Tumble Ratio Research Articles

Cycle-to-cycle variation analysis of in-cylinder flow in a gasoline engine with variable valve lift

In spark ignition engines, cycle-to-cycle variation (CCV) limits the expansion of the operating range because it induces the load variations and the occurrence of misfire and/or knock. Variable valve actuation (VVA) or variable valve lift (VVL) has been widely used in SI engines to improve the volumetric efficiency or to reduce the pumping losses. It is necessary to investigate the CCV of in-cylinder gas motion and mixing processes in SI engines with VVA/VVL system. This study is aimed to analyze the CCV of the tumble flow in a gasoline direct injection (GDI) engine when VVL is employed. Cycle-resolved digital particle image velocimetry (CRD-PIV) data were acquired for the in-cylinder flow field of a motored four-stroke multi-valve GDI optical engine. The CCV of in-cylinder gas motion with a series of valve profiles and different maximum valve lift (MVL) was analyzed, including cyclic variation characteristics of bulk flow (tumble centre and tumble ratio), large- and small-scale fluctuation, total kinetic energy, and circulation. The results show that the CCV of the in-cylinder flow is increased with reduced MVL. With lower MVLs, stable tumble flow cannot be formed in the cylinder, and the ensemble-averaged tumble ratio decreases to zero before the end of the compression stroke due to violent variation. In addition, the evolution of the circulation shows larger variation with lower MVLs that indicates the ‘spin’ of the small-scale eddy in the flow field presents violent fluctuation from one cycle to another, especially at the end of the compression stroke. Moreover, the analyze of the kinetic energy indicates the total energy of the flow field with lower MVLs increases significantly comparing with higher MVL conditions due to the intake flow jet at the intake valve seat in the intake stroke. However, the CCV of the in-cylinder flow becomes more violent under lower MVL conditions, especially for the low-frequency fluctuation kinetic energy. Thus, present strong tumble flow can lower the CCV of the air motion. It is necessary to manage strong tumble or other bulk flow (such as swirl flow) in order to improve the stability of ignition and combustion for GDI engines with VVL, especially at the lower MVL conditions.

Computational Study on the Effect of Inlet Port Configuration on In-Cylinder Flow of a Motored Four-Valve Internal Combustion Engine

A numerical simulation is carried out to investigate the effect of inlet port cross-section geometry on the in-cylinder flow of a motored four-valve, single-cylinder, four-stroke internal combustion engine during the intake and compression strokes. The simulation is performed by solving the three-dimensional time-dependent compressible RANS equations in conjunction with the standard k-e turbulence model using the commercial CFD software STAR-CD. To simulate the reciprocating piston motion, the governing equations are solved on a multiblock unstructured moving mesh. Two inlet port cross-section geometries are considered in the present study: circular cross section and elliptical cross section. The emphasis of the present study is on the tumble motion. The evolution of the flow structure and the quantified strengths of the tumble motions, namely, tumble ratio and cycle-averaged tumble ratio in the symmetry and offset planes for the two cases, are presented. It is found that inlet port with elliptical cross-...

Effect of Engine Speed on In-Cylinder Tumble Flows in a Motored Internal Combustion Engine An Experimental Investigation Using Particle Image Velocimetry

Now-a-days, the stratified and direct injection spark ignition engines are becoming very popular because of their low fuel consumption and exhaust emissions. But, the challenges to them are the formation and control of the charge which is mainly dependent on the in-cylinder fluid flows. Today, an optical tool like particle image velocimetry (PIV) is extensively used for the in-cylinder fluid flow measurements. This paper deals with the experimental investigations of the in-cylinder fluid tumble flows in a motored internal combustion engine with a flat piston at different engine speeds during intake and compression strokes using PIV. The two-dimensional in-cylinder flow measurements and analysis of tumble flows have been carried out in the combustion space on a vertical plane at the cylinder axis. To analyze the fluid flows, ensemble average velocity vectors have been used. To characterize the tumble flow, tumble ratio has been estimated. From the results, it is found that the tumble ratio mainly varies with crank angle positions. At the end of compression stroke, maximum turbulent kinetic energy is more at higher engine speeds. Present study will be very useful in understanding the effect of engine speeds on the in-cylinder fluid tumble flows under real engine conditions.

Aerodynamic control inside an internal combustion engine

The aim of this study is to quantify the impact of intake port geometry on in-cylinder flow. The in-cylinder aerodynamics of an optical engine has been characterized using particle image velocimetry (PIV). Many geometries have been tested and their impact has been evaluated by an estimation of the tumble ratio, an analysis of the cycle-to-cycle variations and a flow structure analysis based on proper orthogonal decomposition (POD). Such a tool allows the reduction of the PIV database in order to consider in-cylinder aerodynamic control by a device placed in the intake port. This simplification is based on a reduction of the number of modes and a polynomial fitting of the POD coefficients. Thus, some new geometries have been numerically created, and their impact on the tumble ratio has been evaluated.

Characterization of Flow through the Intake Valve of a Single Cylinder Engine Using Particle Image Velocimetry

This paper deals with the investigations of the in-cylinder flow pattern around the intake valve of a single-cylinder internal combustion engine using Particle Image Velocimetry (PIV) at different intake air flow rates. The intake air flow rates are corresponding to the three engine speeds of 1000, 2000 and 3000 rev/min., at all the static intake valve opening conditions. In this study, in-cylinder flow structure is characterized by the tumble ratio and maximum turbulent kinetic energy of the flow fields. In addition, at two specified lines of the combustion chamber, the radial and axial velocity profiles have been plotted. From the results, it is found that the overall airflow direction at the exit of the intake valve does not change significantly with the air flow rate and intake valve opening conditions. The tumble ratio increases with increase in intake valve opening and not much affected by the change in the air flow rates. It is also found that, the variations of the velocity profiles at the two specified lines are smooth at full intake valve opening irrespective of the air flow rate. Also, their magnitudes increase with increase in the intake valve openings at all the air flow rates. The in-cylinder flow analysis carried out in this study may be useful for optimizing the intake valve opening of an internal combustion engine with respect to it’s speed.

INFLUENCE OF AUXILIARY INTAKE VALVE WITH VARIABLE TIMING ON SPARK IGNITION ENGINE PERFORMANCE

A new variable valve timing strategy based on using an auxiliary valve having a variable timing (VVT) is used in this study. The valve is driven by a new VVT mechanism achieving valve duration and opening angle variations. The auxiliary valve acts as intake valve. Experiments and simulation models are carried out at different loads. The results show improvements in brake thermal efficiency, fuel consumption, volumetric efficiency, residual gas fraction and engine emissions over the whole range of load. Swirl and tumble ratios are decreased.

Turbulence study in the internal combustion engine

In this paper, we are interested in the study of turbulent and time dependant flow inside a cylinder of an alternative engine through the investigation of the distribution of the turbulent kinetic energy in the whole space of the chamber. This research is carried out during the intake stroke. The arbitrary lagrangian eulerian technique coupled with the finite element method is used to solve the Navier Stokes equations. The turbulence model of the inlet air in the cylinder has a great influence in to the performance of the engine. It governs directly the rate of filling up, the thermal exchanges and the combustion quality. We present distribution of the velocity, pressure and turbulence field inside the engine room. Key words: Turbulence, internal combustion engine, arbitrary lagrangian eulerian, tumble ratio, k-e model, prandtl model, finite element method.

Comparative study of in-cylinder tumble flows in an internal combustion engine using different piston shapes—an insight using particle image velocimetry

This paper deals with the experimental investigations of the in-cylinder tumble flows in a single-cylinder engine with five different piston crown shapes at an engine speed of 1,000 rev/min., during suction and compression strokes under motoring conditions using particle image velocimetry. Two-dimensional in-cylinder tumble flow measurements and analysis are carried out in combustion space on a vertical plane passing through cylinder axis. Ensemble average velocity vectors are used to analyze the tumble flow structure. Tumble ratio and average turbulent kinetic energy are evaluated and used to characterize the tumble flows. From results, it is found that at end of compression, pentroof-offset-bowl piston shows about 41 and 103% improvement in tumble ratio and average turbulent kinetic energy respectively, compared to that of flat piston. The present study will be useful in understanding effect of piston crown shapes on nature of the in-cylinder fluid tumble flows under real engine conditions.

Manipulating Tumble and Swirl Flows in Cylinder of a Motored Four-Valve Engine by Inlet Deflection Valve

AbstractEffects of the inlet-stream deflection on the temporal and spatial evolution processes of the in-cylinder flow structures (tumble/swirl) and turbulence intensities in the symmetry and diametral planes of a motored four-valve, four-stroke engine are diagnosed by using a particle image velocimeter. The inception, establishment, and evolution of the tumbling/swirling vortical flow structures during the intake and compression strokes in the engine cylinder with/without inlet-stream deflection are depicted and compared. Quantitative strengths of the rotating vortical flow motions are presented by dimensionless parameters (tumble and swirl ratios) which can represent the mean angular velocity of the vortices in the target plane. The turbulence intensity is calculated by using the measured time-varying velocity data. The results show that by deflecting the inlet air-stream the tumble and swirl ratios of the in-cylinder flow are appreciably increased by about 0.1 and the turbulence intensity is increased by about 5 ∼ 10%.

In-cylinder tumble flows and performance of a motorcycle engine with circular and elliptic intake ports

The temporal and spatial evolution processes of the flows in the cylinder of a four-valve, four-stroke, single cylinder, reciprocating motorcycle engine installed with the elliptic and circular intake ports were experimentally studied by using the particle image velocimetry (PIV). The engine was modified to fit the requirements of PIV measurement. The velocity fields measured by the PIV were analyzed and quantitatively presented as the tumble ratio and turbulence intensity. In the symmetry plane, both the circular and elliptic intake ports could initiate a vortex around the central region during the intake stroke. During the compression stroke, the central vortex created in the cylinder of the engine with the circular intake port disappeared, while that in the engine cylinder with the elliptic intake port further developed into the tumble motion. In the offset plane, weak vortical structures were initiated by the bluff-body effect of the intake valves during the intake stroke. The vortical structures induced by the elliptic intake port were more coherent than those generated by the circular intake port; besides, this feature extends to the compression stroke. The cycle-averaged tumble ratio and the turbulence intensity of the engine with the elliptic intake port were dramatically larger than those of the engine with the circular intake port. The measured engine performance was improved a lot by installing the elliptic intake port. The correlation between the flow features and the enhancement of the engine performance were argued and discussed.

CFD Analysis of VVT/VVA on the Gas Exchange and Fuel-Air Mixing in a Diesel Engine

A three-dimensional simulation was carried out for investigating effects of negative valve overlap (NVO) on gas exchange and fuel-air mixing processes in a diesel homogeneous charge compression ignition (HCCI) engine with early fuel injection. It was found that the case with longer NVO produced a stronger swirl motion and a more significant vortex below the intake valve due to the high annular jet flow through the valve curtain area during the intake stroke. However, there was not much difference in the values of swirl ratio, tumble ratio and turbulence intensity between different NVOs at the end of compression stroke. It was also seen that enlarged NVO not just increased in-cylinder temperature but also improved the temperature homogeneity. With increased NVO, there is a bigger spray shape and more droplets exist in gaps of sprays. This demonstrates that stronger turbulence intensity and higher temperature homogeneity with higher NVO improve fuel vaporization and air-fuel mixing.

Investigation of the grid and intake-generated tumble on the in-cylinder flow in a compression ignition direct-injection engine

The in-cylinder flow field was numerically investigated for a four-valve per cylinder Caterpillar diesel CAT3401 engine. The computer program used was the KIVA3V code developed by Los Alamos National Laboratory. To assess the effect of modelling assumptions made during the domain discretization, three grid models were developed. The first grid or the ‘complete’ grid was a full 360° mesh with moving valves, intake ports, exhaust ports, and runners. The second grid was a full 360° mesh without moving valves, intake ports, or exhaust ports. The third grid assumed that the in-cylinder flow field was periodic and a 60° mesh was generated to accommodate one of the six centrally located fuel injectors. It also neglected the valves and the intake and exhaust ports. The simplification of the grids is to reduce the massive computational and memory requirements to model these flows. For the complete grid, the computation was initiated when the piston was at the top dead centre location on the intake stroke. For the second and third grids, the computation was initiated after the intake valve had closed. Complex three-dimensional vortical flow structures or tumble is developed during the intake stroke. These structures were clearly shown when the complete grid was used. By comparing the solution of the complete grid with the solutions of the second and third grids, it was seen that important in-cylinder flow information is lost. To overcome this deficiency, a new parameter, namely the initial tumble ratio, was embedded into the standard KIVA3V code by the present authors. When the simplified second grid is used in conjunction with the initial tumble ratio option, an in-cylinder flow pattern similar to that which was computed with the complete grid was obtained. This indicates that the new option significantly improves the accuracy of in-cylinder flow prediction when the moving valves and intake or exhaust ports are not modelled. The effects of the values of the initial turbulence kinetic energy (TKEi) and the initial turbulence length scale (SCLi) were also studied. It is found that the suggested value of TKEi used in KIVA3V is too small to predict the actual turbulence kinetic energy in the cylinder when the second and third grids are used. Therefore, a larger value for TKEi is recommended. The effects of the different grids, the new initial tumble ratio, and the different values of SCLi and TKEi on important flow parameters, such as the swirl ratio, the tumble ratio, and the turbulence kinetic energy are compared in detail in this article.

In-cylinder flows of a motored four-stroke engine with flat-crown and slightly concave-crown pistons

The temporal and spatial evolution processes of the in-cylinder flow structures and turbulence intensities in the symmetry and offset planes of a motored four-valve, four-stroke engine during the intake and compression strokes are diagnosed by using a particle image velocimeter. Two pistons of different crown shapes (flat-crown and slightly concave-crown pistons) are studied. The inception, establishment, and evolution of the tumbling vortical flow structures during the intake and compression strokes are clearly depicted. Quantitative strengths of the rotating vortical flow motions are presented by a dimensionless parameter, the tumble ratio, which can represent the mean angular velocity of the vortices in the target plane. The turbulence intensity of the in-cylinder flow is also calculated by using the measured time-varying velocity data. The results show that the flat-crown piston induces higher bulk-averaged tumble ratio and turbulence intensity than the slightly concave-crown piston does because the tumble ratio and turbulence generated by the flat-crown piston in the offset planes during the compression stroke are particularly large. The engine with the flat-crown piston also presents larger torque and power outputs and lower hydrocarbon emission than that with the slightly concave-crown piston. This might be caused by the enhanced combustion in the engine cylinder due to the stronger tumble ratio and turbulence intensity.

Quantification of Volumetric In-Cylinder Flow of SI Engine Using 3-D Laser Doppler Velocimetry ( II )

Simultaneous 3-D LDV measurements of the in-cylinder flows of three different engine setups were summarized for the quantification of the flow characteristics in each vertical or horizontal plane, and in entire cylinder volume. The ensemble averaged-velocity, tumble and swirl motions, and turbulent kinetic energy during the intake and compression strokes were examined from the measured velocity data (approximately 2,000 points for each engine setup). The better spatial resolution of the 3-D LDV allows measurements of the instantaneous flow structures, yielding more valuable information about the smaller flow structures and the cycle-to-cycle variation of these flow patterns. Tumble and swirl ratios, and turbulent kinetic energy were quantified as planar and volumetric quantities. The measurements and calculation results were animated for the visualization of the flow, and hence ease to analysis.

PIV analysis of in-cylinder flow structures over a range of realistic engine speeds

In-cylinder PIV measurements have been performed in a four-valve single cylinder optical gasoline direct injection engine, motored at speeds of 750, 2,000 and 3,500 rpm. Mean vector flow fields have been produced during the latter half of the intake stroke in the symmetry plane between the valve pairs. The flow fields show the development of the in-cylinder flow structures at 1.6, 2.4 and 3.2° crank angle steps for a time period of approximately 5 ms at each of the three engine speeds, respectively. Tumble ratios have been calculated for the available field of view showing a change in the flow structure between 2,000 and 3,500 rpm. This is believed to be caused by an increase in the flow of air traveling underneath the recirculation vortex at the higher engine speed. This translates the vortex position upwards and further to the right when compared to the lower engine speeds.

Cyclic Variability in I.C. Engines : Insights from Particle Image Velocimetry Measurements(S.I. Engines, Combustion Diagnostics)

The cycle-to-cycle variation in the flow field inside a four stroke ignition engine has been studied. The particle image velocimetry (PIV) technique has been used to measure the flow field inside the engine. The measurements have been carried out in a motored engine equipped with suitable access. The measurements have been carried out in both the sectional and the planar directions such that the necessary data for calculating the swirl ratio and tumble motions becomes available. The standard deviations from the ensemble averaged measurements for these two motions have been used as indicators for the cyclic variations in the flow field. The effect of the engine speed, inlet valve shrouding and piston geometry on the cyclic variations in the flow has been assessed. According to the analysis of the measurements, it has been found that increasing the engine speed increases both the swirl ratio as well as the cycle-to-cycle variation. The cyclic variability in the swirl ratio decreases when 120° shrouded inlet valve is used. This trend is reverted when the shroud is increased to 180°. Also the cyclic variability in the tumble ratio increases when using the 120° and 180° shrouded inlet valves. The cyclic variability based on the swirl ratio decreases with wider and less deep piston bowel. On the contrary, the cyclic variability in the tumble motion increases with shallow and wider piston bowel. Also the cyclic variability in the swirl ratio increases as the compression ratio increases.

New evaluation indices for bulk motion of in-cylinder flow through intake port system in cylinder head

The purpose of this study is to find new evaluation indices for the bulk motion of in-cylinder flow instead of the current swirl or the tumble coefficient and ratio using a steady flow test rig on intake port systems. To do this, port flow rig tests were conducted on the double-overhead cam head. Finally, the angular flow coefficient (NA), the inclination angle (γ) the angular flow parameter (PA) and the flow angle (φ) were introduced as new evaluation indices for the bulk motion of in-cylinder flow.

Tumbling flow analysis in a four-valve spark ignition engine using particle image velocimetry

Tumble motion in the cylinder of a four-valve spark ignition (SI) engine with a production-type cylinder head was studied using cross-correlation digital particle image velocimetry (PIV). The in-cylinder flow field was measured on three planes: the vertical symmetric plane of the combustion chamber, the vertical plane through centres of the intake and exhaust valves, and a horizontal plane 12 mm below the cylinder head. Ensemble-averaged mean velocity, velocity fluctuation distribution and cyclic variation of the instantaneous velocity field were analysed. Analysis results show that the tumble vortex is formed in the early stage of the compression stroke and distorted in the late stage of the compression stroke. The tumble centre is nearly in the centre of the cylinder when the tumble forms. Then it moves gradually to the underneath of the exhaust valves as the piston moves up. It is found that the cyclic variation of the tumble motion at a tumble ratio of 0.9 is so great that the ensemble-averaged flow characteristics hardly represent any individual cycle flow behaviours. Distribution of the velocity fluctuation field is inhomogeneous during the whole compression process. As the engine speed changes the large-scale flow structure seems to remain unaffected.

이색 PIV 기술을 이용한 5밸브 가솔린엔진 연소실 내의 유동특성 분석

A 5-valve(intake 3-valve) engine has been developed to increase engine performance. These engines have a high power caused by the decrease of inertia mass of an intake valve and the increase of intake effective area. In this study, in-cylinder flow patterns were visualized with laser sheet method and velocity profiles at near intake valves were inspected by using a two-color PIV. In addition, steady flow tests were performed to quantify tumble ratio of flow-fields generated by a tumble control valve(TCV). Experimental results of steady flow test show that the cure of tumble ratio in intake 3-valve engine farmed as a S shape with valve lift changes. This tendency is different from the one in intake 2-valve engine. Using laser sheet method and two color PIV method, we can find that the intake flow through upper valve increases and the velocity gradient also slightly increases as valve lift increases. From this study, the in-cylinder flow characteristics around intake valves were made clearly.

New evaluation index for bulk motion of in-cylinder flow through intake port system in cylinder head (II)

The variable intake systems recently tend to be adopted in gasoline engines for fuel economy and emission regulation. In the cases, because both swirl and tumble flows are together induced to the cylinder, in-cylinder flow pattern becomes very complicated so that we cannot decide this flow as one major pattern like swirl or tumble. The purpose of this study is to find new evaluation indexes for in-cylinder flow characteristics instead of a current swirl or a tumble ratio at the end of intake stroke using a steady flow test rig. To do this, port flow rig tests were conducted on the DOHC head varying lift of intake valves. Finally, the angular flow parameter PA and the flow angle (φ) were introduced as new evaluation indexes for in-cylinder angular flow characteristics at the end of intake stroke.