The time evolution of the size distribution of droplets effects on the thermal explosion of polydisperse fuel spray

In this paper we investigate the problem of thermal explosion in a two-phase polydisperse combustible mixture (oxygen and fuel concentrations are takes into account). The current work presents a new, simplified model of the thermal explosion in a combustible gaseous mixture containing vaporizing fuel droplets of different radii (polydisperse). The polydispersity is modeled using a probability density function (PDF). The evolution of the size distribution of droplets due to the evaporation process is described by the kinetic equation for the PDF. An explicit expression of the critical condition for thermal explosion limit is derived analytically and represents a generalization of the critical parameter of the classical Semenov theory.     

Customer rebates and retailer incentives in the presence of competition and price discrimination

Promotions are important tools for matching supply and demand in many industries. In the United States automotive industry, promotions are frequently offered, which may be given directly to customers (rebates) or given to dealers (incentives) to stimulate demand. We analyze the performance of customer rebate and retailer incentive promotions under competition. We study a setting with two manufacturers making simultaneous pricing and promotion decisions, and with two price-discriminating retailers as Stackelberg followers making simultaneous order quantity decisions. In the benchmark case with no promotions, we characterize the equilibria in closed form. We find that retailer incentives can be used by manufacturers to simultaneously improve each of their profits but can potentially lead to lower retailer profits. When manufacturers use customer rebates, we show that a manufacturer is able to decrease the profit of her competitor while increasing her own profit, although she is also at risk for her competitor to use rebates in a similar fashion. Unlike the monopoly case where the manufacturers are always better off with retailer incentives, customer rebates can be more profitable under some cases in the presence of competition. Using numerical examples we generate insights on the manufacturers’ preference of promotions in different market settings.     

Flame/flow dynamics at the piston surface of an IC engine measured by high-speed PLIF and PTV

Resolving fluid transport at engine surfaces is required to predict transient heat loss, which is becoming increasingly important for the development of high-efficiency internal combustion engines (ICE). The limited number of available investigations have focused on non-reacting flows near engine surfaces, while this work focuses on the near-wall flow-field dynamics in response to a propagating flame front. Flow-field and flame distributions were measured simultaneously at kHz repetition rates using particle tracking velocimetry (PTV) and planar laser induced fluorescence (PLIF) of sulfur dioxide (SO₂). Measurements were performed near the piston surface of an optically accessible engine operating at 800?rpm with homogeneous, stoichiometric isooctane-air mixtures. High-speed measurements reveal a strong interdependency between near-wall flow and flame development which also influences subsequent combustion. A conditional analysis is performed to analyze flame/flow dynamics at the piston surface for cycles with ‘weak’ and ‘strong’ flow velocities parallel to the surface. Faster flame propagation associated with higher velocities before ignition demonstrates a stronger flow acceleration ahead of the flame. Flow acceleration associated with an advancing flame front is a transient feature that strongly influences boundary layer development. The distance from the wall to 75% maximum velocity (δ₇₅) is analyzed to compare boundary layer development between fired and motored datasets. Decreases in δ₇₅ are strongly related to flow acceleration produced by an approaching flame front. Measurements reveal strong deviations of the boundary layer flow between fired and motored datasets, emphasizing the need to consider transient flow behavior when modeling boundary layer physics for reacting flows.     

Numerical study on the effect of the injection pressure on spray penetration length

This paper investigates the fuel spray behavior and variation of the spray characteristics under different injection pressures in internal combustion engines. In diesel engines the fuel spray is affected by the cavitation phenomenon which occurs in the injector orifice. The cavitation is one of the important phenomena which has a significant effect on the fuel spray characteristics. In this paper, for a specified geometry of the nozzle and the combustion chamber, the effect of the cavitation phenomenon on the spray characteristics, i.e. spray penetration length, the Sauter main diameter and evaporation are studied numerically for different values of the injection pressures. High injection pressure causes high velocity of the fuel in the injector orifice which leads to an effective atomization process with small and dispersed fuel droplets. The fluid flow equations are calculated in the combustion chamber to obtain the spray model. Since it is known that, high injection pressure together with low discharge pressure leads to creation of cavitation phenomenon inside the injector orifice, then for having cavitation phenomenon inside the injector orifice and consequently for investigating the cavitation phenomenon effects on the spray characteristics, the injection pressure values of 10–150 MPa are considered while the discharge pressure remains constant. The injector and combustion chamber are simulated in separated regions and the results of the outlet of the nozzle are used as the boundary conditions for solving the fuel flow inside the combustion chamber to achieve the spray simulation. The results of this study show that by increasing the injection pressure, the value of the spray penetration length increases and the Sauter main diameter decreases for constant discharge pressure. The Hydraulic Flip phenomenon occurs after the injection pressure of 120 MPa on the base of the results of this work.     

Cu-SAPO-34/堇青石的原位制备及其催化丙烷还原柴油机车尾气中NOx

采用原位水热法制备了Cu-SAPO-34/堇青石整体式催化剂,运用X射线衍射、扫描电镜和N2吸附-脱附等技术对其进行了表征,并在固定床反应器上评价了其催化丙烷还原模拟柴油机车尾气中NOx性能,考察了丙烷和O2浓度以及水蒸气对催化剂性能的影响.结果表明,所制整体式催化剂中Cu-SAPO-34涂层与载体结合牢固紧密,经一次...     

Absorption of thermal radiation in a semi-transparent spherical droplet: a simplified model

The boundary-value problem for calculation of differential absorption of thermal radiation is formulated based on the modified DP₀ approximation. The solution of this problem is supplemented by simple analytical approximations for the normalised absorbed radiation power. The latter is used together with the analytical approximation for the efficiency factor of absorption, suggested earlier. The resulting simplified model is applied to the specific problem of absorption of thermal radiation by a diesel fuel droplet. Two types of diesel fuel have been considered. It is pointed out that the radial distribution of absorbed thermal radiation power is non-monotonic. The power absorbed in the droplet core is shown to be rather large and almost homogeneous. Also, the absorbed power is large in the vicinity of the droplet surface, but is minimal in the intermediate region. It is pointed out that the variations of the refractive index of diesel fuel with wavelengths can smooth the predicted radial dependence of the thermal radiation power, absorbed in diesel fuel droplets.     

R1234yf/RE170混合工质用于汽车空调的可行性

目前汽车空调常用的制冷剂四氟乙烷(R134a)存在较高的温室效应指数(GWP =1 300),会对环境造成不利的影响.将R1234yf和RE170以质量配比为70∶30组成新型混合制冷剂(代号NCUR04)应用于汽车空调中,通过热力学性质、环境特性、循环性能、安全特性、润滑特性方面综合考虑替代R134a的可行性,并与潜...     

Modelling compression ignition engines by incorporation of the flamelet generated manifolds combustion closure

Tabulated chemistry models allow to include detailed chemistry effects at low cost in numerical simulations of reactive flows. Characteristics of the reactive fluid flows are described by a reduced set of parameters that are representative of the flame structure at small scales so-called flamelets. For a specific turbulent combustion configuration, flamelet combustion closure, with proper formulation of the flame structure can be applied. In this study, flamelet generated manifolds (FGM) combustion closure with progress variable approach were incorporated with OpenFOAM® source code to model combustion within compression ignition engines. For IC engine applications, multi-dimensional flamelet look-up tables for counter flow diffusive flame configuration were generated. Source terms of non-premixed combustion configuration in flamelet domain were tabulated based on pressure, temperature of unburned mixture, mixture fraction, and progress variable. A new frozen flamelet method was introduced to link one dimensional reaction diffusion space to multi-dimensional Computational Fluid Dynamics (CFD) physical space to fulfill correct modelling of thermal state of the engine at expansion stroke when charge composition was changed after combustion and reaction rates were subsided. Predictability of the developed numerical framework were evaluated for Sandia Spray A (constant volume vessel), Spray B (light duty optical Diesel engine), and a heavy duty Diesel engine experiments under Reynolds averaged Navier Stokes turbulence formulation. Results showed that application of multi-dimensional FGM combustion closure can comprehensively predict key parameters such as: ignition delay, in-cylinder pressure, apparent heat release rate, flame lift-off , and flame structure in Diesel engines.     

Optical design and optimization of light emitting diode automotive head light with digital micromirror device light emitting diode

This research proposes a new method for light emitting diode automotive headlight design with digital micromirror device (DMD). The optical design is advanced because of the following features. First, this optical design controls the angle of light pattern without light masking so as to achieve much higher light efficiency compared with traditional optical design for headlight systems. Second, in view of the tendency that the advanced light emitting diode automobile headlight is designed to be a low beam light module and a high beam light still needs an auxiliary lighting system, the optical system designed in this research, mainly adopting DMD module as high/low beam light switch, can switch on and off both the high and low beam lights. Because DMDs function of accepting a bidimensional image, high/low beam light patterns can be determined by DMD. Third, a light pattern will be created and compensated simultaneously by DMD, which might replace mechanical adaptive front-lighting system in the future because DMD takes advantage of fast response and simultaneous compensation. Fourth, a design using a multiple reflection curved mirror is employed in this research to adjust light energy distribution; therefore, the articulation of the light pattern can be enhanced. For this method, experimental results of light efficiency are up to 85%, which is superior to current products in the market.     

Diesel engine emissions and combustion predictions using advanced mixing models applicable to fuel sprays

An advanced mixing model was applied to study engine emissions and combustion with different injection strategies ranging from multiple injections, early injection and grouped-hole nozzle injection in light and heavy duty diesel engines. The model was implemented in the KIVA-CHEMKIN engine combustion code and simulations were conducted at different mesh resolutions. The model was compared with the standard KIVA spray model that uses the Lagrangian-Drop and Eulerian-Fluid (LDEF) approach, and a Gas Jet spray model that improves predictions of liquid sprays. A Vapor Particle Method (VPM) is introduced that accounts for sub-grid scale mixing of fuel vapor and more accurately and predicts the mixing of fuel-vapor over a range of mesh resolutions. The fuel vapor is transported as particles until a certain distance from nozzle is reached where the local jet half-width is adequately resolved by the local mesh scale. Within this distance the vapor particle is transported while releasing fuel vapor locally, as determined by a weighting factor. The VPM model more accurately predicts fuel-vapor penetrations for early cycle injections and flame lift-off lengths for late cycle injections. Engine combustion computations show that as compared to the standard KIVA and Gas Jet spray models, the VPM spray model improves predictions of in-cylinder pressure, heat released rate and engine emissions of NOx, CO and soot with coarse mesh resolutions. The VPM spray model is thus a good tool for efficiently investigating diesel engine combustion with practical mesh resolutions, thereby saving computer time.