Explore the vast range of titles available.

Computational fluid dynamics (CFD) modelers require high-quality experimental data sets for validation of their numerical tools. Preferred features for numerical simulations of a sooting, turbulent test case flame are simplicity (no pilot flame), well-defined boundary conditions, and sufficient soot production. This paper proposes a non-premixed C2H 4/air turbulent jet flame to fill this role and presents an extensive database for soot model validation. The sooting turbulent jet flame has a total visible flame length of approximately 400 mm and a fuel-jet Reynolds number of 10,000. The flame has a measured lift-off height of 26 mm which acts as a sensitive marker for CFD model validation, while this novel compiled experimental database of soot properties, temperature and velocity maps are useful for the validation of kinetic soot models and numerical flame simulations. Due to the relatively simple burner design which produces a flame with sufficient soot concentration while meeting modelers' needs with respect to boundary conditions and flame specifications as well as the present lack of a sooting \"standard flame\", this flame is suggested as a new reference turbulent sooting flame. The flame characterization presented here involved a variety of optical diagnostics including quantitative 2D laser-induced incandescence (2D-LII), shifted-vibrational coherent anti-Stokes Raman spectroscopy (SV-CARS), and particle image velocimetry (PIV). Producing an accurate and comprehensive characterization of a transient sooting flame was challenging and required optimization of these diagnostics. In this respect, we present the first simultaneous, instantaneous PIV, and LII measurements in a heavily sooting flame environment. Simultaneous soot and flow field measurements can provide new insights into the interaction between a turbulent vortex and flame chemistry, especially since soot structures in turbulent flames are known to be small and often treated in a statistical manner. © 2011 Springer-Verlag.

Soot particles, carbon monoxide, oxides of nitrogen, oxides of sulphur, and hydrocarbon are the emissions produced from diesel engine combustion. Those emissions species are undesirable since they give detrimental impacts to the atmosphere and human well-being. Several numerical investigations conducted by various researchers provide different soot mass concentration values. As an alternative, this study was carried out to investigate the soot mass level produced by a single cylinder diesel engine, using a commercial multidimensional computational fluid dynamic software. The result obtained from simulation effort was then validated by experimental testing during the same engine condition (engine speed of 1600 rpm at 40% load). Soot mass predicted by simulation gives a value of 3.43 × 10-8 kg at end of simulation, while measured soot mass via experimental testing gives a value of 1.52 × 10-8 kg. Both results differ by 56% thus indicating that the simple soot model applied was not sufficient to represent the actual soot mass emitted through exhaust manifold. This leads to the conclusion that more detailed soot model is needed to make the simulation results more meaningful and comparable to the experimental testing.

Single-cylinder engine experiments and computational fluid dynamics (CFD) modeling were used in this study to conduct a comprehensive evaluation of the accuracy of the modeling approach, with a focus on soot emissions. A semi-empirical soot model, the classic two-step Hiroyasu model with Nagle and Strickland-Constable oxidation, was used. A broad range of direct-injected (DI) combustion systems were investigated to assess the predictive accuracy of the soot model as a design tool for modern DI diesel engines. Experiments were conducted on a 2.5 liter single-cylinder engine. Combustion system combinations included three unique piston bowl shapes and seven variants of a common rail fuel injector. The pistons included a baseline “Mexican hat” piston, a reentrant piston, and a non-axisymmetric piston similar to the Volvo WAVE design. The injectors featured six or seven holes and systematically varied included angles from 120 to 150 degrees and hole sizes from 170 to 273 μm. A single nominal operating condition was studied: 100% load at 1800 rpm. Variations in the start of injection (SOI), injection pressure, intake pressure, and exhaust gas recirculation (EGR) level were also studied. These broad hardware and operational variations were modeled using Reynolds-averaged Navier-Stokes (RANS) CFD simulations with direct combustion chemistry integration. The focus of the work was to assess the ability of the model with Chalmers n-heptane combustion chemistry to predict the soot emissions from the various combustion systems. The results show that while the model predicts some general trends regarding SOI and injection pressure, it tends to fail as a comprehensive predictive simulation tool for designing DI diesel combustion systems regarding soot emissions. This suggests that further improvements in diesel engine CFD modeling for predicting soot emissions are needed.

The soot formation model based on inverse ethylene diffusion flames was performed to study the sensitivity of the soot formation process to the prediction results. The effects of efficiency parameters such as soot inception, surface growth and coagulation on the simulation results were studied by using the adjustable efficiency model. In addition, the reversible soot model and conjugate heat transfer (CHT) model were also introduced to explore their advantages. Results indicated that, among adjustable efficiency parameters, the nucleation efficiency had the greatest influence on the predicted soot and PAHs distributions, while the H-abstraction-C 2 H 2 -addition (HACA) process and PAH adsorption surface growth efficiencies impacted little. The adjustable efficiency parameters had a significant effect on the concentration of soot gaseous precursors and soot particles, but their effects on temperature, gas phase molecules, and intermediate species were not obvious. When the nucleation efficiency increased from 2×10 −6 to 1×10 −4 , the predicted value of the integrated soot was increased by nearly 50%, and the maximum primary particle number density and the number of aggregates were increased by an order of magnitude. The maximum concentration of BAPYR was doubled. However, the peak temperature along the axial direction increased by only 3.5 K. Using the reversible soot model, the approximation results of the adjustable efficiency parameters could be modified, which showed the feasibility of the model. The use of the CHT model promoted pyrolysis of the fuel below the outlet of the fuel tube, with high-temperature zones, soot zones, and PAHs zones moving towards higher flame heights. Besides, when using the reversible model and the CHT model, the maximum soot volume fraction decreased by 39% compared with the basic efficiency parameters, while the concentration of BAPYR increased by 162%, and the concentrations of gas phase species were decreased.

Monitoring the filtration efficiency of the diesel particulate filter (DPF), is a legislative requirement for minimizing particulate matter (PM) emissions from diesel engines of passenger cars and heavy-duty vehicles. To reach this target, on-board diagnostics (OBD) in real-time operation are required. Such systems in passenger cars are often utilizing a soot sensor, models for PM emissions simulation and algorithms for diagnosis. Their performance is associated with a series of challenges related to the accuracy and effectiveness of involved models, algorithms and hardware. This paper analyzes the main influencing factors and their impact on the effectiveness of the OBD system. The followed method comprised an error propagation analysis to quantify the error of detection during a New European Driving Cycle (NEDC). The results of the study regarding the performance of the OBD model showed that the total error of diagnosis is ±28%. This performance can be improved by increasing the sensor accuracy and the soot model, which can make the model appropriate for even tighter legislation limits and other approaches such as on-board monitoring (OBM).

This paper studies the generation process and emission characteristics of soot from Marine diesel engine. On the basis of Particulate size mimic (PSM) detailed soot model, the parameters related to soot generation obtained from the reaction mechanism calculation of 3 surrogate of different carbon chain length: n-heptane, n-tetradecane and n-tetradecane-toluene were compared and analyzed including precursor of soot, quality and density of soot, particle size distribution of empirical soot model. The results show that the soot nucleation stage of n-tetradecane-toluene mechanism was slightly more consistent than that of n-tetradecane mechanism with the experimental results, far more consistent than that of n-heptane mechanism. The intensity of surface growth and aggregation stage is greater, which is reflected in the soot precursor: acetylene and A4, and leads to that the soot produced by the mechanism of n-tetradecane and n-tetradecane-toluene is small in quality but large in quantity. The particle size distribution calculated by n-tetradecane and n-tetradecane-toluene mechanism is closer to the experimental data than that calculated by n-heptane mechanism. Then combustion process of n-tetradecane and n-tetradecane-toluene mechanism is more suitable for marine engine, which is reflected in the higher temperature and the smaller equivalent ratio in the cylinder.

The ducted fuel injection strategy is an innovative method that significantly prevents soot formation in direct injection compression ignition engines. This method is based on the injection of the fuel directly into the combustion chamber through the tube placed in front of the injector hole. The fuel mixes with air inside the duct before ignition. Thus, the formation of soot can be prevented by reducing the local equivalence ratio in the lift-off length in the combustion chamber. In this study, the implementation of the duct geometry to the compression ignition engine was evaluated in-cylinder flow and emission formation. The duct geometry was adopted for the test engine. The effects of the ducted fuel injection (DFI) on the combustion and performance of a compression ignition diesel engine were investigated. Conventional diesel combustion (CDC) and DFI system at low (25%), medium (50%), and high (75%) loads were compared in terms of performance, combustion, and emission using an experimentally validated engine model. Particle size mimic (PSM) detailed soot mechanism was used in the CFD model in order to solve the complex soot formation and oxidation with detailed chemistry. Compared to CDC, the DFI method reduces soot emissions up to 67%. In addition, the DFI strategy decreases CO and HC emissions up to 39% and 26%, respectively. With this innovative method, it has been observed that exhaust emissions are reduced without compromising engine performance.

Generally, homogeneous mixture combustion is preferred at high loads in conventional spark-ignition engines. But homogeneous mixture combustion can lead to high hydrocarbon (HC) emissions at low loads. Thereby, stratified mixture combustion with an overall lean mixture is preferred at low loads, which can significantly reduce HC emissions, but NOx and soot emissions will increase. Nowadays, gasoline direct injection (GDI) engines are becoming popular because of better thermal efficiency and low emissions at all loads. These engines work with a stratified mixture at low-load conditions and a homogeneous mixture at high-load conditions. But the problem with these engines is high nitrogen oxides (NOx) and soot emissions at low-load conditions. Therefore, today, the concept of partial stratification is tried in these engines, which is a combination of the combustion of stratified and homogeneous mixtures, using both GDI and port fuel injection (PFI) techniques. With the partial stratified mixture combustion, HC, NOx, and soot emissions are expected to reduce. Also the use of laser ignition instead of spark ignition can reduce NOx and HC emissions. Therefore, this study deals with a computational fluid dynamics (CFD) analysis of the effect of spark and laser ignitions on the combustion, performance, and emission characteristics of a single-cylinder engine operating under GDI-PFI mode operating with a partially stratified mixture. Three overall equivalence ratios (OERs) of 0.5, 0.7, and 0.9 are considered for the analysis. The effects of spark and laser ignitions on turbulent kinetic energy (TKE) formation at the ignition spot, indicated mean effective pressure (IMEP), and emissions are analyzed. To quantify the flame speed, a parameter called relative combustion phasing (RCP) is used. The analysis is performed by maintaining a constant CA50 (crank angle degree [CAD] position where 50% of the total heat release occur in a combustion) by adjusting the start of spark (SOS). Analysis of results showed that the combustion with the laser ignition is faster than that of the spark ignition. The laser ignition with the OER of 0.7 reduced the HC and soot emissions by 5.8% and 2.2 times, respectively, if compared to those of the spark ignitions. The RCP of the laser ignition is about 34.5% lower than that of the corresponding spark ignition. The IMEP for the laser ignition is improved by about 10.4% and the NOx emissions increased by about 3.2% than that of the spark ignition.

Purpose The purpose of this paper is to study the soot formation and evolution by using this newly developed Lagrangian particle tracking with weighted fraction Monte Carlo (LPT-WFMC) method. Design/methodology/approach The weighted soot particles are used in this MC framework and is tracked using Lagrangian approach. A detailed soot model based on the LPT-WFMC method is used to study the soot formation and evolution in ethylene laminar premixed flames. Findings The LPT-WFMC method is validated by both experimental and numerical results of the direct simulation Monte Carlo (DSMC) and Multi-Monte Carlo (MMC) methods. Compared with DSMC and MMC methods, the stochastic error analysis shows this new LPT-WFMC method could further extend the particle size distributions (PSDs) and improve the accuracy for predicting soot PSDs at larger particle size regime. Originality/value Compared with conventional weighted particle schemes, the weight distributions in LPT-WFMC method are adjustable by adopting different fraction functions. As a result, the number of numerical soot particles in each size interval could be also adjustable. The stochastic error of PSDs in larger particle size regime can also be minimized by increasing the number of numerical soot particles at larger size interval.

Abstract An improved phenomenological soot model coupled with a reduced n-heptane chemical mechanism was implemented into KIVA-3V code to describe soot formation and oxidation processes in diesel homogeneous charge compression ignition (HCCI) combustion. This model was first validated by the shock tube experiments with a rich n-heptane mixture over wide temperature and pressure ranges. The computational results demonstrate that the phenomenological soot model is capable of predicting the soot yield, particle diameter, and number density with satisfactory accuracy. Then the model was applied to investigate the influence of the orifice diameter and injection pressure on soot emissions in a constant-volume combustion vessel under typical diesel combustion conditions. The predictions showed qualitative agreement with the measurements on the soot volume fraction distribution. The results also indicate that the soot formation can almost be suppressed as the local equivalence ratio is kept lower than 2.0. Finally, the model was used to explore the potentials of soot reduction with HCCI combustion for diesel engines. The overall trend of soot with the variations in the start of injection timing was well reproduced by the model. With the help of an equivalence ratio—temperature map, it was found that nitrogen oxide emissions could be markedly reduced by applying a high exhaust gas recirculation rate and relative low compression ratio for diesel HCCI engines. However, the mixture preparation by using a multi-hole injector with early injection strategy remains a limitation for further reduction in soot emissions.