an important role in the growth of in-cylinder PAHs. When adding 20 vol.% toluene to n -heptane, the evolution of ΣM PAHs was varied. The Σ M PAHs for n -heptane/toluene increased in premixed and early diffusion combustion phases, and decreased in late diffusion and late combustion phases. Toluene addition reduced the ΣM PAHs in the premixed combustion phase by up to 48% but increased ΣM PAHs by 30% in the early diffusion combustion phase. In the subsequent combustion phase, the ΣM PAHs was reduced by approximately 67%. For in-cylinder individual PAHs, toluene addition generally reduced the percentages of Nap in ΣM PAHs during the engine combustion process but increased the percentages of larger PAHs, indicating that toluene addition was conducive to the growth of PAHs to form larger PAHs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Reductions in CBC emissions were assessed for CFT diesel. [•] Significant reductions in emissions of total and individual CBCs were obtained. [•] The percentage reduction in the total CBCs decreased with an increase in engine load. [•] The percentage reduction in the total CBCs increased with increase in engine speed. [•] The ozone formation potential of CBCs emitted was strongly reduced with use of CFT. [ABSTRACT FROM AUTHOR]

The oxidation rates of diesel soot from the combustion chamber of a running diesel engine were calculated based on the particle size distributions at different crank angles. The primary particle diameter and nanostructure of soot were obtained by means of high-resolution transmission electron microscopy (HRTEM). The soot characteristics were also investigated by oxidative thermogravimetry and Raman scattering spectrometry. The results showed the soot nanostructures were dependent on engine operation conditions and combustion phases. The oxidation rates were found to differ by nearly fourfold from that calculated by the Nagle/Strickland-Constable (NSC) model for the soots studied here. The varied oxidation rates were interpreted in terms of differences in nanostructure between the soots. The experimental results were used to modify the NSC model and the fringe length of in-cylinder diesel soot was chosen to describe the influence of graphitisation on the oxidation of soot. The modified NSC model lessened the deviation between measurements and predictions. [ABSTRACT FROM AUTHOR]

Abstract: The diesel soot was extracted from the chamber of a running diesel engine using a total cylinder sampling system. A structural description and size distribution of the soot spherules were performed by means of high-resolution transmission electron microscopy (HRTEM). HRTEM image analysis was carried out to achieve semi-quantitative information about the soot organization. Different nanostructures were found in dependence upon the engine test conditions. A better organization of the graphitic layers occurred for the in-cylinder soot as the expansion stroke developed. The oxygen concentrations at sampling angles and the cylinder pressure were measured. The oxidation rates of the in-cylinder soot during the late combustion phase were calculated according to the differences of spherules size distributions between two consecutive sampling angles. The soot reactivity in dependence on the nanostructure was shown after deducting the effect of oxygen concentration and temperature. The increase of resistance toward oxidation was associated to the increase of the structural order for the in-cylinder soot. The results are a useful database for testing the structure–property relationship between the nanostructure and the reactivity of the in-cylinder diesel soot. [ABSTRACT FROM AUTHOR]

The present study investigated the effects of adding 20 vol.% biodiesel to petroleum diesel (to produce a mixture termed B20) on the physical properties and reactivity of the resulting exhaust soot particles. Tests were performed at different engine loads of a constant speed, and the soot particles from the combustion of B20 and petroleum diesel fuel (DF) were collected from the engine exhaust stream. Transmission electron microscopy and Raman spectroscopy were employed for the analysis of soot morphology and nanostructure. The thermogravimetric analysis was used to determine the oxidative reactivity of the soot. For both the DF and B20 soot, increased engine loads result in soot aggregates with more compact morphology and primary soot particles with larger size and more organized structure. Compared to the DF soot, the B20 aggregates have a slightly more compact morphology and smaller primary particle size. No appreciable differences are observed in nanostructure between the DF and B20 soot. The thermogravimetric analysis demonstrates that the B20 soot is associated with lower peak temperature, burnout temperature and apparent activation energy, suggesting that it is more reactive than the DF soot. [ABSTRACT FROM AUTHOR]

In this study, programmed temperature vaporization in the solvent vent mode (PTV-SV) of gas chromatography-mass spectrometry was optimized and validated for the analysis of particle-phase and gas-phase polycyclic aromatic hydrocarbons from diesel engine combustion. Because of the large number of experimental and response variables to be studied, central composite inscribed design was used to optimize the PTV-SV injection factors, including initial inlet temperature, vaporization flow and time. The optimized PTV-SV method was validated by linearity, accuracy and sensitivity. For the 16 Polycyclic aromatic hydrocarbons (PAHs) studied, the correlation coefficients for the calibration plots of peak areas versus concentrations (0.5–300 ng mL−1) ranged from 0.9812–0.9998. Limits of detection ranged from 0.016–20,130.375 ng mL−1, and limits of quantification ranged from 0.055–1.25 ng mL−1. The optimized method was used for the analysis of real samples collected from a diesel engine, which included particle-phase and gas-phase PAHs. The results showed that the improved PTV-SV method was satisfying for simultaneously identifying and quantifying PAHs produced during diesel combustion. [ABSTRACT FROM AUTHOR]