Cold Startup Conditions Research Articles

Energy harvesting in diesel engines to avoid cold start-up using phase change materials

In diesel engines, a significant amount of energy is wasted to the environment by the exhaust gases and coolants. In this study, a new design of the exhaust waste heat recovery (WHR) heat exchanger is proposed to preheat the intake air before supplying it into a diesel engine at the cold start-up conditions. The heat exchanger is designed of ribbed plates containing paraffin wax phase change material (PCM). This PCM is used to store the thermal energy coming out from the engine during the operation for later use in cold start-up conditions. A numerical model is developed and validated with the experimental results in the literature. The effect of different design conditions along with various operating conditions is evaluated. The influences of ribs height and spacing, engine rotational speed, and intake air temperature on the thermal energy storage were evaluated. Based on the results, it can be concluded that the highest thermal performance was obtained at a rib gap of 90 mm and a rib height of 7.5 mm. Through the warming-up process, in less than 1 min, the cold intake air temperature can be increased from 273 to 302.2 and from 283 K to 300.7 K. This results in overcoming the cold start-up difficulties, specifically in icy weather, and delivers preheated air to the engine after 1 min.

TRANSIENT CALCULATIONS OF SPERT III EXPERIMENTS

Cold-startup and hot-standby reactivity accident tests conducted at the SPERT III E-core research reactor are analysed with the coupled neutron-kinetic/thermal-hydraulic code system DYN3D-ATHLET. Homogenised 2-group cross sections for DYN3D are thereby generated with the Monte Carlo neutron transport code Serpent 2 in combination with the ENDF/B-VII.1 cross section library. Results in terms of maximum power, energy release, and reactivity compensation are in good agreement with the experimental values. The time-dependent contributions to the reactivity feedback are investigated for both a cold-startup test and a hot-standby test. These findings prove the suitability of the combined application of the simulation codes to predict the reactor dynamic behaviour in the event of prompt-critical and super-prompt critical transients even for small reactor cores. Furthermore, static core characteristics of the SPERT III E-core reactor at cold-startup condition are analysed with using a static DYN3D model, a detailed Serpent reference model, and a simplified Serpent model consistent with the DYN3D model. The critical control rod position and the excess reactivities of both the control rods and the transient rod obtained with the Serpent reference model are consistent with the experimental values. For the same parameters, the DYN3D model is in good agreement with the Serpent simplified model.

Numerical study on the LNG application for start-up fuel in the commercial scale CFBC boiler

We evaluated the applicability of liquid natural gas (LNG) as a start-up fuel in the circulating fluidized bed combustion (CFBC) boiler. A 250 ton/hr scale CFBC boiler, which adopts four LNG over bed burners for the operation at start-up procedure, was investigated through the commercial computational fluid dynamics (CFD) analysis. The complex LNG reactions were simplified and the Eulerian-Granular multiphase model was used to consider the behavior of bed materials and gas-solid interaction. The model reliability was obtained by comparing with design values. The simulation results showed that the bed materials have a significant impact on the internal temperature distribution of boiler despite the cold start-up condition which contains a small amount of bed material. With the consideration of two representative particle size distributions in the modeling, the calculated maximum gas temperature near the refractory was below the allowable temperature of refractory material. Further, it was predicted that the application of the actual particle size distribution on the simulation leads to a decrease of maximum gas temperature adjacent to the refractory wall. Based on the present results, LNG fuel could be acceptable for the start-up operation of CFBC boilers.

Validation of PSI best estimate plus uncertainty methodology against SPERT-III reactivity initiated accident experiments

This research aims at validating the SIMULATE-3K code and complementing the results with the quantification of nuclear data uncertainties against the Special Power Excursion Reactor Test III (SPERT-III) experiments. To that aim, the SHARK-X methodology, under development at PSI, for the propagation of nuclear data uncertainties in CASMO5 2-D lattice calculations to 3-D core transient simulations is applied for the analysis of a SPERT-III super-prompt critical test conducted at cold startup conditions. Concerning transient results, both total power and reactivity show a good agreement with the measurements at the initial phase of power excursion, while a slight discrepancy is obtained at the final phase of the transient. The estimated uncertainties regarding both steady-state parameters such as k-eff and static reactivity worth, as well as dynamical quantities such as power pulse width and enthalpies are presented. Results show non-negligible sensitivity upon the employed nuclear data library. The uncertainty quantification results show relatively small biases for k-eff and reactivity. The uncertainty in peak power is around 3%, while it is negligible for the time to peak power and the pulse width. The time evolution of the standard deviation and skewness of the total power showed special shapes with relatively high maximum values. In addition, the uncertainty due to nuclear data in the two important safety parameters, i.e. maximum nodal fuel temperature and enthalpy reaches maximum value around 2% and 10%, respectively.

Transient tribodynamic analysis of crankshaft-main bearing system during engines starting up

The starting-up process of internal combustion engines presents a great challenge to the tribodynamic performance of the crankshaft-main bearing system. In this study, a transient mixed elastohydrodynamic lubrication model is presented to investigate the transient process. In the model, the average Reynolds equation is adopted with considering the influences of surface deformation and starting temperature. Then the oil film and friction loss of the system and the journal center trajectory during engines starting up are analyzed. The results at different starting temperatures show that the asperity contact under the hot start-up condition is more serious. However, during the engine run-up and transition to idling phases, more viscous friction loss is generated under the cold start-up condition.

Performance analysis of vapor injection heat pump system for electric vehicle in cold startup condition

In this study, a vapor-injection (VI) cycle designed for indoor heating of electric vehicle (EV) was investigated for low temperature heating purposes. The heating capacity variation was observed both in mathematical and experimental ways to verify the influence of vapor injection at different injecting positions and under different intermediate pressure. From this study, the optimal injection position of the scroll compressor and intermediate pressure ratio were evaluated that maximizes heating capacity and coefficient of performance (COP) of the cycle. To validate the numerical results, the experiment was also conducted in the prototype of a vapor-injection (VI) heating system for electric vehicle. The experiment was carried out under the steady-state condition and the same parameters as those of numerical analysis were employed. The comparison between the results of numerical analysis and that of experiments showed a good agreement. For the increase of heating capacity, the optimal injecting port position was observed in specific value which was close to 300°. As the opening of the main expansion valve was decreased, the performance of the VI system generally got better but the system had much restricted intermediate pressure ratio in which the performance was drastically decreased. As a result, the optimal intermediate pressure ratio occurred in specific value below 0.25 in startup condition.

Performance of Surface Texturing During Start-Up Under Starved and Mixed Lubrication

In this paper, the start-up process of the ring/liner system with surface texturing is studied. By employing a thermal-mixed lubrication model considering the oil supply, the tribological behavior of the textured surface under the cold and hot start-up conditions is investigated. It is found that the friction coefficient curve under the cold start-up condition is different from the hot start-up result. The textured surface is easier to form the hydrodynamic lubrication than the smooth surface, which is helpful to separate the mixed lubricated contact surfaces. With the textured features on the ring face, the less friction heat is generated at the start-up phase. These effects could prove beneficial in applications with the frequent start and stop conditions. Besides, the inlet wedge of ring can also influence the start-up performance.

Validation of the Serpent 2-DYNSUB code sequence using the Special Power Excursion Reactor Test III (SPERT III)

The Special Power Excursion Reactor Test III (SPERT III) is studied using the Serpent 2-DYNSUB code sequence in order to validate it for modeling reactivity insertion accidents (RIA) in PWRs. The SPERT III E-core was a thermal research reactor constructed to analyze reactor dynamics. Its configuration resembles a commercial PWR on terms of fuel type, choice of moderator, coolant flow and system pressure. The initial conditions of the rod ejection accident experiments (REA) performed cover cold startup, hot startup, hot standby and operating power scenarios. Eight of these experiments were analyzed in detail. Firstly, multi-dimensional nodal diffusion cross section tables were created for the three-dimensional reactor simulator DYNSUB employing the Monte Carlo neutron transport code Serpent 2. In a second step, DYNSUB stationary simulations were compared to Monte Carlo reference three-dimensional full scale solutions obtained with Serpent 2 (cold startup conditions) and Serpent 2/SUBCHANFLOW (operating power conditions) with a good agreement being observed. The latter tool is an internal coupling of Serpent 2 and the sub-channel thermal-hydraulics code SUBCHANFLOW. Finally, DYNSUB was utilized to study the eight selected transient experiments. Results were found to match measurements well. As the selected experiments cover much of the possible transient (delayed super-critical, prompt super-critical and super-prompt critical excursion) and initial conditions (cold and hot as well as zero, little and full power reactor states) one expects in commercial PWRs, the obtained results give confidence that the Serpent 2-DYNSUB tool chain is suitable to model REAs and other RIAs in PWRs.

Transient lubrication of piston compression ring during cold start-up of SI engine

Cold start-up conditions differ from the normal operating conditions for an engine, and this discrepancy adversely affects the tribological performance of interfaces. The majority of health-hazardous engine exhaust emissions occur during the cold start-up of an engine; consequently this condition generates a major environmental concern. This study numerically investigates the transient hydrodynamic lubrication of the first compression ring during initial start-up of a cold engine by combining lubrication theory with the realistic oil rheology of multigrade oils. Specifically, in this study transient speed, variation in cylinder pressure, and high lubricant viscosity during start-up are considered to determine developing pattern of the lubricating film and of other tribological performance parameters. The cycle-by-cycle developments of lubricating film, friction force, power loss, and oil transport are analyzed as well. The start-ups of a cold and a warm engine are also compared in terms of frictional losses and oil transport. Different monograde and multigrade engine oils are used to evaluate oil-dependent performance. Results show that in all cases, performance during cold start-up is of greater significance than that of a warm engine. Low lubricant temperature and stated start-up conditions substantially increase amount of energy loss and net oil transport. Temperature-dependent variations in performance are also more significant in high viscosity-grade oils.

Cold start-up condition model for heat recovery steam generators

A dynamic modeling of Heat Recovery Steam Generator (HRSG) during cold start-up operation in Combined Cycle Power Plant (CCPP) is introduced. In order to characterize the essential dynamic behavior of the HRSG during cold start-up; Dynamic equations of all HRSG's components are developed based on energy and mass balances. To describe precisely the operation of HRSG; a method based on nonlinear estimated functions for thermodynamic properties is applied to estimate the model parameters. Model parameters are evaluated by a designed algorithm based on Genetic Algorithm (GA). A wide set of experimental data is used to validate HRSG model during cold start-up operation. The simulation results show the reliability and validity of the developed model for cold start-up operation.

I211 ガソリンの壁面付着に伴うすす生成の数値解析

Liquid fuel films attached on wall surfaces are presumed to cause soot emissions during the cold startup period of gasoline direct injection spark ignition engines. In this study, soot formation originated in combustion of liquid fuel films was investigated by using a 3D simulation. Calculations were performed for a Rapid Compression and Expansion Machine model. Effects of physical properties and the composition of the fuel were examined. Results showed that a portion of liquid fuel films remained until the end of the expansion stroke without evaporating even with the passage of the flame under the cold startup condition. Emission factors of liquid fuel films and soot were lager for PRF095 (i-C_8H_<18> 83%, n-C_7H_<16> 4%, C_6H_5CH_3 13%) than those of PRF100 (i-C_8H_<18> 100%). PRF100-ND having evaporation properties same as n-C_<10>H_<22> and chemical kinetics same as i-C_8H_<18> was prepared numerically. Emission factors of PRF100-ND were larger for liquid fuel films and smaller for soot than other fuels under the cold startup condition.

Control of a Supercritical CO2 Recompression Brayton Cycle Demonstration Loop

The U.S. Department of Energy is currently focused on the development of next-generation nuclear power reactors, with an eye towards improved efficiency and reduced capital cost. To this end, reactors using a closed-Brayton power conversion cycle have been proposed as an attractive alternative to steam turbines. The supercritical-CO2 recompression cycle has been identified as a leading candidate for this application since it can achieve high efficiency at relatively low operating temperatures with extremely compact turbomachinery. Sandia National Laboratories has been a leader in hardware and component development for the supercritical-CO2 cycle. With contractor Barber-Nichols Inc., Sandia has constructed a megawatt-class S-CO2 cycle test-loop to investigate the key areas of technological uncertainty for this power cycle and to confirm model estimates of advantageous thermodynamic performance. Until recently, much of the work has centered on the simple S-CO2 cycle—a recuperated Brayton loop with a single turbine and compressor. However, work has recently progressed to a recompression cycle with split-shaft turbo-alternator-compressors, unlocking the potential for much greater efficiency power conversion, but introducing greater complexity in control operations. The following sections use testing experience to frame control actions made by test loop operators in bringing the recompression cycle from cold startup conditions through transition to power generation on both turbines, to the desired test conditions, and finally to a safe shutdown. During this process, considerations regarding the turbocompressor thrust state, CO2 thermodynamic state at the compressor inlet, compressor surge and stall, turbine u/c ratio, and numerous other factors must be taken into account. The development of these procedures on the Sandia test facility has greatly reduced the risk to industry in commercial development of the S-CO2 power cycle.