Low-pressure Injection System Research Articles

Virtual Development of a Single-Cylinder Hydrogen Opposed Piston Engine

A significant challenge in utilizing hydrogen in conventional internal combustion engines is achieving a balance between NOx emissions and brake power output. A lean premixed charge (Lambda ≈ 2.5) allows for efficient and stable combustion with minimal NOx emissions. However, this comes at the cost of reduced power density due to the higher air requirements of the thermodynamic process. While supercharging can mitigate this drawback, it introduces increased complexity, cost, and size. An intriguing alternative is the 2-stroke cycle, particularly in an opposed piston (OP) configuration. This study presents the virtual development of a single-cylinder 2-stroke OP engine with a total displacement of 0.95 L, designed to deliver 25 kW at 3000 rpm. Thanks to its compact size, high thermal efficiency, robustness, modularity, and low manufacturing cost, this engine is intended for use either as an industrial power unit or in combination with electric motors in hybrid vehicles. The overarching goal of this project is to demonstrate that internal combustion engines can offer a practical and cost-effective alternative to hydrogen fuel cells without significant penalties in terms of efficiency and pollutant emissions. The design of this novel engine started from scratch, and both 1D and 3D CFD simulations were employed, with particular focus on optimizing the cylinder’s geometry and developing an efficient low-pressure injection system. The numerical methodology was based on state-of-the-art commercial codes, in line with established engineering practices. The numerical results indicated that the optimized engine configuration slightly surpasses the target performance, achieving 29 kW at 3000 rpm, while maintaining near-zero NOx emissions (<20 ppm) and high brake thermal efficiency (~40%) over a wide power range. Additionally, the cost of this engine is projected to be lower than an equivalent 4-stroke engine, due to fewer components (e.g., no cylinder head, poppet valves, or camshafts) and a lighter construction.

Coupling of the best-estimate system code and containment analysis code and its application to TMLB’ accident

With the development of advanced pressurized water reactor technology, the thermal-hydraulic coupling effect between the containment and the primary system becomes increasingly tight. In order to meet the demand for integrated safety analysis between the containment and the primary system, this paper investigates a direct coupling method between the best-estimate system code Advanced Reactor Safety Analysis Code and the containment analysis program ATHROC (Analysis of Thermal Hydraulic Response Of Containment). The feasibility of this direct coupling method and the applicability of the coupled program for overall safety analysis are demonstrated using Marviken two-phase flow release experiments. The ATHROC/ARSAC coupled program is employed to analyze the impact of the pressure relief function of the CPR1000 nuclear power plant pressurizer on the behavior of the primary system and containment during the TMLB’ accident. The calculation results indicate that these measures can reduce the pressure of the primary system to the level acceptable by the low-pressure injection system, but at the same time, they cause the pressure in the containment to rise to nearly 0.4 MPa. Therefore, to ensure the structural integrity of the containment, it is necessary for the non-passive hydrogen recombiner to effectively reduce the hydrogen concentration, thereby avoiding additional pressure increase in the containment due to hydrogen deflagration, which could lead to overpressure failure. The findings of this study are of significant reference value for improving the safety performance of thermal-hydraulic systems in operational Gen-II and advanced Gen-III pressurized water reactor nuclear power plants.

Simulation of Branch Pipes Fracture Condition in Low-Pressure Safety Injection System of PWR

In the low-pressure injection system (LHSI) of the PWR unit, two branch pipes of the recirculation pipeline are vulnerable to fracture during minimal-flow operation. Flowmaster was used to create a hydraulic model for the LHSI minimal-flow operation and to simulate the branch double-end shear fracture condition in order to predict the leakage flow volume and the water level drop rate of the refueling water storage tank (RWST) in order to analyze the impact of branch pipe fracture on the water leakage of the RWST. According to the study results, there is very little deviation between the operating condition of the system as it actually is and the Flowmaster model, and the leakage volume following branch pipe fracture is considerably less than that of the RWST. Leakage volume per minute is around 0.025% of the RWST’s overall volume, which has negligible influence on the unit’s safety. Based on the results of the simulation, this study suggests LHSI system operation recommendations.

Development of a pneumatic actuated low-pressure direct injection gas injector for hydrogen-fueled internal combustion engines

Mixture formation is one of the greatest challenges for the development of robust and efficient hydrogen-fueled internal combustion engines. In many reviews and research papers, authors pointed out that direct injection (DI) has noteworthy advantages over a port fuel injection (PFI), such as higher power output, higher efficiency, the possibility of mixture stratification to control NOx-formation and reduce heat losses and above all to mitigate combustion abnormalities such as back-firing and pre-ignitions. When considering pressurized gas tanks for on-vehicle hydrogen storage, a low-pressure (LP) injection system is advantageous since the tank capacity can be better exploited accordingly. The low gas density upstream of the injector requires cross-sectional areas far larger than any other injectors for direct injection in today's gasoline or diesel engines. The injector design proposed in this work consists of a flat valve seat to enable the achievement of lifetime requirements in heavy-duty applications. The gas supply pressure is used as the energy source for the actuation of the valve plate by means of a pneumatic actuator. This article describes the design and the performed tests carried out to prove the concept readiness of the new LP-DI-injector.

Spray collapse in low-pressure injection systems operating in flash-boiling conditions

Spray collapse in low-pressure injection systems operating in flash-boiling conditions

Large-break LOCA analysis of CSR1000

Large-break loss of coolant accident (LBLOCA) analysis of China Supercritical water-cooled Reactor (CSR1000) has been carried out to evaluate its safety system capability. Analysis results indicate that one significant feature of cold-leg LBLOCA is the reverse-flow which occurs in the core due to the break blowdonwn. The reverse-flow drives the pseudo steam into the core and results in the core heat transfer deterioration which induces a quick increasing of the cladding temperature. After the actuation of the automatic depressurization system (ADS) valves, the core coolant forward-flow recovers and the excessive core heat-up is mitigated. The high feed water tank (HFT) provides enough coolant supply to give the low pressure injection system (LPSI) more response time. After the blowdown phase, the core can be re-flooded by LPSI system. The calculated maximum cladding temperature keeps below the safety criterion.

Low-Pressure Injection of Water and Urea-Water Solution in Flash-Boiling Conditions

<div class="section abstract"><div class="htmlview paragraph">The flash-boiling effect in sprays has been shown to have the capability to decrease droplet diameters and spray penetration, as well as improve the vaporization process in gasoline direct injection systems. It has also been shown that in certain conditions, the effect on spray penetration can be the opposite. Under a high degree of overheating the spray collapse effect may appear and lead to increased spray penetration - flare flash boiling. Moreover, when the boiling is already strongly present in the nozzle it may lead to flow choking. Thus, the process is difficult to be controlled. While most studies so far have focused on high-pressure direct injection systems, we investigate the process in a low-pressure system to verify if the effects observed in high-pressure systems will be similar. The study was performed on two liquids, water and a urea-water solution, to limit any individual substance’s effects on the results and to improve the practical importance of the study. The results showed no increased penetration in any of the flash-boiling cases, although at the highest considered temperatures the two plumes tend to form a single spray cloud. Although the characteristics were similar for both studied liquids, in certain measurement conditions the differences in almost all analysed spray parameters were considerable. Moreover, the study has shown that the flash-boiling effect can be considered as an effective way to improve jet and droplet break-up while avoiding a pressure increase in low-pressure injection systems.</div></div>

Scaling analysis of an IBLOCA counterpart test between the ATLAS and LSTF facilities

The experiments carried out in test facilities improve knowledge of the phenomena that would occur in a nuclear power plant during an accident, and support the validation of the thermal-hydraulic codes used in the nuclear safety analysis. Among them, counterpart tests between two facilities allow analyzing the different technology and scale effects, and the inherent distortion, in the evolution of a specific transient. Thus, counterparts contribute to address the scaling methodologies and enhance confidence in extrapolating results from the facilities to their reference power plants.The objective of this study is to analyze an Intermediate Break Loss-Of-Coolant Accident (IBLOCA) counterpart test at the ATLAS and LSTF facilities. The experiment is based on a 13% break in a cold leg, followed by the actuation of the High Pressure Injection (HPI), accumulators and Low Pressure Injection (LPI) systems. The study is supported by the simulation of the experiment with the TRACE5 thermal-hydraulic code. The results are compared with the available data of the A5.2 and IB-CL-05 tests, in the OECD-ATLAS and OECD/NEA ROSA-2 projects, respectively, in order to evaluate the prediction capabilities of TRACE5 and clarify the causes of the important differences between the transients. The analysis is completed by calculating the dimensionless groups derived from the first approach in the top-down scaling. The comparison of the groups determines, since an analytic point of view, the relevant phenomenology during the transient and the scaling distortion between both facilities. The system scaling analysis assesses a great similarity in the evolution of the main thermal-hydraulic parameters and in the operation of the safety systems throughout this transient.

Experimental studies on performance and emission characteristics of reactivity controlled compression ignition (RCCI) engine operated with gasoline and Thevetia Peruviana biodiesel

Abstract Higher fuel economy associated with lower emissions of diesel engines cannot be achieved with conventional low-pressure injection systems. However high-pressure CRDI facilitated diesel engines with electronic control systems can overcome the twin problems of higher emissions of smoke and nitric oxide with acceptable higher brake thermal efficiency as well. Further use of both high-octane fuels like petrol, ethanol as manifold injected fuels along with high pressure CRDI injected high cetane fuels like diesel, biodiesel can successfully overcome the drawbacks of diesel engine emissions. In this direction a newer concept of RCCI operated modified diesel engine was developed in house and was powered with both high octane and high cetane fuels. Comprehensive experiments were conducted on the RCCI engine to obtain its performance, emission characteristics fueled with selected fuel combinations. From the results for B20 and gasoline operation it was concluded that, injection of 10% gasoline drastically reduces the nitric oxide by 6.67% and soot emission by 4.52% compared to diesel mode. However, there was penalty of high hydrocarbon and carbon monoxide emissions by 12.5% and 7.6% respectively.

Research on Time-Dependent Failure Modeling Method of Integrating Discrete Dynamic Event Tree With Fault Tree

Classical PRA methods such as Fault Tree Analysis (FTA) and Event Tree Analysis (ETA) are characterized as static methods due to predetermined event sequences and success criteria of frontline systems. Unlike classical PRA, Dynamic PRA (DPRA) couples the stochastic random process such as random failure of system with deterministic analysis（by simulation）to determine the risk level of complex systems. It considers the safety significance of the timing and order of events on accident progression and consequences. However, it is time-consuming to establish a complicated system simulation model with all safety systems, equipment in an accident. Meanwhile, thousands of accident scenarios are generated due to various state transitions and parameter uncertainty. In fact, most of accident scenarios in nuclear power plants have been modeled for risk analysis using classical PRA models (such as ET). Some of the components to be analyzed could be modeled by a ETs and FTs, instead of establishing a computationally expensive simulation model. However, it is still challenging to combine the classical PRA method with the dynamic PRA method. For dynamic PRA, timing of events is explicitly modeled while the classical PRA model defines Boolean logic variables (such as True, False, Normal). Therefore, the method requires that these models must be able to handle Boolean logic variables and the timing of specific events. So in this paper, an integration model is illustrated about how to couple the time-dependent simulation model with the probabilistic analysis. Then possible dependencies and configuration consistency issue accounted for Discrete Event Tree (DET) branch probabilities are discussed. After that, a detailed method of integration FT into DET is introduced which emphasizes method of computing the conditional branch probability with FTs online, as well as developing the DET model in case of temporal relations of failure. Finally, a simple case of Low Pressure Injection System in Large Break Loss-of-Coolant Accident (LBLOCA) scenario is provided as a demonstration.

Modelowanie zachowania systemu kondensatora awaryjnego w przypadku awarii utraty chłodziwa w reaktorze BWR generacji III+

Emergency Condenser (EC) is a heat exchanger composed of a large number of slightly inclined U-tubes arranged horizontally. The inlet header of the condenser is connected with the top part of the Reactor Pressure Vessel (RPV), which is occupied by steam during critical operation. The lower header in turn is linked with the RPV below the liquid water level during normal operation of the reactor. The tube bundle is filled with cold water and it is located in a vessel filled with water of the same temperature. Thus, the EC and RPV form together a system of communicating vessels. In case of an emergency and a decrease of the water level in the RPV, the water flows gravitationally from U-tubes to the RPV. At the same time the steam from the RPV enters to the EC and condenses due to its contact with cold walls of the EC. The condensate flows then back to the RPV due to the tubes inclination. Hence, the system removes heat from the RPV and serves as a high- and low-pressure injection system at the same time. In this paper a model of the EC system is presented. The model was developed with Modelica modeling language and OpenModelica environment which had not been used in this scope before. The model was verified against experimental data obtained during tests performed at INKA (Integral Test Facility Karlstein) ̶ a test facility dedicated for investigation of the passive safety systems performance of KERENA ̶ generation III+ BWR developed by Framatome.

RELAP5 uncertainty evaluation using ROSA/LSTF test data on PWR 17% cold leg intermediate-break LOCA with single-failure ECCS

An experiment was conducted for the OECD/NEA ROSA-2 Project using the large scale test facility (LSTF), which simulated a cold leg intermediate-break loss-of-coolant accident with 17% break in a pressurized water reactor. Assumptions were made such as single-failure of high-pressure and low-pressure injection systems of emergency core cooling system. In the LSTF test, core dryout took place because of a rapid drop in the core collapsed liquid level before loop seal clearing (LSC). Liquid was accumulated in upper plenum, U-tube upflow-side and inlet plena of steam generators before the LSC because of counter-current flow limiting (CCFL) by high steam velocity, which caused further decrease in the core collapsed liquid level. The post-test analysis by RELAP5/MOD3.3 code revealed that peak cladding temperature (PCT) was overpredicted because of the underprediction of the core collapsed liquid level due to inadequate prediction of accumulator flow rate. We created the phenomena identification and ranking table for each component from the viewpoint of the importance of phenomena in determining the PCT. We found the combination of multiple uncertain parameters including slope m and intercept C of the Wallis CCFL correlation at the upper core plate, core decay power, and steam convective heat transfer coefficient in the core within the defined uncertain ranges largely affected the PCT.

ROSA/LSTF Tests and RELAP5 Posttest Analyses for PWR Safety System Using Steam Generator Secondary-Side Depressurization against Effects of Release of Nitrogen Gas Dissolved in Accumulator Water

Two tests related to a new safety system for a pressurized water reactor were performed with the ROSA/LSTF (rig of safety assessment/large scale test facility). The tests simulated cold leg small-break loss-of-coolant accidents with 2-inch diameter break using an early steam generator (SG) secondary-side depressurization with or without release of nitrogen gas dissolved in accumulator (ACC) water. The SG depressurization was initiated by fully opening the depressurization valves in both SGs immediately after a safety injection signal. The pressure difference between the primary and SG secondary sides after the actuation of ACC system was larger in the test with the dissolved gas release than that in the test without the dissolved gas release. No core uncovery and heatup took place because of the ACC coolant injection and two-phase natural circulation. Long-term core cooling was ensured by the actuation of low-pressure injection system. The RELAP5 code predicted most of the overall trends of the major thermal-hydraulic responses after adjusting a break discharge coefficient for two-phase discharge flow under the assumption of releasing all the dissolved gas at the vessel upper plenum.

RELAP5 Analyses of ROSA/LSTF Experiments on AM Measures during PWR Vessel Bottom Small-Break LOCAs with Gas Inflow

RELAP5 code posttest analyses were performed on ROSA/LSTF experiments that simulated PWR 0.2% vessel bottom small-break loss-of-coolant accidents with different accident management (AM) measures under assumptions of noncondensable gas inflow and total failure of high-pressure injection system. Depressurization of and auxiliary feedwater (AFW) injection into the secondary-side of both steam generators (SGs) as the AM measures were taken 10 min after a safety injection signal. The primary depressurization rate of 55 K/h caused rather slow primary depressurization being obstructed by the gas accumulation in the SG U-tubes after the completion of accumulator coolant injection. Core temperature excursion thus took place by core boil-off before the actuation of low-pressure injection (LPI) system. The fast primary depressurization by fully opening the relief valves in both SGs with continuous AFW injection led to long-term core cooling by the LPI actuation even under the gas accumulation in the SG U-tubes. The code indicated remaining problems in the predictions of break flow rate during two-phase flow discharge period and primary pressure after the gas inflow. Influences of the primary depressurization rate with continuous AFW injection onto the long-term core cooling were clarified by the sensitivity analyses.

Effect of Turbocharged Diesel Engine Operating Conditions on Intake Premixed Methanol Quantity and Performance

A multi-point low-pressure methanol injection system was installed on manifold of a four cylinder turbocharged diesel engine, and the experiments on the engine operated with intake premixed methanol were conducted under wide operating conditions. The influence of the engine operating conditions on premixed methanol quantity was analyzed. The results show that, compared with straight diesel model, premixed methanol prolongs the ignition delay time of pilot diesel at the engine high load with low speed, and more methanol quantity can be premixed. At more than medium load with high speed, diesel ignition delay time with premixed methanol is shorter than with straight diesel model, and substitution ratio of methanol for diesel is significantly lower than that of low speed. Compared with the straight diesel mode at high speed, the fuel economy of the dual fueling mode is better, and NOx and soot emissions also are decreased, but CO and HC emissions are increased.

Analysis of PWR RPV lower head SBLOCA scenarios with the failure of high-pressure injection system using MAAP5

Through the use of MAAP5 code we carried out an analysis of the severe accident scenarios initiated by an unusual small-break loss-of-coolant accident (SBLOCA) located at the reactor pressure vessel (RPV) lower head with the failure of high-pressure injection system (HPIS) in a PWR power plant. The cases of 0.4-inch-break LOCA with and without manual depressurization of the reactor coolant system (RCS), and 1.0-inch-break LOCA were studied. The results showed that without manually depressurizing the RCS, reactor core underwent slow heatup and completely melted and eventually failed the RPV lower head at the primary system pressure of 6.87 MPa for 0.4-inch-break LOCA and 2.71 MPa for 1.0-inch-break LOCA. There was a strong interaction between the discharged melt and collected pool water in the reactor cavity at the time of RPV lower head failure by creep. A 0.472 MPa containment peak pressure was caused by hydrogen combustion for 0.4-inch-break LOCA. For 1.0-inch-break LOCA the pressure peaked twice, the first one (0.396 MPa) by intense steam generation and the second one (0.331 MPa) by hydrogen combustion. These pressure spikes were lower than the containment design pressure of 0.52 MPa. It was not likely to stop the cavity from being eroded by molten corium through continuously pouring water down into the cavity. Thus there were constant reactor cavity ablation and hydrogen generation, leading to dangerous erosion depths and elevated hydrogen volume fraction in the presence of containment spray system. On the other hand, timely manually opening the pressurizer (PZR) safety valves (SVs) was an effective mitigation measure to recover the core coolabilty by cold-leg accumulator injection system (AIS) and low-pressure injection system (LPIS). Besides, reasonably manually opening the steam generators (SGs) SVs while keeping the auxiliary feedwater on also helped to depressurize the RCS and prevent the severe accident. Both of the two mitigation measures successfully prevented the core from complete melt, but the latter one is preferable to the former one provided no steam generator tube rupture takes place.

Influence of engine load and fuel droplet size on performance of a CI engine fueled with cottonseed oil and its blends with diesel fuel

In this study, favorable conditions to achieve good combustion of cottonseed oil and its blends with diesel fuel in a direct injection diesel engine have been highlighted. This has been performed by analyzing fuel droplet size distribution and determining engine specific fuel consumption and thermal efficiency, combustion parameters (ignition delay, rate of heat release) and emissions (carbon monoxide (CO), nitrogen oxides (NOx) and carbon dioxide (CO2)). Results show that thermal efficiency and CO2 are almost similar for all tested fuels while the specific fuel consumption and CO emissions increase and NOx emissions decrease with increasing percentage of cottonseed oil in blends. Cylinder pressures are very close and rates of heat release are slightly different for cottonseed oil and diesel fuel. Results on droplet size analysis show that to obtain an adequate droplet size distribution, the percentage of cottonseed oil in diesel fuel should be limited to 40% by volume. Results on engine performance show that engine loads must be above 50%. These results are valid for diesel engines of conventional design, using low-pressure injection systems; they do not apply to modern high injection pressure engines.

Intermittent multijet sprays for improving mixture preparation with low-pressure injection systems

In this work, the characteristics of droplets produced by a multijet impingement atomization process are measured with a Phase-Doppler Interferometer and statistically described using finite mixtures of weighted probability density functions. Through this statistical tool, drop size and axial velocity distributions are involved in the physical interpretation of the flow, instead of limiting it to first- and second-order distribution moments. Each group of droplets with similar size characteristics has been modeled by lognormal distributions and normal distributions relatively to drop axial velocity. The analysis based on finite mixtures identified three groups of droplets with similar size characteristics, although the group with smaller sizes is negligibly represented in the statistical finite mixture. Also, the lognormal standard deviation in all groups is well correlated with the corresponding geometric mean diameter allowing to simplify the description of the spray. In terms of axial velocity, mainly one distribution has been identified with a relatively constant standard deviation, and a characteristic velocity slightly dependent on the duty cycle associated with the spray intermittent condition. Furthermore, droplets characteristics are correlated with the heat transfer rate obtained for several operating conditions that maintain the surface temperature in steady-state at 125 °C. The effect of the time between consecutive injections is analyzed. Concerning the potential use of multijet impingement sprays for fuel injection systems, results evidence the importance of an interaction between thin liquid film heat transfer and droplets axial velocity for enhancing heat transfer and promote evaporation. This would decrease the amount of fuel deposited on interposed surfaces, thus, improving mixture preparation in low-pressure injection systems for internal combustion engines.

Safety Evaluation of the Uprated BWR Using the Large Assembly with Small Pins Concept

An advanced design of a Large Assembly with Small Pins (LASP) has been proposed at the Massachusetts Institute of Technology to increase the power density of boiling water reactors (BWRs) while keeping most of the operating conditions of current BWRs. LASP is based on replacing four traditional assemblies and the large water gap regions with a single large assembly having a 22 × 22 square lattice. In-assembly water rods accommodate control rods as well as provide help to the moderation of neutrons. Previous steady-state analysis showed that the LASP core allows for operation with 20% higher power density than the core with traditional 9 × 9 fuel assemblies. However, the void reactivity coefficient of the LASP core is 25% more negative and the steam flow rate is 20% higher than that of the reference core. In this study, the performances of the LASP core and reference core are compared for selected design-basis accidents and transients. Generally, the LASP design is found to behave in a manner similar to the traditional assemblies. First, the clad peak temperature during a large-break loss-of-coolant accident analysis satisfies regulatory criterion, and it is possible to preserve peak cladding temperature margin of the reference design if the capacity of the low-pressure core injection system is increased by 20%. Second, the generator load rejection with bypass failure and feedwater controller failure analyses show a decrease in dryout margin for the LASP core because of the combination of more negative void coefficient and increased steam load. However, this problem could be remedied by increasing the steam line flow area or allowing an additional flow restrictor in the steam line to attenuate the back propagating pressure wave in the main steam pipe following the turbine stop valve closure. Finally, the LASP core preserved the same level of margin to dryout as the reference core in the cases of four other evaluated events.

Design and analysis of a thermal hydraulic integral test facility for Bushehr nuclear power plant

In this paper, design and analysis of a thermal hydraulic integral test facility for Bushehr Nuclear Power Plant (NPP) is presented. The Bushehr Integral Test Facility (BITF) is a test facility designed to model the thermal-hydraulic behaviours of the Bushehr NPP (VVER-1000) pressurized water reactors currently in use in IRAN. These reactors have unique features that differ from other PWR designs. The BITF simulates the major components and systems of the reference NPP, making it possible to examine postulated small and medium break a loss of coolant accidents (LOCAs) and operational transients. The BITF is a volume-scaled model (1:1375). To ensure that gravitational forces remain equal to those in the reference reactor, the major components and systems in the BITF preserve 1:1 elevation equivalence to the reference reactor. The facility has four loops (each one consists of a hot leg, a steam generator, a loop seal, a main circulation pump and a cold leg), a pressurizer connected via two surge line to the hot leg of the loops 2, 4, the emergency-core-cooling system (ECCS) which is provided by an active pump simulating high and low pressure injection systems, and four hydro-accumulators. The report also contains a comparison between experimental data of PSB test facility and RELAP5 calculations of BITF facility under steady state condition of the reactor power 15% from the nominal.