Chun Guan

Effects of Injection Pressure on Diesel Engine Particle Physico-Chemical Properties

The effects of injection pressure on diesel particle physical and chemical properties were investigated on a heavy-duty diesel engine. Three injection pressures (600 bar, 800 bar, and 1000 bar) were selected at two engine loads (0.3 MPa BMEP and 0.9 MPa BMEP). The exhaust particle size distribution was measured by a scanning mobility particle sizer (SMPS). Consistent with previous studies, increasing injection pressure effectively removes accumulation mode particles, which results in a significant decrease in particle total mass concentration. The elemental carbon emission factors were then tested through organic carbon/element carbon (OC/EC) analysis. The emitted EC is decreased by 64% and 50% with increasing injection pressure from 600 bar to 1000 bar at the low and high engine loads, respectively. Particle morphology and oxidation reactivity were investigated by means of transmission electron microscope (TEM) imaging and thermogravimetric analysis (TGA) technology, respectively. Smaller primary particles with shorter and flatter graphene layer segments are observed at higher injection pressure conditions, and the particle oxidation reactivity is increased with injection pressure. Copyright 2014 American Association for Aerosol Research

Heterogeneous reaction of NO2 on α-Al2O3 in the dark and simulated sunlight.

Although there have been a number of publications focused on heterogeneous of NO2 on mineral particles, most of these studies were focused on β-Al2O3 and performed in the dark. Less was known about the reaction process of NO2 on α-Al2O3, especially the effect of sunlight factor. The heterogeneous reaction between NO2 and α-Al2O3 was investigated by using diffuse reflectance infrared Fourier transform spectrometry. The effects of NO2 and O2 concentrations as well as simulated sunlight were examined, and the reaction mechanism including the consumption of surface OH groups, oxidation process of nitrites, and the formation of water was also discussed in detail. It was observed that the formation rates of nitrates and nitrites were sensitive to NO2 concentrations and O2 concentrations. Nitrite was identified to be an intermediate production and disappeared very soon as [NO2] was up to 4.035 × 10(15) molecules/cm(3). Light played an important role in the changes of the electronic configuration of mineral dust, such as electronic donating ability, surface OH groups orientation, as well as the conversion efficiency between proton acid and nonproton acid, all of which could significantly enhance the heterogeneous reaction process. The reaction order for NO2 and O2 was determined to be 0.960 ± 0.111 and 0.620 ± 0.028, respectively. The uptake coefficient of NO2, which dominated the first step of the heterogeneous reaction, was calculated by the infrared absorbance with the use of ion chromatography and determined to be 9.9 × 10(-10) in the dark and varied from 2.54 to 3.33 × 10(-9) under simulated sunlight from 0.45 to 1.35 mW/cm(2). It was also found that γNO2 was independent of [NO2] and sunlight increased the uptake coefficient by three times, indicating that the heterogeneous reaction between NO2 and α-Al2O3 was enhanced under sunlight.

Oxidative Reactivity of Particles Emitted from a Diesel Engine Operating at Light Load with EGR

The impact of exhaust gas recirculation (including three levels: 0, 10%, and 30%) on engine combustion characteristics, gaseous emissions, and particulate properties (i.e., oxidative reactivity, carbonaceous compositions, size distribution, and nanostructure) was studied on a common rail diesel engine operating at low engine load. The results showed that the lack of oxygen with EGR prolongated ignition delay and the premixed portion of combustion started to rise significantly. Higher EC (accumulation mode) with larger particle size could be observed with increasing EGR from 0 to 30%, which is attributed to the promotion of soot formation with less available oxygen and the inhibition of soot oxidation with low in-cylinder temperature with increasing EGR. The soot nanostructure observation showed that soot changed from smooth surface under 0 EGR to rugose surface under 10% EGR. Moreover, the amorphous core turned larger with increasing EGR. With increasing EGR to 30%, the amorphous core appeared to include the whole primary soot particle. The increase of accessible carbons on the edge sites correlates with the high reactivity with increasing EGR. Through the quantitative analysis of the correlation between the combustion parameters and particle properties, we speculated that in this work, the engine at low load producing very little to no conventional soot or soot-EC coupling with low combustion temperature and short residence time with increasing EGR lead to the soot exhibiting less carbonization level (short fringe length and large fringe curvature) and result in higher reactivity. Copyright 2015 American Association for Aerosol Research

Effect of biodiesel on PAH, OPAH, and NPAH emissions from a direct injection diesel engine

Polycyclic aromatic hydrocarbon (PAH), oxy- and nitro-derivate PAH (OPAH and NPAH) emissions from a direct injection diesel engine fueled with conventional fossil diesel (D), waste cooking oil biodiesel (B100), and their two blends (B20 and B50) were compared. The results show that B100 can reduce low molecular weight PAHs such as naphthalene, acenaphthylene, and fluorene as much as 90% compared with diesel. However, the emissions of high molecular weight PAHs including benzo[b]fluoranthene, benzo[k]fluoranthene, and benzo[a]pyrene decrease slightly when using B100. The emission levels for PAHs and OPAHs present comparable, while NPAH emission levels are five to ten times lower than those of PAHs and OPAHs. Compared with diesel, PAH and NPAH emissions significantly decrease. On the contrary, an increase trend of OPAH emission has been observed with adding biodiesel. For the specific parent PAHs and its oxygenated and nitrated derivatives, the fractions of parent PAHs gradually decrease with increasing biodiesel content in the blends, while the corresponding oxygenated and nitrated derivative fractions observably increase, especially for the high molecular weight compounds. Considering the increase of OPAH and NPAH fractions in total particle-phase PAHs when using biodiesel, in-depth biodiesel cytotoxicity assessment should be conducted.