Instantaneous Mass Flow Research Articles

Development of a Lumped Model for the Characterisation of the Intake Phase in Spark-ignition Internal Combustion Engines

The present work aims to develop a control-oriented lumped model to investigate the fluid dynamic behaviour of multi-valve spark-ignition engines (ICEs). Specifically, the attention has been focused on the intake phase and in-cylinder air charge estimation. To this purpose, a spark-ignition engine has been characterised at a flow rig in terms of flow coefficients. The experimental data have been used to define the fluid dynamic behaviour of the different intake system components and to calibrate and validate the proposed model that has been developed in Matlab/Simulink environment. Furthermore, in order to evaluate the capability of the zero-dimensional code and to estimate the instantaneous in-cylinder mass flow in different operating conditions, the numerical data have been compared to the results of a one-dimensional commercial software.The comparison between numerical and experimental data shows a good agreement. The investigation highlights that the proposed control-oriented lumped model represents a useful and simple tool to evaluate the engine breathability and to define the proper valve timing.

Mathematical model of time difference for Coriolis flow sensor output signals under gas-liquid two-phase flow

Abstract The features of Coriolis mass flow sensor output signal are analyzed, and a mathematical model of the time difference for the signals is built to evaluate the rationality and limitation of the proposed correction method when Coriolis mass flowmeter (CMF) is used to measure the gas-liquid two-phase flow. According to the experimental data of Coriolis mass flow sensor output signals under the gas-liquid two-phase flow condition, the time differences of the sensor output signals are extracted as a characteristic quantity to obtain the time difference sequence by adopting a digital zero-crossing detection method. The distribution pattern of the time difference sequence is analyzed with the probability density function, and the mathematical model of the time difference sequence is built by the correlation analysis. The mathematical model consists of a stable component and a fluctuating component. Correcting the stable component can improve the measurement accuracy of cumulative mass flow rate, and reducing the fluctuating component can enhance the measurement stability of instantaneous mass flow rate. Although the stable component cannot be completely corrected because its variation is nonlinear with the flow rate and drop in density, and the fluctuating component can only be reduced to a certain extent due to the real-time processing limitation of the instrument, CMF can provide relatively reliable measurement results of the liquid mass flow rate when the gas-liquid two-phase flow occurs.

Numerical modelling of twin-screw pumps based on computational fluid dynamics

Increasing demands for high-performance screw pumps in oil and gas as well as other applications require deep understanding of the fluid flow field inside the machine. Important effects on the performance such as dynamic losses, influence of the leakage gaps and presence and extent of cavitation are difficult to observe by experiments. However, it is possible to study such effects using well-validated computational fluid dynamics models. The novel-structured numerical mesh consisting of a single-computational domain for moving screw pump rotors was developed to allow three-dimensional computational fluid dynamics simulation of such machine possible. Based on finite volume method, the instantaneous mass flow rates, rotor torque, local pressure field, velocity field and other performance indicators including the indicated power were predicted. A calculation model for the bearing friction losses was introduced to account for mechanical losses. The geometry of the inlet and outlet passages and piping system are taken into consideration to evaluate their influences on the pressure distribution and shaft power. The paper also shows the influence of rotor clearances on the pump performance. The computational fluid dynamics model was validated by comparing the numerical results with the measured performance obtained in the experimental test rig through the comprehensive experiment performed for a set of discharge pressures and rotational speeds. Validation includes comparison of mass flow rates, shaft power and efficiency under variety of speeds and discharge pressure. It has been found that the predicted results match well with the measurements. The results also showed that the radial clearances have larger influence on the mass flow rate than the interlobe clearance. The correct design of the flow passages within the screw pump plays significant role in minimizing required power consumption. The analysis presented in this paper contributes to better understanding of the working process inside the screw pump and offers a good reference to improve design and optimize such machines in terms of clearance selection, shape of the ports, piping system, etc. In future, this model will be used for analysis of cavitating flows and determining performance of other multiphase screw pumps.

Numerical analysis of blood flow through an elliptic stenosis using large eddy simulation.

The presence of a stenosis caused by the abnormal narrowing of the lumen in the artery tree can cause significant variations in flow parameters of blood. The original flow, which is believed to be laminar in most situations, may turn out to turbulent by the geometric perturbation created by the stenosis. Flow may evolve to fully turbulent or it may relaminarise back according to the intensity of the perturbation. This article reports the numerical simulation of flow through an eccentrically located asymmetric stenosis having elliptical cross section using computational fluid dynamics. Large eddy simulation technique using dynamic Smagorinsky sub-grid scale model is applied to capture the turbulent features of flow. Analysis is carried out for two situations: steady inflow as ideal condition and pulsatile inflow corresponding to the actual physiological condition in common carotid artery. The spatially varying pulsatile inflow waveforms are mathematically derived from instantaneous mass flow measurements available in the literature. Carreau viscosity model is used to estimate the effect of non-Newtonian nature of blood. The present simulations for steady and pulsatile conditions show that post-stenotic flow field undergoes transition to turbulence in all cases. The characteristics of mean and turbulent flow fields have been presented and discussed in detail.

Methodology for instantaneous average exhaust gas mass flow rate measurement

This paper presents a new methodology for measurement of the instantaneous average exhaust mass flow rate in reciprocating internal combustion engines to be used to determinate real driving emissions on light duty vehicles, as part of a Portable Emission Measurement System (PEMS). Firstly a flow meter, named MIVECO flow meter, was designed based on a Pitot tube adapted to exhaust gases which are characterized by moisture and particle content, rapid changes in flow rate and chemical composition, pulsating and reverse flow at very low engine speed. Then, an off-line methodology was developed to calculate the instantaneous average flow, considering the “square root error” phenomenon. The paper includes the theoretical fundamentals, the developed flow meter specifications, the calibration tests, the description of the proposed off-line methodology and the results of the validation test carried out in a chassis dynamometer, where the validity of the mass flow meter and the methodology developed are demonstrated.

Dynamic modelling of the expansion cylinder of an open Joule cycle Ericsson engine: A bond graph approach

A dynamic model using the bond graph formalism of the expansion cylinder of an open Joule cycle Ericsson engine intended for a biomass-fuelled micro-CHP system is presented. Dynamic phenomena, such as the thermodynamic evolution of air, the instantaneous air mass flow rates linked to pressure drops crossing the valves, the heat transferred through the expansion cylinder wall and the mechanical friction losses, are included in the model. The influence on the Ericsson engine performances of the main operating conditions (intake air pressure and temperature, timing of intake and exhaust valve closing, rotational speed, mechanical friction losses and heat transfer at expansion cylinder wall) is studied. The operating conditions maximizing the performances of the Ericsson engine used in the a biomass-fuelled micro-CHP unit are an intake air pressure between 6 and 8 bar, a maximized intake air temperature, an adjustment of the intake and exhaust valve closing corresponding to an expansion cycle close to the theoretical Joule cycle, a rotational speed close to 800 rpm. The heat transfer at the expansion cylinder wall reduces the engine performances.

The Influence of Pulse Shape on the Performance of a Mixed Flow Turbine for Turbocharger Applications

Engine downsizing allows automotive manufactures to achieve improved efficiency and reduce emissions. Turbocharging can increase the power density of the engine, and therefore plays a vital role in downsizing. Due to the nature of the reciprocating engine, a turbocharger turbine operates in a highly unsteady environment. This paper presents a computational investigation looking at the impact of pulse shape on the performance of a mixed flow turbine for turbocharger applications. While the impact of pulse frequency and amplitude on turbine unsteady performance has received significant attention in the past, little work has been done on the impact of the pulse shape. In the current study, four inlet pulse shapes have been investigated and shown to have a significant impact on turbine instantaneous performance, where efficiency and mass flow hysteresis varied significantly between test cases. This result shows for in-depth analyses of turbine flow physics and loss mechanisms, accurately modelling the inlet pulse shape is vital. The square pulse showed the most distinct impact with normalized cycle average efficiency decreasing by 1.37% and a 2.23% reduction in normalized stage MFP when compared to the sinusoidal wave. The variation in normalized cycle averaged stage efficiency was found to be less than 0.25% for the remaining three wave forms and the variation in normalized cycle averaged MFP less than 0.5%. This finding suggests that a simple sinusoidal wave form can be used for the majority of cycle-averaged performance comparisons.

Hydraulic characterization of Diesel and water emulsions using momentum flux

Diesel and water emulsions have the potential to be used in compression ignition engines to control the emissions of NOx and PM. Very little is known about the influence emulsification will have on the fuel sprays formed during injection. This paper outlines the measurement of the momentum flux of injection sprays of Diesel fuel and Diesel fuel emulsions containing 10% and 20% water, with the goal of hydraulically characterizing the sprays and identifying the influence emulsification may have on them. The momentum flux, mass flow, instantaneous mass flow, discharge coefficient, injection velocity, momentum coefficient and momentum efficiency have been examined. The injections were carried out in a high pressure chamber filled with nitrogen. The measured momentum flux is observed to increase with increasing injection pressure in a linear form. Increasing the ambient density in the chamber resulted in a decrease in the measured momentum flux. The emulsified fuel sprays had a very similar momentum flux as the neat Diesel fuel sprays. The total mass of emulsified fuel injected was less than for neat Diesel at corresponding condition. The instantaneous mass flow rate was determined using a normalized form of the momentum flux measurement and the independently measured total mass injected. The emulsions tended to have a lower discharge coefficient and there is no evidence that the nozzle is cavitating at these conditions. The emulsified fuels have tended to have a higher injection velocity than the neat Diesel fuel sprays. The momentum efficiency is introduced, which uses the instantaneous mass measurement and the theoretical velocity of the spray. The emulsified fuels have a larger momentum efficiency, a result of their high injection velocity compared with the neat Diesel fuel.

One-dimensional simulations and experimental analysis of a wastegated turbine for automotive engines under unsteady flow conditions

In this paper, the unsteady-state behaviour of a turbocharger wastegated turbine (IHI-RHF3) is investigated using both an experimental approach and a numerical approach. First, an experimental campaign is performed in a specialized test rig operating at the University of Genoa, for different openings of the wastegate valve and under steady flow and unsteady flow operations. An appropriate configuration of the turbine outlet circuit fitted with a separating wall is used to carry out instantaneous measurements downstream of the turbine wheel and the wastegate valve. The above data constitute the basis for the tuning and validation of a one-dimensional turbine model recently developed at the University of Naples. Preliminary model tuning is carried out on the basis of the characteristic map measured for a completely closed wastegate valve under steady flow operations. A refined one-dimensional schematization of the experimental apparatus is implemented within the commercial GT-Power® software, including the turbine, the wastegate circuit and the upstream and downstream measuring stations. In particular, the classical map-based approach is suitably corrected with a sequence of pipes that schematizes each component of the turbine (the inlet and outlet ducts, the volute and the wheel) to account for the wave propagation and storage phenomena inside the machine. A detailed one-dimensional schematization of the wastegate circuit is also implemented and independently tuned. The turbine model capability under unsteady flow conditions is tested for different wastegate openings and pulse frequencies, by applying time-dependent boundary conditions. In particular, the pressures and temperatures measured upstream and downstream are imposed at the model ends, and the instantaneous mass flow rate and the actual power are numerically evaluated. The results are compared with the experimental data, demonstrating good accuracy and showing some improvements with respect to the standard turbine modelling in the case of the mass flow rate prediction. On the contrary, the computed actual power shows some inaccuracies, especially at higher pulse frequencies.

Prevention of drug delivery disturbances during continuous intravenous infusion: An in vitro study on a new multi-lumen infusion access device

ObjectiveStopping and restarting carrier fluid flow and performing simultaneous drug infusions can lead to hazardous disturbances in drug delivery. The present study was designed to assess in vitro whether using a multi-lumen infusion access device could prevent noradrenaline disturbances. Study designIn vitro laboratory work. MethodsTwo infusion devices were studied: a standard device with a four-port manifold and a 150cm extension line and a nine-lumen infusion device (Edelvaiss-Multiline®) with eight accesses connected to nine separate lumens in a single tube of 150cm: seven accesses connected to seven peripheral lumens and one for the carrier fluid access connected to two lumens. Two experimental protocols of noradrenaline infusion were made: (a) drug flow rate change and (b) stop-and-go carrier fluid flows. Two parameters were studied: drug mass flow rate and flow change efficiency (FCE) calculated from the ratio of the area under the experimental mass flow rate curve to the area under the theoretical instantaneous mass flow rate curve. ResultsVariations in noradrenaline mass flow rate were more rapid with the Edelvaiss-Multiline® when the noradrenaline infusion rate was increased or decreased. FCE was significantly different from one infusion device to the other during both noradrenaline flow rate increase (standard vs. nine-lumen: 58% vs. 84%; P=0.008) and decrease (175% vs. 108%; P=0.008). Decreased drug delivery after stopping carrier fluid flow (standard vs. nine-lumen: 21% vs. 98%; P=0.008) and sudden temporary increases on resumption (253% vs. 103%; P=0.008) were reduced in magnitude and duration when using the Edelvaiss-Multiline® with a significant difference in FCE between the two infusion devices. ConclusionsUsing the nine-lumen infusion device reduces drug delivery disturbances during continuous intravenous infusion.

Numerical Study of the Implementation of an Active Control Turbocharger on Automotive Diesel Engines

Active control turbocharger (ACT) has been proposed as a way to improve turbocharger performance under highly pulsating exhaust flows. This technique implies that the variable geometry mechanism in the turbine is used to optimize its position as a function of the instantaneous mass flow during the engine cycle. Tests presented in the literature showed promising results in a pulsating gas-stand. In this work, a modeling study has been conducted at different engine conditions aimed to quantify the gain in on-engine conditions and to develop a strategy to integrate the ACT system within the engine. Different ways of changing the displacement of the variable mechanism have been analyzed by means of a one-dimensional gas dynamic model. The simulations have been carried out at constant engine operating points defined by fixed air-to-fuel ratio for different mechanism displacement functions around an average position that guarantees the desired amount of intake air. The benefits in overall engine efficiency are lower to those predicted in the literature. It can be concluded that it is not possible to use the ACT system to optimize the turbine operating point and at the same time to control the engine operating point.

Frequency based approach for simulating pressure waves at the inlet of internal combustion engines using a parameterized model

Today’s downsized turbocharged engines mainly focus on improving low end torque and increasing mass flow rate, this is done in order to improve the overall thermodynamic efficiency of the engine and to gain a lower BSFC. An integral part of any combustion engine is the air intake line that has a first order effect on engine filling and emptying. The wave action that takes place is usually simulated using one-dimensional codes. This paper presents a novel technique based on a frequency domain characterization of the intake line. A link over a wide frequency spectrum is identified between the instantaneous mass flow at the valve and the dynamic pressure response. This model is implemented into Simulink via a transfer function and coupled to GT-Power to produce an engine simulation. A shock tube experimental campaign was conducted for a number of tubes with varying lengths and diameters. The parameters of this transfer function are measured for each case then combined with gas dynamic theory and a frequency analysis to identify a law of behavior as a function of pipe geometry. The final model is validated on a single cylinder engine in GT-Power for a variety of pipe geometry.

Design and integrated simulation of a pressurized feed system of the dual-thrust hybrid rocket motor

A new pressurized feed system of the dual-thrust hybrid rocket motor for flight is presented in this paper. The feed system supplies 90% hydrogen peroxide (90%H2O2) with two different flows of 4.5 and 2 kg s−1. The oxidizer flow is changed through regulating the mass flow of the high-pressure gas and switching the performance modes of the unique oxidizer flow control valve simultaneously. The models of the gas storage container, pressure regulator valve, control orifice, propellant tank, oxidizer flow control valve and cavitating venturi are generated and used to compute the instantaneous pressure, temperature and mass flow rate. There is a good agreement between the simulated and experimental results. Parameter sensitivity analysis is also conducted. It is found that the throat diameter of the cavitating venturi in feed line 1 is the main factor affecting the mass flow in both boost and sustaining phase. Other parameters have limited effects on the mass flow rate and the transition time of the system.

Characterization of a radial turbocharger turbine in pulsating flow by means of CFD and its application to engine modeling

This paper presents a numerical study analyzing the effect of pulsating flow in a variable geometry radial inflow turbine. The turbine behavior is analyzed under isentropic pulses, which are similar to those created by a rotating disk in a turbocharger test rig. Three different pulse frequencies (50, 90 and 130Hz) and two pulse amplitudes (100 and 180kPa) were considered. Turbine flow was studied throughout the pressure pulsation cycles in a wide range of off-design operating conditions, from low pressure ratio flow detachment to high pressure ratio choked flow. An overall analysis of the phasing of instantaneous mass flow and pressure ratio was first performed and the results show the non-quasi-steady behavior of the turbine as a whole as described in the literature. However, the analysis of the flow in the different turbine components independently gives a different picture. As the turbine volute has greater length and volume than the other components, it is the main source of non-quasi-steadiness of the turbine. The stator nozzles cause fewer accumulation effects than the volute, but present a small degree of hysteretic behavior due to flow separation and reattachment cycle around the vanes. Finally, the flow in the moving rotor behaves as quasi-steady, as far as flow capacity is concerned, although the momentum transfer between exhaust gas and blades (and thus work production and thermal efficiency) is affected by a hysteretic cycle against pressure ratio, but not if blade speed ratio is considered instead. A simple model to simulate the turbine stator and rotor is proposed, based on the results obtained from the CFD computations.

Experimental Investigation on the Unsteady Performance of Automotive Turbocharger Turbine

This paper presents some development of the turbocharger turbine unsteady measurement under pulsating conditions. On the basis of the indirect turbine power measuring principle by using a radial compressor to load turbine, a new turbine test rig is set up, which uses an “auxiliary” turbocharger instead of the intercooler to achieve a close-cycle loading. The experimental results show that it can enlarge the load range and achieve a benefit of compactness. Some key instantaneous data measurements including speed and inlet temperature are discussed and a new method of phase shift is introduced. Using the newly developed test rig, an automotive turbocharger turbine is measured under two pulse frequencies of 40 and 60 Hz. The instantaneous mass flow and efficiency maps are obtained with the instantaneous data measurement, and the obvious hysteresis surrounding the steady curve was also found.

Development length of sinusoidally pulsating laminar pipe flows in moderate and high Reynolds number regimes

Recent studies on laminar, fully-developed, sinusoidally pulsating pipe flows have revealed the existence of a unique signature map that can be used for the measurement of the arbitrary time-varying, instantaneous mass flow rate from the recorded axial pressure gradient data and vice versa. This measuring technique is, however, valid for the hydrodynamically fully-developed flow of an incompressible fluid. The present study, therefore, deals with the numerical evaluation of the required development length as functions of the mean Reynolds number, the amplitude of mass flow rate pulsation and the pulsation frequency in the moderate and high Reynolds number regimes. The investigation shows that in the low-frequency, quasi-steady regime, the instantaneous variations of L/D can be predicted by the steady-state results for corresponding instantaneous Reynolds numbers. On the other hand, at higher pulsation frequencies, considerable deviation from the pure sinusoidal signal occurs for the development length and its amplitude decreases with increase in pulsation frequency. Finally, using the results of the present simulations, a simple correlation is proposed that can be used in order to predict the maximum development during a cycle as functions of ReM,m˙A∗ and F.

Analysis of the effects of heat sink temperature on single-phase natural circulation loops behaviour

During the past years, several authors performed numerical and experimental studies on single-phase natural circulation loops (thermosiphons-NCL). However the problem of the loop stability, which is of interest in many industrial applications, cannot be considered solved.This paper is focused on the evaluation of the instantaneous mass and heat flow rates in the main loop sections.The available experimental apparatus is provided with a heat sink which can be feed with cooling fluid at controlled temperature. In this way the NCL mean temperature and heat flow rate can be varied independently.A set of CFD simulations with various heat sink temperatures, at fixed heat flow rate, has been carried out in order to improve the comprehension of the data collected during the experimental campaigns.

Replicating Instantaneous Cylinder Mass Flow Rate with Parallel Continuously and Discretely Actuating Intake Plenum Valves

Replicating Instantaneous Cylinder Mass Flow Rate with Parallel Continuously and Discretely Actuating Intake Plenum Valves

Proposed method for measurement of flow rate in turbulent periodic pipe flow

The present investigation deals with a previously proposed flow metering technique for laminar, fully-developed, time-periodic pipe flow. Employing knowledge of the pulsation frequency-dependent relationship between the mass flow rate and the pressure gradient, the method allows reconstruction of the instantaneous mass flow rate on the basis of a recorded pressure gradient time series. In order to explore if the procedure can be extended for turbulent flows, numerical simulations for turbulent, fully-developed, sinusoidally pulsating pipe flow with low pulse amplitude have been carried out using a ν2-f turbulence model. The study covers pulsation frequencies, ranging from the quasi-steady up to the inertia-dominated frequency regime, and three cycle-averaged Reynolds numbers of 4360, 9750 and 15400. After providing the theoretical background of the flow rate reconstruction principle, the numerical model and an experimental facility for the verification of simulations are explained. The obtained results, presented in time and frequency domain, show good agreement with each other and indicate a frequency dependence, similar to that used for the signal reconstruction for laminar flows. A modified dimensionless frequency definition has been introduced, which allows a generalised representation of the results considering the influence of Reynolds number.

The Impact on Drug Mass Flow Rate of Interrupting and Resuming Carrier Fluid Flow

Stopping and resuming carrier fluid flow can lead to potentially dangerous transient disturbances in drug mass flow rate. We compared the impact of 2 infusion sets, one with very low dead-space volume and the other with greater dead-space volume, on the amount of drug delivered during stop-and-go carrier fluid flows. Two infusion sets, both with antireflux, connected to an angiocatheter and with dead-space volumes of 6.185 mL and 0.071 mL, respectively, were assessed. Two protocols were studied: carrier fluid flow of 90 mL/h associated with noradrenaline infused at 7 mL/h and carrier fluid flow of 350 mL/h with a noradrenaline infusion flow of 65 mL/h. During both protocols, the carrier fluid was stopped and resumed at the same rate 30 minutes later. Effluent noradrenaline concentration was measured using UV spectrophotometry. Flow change efficiency was calculated from the ratio of the area under the experimental mass flow rate curve to the area under the theoretical instantaneous mass flow rate curve. For both flow rate conditions, flow change efficiency was significantly different for the 2 infusion sets during the 10-minute period after stopping carrier fluid flow and the 10-minute period after restarting it. The major phenomena were sudden decreases in drug delivery after stopping carrier flow and sudden, temporary increases when it was resumed. The very low dead-space volume infusion set resulted in significant reduction in changes in drug delivery compared with the standard set, even at high flow rates. The use of a very low dead-space volume set attenuates disturbances in drug delivery caused by interrupting and resuming carrier fluid flow.