ABSTRACT
A numerical investigation on the soot laden flow of gas in a partial diesel particulate filter (PDPF) is presented based on solving the momentum equations for a continuous phase in the Euler frame and the motion equations for the dispersed phase in the Lagrangian frame. The interaction between the gas phase and the particles is considered as a one-way coupling for dilute particle concentration, while the interaction between particles and porous wall is implemented through user-definedsubroutines. To accurately track motion of nanoscale particles, the Brownian excitation and drag force as well as partial slip are taken into account in the particulate motion equation. Two methods are used to verify the gas flow model and reasonable agreements for both comparisons are observed. The effects of inlet velocity, wall permeability and particle size on the filtration efficiency and deposition distribution of the particles along with wall surface of inlet channel are quantitatively studied. The results show that (i) wall permeability plays the primary role in determining the filtration efficiency of PDPF, (ii) both upstream velocity and particle size have an effect on the initial deposition position of particles and (iii) filtration efficiency of PDPF is not markedly proportional to gas flow into inlet channels at a low wall permeability.
ABSTRACT
In this article, a new diesel particulate filter (DPF) system with reciprocating flow is proposed, and an experimental study on the characteristics of the active-passive component regeneration of the DPF system is carried out. Several control parameters such as temperature distribution, pressure difference, and pollution emissions of the DPF system are measured for different reciprocating cycles. The mechanism of reciprocating flow regeneration of the DPF system and the effects of the reciprocating flow cycle on the performance of the DPF system are analyzed. Results show that (1) the DPF system can use a tiny amount of extra fuel to maintain the chemical reaction, which in turn realizes the regeneration of the catalyzed DPF because of its properties of heat recovery and reverse blowing of ash; (2) with the increase in the reciprocating flow cycle, the temperature profile moves toward the downstream side of the DPF system and the fluctuation amplitudes of the components of CO, NO, and NO2 increase; (3) if reasonable temperature distribution is formed in the DPF system for a certain reciprocating cycle, the regeneration efficiency can be obviously improved and the average content of particulate matter emission can be kept at quite a low level.
ABSTRACT
Soil erosion and reforestation greatly affects the functionality of many terrestrial ecosystems. However, the effects of soil erosion and reforestation on soil respiration (SR), and soil organic carbon (SOC) and total nitrogen (TN) stocks remain unclear. Therefore, we investigated the changes in SR, and SOC and TN stocks at four different soil erosion levels (severely, moderately, lightly, and non-eroded) and two different aged Pinus massoniana plantations (8- and 36-year-old) in the hilly red soil regions of Southern China. Our results showed that soil erosion level and reforestation significantly influenced SR, and SOC and TN stocks. Meanwhile, the mean SR, and SOC and TN stocks all significantly decreased with erosion level but increased significantly with times since reforestation. Soil temperature (ST) could explain 70-92% of SR seasonal variation based on exponential models, whereas no significant relationship between SR and soil water content were found. Furthermore, the structural equation modeling indicated that SOC stocks at 0-20â¯cm had a much stronger effect on SR than ST. Meanwhile, the SOC stocks for 0-20â¯cm increased by 177% and 558% in the 8- and 36-year-old Pinus massoniana plantations in comparison with the severely eroded forestland, respectively. This study highlights that reforestation could be an effective strategy for restoring the carbon and nitrogen storage in eroded regions of Southern China and emphasizes the need to consider the effects of soil erosion and reforestation when assessing regional carbon budgets under different climate scenarios.
ABSTRACT
Numerical investigations on partial oxidation combustion of CO2/CH4 mixture were executed for a two-layer burner using a two-dimensional two-temperature model with different detailed chemical reaction mechanisms that are DRM 19, GRI-Mech 1. 2, and GRI-Mech 3.0. Attention was focused on the influence of these mechanisms on predictions of the temperature distributions in the burner, chemical structure as well as syngas production. The equivalence ratio was a fixed value of 1.5, while the volumetric ratio of CO2 to CH4 was changed from 0 to 1. The predicted results were compared with the available experimental data. It was revealed that the chemical reaction mechanisms have little effect on the temperature distribution in the burner except for the exothermic zone. It indicted that the smaller kinetic DRM 19 can precisely predict the temperature distributions in the burner, using DRM 19 was recommended to save computational time when the detailed components of the syngas was not taken into consideration. In addition, all the three mechanisms predicted the same trend of molar fraction of CO, H2, and CO2 with experimental results. Good agreement between the experiment and predictions of major species was obtained by GRI-Mech 1.2 and GRI-Mech 3.0, the two mechanisms had the same accuracy in predicting CO, H2, and CO2 production. However, computations with DRM 19 under-predicted the molar fraction of CO and H2. Furthermore, it was shown that the thermal conductivity of porous media has significant effect on the syngas production. In general, the temperature was increased as the thermal conductivity of the porous media was reduced and the H2 production was increased.
