Range Of Coolant Temperatures Research Articles

Visualization of soot formation in load transients during GDI engine warm-up

Reducing the emissions of pollutants, and particularly soot particles, from internal combustion engines is one of the greatest challenges faced by car manufacturers. Although modern gasoline direct injection (GDI) engines produce relatively low particulate emissions during steady state operation under near-stoichiometric conditions, they can produce much higher particulate emissions during transients that cause abrupt changes in load, fuel consumption, and the air-to-fuel ratio. Emissions during transients are particularly high when the engine coolant temperature is low, as occurs during engine start-up. Consequently, there is a need to find ways of reducing particulate emissions during load transients. This paper therefore investigates particulate formation during load transients in a single-cylinder GDI engine equipped with an endoscope in the cylinder head. A transient sequence was designed in which the engine load was increased from 4 bar NMEP to a maximum of 12 bar NMEP in 2 s at an engine speed of 2000 rpm. During the transients, the engine’s particulate emissions were measured in terms of particulate number (PN) and images of the combustion process inside the cylinder were captured via the endoscope using a high-speed camera to identify locations where soot formation occurred. Experiments were conducted at a range of coolant temperatures and using different injection strategies to determine how these parameters affect PN emissions. The coolant temperature was found to be the dominant factor governing PN emissions during transients. Luminescence data obtained by analyzing the flame images agreed well with the measured PN emissions during transients. Under all varied parameters in the transients except delayed injection, soot was mainly formed from wall films. For transients with delayed fuel injection, much of the piston film could be avoided but soot formation instead became mixing-dominated. Variation of the air-fuel ratio had little effect on PN emissions during transients. At all coolant temperatures, PN emissions were lowest when using a split injection strategy but delaying the injection timing increased PN emissions even though the endoscope images suggested a lower frequency of diffusion flame formation. No conditions were found under which the PN emissions during transients with low coolant temperatures could be reduced to levels comparable to those seen with warm coolant.

Методы расчета термодинамических потенциалов при оценке состава оксидного слоя на поверхности металлов

To select proper water chemistry at fossil and nuclear power plants, data on the composition of oxide film formed on the metal surface contacting with aqueous coolant are necessary. By using these data, the processes occurring on the metal surface can be estimated. Calculation of Pourbaix diagrams is one of the methods using which the processes that take place on metal surface depending on the redox potential and pH can be established. To calculate these diagrams, it is necessary to have a certain set of thermodynamic data based on which it is possible to estimate the possibility of various chemical reactions to occur in the “aqueous coolant – metal” system. However, not all thermodynamic data are available from the literature, especially at high parameters. The article discusses two new methods for calculating the thermodynamic potentials of metal oxides and hydroxides. The first one, called the relative deviation method, is used for carrying out calculations in the coolant temperature range 25–327°C, and the second method, called the relative variation method, is used for carrying out calculations in the coolant temperature range 327–827°C and can also be used for more exactly determining the data obtained using the first method. Both methods can be used for estimating the most probable region for forming protective oxide films on structural material surfaces contacting with aqueous coolant.

ALFRED reactor coolant system design

Lead-cooled fast reactors represent the forefront of Generation IV reactor concepts thanks to the technological development that has taken place over the last 20 years. Lead technology is object of steady attention in many Countries thanks to several development projects and an exponentially increasing industrial interest in recent years. One of the most advanced European projects is focused on the development of ALFRED (Advanced Lead-cooled Fast Reactor European Demonstrator) and is supported by the FALCON (Fostering ALfred CONstruction) international consortium. The goal is to construct a technology demonstrator which is also prototypic for a lead-cooled-based small modular reactor. To reach this ambitious goal, an important research, development and qualification infrastructure is planned in Romania, leveraging on the know-how cumulated within European and nationally funded endeavors. In particular, the infrastructure will support the scientific program with experimental campaigns dedicated to bridging the technological and scientific gaps, as well as to support the design and licensing of the reactor. This paper presents the configuration of the ALFRED reactor coolant system showing its present state of development and technological innovations. The current plant architecture provides for a thermal power up to 300 MWth and a coolant temperature range from a minimum of 390 °C to a maximum of 520 °C.

Effect of coolant temperature and cooling time on fractional crystallization of biodiesel and glycerol

In the middle of the era of technology and fast-growing industry nowadays, biodiesel (methyl ester) has been identified as a sustainable fuel to replace petroleum. Hence, the separation and purification of the methyl ester after the trans-esterification process is essential since the purification of methyl ester is compulsory for the fuel industry in order to fulfill the strict global standard particulars for methyl ester. One of the current method used for separation and purification of methyl ester is called wet washing technology. However, this technology has its own drawbacks such as huge amount of water consumption as well as high cost for the wastewater treatment process. Due to these drawbacks, fractional crystallization process is proposed in order to save water and minimize the time consumed for the process of separation and purification of methyl ester. Fractional crystallization is a process that involved a solid-liquid separation where the process takes place in a crystallizer. In this process, methyl ester was separated from the glycerol based on their differences in term of melting point of the components. By observing the layer formation of the components, the effect of cooling time and coolant temperature on the performance of separation and purification of methyl ester by fractional crystallization process were studied. The purified methyl ester obtained was placed in a gas chromatographer in order to test the purity of methyl ester and to evaluate the efficiency of the process based on two parameters that has been investigated which are effective partition constant (K) and concentration efficiency (Eff). It was found that to achieve highest effectiveness of fractional crystallization system and highest concentration efficiency where K and Eff are 0.51 and 47.71%, respectively, the fractional crystallization must operate at coolant temperature range of -10 to -12ºC and cooling time range of 30 to 35 minutes.

Condensation flow patterns and heat transfer in horizontal microchannels

An experimental investigation was carried out to study the effect of refrigerant mass flux, local vapour quality, coolant flow rate and inlet coolant temperature on the local condensation heat transfer coefficient. Flow visualization was also conducted to capture flow patterns during flow condensation using a high-speed camera integrated with a microscope. HFE-7100, a dielectric and eco-friendly refrigerant was used in rectangular multi-microchannels with a hydraulic diameter of 0.57mm. Experiments were performed at a saturation temperature of 60°C, mass flux range 48–126kg/(m2s), coolant flow rate range 0.5–1.1L/min and inlet coolant temperature range 20–40°C. The results showed that the local condensation heat transfer coefficient increases with increasing mass flux and decreases with decreasing local vapour quality. A negligible effect of the coolant side conditions, saturation-to-wall temperature difference, on the local condensation heat transfer coefficient was found. The main flow regime was annular flow, while slug and bubbly flow were found at some operating conditions. The experimental results were compared with the existing correlations for heat transfer rates. Also, two existing flow pattern maps, for conventional and mini/microchannels, were used to compare the current flow pattern results.

The stability-analysis code FIAT development for density wave oscillations and its application to PV/PT SCWR

SuperCritical Water Reactor owns a high operation pressure and a wide coolant temperature range. The thermo-physical properties and transport properties of the coolant in the core would change greatly both in the operation condition and startup process, which may causes density wave oscillations. In this paper, a stability analysis code named FIAT is developed based on frequency domain method to analyze the density wave oscillations (DWO) for SCWR. Frequency domain method and assumptions of constant pressure drop between core inlet and outlet are applied in the code. The neutron/thermal-hydraulic coupling characteristic equation is derived through using linearization and laplace transformation for the mass, momentum and energy conservation equations. With analyzing the characteristic equation, the onset of DWO instabilities can be confirmed with non-dimensional parameters plane. The prediction accuracy of the FIAT code is verified through experiment data and code-to-code comparison under subcritical and supercritical pressure. The FIAT code is applied to evaluate the effects of basic core model on the stability for pressure vessel type SCWR and optimize the startup procedure for pressure tube type SCWR. The results show that for pressure vessel type SCWR, fuel rods heat transfer model and neutron kinetics model help stabilize the system while water rods model produces an opposite effect. For pressure tube type SCWR, two pressurization phases are required during sliding pressure start-up process to meet both the thermal–hydraulic and stability requirements.

Investigation of Cold Starting and Combustion Mode Switching as Methods to Improve Low Load RCCI Operation

Reactivity controlled compression ignition (RCCI) is an engine combustion strategy that utilizes in-cylinder fuel blending to produce low NOx and particulate matter (PM) emissions while maintaining high thermal efficiency. The current study investigates RCCI and conventional diesel combustion (CDC) operation in a light-duty multicylinder engine (MCE) using a transient capable engine test cell. The main focus of the work uses engine experiments to investigate methods which can improve low load RCCI operation. The first set of experiments investigated RCCI operation during cold start conditions. The next set of tests investigated combustion mode switching between RCCI and CDC. During the cold start tests, RCCI performance and emissions were measured over a range of engine coolant temperatures (ECTs) from 48 °C to 85 °C. A combination of open- and closed-loop controls enabled RCCI to operate at a 1500 rpm, 1 bar BMEP operating point over this range of coolant temperatures. At a similar operating condition, i.e., 1500 rpm, 2 bar BMEP, the engine was instantaneously switched between CDC and RCCI combustion using the same open- and closed-loop controls as the cold start testing. During the mode switch tests, emissions and performance were measured with high-speed sampling equipment. The tests revealed that it was possible to operate RCCI down to 48 °C with simple open- and closed-loop controls with emissions and efficiency similar to the warm steady-state values. Next, the mode switching tests were successful in switching combustion modes with minimal deviations in emissions and performance in either mode at steady state.

Influence of water vapor condensation on exhaust gas recirculation cooler fouling

Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine out NOx (oxides of nitrogen) emissions. A portion of the exhaust gases is re-circulated into the intake manifold of the engine after cooling it through a heat exchanger known as an EGR cooler. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface due to transport of soot particles and condensing species to the cooler walls. The focus of this study was to investigate whether surface condensation of water vapor could be used to remove the accumulated deposit mass from various types of deposit layers typically encountered in EGR coolers. Both visual and quantitative evidence of water vapor condensation and deposit removal were collected. A multi-cylinder diesel engine was used to produce three different deposit layers in a custom built single rectangular channel EGR cooler. The deposit layers were then exposed to water vapor condensation over a range of coolant temperatures, flow rates and exposure times by adjusting the engine operating conditions. Significant flaking and removal of deposit layers made up of mostly soot particles was observed when exposed to condensation of water vapor even with an exposure duration as low as 5min. However, very little removal of deposit mass with exposure to water vapor condensation was observed when the deposit layer consisted of condensed exhaust hydrocarbon species in addition to soot. In addition to engine experiments a visualization test rig was setup to visualize condensation of water vapor from clean humid air and its effect on different deposit layers. Surface condensation of water vapor can lead to significant removal of certain deposit layers from the cooler walls and, thus, mitigate fouling of the EGR cooler. It could potentially be used as regeneration strategy for periodic on-board regeneration of fouled EGR coolers.

Fusion power core engineering for the ARIES-ST power plant

ARIES-ST is a 1000 MWe fusion power plant based on a low aspect ratio ‘spherical torus’ (ST) plasma. The ARIES-ST power core was designed to accommodate the unique features of an ST power plant, to meet the top-level requirements of an attractive fusion energy source, and to minimize extrapolation from the fusion technology database under development throughout the world. The result is an advanced helium-cooled ferritic steel blanket with flowing PbLi breeder and tungsten plasma-interactive components. Design improvements, such as the use of SiC inserts in the blanket to extend the outlet coolant temperature range were explored and the results are reported here. In the final design point, the power and particle loads found in ARIES-ST are relatively similar to other advanced tokamak power plants (e.g. ARIES-RS [Fusion Eng. Des. 38 (1997) 3; Fusion Eng. Des. 38 (1997) 87]) such that exotic technologies were not required in order to satisfy all of the design criteria. Najmabadi and the ARIES Team [Fusion Eng. Des. (this issue)] provide an overview of ARIES-ST design. In this article, the details of the power core design are presented together with analysis of the thermal–hydraulic, thermomechanical and materials behavior of in-vessel components. Detailed engineering analysis of ARIES-ST TF and PF systems, nuclear analysis, and safety are given in the companion papers [4–7].