Dynamics of Post-Injection Fuel Flow in Mini-Sac Diesel Injectors Part 1: Admission of 1 External Gases and Implications for Deposit Formation

Samples of unadditized, middle distillate diesel fuel were injected through real-size optically accessible mini-sac diesel injectors into ambient air at common rail pressures of 250 bar and 350 bar respectively. High-resolution images of white light scattered from the internal mini-sac and nozzle flow were captured on a high-speed monochrome video camera. Following the end of each injection, the momentum-driven evacuation of fuel liquid from the mini-sac and nozzle holes resulted in the formation of a vapour cloud and bubbles in the mini-sac, and vapour capsules in the nozzle holes. This permitted external gas to gain entrance to the nozzle holes. The diesel fuel in the mini-sac was observed to rotate with large initial vorticity, which decayed until the fuel became stationary. The diesel fuel remaining in the nozzle holes was observed to move inwards towards the mini-sac or outwards towards the nozzle exit in concert with the rotational flow in the mini-sac. The mini-sac bubbles’ internal pressure differences revealed that the bubbles must have contained previously dissolved oxygen and nitrogen. Under diesel engine operating conditions, this multi-phase mixture would be highly reactive and could initiate local pyrolysis and/or oxidation reactions. Finally, the dynamical behaviour of the diesel fuel in the nozzle holes would support the admission of external hot combustion gases into the nozzle holes, establishing the conditions for oxidation/pyrolysis reactions with surrounding liquid fuel films

A preconditioning scheme for minimum energy path finding methods

Popular methods for identifying transition paths between energy minima, such as the nudged elastic band and string methods, typically do not incorporate potential energy curvature information, leading to slow relaxation to the minimum energy path for typical potential energy surfaces encountered in molecular simulation. We propose a preconditioning scheme which, combined with a new adaptive time step selection algorithm, substantially reduces the computational cost of transition path finding algorithms. We demonstrate the improved performance of our approach in a range of examples including vacancy and dislocation migration modeled with both interatomic potentials and density functional theory

An Optical Characterization of Atomization in Non-Evaporating Diesel Sprays

High-speed planar laser Mie scattering and Laser Induced Fluorescence (PLIF) was employed for the determination of Sauter Mean Diameter (SMD) distribution in non-evaporating diesel sprays. The effect of rail pressure, distillation profile, and consequent fuel viscosity on the drop size distribution developing during primary and secondary atomization was investigated. Samples of conventional crude-oil derived middle-distillate diesel and light distillate kerosene were delivered into an optically accessible mini-sac injector, using a customized high-pressure common rail diesel fuel injection system. Two optical channels were employed to capture images of elastic Mie and inelastic LIF scattering simultaneously on a high-speed video camera at 10 kHz. Results are presented for sprays obtained at maximum needle lift during the injection. These reveal that the emergent sprays exhibit axial asymmetry and vorticity. An increase in the rail pressure was observed to lead to finer atomization, with larger droplets observable in the neighbourhood of the central axis of the spray, decreasing with radius towards the spray boundaries. Finally, the light kerosene was observed to produce smaller droplets (as measured by Sauter mean diameter), relative to the conventional diesel, suggesting a correlation between distillation profile and viscosity, and mean spray droplet size

The effect of cavitation on atomization in non-evaporating diesel sprays

The determination of the distribution of the local liquid volume fraction (LVF) in non-evaporating diesel sprays was achieved using Laser Induced Fluorescence (LIF). The LVF distribution developing during the primary and secondary atomisation was investigated as a function of rail pressure, physical properties and needle lift. Samples of conventional diesel and light kerosene were injected through an optically accessible mini-sac type injector, employing a custom diesel fuel injection system. The optical arrangement facilitated the acquisition of images with an image resolution of 28μm/pixel using a high speed camera operating at 10 kHz. The analysis is focused on images obtained at different injection stages (1.8ms, 3.7ms, 5.6ms after start of injection (SoI)). The results revealed that the diesel spray developed an asymmetric structure, especially at the intermediate and later stages of the injection. The LVF decreases with increasing axial distance and the primary atomisation occurs immediately after the spray enters the surrounding gas. Lastly, the findings of the phenomenological analysis suggests that conventional diesel shows a later primary and secondary atomisation than light kerosene, due to their difference in the physical properties

Electron transfer rates for asymmetric reactions

We use a numerically exact real-time path integral Monte Carlo scheme to compute electron transfer dynamics between two redox sites within a spin-boson approach. The case of asymmetric reactions is studied in detail in the least understood crossover region between nonadiabatic and adiabatic electron transfer. At intermediate-to-high temperature, we find good agreement with standard Marcus theory, provided dynamical recrossing effects are captured. The agreement with our data is practically perfect when temperature renormalization is allowed. At low temperature we find peculiar electron transfer kinetics in strongly asymmetric systems, characterized by rapid transient dynamics and backflow to the donor.Comment: 13 pages, 4 figures, submitted to Chemical Physics Special Issue on the Spin-Boson Problem, ed. by H. Grabert and A. Nitza

Socioemotional wealth : an obstacle or a springboard to creativity, innovation, and entrepreneurship in family firms?

This chapter takes a socioemotional wealth (SEW) perspective to explain how families influence the sensing and seizing of entrepreneurial opportunities in family firms. Specifically, this model proposes that some aspects of the family's SEW are conducive to opportunity recognition, while others impair it. Moreover, the presence of SEW goals leads family owners to favor certain entrepreneurial outcomes because there is a socioemotional reward for the family, even if there are no clear economic advantages. It is also suggested that family ownership negatively affects firms' transforming capacity in innovation. The end goal of this presentation is to enhance understanding of the positive and negative aspects of the family dimension on entrepreneurship and to guide future research in this area

Nonequilibrium transport in quantum impurity models: Exact path integral simulations

We simulate the nonequilibrium dynamics of two generic many-body quantum impurity models by employing the recently developed iterative influence-functional path integral method [Phys. Rev. B {\bf 82}, 205323 (2010)]. This general approach is presented here in the context of quantum transport in molecular electronic junctions. Models of particular interest include the single impurity Anderson model and the related spinless two-state Anderson dot. In both cases we study the time evolution of the dot occupation and the current characteristics at finite temperature. A comparison to mean-field results is presented, when applicable

Iterative algorithm versus analytic solutions of the parametrically driven dissipative quantum harmonic oscillator

We consider the Brownian motion of a quantum mechanical particle in a one-dimensional parabolic potential with periodically modulated curvature under the influence of a thermal heat bath. Analytic expressions for the time-dependent position and momentum variances are compared with results of an iterative algorithm, the so-called quasiadiabatic propagator path integral algorithm (QUAPI). We obtain good agreement over an extended range of parameters for this spatially continuous quantum system. These findings indicate the reliability of the algorithm also in cases for which analytic results may not be available a priori.Comment: 15 pages including 11 figures, one reference added, minor typos correcte

Dynamical simulation of transport in one-dimensional quantum wires

Transport of single-channel spinless interacting fermions (Luttinger liquid) through a barrier has been studied by numerically exact quantum Monte Carlo methods. A novel stochastic integration over the real-time paths allows for direct computation of nonequilibrium conductance and noise properties. We have examined the low-temperature scaling of the conductance in the crossover region between a very weak and an almost insulating barrier.Comment: REVTex, 4 pages, 2 uuencoded figures (submitted to Phys. Rev. Lett.