Effect Of Fuel Temperature Research Articles

Use of Zirconium-Based Moderators to Enhance Feedback Coefficients in a MOX-Fueled Sodium-Cooled Fast Reactor

This work shows the effect of the use of moderating layers on the sodium void effect in sodium-cooled, mixed oxide-fueled fast breeder reactors. The moderating layers consist of either zirconium boride ZrB2 or zirconium hydride ZrH2. The two investigated ZrH2 layers (0.1 and 0.2 mm thick) cause a strong reduction of the sodium void effect. Additionally, these layers significantly improve the fuel temperature effect and the coolant effect of the system. All changes caused by the insertion of the ZrH2 layers result in a significantly increased stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides. The effect in the infinite system can be fully combined with the traditional methods of increasing the neutron leakage.

Thermal–hydraulic modeling of reactivity insertion in a research reactor

Transient reactivity insertion for a pool type research reactor with scram enabled is numerically investigated. The analyses were performed by developing a coupled kinetic–thermal–hydraulics code, with continuous feedback due to coolant and fuel temperature effects. A modified Runge–Kutta method was adopted for a better solution to a system of stiff point kinetic equations. Transient thermal–hydraulics during the process of slow and fast reactivity insertion were considered for a IAEA 10-MW research reactor. The code was used to carry out transient thermal–hydraulics analysis for both high-enriched uranium (HEU) and low enriched uranium (LEU) fuel. Reactor power, fuel, clad and coolant temperatures, MDNBR, reactor period, energy released for slow and fast reactivity insertion transients were predicted. The model prediction was verified through comparison with the PARET code and other institution results reported in the literature for detailed simulations of reactivity insertion. The comparison of simulation results and the PARET code showed good agreement for the main thermal–hydraulic parameters.

ENGINE COMBUSTION NETWORK (ECN): CHARACTERIZATION AND COMPARISON OF BOUNDARY CONDITIONS FOR DIFFERENT COMBUSTION VESSELS

The Engine Combustion Network (ECN) is a worldwide group of institutions using combustion vessels and/or performing computational fluid dynamics (CFD) simulation, whose aim is to advance the state of spray and combustion knowledge at engine-relevant conditions. A key activity is the use of spray chamber facilities that operate at high-temperature, high-pressure conditions typical of diesel combustion, which are operated at specific target conditions in order to leverage research capabilities and advanced diagnostics of all ECN participants. The first target condition, called A, has been defined with detailed ambient (900 K, 60 bar, 22.8 kg/m(3), 15% oxygen) and injector (common rail, 1500 bar, KS1.5/86 nozzle, 0.090-mm orifice diameter, n-dodecane, 363 K) conditions. Establishing and improving these experimental boundary conditions in unique facilities throughout the world represents a major step forward in the establishment of high-quality, quantitative data sets for engine spray combustion. This paper is a review of the methodology to characterize and control the ambient and fuel-injector boundary conditions (e.g., temperature, pressure, composition) as offered by six different participating institutions of the ECN, each targeting the Spray A conditions and quantifying experimental uncertainty. Constant-pressure flow (CPF) and constant-volume preburn (CVP) chambers with various ambient gas composition are compared for the first time. Experimental diagnostics include the use of fast-response, radiation-corrected thermocouples for spatially resolved gas and fuel-injector temperature, laser-induced phosphorescence for surface temperature, and high-speed transducers for pressure. With guidance about the uncertainty and variation that exists between facilities, simplified models are then employed to understand how these boundary condition variations may affect aspects of spray combustion. Ambient gas and fuel temperature effects on liquid- and vapor-phase penetration are examined with established one-dimensional models. Chemical kinetics modeling in single- or multi-zone reactors is used to predict the influence of different preburn environments on the major and minor species present in the ambient gas at the start of injection, and their subsequent effect on spray ignition. This review article provides recognition of the challenge in creating well-controlled high-temperature, high-pressure environments, and identifies which boundary condition variations are expected to have the highest impact on spray combustion.

Fuel temperature influence on diesel sprays in inert and reacting conditions

Abstract The detailed knowledge of the evaporation–combustion process of the Diesel spray is a key factor for the development of robust injection strategies able to reduce the pollutant emissions and keep or increase the combustion efficiency. In this work several typical measurement applied to the diesel spray diagnostic (liquid length, lift-off length and ignition delay) have been employed in a novel continuous flow test chamber that allows an accurate control on a wide range of thermodynamic test conditions (up to 1000 K and 15 MPa). A step forward in the control of the test boundary conditions has been done employing a special system to study the fuel temperature effect on the evaporation and combustion of the spray. The temperature of the injector body has been controlled with a thermostatic system and the relationship between injector body and fuel temperature has been observed experimentally. Imaging diagnostics have been employed to visualize the liquid phase penetration in evaporative/inert conditions and, lift-off length and ignition delay in reactive condition. The results underline a clear influence of the injector body temperature on both conditions, evaporative and, in a lesser degree, reactive; finally the physical models found in the literature have been compared with the results obtained experimentally.

On the use of a moderation layer to improve the safety behavior in sodium cooled fast reactors

This work shows the effect of the use of moderating layers on the sodium void effect in sodium cooled fast breeder reactors. The moderating layers consisting of either boron carbide B4C or uranium–zirconium hydride UZrH cause a strong reduction of the sodium void effect. Additionally these layers improve the fuel temperature effect and the coolant effect of the system. The use of the UZrH is significantly more effective for the reduction of the sodium void effect as well as for the improvement of the fuel temperature and the coolant effect. All changes cause by the insertion of the UZrH layer cause a significantly increased stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides.

Initial fuel temperature effects on burning rate of pool fire

The influence of the initial fuel temperature on the burning behavior of n-heptane pool fire was experimentally studied at the State Key Laboratory of Fire Science (SKLFS) large test hall. Circular pool fires with diameters of 100 mm, 141 mm, and 200 mm were considered with initial fuel temperatures ranging from 290 K to 363 K. Burning rate and temperature distributions in fuel and vessel wall were recorded during the combustion. The burning rate exhibited five typical stages: initial development, steady burning, transition, bulk boiling burning, and decay. The burning rate during the steady burning stage was observed to be relatively independent of the initial fuel temperature. In contrast, the burning rate of the bulk boiling burning stage increases with increased initial fuel temperature. It was also observed that increased initial fuel temperature decreases the duration of steady burning stage. When the initial temperature approaches the boiling point, the steady burning stage nearly disappears and the burning rate moves directly from the initial development stage to the transition stage. The fuel surface temperature increases to its boiling point at the steady burning stage, shortly after ignition, and the bulk liquid reaches boiling temperature at the bulk boiling burning stage. No distinguished cold zone is formed in the fuel bed. However, boiling zone is observed and the thickness increases to its maximum value when the bulk boiling phenomena occurs.

The Effect of Fuel Temperature on Particulate Matter Formation in Gasoline Direct-Injection Engines

The Effect of Fuel Temperature on Particulate Matter Formation in Gasoline Direct-Injection Engines

Study of Fuel Temperature Effects on Fuel Injection, Combustion, and Emissions of Direct-Injection Diesel Engines

The influence of inlet liquid fuel temperature on direct-injection diesel engines can be noticeable and significant. The work in this paper investigates the effects of inlet fuel temperature on fuel-injection in-cylinder combustion, and output performance and emissions of medium-speed diesel engines. An enhanced understanding and simplified modeling of the variations in the main fuel-injection parameters affected by inlet fuel temperature are developed. The study indicates that the main injection parameters affected include the injection timing at the injector end relative to the injection-pump actuation timing, the fuel-injection rate, the fuel-injection duration, and the injection spray atomization. The primary fuel temperature effects on the injection parameters are from the fuel bulk modulus of elasticity and the density with the fuel viscosity less significant as the injector-nozzle flow is usually in a turbulent region. The developed models are able to predict the changes in the injection parameters versus the inlet fuel temperature. As the inlet fuel temperature increases, the nozzle fuel-injection-start timing is predicted to be relatively retarded, the injection rate is reduced, and the needle-lift duration is prolonged from the baseline. The variation trends of the engine outputs and emissions versus fuel temperature are analyzed by considering its consequent effect on in-cylinder combustion processes. It is predicted that raising fuel temperature would result in an increase in each of CO, HC, PM, and smoke emissions, and in a decrease in NOx, and may adversely affect the fuel efficiency for a general type of diesel engine at a full-load condition. The experimental results of the outputs and emissions from testing a medium-speed four-stroke diesel engine agreed with the trends analytically predicted. The understanding and models can be applied to compression-ignition direct-injection liquid fuel engines in general.

Thermal-hydraulic modeling of flow inversion in a research reactor

The course of loss of flow accident and flow inversion in a pool type research reactor, with scram enabled under natural circulation condition is numerically investigated. The analyses were performed by a lumped parameters approach for the coupled kinetic–thermal-hydraulics, with continuous feedback due to coolant and fuel temperature effects. A modified Runge–Kutta method was adopted for a better solution to the set of stiff differential equations. Transient thermal-hydraulics during the process of flow inversion and establishment of natural circulation were considered for a 10-MW IAEA research reactor. Some important parameters such as the peak temperatures for the hot channel were obtained for both high-enriched and low enriched fuel. The model prediction is also verified through comparison with other computer code results reported in the literature for detailed simulations of loss of flow accidents (LOFA) and the agreement between the results for the peak clad temperatures and key parameters has been satisfactory. It was found that the flow inversion and subsequent establishment of natural circulation keep the peak cladding surface temperature below the saturation temperature to avoid the escalation of clad temperature to the level of onset of nucleate boiling and sub-cooled void formation to ensure the safe operation of the reactor.

Effect of Fuel Temperature on the Droplet Dispersion Area of the Liquid Injector with the Local Contact Microwave Heating (Evaluation with the Simple Image Data Processing)

Effect of Fuel Temperature on the Droplet Dispersion Area of the Liquid Injector with the Local Contact Microwave Heating (Evaluation with the Simple Image Data Processing)

Reactivity insertion limits in a typical pool-type research reactor cooled by natural circulation

The course of reactivity insertion in a pool type research reactor, with scram disabled under natural circulation condition is numerically investigated. The analyses were performed by a coupled kinetic–thermal–hydraulic computer code developed specifically for this task. The 10-MW IAEA MTR research reactor was subjected to unprotected reactivity insertion (step and ramp) for both low and high-enriched fuel with continuous reactivity feedback due to coolant and fuel temperature effects. In general, it was found that the power, core mass flow rate and clad temperature under fully established natural circulation are higher for high-enriched fuel than for low enriched fuel. This is unlike the case of decay heat removal, where equal clad temperatures are reported for both fuels. The analysis of reactivity represented by the maximum insertion of positive reactivity ($0.73) demonstrated the high inherent safety features of MTR-type research reactor. Even in the case of total excess reactivity without scram, the high reactivity feedbacks of fuel and moderator temperatures limit the power excursion and avoid consequently escalation of clad temperature to the level of onset of nucleate boiling and sub-cooled void formation. The code can also be modified to provide an accurate capability for the analyses of research reactor transients under forced convection.

The Effects of Fuel Temperature on a Spray of a Swirl Type Injector Manufactured for the Use of Direct Injection Gasoline Engines

The Effects of Fuel Temperature on a Spray of a Swirl Type Injector Manufactured for the Use of Direct Injection Gasoline Engines

Lumped parameters analysis of coupled kinetics and thermal-hydraulics for small reactors

A useful model is presented that permits to predict with simple means the dynamic response of a small research reactor core. The model uses a lumped parameters approach for the coupled kinetics (point reactor) and thermal-hydraulics, with continuous reactivity feedback due to coolant and fuel temperature effects. The model predictions are qualified by comparing with results from detailed simulations of reactivity insertion transients reported in the literature. Satisfactory results have been obtained for various reactivity insertion rates, up to insertions as high as $1.5. A simple criterion on the applicability range of the model is suggested, namely, the model can provide reasonably accurate predictions as long as the exit coolant temperature remains below saturation, i.e. no bulk boiling occurs in the core.

Effect of fuel temperature on spray characteristics of diesel spray impinging on a ringed wall

Effect of fuel temperature on spray characteristics of diesel spray impinging on a ringed wall

Ignition and combustion study of JP-8 fuel in a supersonic flowfield

The ignition and combustion process of fuels in a supersonic combustion chamber plays an important role in the design of hypersonic propulsion system. However, it is a quite complicated process, due to the large variation of inlet air velocity, temperature, oxygen concentration, and shocks in the supersonic combustion chamber. The purpose of this paper is to observe the ignition delay and combustion phenomenon of the JP-8 fuel droplets in a supersonic flowfield experimentally. A shock tube is used as a basic test facility to create a high-speed and high-temperature flowfield as a supersonic combustor. In the experiments, several test parameters are controlled, such as shock velocity, gas temperature, fuel droplet size and distance, initial fuel temperature, and oxygen concentration, etc. The test results show the influence of these parameters on ignition delay, ignition limitation, and detonation. The most important factor in the experiment is the initial fuel temperature effect, which is influenced by the altitude variation during a flight.

On the definition of the fuel temperature coefficient of reactivity for pin-cell calculations on an infinite lattice

The fuel temperature coefficient of reactivity is an important parameter in the evaluation of transients in light water reactors. The fuel temperature coefficient ( α f = 1 k 2 · ∂k ∂T f of an infinite lattice, often used in pin-cell calculations, is not a correct measure for the fuel temperature effect in such a lattice. We present a somewhat different definition of the fuel temperature coefficient of reactivity ( α ∗ f = 1 k · ∂k ∂T f ). This definition gives a more correct measure for the fuel temperature effect. Some calculations on lattices which are characteristic for a PWR show its accuracy. The newly defined fuel temperature coefficient is much less dependent on the fuel enrichment and the 10B-concentration. The fuel temperature co-efficient is analysed by calculating the different components constituting this coefficient.

Structure of turbulent reacting gas jets in liquids at different temperatures and pressures

New equilibrium state relationships have been constructed for the liquid metal combustion simulation reactants: hydrogen chloride gas as oxidant and ammonia aqueous solution as fuel. The state relationships have been employed to predict the structure of sonic, turbulent, reacting HCl gas jets submerged in ammonia aqueous solutions. Fuel temperature and ambient pressure effects have been examined. It is found that either raising fuel temperature or lowering ambient pressure will increase the fuel evaporation, decrease the entrainment rate, delay the completion of reaction and extend greatly the total jet penetration length. Good agreement has been found with reported experimental data of the jet penetration length over a wide range of experimental conditions with varying fuel concentration, temperature and ambient pressure.

Modelling the Fuel Temperature Effect on Flame Spread Limits in Opposed Flow

Abstract A numerical model of flame spread on a thermally thin fuel in opposed flow (Frey and T'ien, 1979) has been used to study the effect of the initial fuel bulk temperature on the extinction limit. The distribution of temperature, fuel fraction, reactivity, and local equivalence ratio are presented and analyzed for the near-limit case. When the fuel temperature is decreased, the fuel pyrolysis rate near the pyrolysis front decreases, the flame spread rate drops, the pyrolysis length diminishes and the flame size is reduced. When the flame reaches a certain critical size, depending on a number of parameters, extinction occurs.

The Effects of Fuel Temperature on Spray Characteristics and Engine Performance in Diesel Engines

本研究では各種燃料を使用して燃料加熱にともなう噴霧特性の変化について調べたのち,それがディーゼル機関の性能に対して及ぼす影響について検討を行った.その結果,燃料の沸点を境にして噴霧形状は大幅な変化を示し,沸点を超えた加熱によって噴霧粒子の顕著な微細化が得られた.また,これをディーゼル機関に対して適用した場合には,特に高負荷域での吐煙と熱費率の改善とを期待し得ることが明らかとなった.

Effect of Pre-Injection Fuel Temperature upon Diesel Engine Ignition Delay and Soot Emission

The effect of pre-injection fuel temperature upon the ignition delay and soot emission has been investigated on an i.d.i. engine running on diesel oil. Effects of evaporation in the engine cycle, at both subcritical and supercritical pressures, are discussed and attention focused on the probable attainment of the critical temperature by liquid droplets in certain ambient conditions. Stress is laid on the future need concurrently to optimize the injection equipment and the level of air swirl to realize the potential of fuel preheating.