Cold Flow Simulation Research Articles

0/1 and 3 - dimensional cold flow analysis of a diesel engine: A case study

Gas motion in the engine cylinder plays a critical role in diesel engines' air-fuel mixing and combustion processes. Moreover, it influences the engine's performance, emissions, and heat transfer. The intake air motion regulates the main phases of the flow in the cylinder, which is characterized by swirl, squish, and turbulence. Inducing swirl and tumble in the intake process provides high turbulence levels at ignition, resulting in more effective flame speeds and better combustion for lean air-fuel ratios or with EGR. Computational fluid dynamics (CFD) software is used to enhance in-cylinder flow characteristics. In this study, a cold flow simulation of a naturally aspirated, direct injection diesel engine was conducted with different piston bowls using AVL Fire M R2022.2. Swirl, tumble, and TKE parameters were investigated to make a detailed analysis of the in-cylinder flow for the relevant engine. Contrary to the expectation, the swirl ratio for the Piston B configuration is less than that for the original piston configuration. It causes a decrement of swirl ratio compared to the initial piston geometry and the maximum decrement is about 19%. In both cases, the second peak of TKE corresponding to the reverse-squish is around at the -30 CA and the difference between the curves is about ±8%.

Experimental study on the life and performance of an improved DC arc plasma torch

A novel DC arc plasma torch is designed in this paper in order to reduce the electrode erosion, and a series of experiments are carried out to investigate how to improve the lifetime and performance of the nitrogen DC arc plasma torch. The analysis of voltage characteristics of the plasma torch indicates that the interelectrode insert can increase the average arc voltage and the sudden expansion structure can reduce the voltage fluctuation, which is helpful to improve the working stability to some extent. The spectrum characteristics at the plasma torch outlet and the cold flow simulations show that the dual shielding gas mainly act near the anode and can effectively cover the entire anode wall. Combining the shielding gas distribution with anode heat transfer processes in argon and nitrogen plasma torch, it is inferred that argon shielding gas plays an important role on reducing the anode heat transfer processes in nitrogen plasma torch, which can effectively suppress the anode erosion. The life testing experimental results find that there is no significant erosion of the cathode, anode, and interelectrode insert after cumulative working time exceeding 20 h. The maximum nitrogen plasma jet length can reach ∼35 mm with the outlet jet temperature of about 20 000 K at the current of 100 A and nitrogen gas flow rate of 10 slm. The maximum average specific enthalpy and thermal efficiency are respectively about 14 MJ kg−1 and 75% in the nitrogen plasma torch. Therefore, this newly designed DC arc plasma torch not only can suppress the electrode erosion but also has good working performance, which is expected to have excellent application prospects.

Impact of Ablation Based Self Blast Nozzles on Load Break Switch Current Interruption Performance

In this contribution, SF6 free ablation assisted medium voltage load break switchgear, has been investigated. In these switches, gases generated by the arc polymer interactions are trapped in expansion chambers and are released back onto the arc at the current zero crossing. This increases the current interruption capability of the switch without the use of additional mechanical parts, as opposed to using a puffer to blow on the arc. Existing self-blast research, in medium voltage load break switchgear, has focused on blowing axially or tangentially onto the arc in a cylindrical arcing channel. More geometries are possible. In this paper, alternative self-blast blow-position and the presence of obstructions in the arcing channel have been investigated experimentally and with cold flow simulation. It has been determined that blowing right onto the arc centre is not optimal for cooling the arc, and that the presence of an obstruction in the arc channel is beneficial to arc interruptions.

Modelling and Simulation of Micro Gas Turbine Performance and Exhaust Gaseous

Numerical simulation of cold flow and explosion in a Capstone C30 micro gas turbine is simulated using OpenFOAM. This study is aimed to investigate the combustion of non-premixed methane/air inside a micro gas turbine. The combustion characteristic inside a micro gas turbine with 100% methane is assumed for the fuel is studied with a three-dimensional model of micro gas turbine. The velocity of the flow increases significantly in the explosion simulation where the combustion of non-premixed methane/air mixture is initialised. The temperature in the micro gas turbine increased to 2400K at the downstream of inlets and reduces to 1500K at the combustion zone. High concentration of CO and CO2 is in the main reaction zone. The fraction of water vapours and hydroxyl on the other hand is lower compared to other species.

Numerical Simulation of HCCI Combustion Fuelled with Gasoline + Methyl Tert-Butyl Ether Blend

Background: Homogeneously charged compression ignition (HCCI) engines are generally popular for low production of NOx and Soot formation, also consuming lower fuel as compared with conventional gasoline and diesel engine. Objectives: In this study, the compression ignition engine (CI) was simulated in HCCI mode fuelled with Gasoline and Methyl tert-butyl ether (MTBE) blends, and the analysis was carried out in similar operating conditions as experimentation carried out. Methods: The chamber pressure was maintained at 2 bar, and the air-fuel ratio was maintained at2.75. The optimal blend for MTBE was fixed as 15 vol % (MTBE 15), and the measured properties of the blends were used in the simulation. ICE simulation module in ANSYS WORKBENCH was used for this current simulation. Both cold flow and combustion simulations were carried out and the results indicate velocity indie the cylinder, cylinder pressure, and temperature distributions for two cases such as gasoline and gasoline with MTBE15. Findings: The average velocity was found high with the MTBE blend, whereas in-cylinder pressure was found low with MTBE blend than with gasoline. The temperature inside the cylinder pressure was found higher with gasoline than MTBE blend. The deviation between the experimentation and simulation was found low. Novelty: The simulation provides a better understanding of the combustion phenomena when gasoline is mixed with MTBE and utilized in a diesel engine at HCCI mode. Keywords: CFD; MTBE; Gasoline; HCCI; Emission reduction

Cold flow simulation for an Internal Combustion Engine with swirl flaps

The paper aims at CFD analysis of engine cold flow when swirl flaps are used. The CFD analysis was performed using a RANS-RNG turbulence model to predict the evolution of engine cold flow at different engine speeds for two operating conditions with swirl flaps and without swirl flaps. The results show that swirl flaps can increase the average turbulent kinetic energy by up to 30% for a speed range of 1000 - 2000 rpm. However, over 3000rpm swirl flaps will worsen volumetric efficiency due to the change in the cross section of fluid flow to the cylinder.

Cold flow simulation for a S.I. engine with shrouded intake valve

The aim of the work is to analyse the impact of the intake valve design on the cold flow of internal combustion engines. Two shrouded intake valves and one basic intake valve were used for the analysis. Tests have been carried out for a wide range of speeds. The two models of shrouded valves use different concepts, and to increase swirl and tumble turbulence respectively. The results of the simulation show a clear increase in turbulence, sometimes at the cost of decreasing the volume efficiency.

Full-loop CFD simulation of lignite Chemical Looping Gasification with phosphogypsum as oxygen carrier using a circulating fluidized bed

The excellent gas-solid mixing efficiency of the Circulating Fluidized Bed (CFB) makes it the recommended choice for coal Chemical Looping Gasification (CLG). In this paper, a 3D Computational Fluid Dynamics (CFD) full-loop model with multiphase distribution was developed to investigate the fluidization behavior and the CLG performance in CFB. Cold flow simulations show that particle size, static particle stock and inlet gas velocity were critical to the CFB stable operation. The optimal conditions for this system were: a static particle stock of 0.300 m, a particle size of 150 μm, and an inlet gas velocity lower than 0.2 m s−1 was recommended. Thermal flow simulations show that increasing the temperature increased the syngas yield. However, extremely high temperatures inhibit the H2 production. The contribution of CO production to syngas production was particularly obvious. To ensure sufficient H2 production, the molar content of water vapor and the PG/lignite molar ratio should be controlled at approximately 0.3 and 0.2, respectively. Cold flow model was extended to thermal simulation. This would lead to an undesirable phenomena, which should be corrected according to the kinetic model. The simulation results were in a well agreement with the experimental results, which verified the validity of the simulation model.

Numerical simulation through Fluent of a cold, confined and swirling airflow in a combustion chamber

The study focuses on modelling a cold, confined and swirling airflow in a magnesium burner. Direct observations of the magnesium combustion in the combustion chamber proved the existence of a significant recirculation zone in the burner. Before modelling the high flame temperature and the turbulent mixture of solid fuel and products in this burner, the correct simulation of a high swirl cold flow and the creation of a recirculation zone is a crucial first step. Experimental measurements were made placing a hot-wire anemometry at different positions in a PMMA replica of the burner, to validate the simulation results returned by the Fluent software. In a low swirl case (S=0.13), simulations performed using different eddy viscosity models were compared and the standard k-ɛ model was proved to more accurately predict the velocity profiles and the central recirculation zone. In a high swirl case (S=2.94), the turbulence and its anisotropy were too strong and the RSM model was proved to more accurately predict the position, size and shape of the central toroidal recirculation zone. Important errors were still observed for the velocity values. Higher discretization orders (second- or higher-order) could not be used in this case, due to induced numerical instabilities.

Multiphase Computational Fluid Dynamics Simulation of Air and Fuel Reactors of Chemical Looping Combustion

The current work presents the simulations of the chemical looping combustion process where the detailed hydrodynamic study of the air reactor and the reactions inside the fuel reactor have been carried out simultaneously. Cold flow simulation of air reactor is performed using Eulerian-Lagrangian dense discrete phase model incorporated with the kinetic theory of granular flow while discrete phase model is used for the investigation of reaction inside the fuel reactor. Hematite is selected as an oxygen carrier because of its active nature of being oxidized and reduced easily. A maximum pressure gradient of 181 kPa is observed between the bottom and top regions of the air reactor which shows maximum turbulence effect and chaotic nature of gas-solid flow in these regions. An average pressure gradient of 75 kPa is obtained between the outlet and inlet of the air reactor which is favorable for particle movement. The circulation rate of hematite is stabilized after 75 s of the particle injection in the air reactor. The analysis of reactions inside the fuel reactor shows the complete formation of CO2 and H2O after 20 s of the reactor operation.

Liftoff of Propane - Air Diffusion Flames By Axis Symmetric Co-flow Air Injection

Combustion of gas with diffusion system is widely used in many residential gas appliances like stove, engine furnaces and industrial furnaces. Phenomenon of lifted flame is often happened at diffusion flame where the stream of fuel and air into combustor flow separately. Hence the combustion process needs time so that mixing of air and fuel reach the condition ready for burnt. This condition make the burner tip protected from high thermal load and more safe to operate. In this paper, propane was ejected into quiescence air through nozzle having 1.8 mm holes diameter. Fuel flow rate was increased until liftoff conditions exceed; hereinafter flow rate of fuel was made constant at 69 ml/s and air was ejected around of fuel with axis symmetric flow. Liftoff behavior of diffusion flames was investigated for various air flow rate: 17.9 ml/s – 89.9 ml/s. Lifted distance decreased from 130 mm to 90 mm when air was injected with flow rate of 19.1 ml/s, however, it increased to 100 mm when air flow rate increased to 35.9 ml/s. Cold-flow simulation showed the moderate air flow rate give a faster density degradation at axial line compared to larger air flow rate. It means moderate flow rate of air support a better air-fuel mixing than faster one.

Investigation of Pobeda furnace bubbling zone physics using cold modeling method Part 2. Hydro-gas dynamics of liquid blowing with gas using bottom gas-protected lance

The cold flow simulation of the Pobeda furnace bubbled bath hydro-gas dynamics was performed using the bottom lance in a protective gas shell. It was shown that gas infusion into liquid at Ar = 5÷60 is carried out in pulse-coupled mode. The gas-liquid interaction area was investigated at Ar = idem for separate and joint air egress through ring and round nozzles. A two-phase zone was formed in liquid that consisted of a «leg» featuring different geometrical shape, a cavity and a gas-liquid layer over the bath surface at all considered Ar values. The most peculiar features of blowing zone formation, flame configuration and its structure depending on blow injection configuration and Ar values were found out. It was detected that ejected liquid prevails in the cavity structure at intensive blowing through the lance center and ring gap, and its content increases as gas flow rate rises in the shell, and the «leg» near the nozzle exit consists of the gas phase. An assumption was made that the presence of additional sulfide melt amount in the oxidative jet provides more complete magnetite destruction in the bath volume and protective skull formation in close proximity to the nozzle. Sizes of most indicative geometrical areas of flame were quantified, and they demonstrated periodical and extreme jet spread behavior in liquid. Empirical equations were obtained that describe the relation between maximum longitudinal and transverse «leg» sizes at dynamical conditions of blow injection into the shell (Ar shell ) and central tube (Ar center ) for two value ranges Ar shell ≥ Ar center and Ar shell ≤ Ar center . It was found that blow injection into the shell increases «leg» extension velocity on the nozzle exit up to 137 mm/s. The dependence of average splash lift height (H avg , m) above the calm bath surface was defined, which is H avg = 0.027(Ar shell + Ar center ) 0.27 within 25 ≥ Ar shell ≥ 5 and 60 ≥ Ar center ≥ 12 ranges. Schlichting equation was used to calculate the value of maximum offset from the nozzle surface where the joint axial movement of ring and round jets in liquid is maintained with equal velocities. It is assumed that the protective effect of the bottom lance with the shell appears in the lance belt area over a distance of 7–10 cm from the nozzle exit. It was noted that the cavity after separation from the nozzle moves down vertically, and the countercurrent liquid flow bounding on the cavity front moves in an opposite direction slipping the phase interface with comparable velocity. Due to more intensive changes in the interaction zone transverse size in the nozzle area and noticeable lateral liquid movement it was recommended to take corrective actions to decrease the erosive effect of melt in the Pobeda furnace lance belt at the initial jet development area.

Three-Dimensional Pore-Scale Simulation of Flow and Thermal Non-Equilibrium for Premixed Gas Combustion in a Random Packed Bed Burner

Pore-scale studies of premixed gas combustion in a packed bed is conducted to study the flow and thermal non-equilibrium phenomenon in packed bed. The 3D random packed bed is generated using the EDEM software and solid surface radiation is computed using Discrete Ordinates (DO) model. The simulations are carried out using a commercial software package based on the finite volume method. It is shown that the local variation of species mass fraction, reaction rate et al. in pores near the flame front is significant, the radiation heat flux is transferred layer-by-layer. Cold flow simulation without reaction reveals that flow non-equilibrium is one of the essential characteristics of packing bed and increase in flow velocity leads to intensify non-equilibrium phenomenon. The distributions for content of axial velocity and gas temperature are wave-like shape in the burner and vary with time.

COMBUSTION ANALYSIS OF HCCI ENGINE AT DIFFERENT OPERATING CONDITIONS

Automobile pollution is causing a huge trouble worldwide and there is an urgent need to reduce it. Researches are being carried out for ways of reducing automobile pollution. The most common tool for converting liquid and gas fuel into useful mechanical work is the internal combustion (IC) engine. The explanation for its well-accepted efficiency, economics, longevity, controllability and other competitive alternatives can be explained by its general appearance. NOx and soot formation are due to the heterogeneous non-premixed combustion of high local temperatures and the local oxygen shortage in the traditional direct injection diesel powered engine. The adjustment to the combustion cycle to boost engine output is an alternative to rising engine efficiency and reducing engine emissions. A simulation software with CFD code was implemented in this context. The cold flow of the working conditions for HCCI engine control by creating a comprehensive model. Furthermore, the use of the in-cylinder model potential for cold flow simulation in the SI engine has been demonstrated. All strokes are replicated, pulling, compressing, expansion and exhaust. The Discrete Phase System is used for injecting, evaporating and boiling water, where the simulation depicts the working conditions of the engine for unravelling the flow physics taking place.

Transient Cold Flow Simulation of Fast-Fluidized Bed Air Reactor with Hematite as an Oxygen Carrier for Chemical Looping Combustion

Chemical looping combustion (CLC) is the most reliable carbon capture technology for curtailing CO2 insertion into the atmosphere. This paper presents the cold flow simulation results necessary to understand the hydrodynamic viability of the fast-fluidized bed air reactor. Hematite is selected as an oxygen carrier due to its easy availability and active nature during the reactions. The dense discrete phase model (DDPM) approach using the commercial software Ansys Fluent is applied in the simulation. An accurate and stable solution is achieved using the second-order upwind numerical scheme. A pressure difference of 150 kPa is obtained between the outlet and inlet of the selected air reactor, which is necessary for the movement of the particle. The stable circulating rate of hematite is achieved after 28 s of particle injection inside the air reactor. The results have been validated from the experimental results taken from the literature.

Experimental Investigation on Combustion Characteristics of Hybrid Rocket Fuels with Multi-Angle Diverging Injector

Injection pattern of the oxidizer injected into the combustion chamber is a significant factor in evaluating the performance of a hybrid rocket. In the hybrid rocket combustion process, oxidizer flows over the solid fuel grain surface, leading to a turbulent diffusion boundary layer formation and the flame is established inside the boundary layer. The heat transfer from flame to the fuel surface leads to pyrolysis of the fuel. The heat fluxes, due to pyrolysis, block the heat transfer further to the fuel surface, thus reducing the fuel regression rate. An attempt has been made in this paper to design and study the effect of the multi-angle diverging injector on the enhancement of the fuel regression rate and combustion efficiency of the hybrid rocket. The designed injector was compared with a shower head injector i.e., axial injector. The fuels used were paraffin wax and polyvinyl chloride (PVC) with gaseous oxygen as oxidizer. The effect of formation of the re-circulation zone and flow velocity were studied numerically by a cold flow simulation using ANSYS-Fluent software. It has been observed that direct impingement of the multi-angle diverging injector produces velocity in three directions, leading to distortion of the boundary layer. An increase of 8% in the average fuel regression rate for PVC fuel grain and 36.14% for paraffin wax fuel grain was observed, as compared to the shower head injector for the same oxidizer mass flow rate. A combustion efficiency increase of 38% and 14% was also observed using multi-angle diverging injector for PVC and paraffin wax fuel grains, respectively. A reduction in sliver and uniform fuel consumption was also observed using the novel multi-angle diverging injector.

To investigate the variation in Swirl Ratio by changing the Valve Lift of an Internal Combustion Engine

In today’s scenario, humans are facing the issue of the global pollution crisis and the authorities worldwide have implemented stringent norms. Poor air quality has a hazardous impact on the lives of the people. The major emissions from exhaust pipe contain Particulate Matter (PM), Nitrogen Oxides (NOx), Carbon Monoxide (CO) and greenhouse gases which exploit the environment due to which the air quality index is degrading. Furthermore, these exhaust gases can trigger acute diseases in humans like headaches, nausea, fatigue, etc. A huge amount of research and development is being carried out on reducing the harmful emissions by changing the properties of fuels, and geometry or mechanical changes in the engine itself can further hold on the emissions well within the range. One of the methods is to improve the swirl formed in the combustion chamber. Swirl motion is the intentional spinning of the air that promotes even mixing of fuel and air when fuel is introduced to the cylinder during intake. Better swirl formed helps in efficient combustion which subsequently leads to lesser emissions. This research paper studies the change in swirl ratio by varying the valve lift of an internal combustion engine. The observations were made through simulations done in ANSYS™ 17.0 FLUENT using Cold Flow Simulation in IC ENGINE module. Meaningful curves of swirl ratio obtained for different valve lifts are then compared.

Cold Flow Simulation of a 30 kWth CFB Riser with CPFD

A 30 kWth Circulating fluidized bed (CFB) combustor is experimentally and numerically investigated under cold flow conditions. Barracuda software based on Computational Particle Fluid Dynamics (CPFD) method is utilized for simulations. The influences of bed inventory and drag model on flow hydrodynamics were investigated considering pressure and velocity profiles and particle concentration. Two advanced drag models, namely Energy minimization multi-scale (EMMS) and Wen-Yu/Ergun were selected for this study. The simulations were performed with initial bed material masses of 3.79, 4.55 and 5.20 kg corresponding to 2.5, 3 and 3.5 diameters height of riser, respectively. With increasing bed inventory pressure drops and solid concentration increase. The axial particle velocities slightly change with bed inventory. The comparison of simulation results with experimental measurements was resulted in good agreement (

Determination of optimal spacing between transverse jets in a SCRAMJET engine

A SCRAMJET engine typically has multiple transverse fuel injectors with a flame holder. In this study, we consider a two-jet SCRAMJET engine design configuration that uses the low speed recirculation region created by a backward facing step as a flame holder. The effect of spacing between the transverse fuel injectors on the performance of a SCRAMJET engine has been studied using cold-flow simulations. The position of the leading jet is kept fixed at the end of the recirculation zone as suggested by previous studies and the second jet is placed at various locations downstream in the distinct flow regions formed behind the leading jet. It is assumed that the two jets are identical in dimensions and flow. The spacing between the jets is expected to play a significant role in determine the performance of the SCRAMJET engine. Three-dimensional simulations have been performed, using Menter's SST model in our in-house parallel 3-D RANS unstructured grid CFD solver. The mixing of inlet air and the injected air-fuel in such a SCRAMJET configuration is augmented by the interaction of the transverse under-expanded jet with the incoming supersonic cross-flow through the generation of strong streamwise vorticity. The performance and mixing of the combustor have been quantified for each of the distinct configurations. It is observed that they are indeed affected by the spacing between the jets. From the results presented in this paper, the optimal location for the second jet is at the end of the zone over which the lateral momentum of the first jet is dominant in affecting the jet penetration into the streamwise flow.

Influence of gas dynamics on arc dynamics and the discharge power of a rotating gliding arc

This work reports the design and characterization of a rotating gliding arc (RGA) reactor developed with novel electrode configuration. This RGA uses gas swirl discs having ‘tangential gas entry ports/holes’ (NH) to achieve arc rotation and does not employ any external magnets. This work investigates the effect of gas dynamics on (1) arc dynamics such as the arc’s rotation and shape; (2) voltage fluctuation pattern; and (3) plasma discharge power for the designed RGA. Experiments were conducted using argon as the plasma forming gas with (a) two gas swirl discs (NH = 3 and 12) and (b) three different gas flow rates (Q = 5, 25 and 50 LPM) as control parameters. Cold flow simulation (CFS) studies using a multidimensional solver were used to understand gas dynamics. The arc rotational frequency (farc) measured from (1) a high-speed camera (HSC) and (2) fast Fourier transform (FFT) analysis of voltage, shows linear dependency on the Reynolds number (Re) calculated from CFS, with an R2 = 0.98. The agreement improves (R2 = 0.99) by applying linear fit only for the cases having turbulent Re. A close match between gas rotational frequency (fgas) calculated from CFS and experimentally measured farc is seen. The turbulent regime of the gas flow causes: (1) twisting and bending of the arc; (2) sawtooth-like voltage fluctuations with irregular and non-sinusoidal waveform; and (3) arc blow off. The high-frequency voltage fluctuations were reduced/absent when the flow Re reduced from ≈6.0 × 104 to ≈1.0 × 104. These findings establish that the gas dynamics, in particular, the bulk flow phenomenon of the gas, has an explicit influence on arc dynamics of the RGA reactor. This novel RGA design has the potential to replace magnetically driven rotating gliding arc systems.