Swirl Control Valve Research Articles

Effects of swirl enhancement on in-cylinder flow and mixture characteristics in a high-compression-ratio, spray-guided, gasoline direct injection engine

In this study, the flow enhancement effects of applying a swirl control valve were investigated with particle image velocimetry and simulation using CONVERGE v2.4 program in a high compression ratio, spray-guided, gasoline direct injection engine. This was followed by analysis of varying the spray structure and the mixture preparation process for different swirl control valve angles. The flow intensity was strengthened in the order of swirl control valve angle 45°, 30°, and 0°, and spark plug gap velocities near TDC were increased 1.89, 4.40, and 6.69 m/s in that order. However, the effect was not significant when it was increased to more than 45°. Also, the swirl-dominant flow and the tumble-dominant flow were differentiated based on the relationship between maximum swirl and tumble ratios. In the swirl dominant flow (swirl control valve angle of 0°), more retarded injection timing produced mixture formation in the order of homogenous to mal-distributed to stratified, whereas in the tumble dominant flow (swirl control valve angle of 45°), the order was homogenous to stratified to mal-distributed. It was determined by characteristic period to which the injection timing belonged, and the characteristic period was defined based on the relationship between the intake valve lift and the piston velocity.

Airflow Characteristics Investigation of a Diesel Engine for Different Helical Port Openings and Engine Speeds

Intake airflow characteristics are essential for the performance of diesel engines. However, previous investigations of these airflow characteristics were mostly performed on two-valve engines despite the difference between the airflow of two-valve and four-valve engines. Therefore, in this study, particle image velocimetry (PIV) investigations were performed on a four-valve diesel engine. The investigations were conducted under different engine speeds and helical port openings using a swirl control valve (SCV). The results suggest that the position of the swirl center does not significantly shift with different engine speeds and helical port openings, as the dynamics of the flow remained closely similar. The trends of the airflow characteristics can be best observed during the compression stroke. A higher engine speed increases the angular velocity of the engine more compared to the increase of the airflow velocity and results in a lower swirl ratio of the flow. On the other hand, a higher engine speed leads to a higher mean velocity and the variation of velocity results in a larger turbulence intensity of the flow. Increasing the helical port opening brings a reduction in the swirl ratio and turbulence intensity as more airflow from the helical port disturbs the airflow from the tangential port.

Effect of flame speed on knocking characteristics for SI engine under critical knocking conditions

Engine knock essentially involves the interplay between end-gas auto-ignition and primary flame propagation. However, literature shows inconsistent correlations between turbulent flame speed and knocking intensity. In this study, different levels of turbulent intensity were achieved by modifying in-cylinder swirl ratios, and the effect of turbulent flame speed on knocking characteristics was firstly investigated by using an optical engine under critical knocking conditions. In-cylinder swirl ratios were controlled by a swirl control valve (SCV) and particle image velocimetry (PIV) experiments were employed to quantify the turbulent flow velocity under different swirl ratio conditions. High-speed photography and instantaneous pressure acquisition were synchronously employed for auto-ignition and knocking measurement. The experimental results show that end-gas auto-ignition is a sufficient condition for engine knock and engine knock is strongly associated with the peak heat release rate when auto-ignition occurs. Under critical knocking conditions, fast turbulent flame propagation always results in advanced auto-ignition timing and concentrated heat release and thereby severe auto-ignition. Consequently, the higher flame speed promotes heavier knocking combustion under enhanced turbulent intensity conditions. The current study shall provide useful insights into the nature of engine knock and the regulation of engine combustion.

Effects of the swirl ratio and injector hole number on the combustion and emission characteristics of a light duty diesel engine

In this study, the effects of swirl and the injector hole number were investigated to enhance the mixing of fuel and air. Both experimental and analytical methods were employed. The KIVA code coupled with the CHEMKIN chemistry solver was used to analyze the swirl intensity at various angles of the swirl control valve and experimental results. For the experimental investigation, a 498.75 cc single cylinder engine and a 55 kW AC dynamometer were employed. The experiments were conducted at IMEP values of 6 and 10 bar with 7, 8, 9, and 10 hole injectors. The swirl intensity was varied by opening of the swirl control valve from 0° to 90°.The experimental results demonstrated that the swirl intensity has an effect on the combustion and emission characteristics. An enhanced swirl intensity reduced the PM and CO emissions but increased the NOx emissions and ISFC. An increase of the injector hole number resulted in decreases of the PM and CO emissions along with a an increase of NOx emissions and no significant difference of output. However, the exhaust characteristics with the 10 hole injector deteriorated as the interference increased.

Characteristics of Early Flame Development in a Direct-Injection Spark-Ignition CNG Engine Fitted with a Variable Swirl Control Valve

An experimental study was conducted to investigate the effect of the structure of the induction flow on the characteristics of early flames in a lean-stratified and lean-homogeneous charge combustion of compressed natural gas (CNG) fuel in a direct injection (DI) engine at different engine speeds. The engine speed was varied at 1500 rpm, 1800 rpm and 2100 rpm, and the ignition timing was set at a 38.5° crank angle (CA) after top dead center (TDC) for all conditions. The engine was operated in a partial-load mode and a homogeneous air/fuel charge was achieved by injecting the fuel early (before the intake valve closure), while late injection during the compression stroke was used to produce a stratified charge. Different induction flow structures were obtained by adjusting the swirl control valves (SCV). Using an endoscopic intensified CCD (ICCD) camera, flame images were captured and analyzed. Code was developed to analyze the level of distortion of the flame and its wrinkledness, displacement and position relative to the spark center, as well as the flame growth rate. The results showed a higher flame growth rate with the flame kernel in the homogeneous charge, compared to the stratified combustion case. In the stratified charge combustion scenario, the 10° SCV closure (medium-tumble) resulted in a higher early flame growth rate, whereas a homogeneous charge combustion (characterized by strong swirl) resulted in the highest rate of flame growth.

Influence of swirl ratio on fuel distribution and cyclic variation under flash boiling conditions in a spark ignition direct injection gasoline engine

One effective way of suppressing the cycle-to-cycle variation in engine is to design a combustion system that is robust to the root causes of engine variation over the entire engine working process. Flash boiling has been demonstrated as an ideal technique to produce stable fuel spray. But the generation of stable intake flow and fuel mixture remains challenging. In this study, to evaluate the capability of enhanced swirl flow to produce repeatable fuel mixture formation, the fuel distribution inside a single cylinder optical engine under two swirl ratios were measured using laser induced fluorescence technique. The swirl ratio was regulated by a swirl control valve installed in one of the intake ports. A 266nm wavelength laser sheet from a frequency-quadrupled laser was directed into the optical engine through the quartz liner 15mm below the tip of the spark plug. The fluorescence signal from the polycyclic aromatic hydrocarbon in gasoline was collected by applying a 320–420nm band pass filter mounted in front of an intensified charge coupled device camera. Test results show that the in-cylinder fuel distribution is strongly influenced by the swirl ratio. Specifically, under high swirl condition, the fuel is mainly concentrated on the left side of the combustion chamber. While under the low swirl flow, fuel is distributed more randomly over the observing plane. This agrees well with the measurements of the stable flame location. Additionally, the cycle-to-cycle variation of the fuel distribution were analyzed. Results show that well organized fuel mixture with lower cycle-to-cycle variation is achieved by enhanced swirl flow.

Investigation of Swirl Ratio Impact on In-Cylinder Flow in an SIDI Optical Engine

Advanced powertrain technologies have improved engine performance with higher power output, lower exhaust emission, and better controllability. Chief among them is the development of spark-ignition direct-injection (SIDI) engines in which the in-cylinder processes control the air flow motion, fuel–air mixture formation, combustion, and soot formation. Specifically, intake air with strong swirl motion is usually introduced to form a directional in-cylinder flowfield. This approach improves the mixing process of air and fuel as well as the propagation of flame. In this study, the effect of intake air swirl on in-cylinder flow characteristics was experimentally investigated. High-speed particle image velocimetry (PIV) was conducted in an optical SIDI engine to record the flowfield on a swirl plane. The intake air swirl motion was achieved by adjusting the opening of a swirl ratio (SR) control valve which was installed in one of the two intake ports in the optical engine. Ten opening angles of the SR control valve were adjusted to produce an intake SR from 0.55 to 5.68. The flow structures at the same crank angle degree (CAD), but under different SR, were compared and analyzed using proper orthogonal decomposition (POD). The flow dominant structures and variation structures were interpreted by different POD modes. The first POD mode captured the most dominant flowfield structure characteristics; the corresponding mode coefficients showed good linearity with the measured SR at the compression stroke when the flow was swirling and steady. During the intake stroke, strong intake air motion took place, and the structures and coefficients of the first modes varied along different SR. These modes captured the flow properties affected by the intake swirl motion. Meanwhile, the second and higher modes captured the variation feature of the flow at various CADs. In summary, this paper demonstrated a promising approach of using POD to interpret the effectiveness of swirl control valve on in-cylinder swirl flow characteristics, providing better understanding for engine intake system design and optimization.

A study on the effects of the intake port configurations on the swirl flow generated in a small D.I. diesel engine

This paper investigates the effect of intake port configuration on the swirl that is generated within a direct injection (D.I.) diesel engine. The in-cylinder flow characteristics are known to have significant effects on fuel-air mixing, combustion, and emissions. To clarify how to intensify the swirl flow, a swirl control valve (SCV) and a bypass were selected as design parameters for enhancing the swirl flow. The optimal intake port shape was also chosen as a parameter needed to efficiently generate a high swirl ratio. The results revealed that a key factor in generating a high swirl ratio was to control the intake airflow direction passing through the intake valve seat. Further, the swirl intensity was influenced by changing the distance between the helical and tangential ports, and the swirl flow was changed by the presence of a bypass near the intake valve seat. Additionally, the effect of intake port geometry on the in-cylinder flow field was investigated by using a laser sheet visualization method. The experimental results showed a correlation of swirl ratio and mass flow rate. In addition, we found that employing the bypass was an effective method to increase swirl ratio without sacrificing mass flow rate.

3D Numerical Simulation on the Variable Swirl Intake Process of Diesel Engine

To study the flow and swirl characteristics in the variable swirl intake system of a four-valve diesel engine, a numerical simulation with using the three dimensional CFD software AVL-FIRE, was calculated on the intake flow in three types of inlet of the engine. Two swirl-control valve plans are posed and a better plan was selected through the comparative study. The result shows that with a lager valve lift the flow characteristic of spiral inlet is better than that of tangential inlet, and in the opposite case the results are also opposite. The double inlets make the swirl torque increase. When a swirl-control valve is set in the spiral inlet, the variable swirl effect is better, and it ensures better flow capacity and larger swirl ratio range.

Characteristics of Induction Flow in SI Direct Injection Engine with Dual Variable Swirl Control Valve

Characteristics of Induction Flow in SI Direct Injection Engine with Dual Variable Swirl Control Valve

Investigation of Mixture Preparation Effects on Gasoline HCCI Combustion Aided by Measurements of Wall Heat Flux

Abstract Expanding the range of HCCI operation will be critical for maximizing the fuel economy benefits in future vehicle applications. The mixture stratification, both thermal and compositional, can have very tangible impact on HCCI combustion, and gaining a deeper insight into these effects is critical for expanding the HCCI range of operation. This paper presents results of the comprehensive experimental investigation of the mixture preparation effects on a single-cylinder gasoline HCCI engine with exhaust reinduction. The effects include the type of mixture preparation (external mixing versus direct injection), charge motion, and injection timing. A combination of pressure-based combustion diagnostics, emission analysis, and heat flux measurements on the combustion chamber wall quantifies the effects on combustion and provides insight into reasons for observed engine behavior. As an example, the instantaneous temperature and heat flux measurements show the fuel impingement locations and allow assessing the fuel film dynamics and their effect on mixture stratification. The effects of direct injection and partial closing of the swirl control valve are relatively small compared with extending the injection timing late into the intake process or completely closing the swirl control valve and allowing charge storage in the intake port.

An experimental investigation of two different methods for swirl induction in a multivalve engine

This paper describes an experimental investigation aimed at comparing the swirl effect induced by unbalancing the mass flow through the two intake ports of a multivalve engine head using two different methods: the first one reduced the curtain area of one of the intake valves [different lifts (DL) method]; the second one adopted a sluice-gate-shaped valve, installed upstream of the intake valves [swirl control valve (SCV) method] in order to cause a pressure drop. A steady-flow test rig (equipped with instrumentation for the discharge coefficient and swirl intensity measurement) was realized in order to compare and evaluate the results of both methods and determine their respective validity and limitations; the procedures used for both experimental methods are discussed in detail. The flow characteristics were analysed through changes of lift difference or SCV position; it was found that both DL and SCV methods are effective in swirl induction but the DL mechanism, acting on the valve curtain area, is more effective in flow unbalancing between intake ports, since the flowrate depends linearly on the curtain area. The SCV method, instead, controls the port flowrate, inducing a localized pressure drop, whose intensity depends on the flow velocity in a non-linear manner. For this reason the SCV method can achieve strong swirl intensity only with high obstruction levels, in a narrow regulation window close to full-obstruction conditions.

Investigation of soot formation in a D.I. diesel engine by using laser induced scattering and laser induced incandescence

Soot has a great effect on the formation of PM (Paniculate Matter) in D.I. (Direct Injection) Diesel engines. Soot in diesel flame is formed by incomplete combustion when the fuel atomization and mixture formation were poor. Therefore, the understanding of soot formation in a D.I. diesel engine is mandatory to reduce PM in exhaust gas. To investigate soot formation in diesel combustion, various measurements have been performed with laser diagnostics. In this study, the relative soot diameter and the relative number density in a D.I. engine was measured by using LIS (Laser Induced Scattering) and LII (Laser Induced Incandescence) methods simultaneously which are planar imaging techniques. And a visualization D.I. diesel engine was used to introduce a laser beam into the combustion chamber and investigate the diffusion flame characteristics. To find the optimal condition that reduces soot formation in diesel combustion, various injection timing and the swirl flow in the cylinder using the SCV (Swirl Control Valve) were applied. From this experiment, the effects of injection timing and swirl on soot formation were established. Effective reduction of soot formation is possible through the control of these two factors.

Steady-flow characteristics and its influence on spray for direct injection diesel engine

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of Dl (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70ΰ and 90ΰ. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.

A Study of the Combustion Characteristics Using a 2-valve Sl Optically Acessible Engine with SCV

This study describes the combustion characteristics under various condition of air excess ratio and ignition timing in a 2-valve SI optically accessible engine with swirl control valve(SCV). It adapted three different types of SCV(open ratio 72.5%, 78%, 59%) to strengthen a swirl flow. Pressure data were acquired using pressure sensor to investigate the effect of swirl flow on combustion, and from these pressure data, IMEP(indicated mean effective pressure) and MFB(mass fraction burnt) were calculated to explain burn rate and flame speed. From acquired flame images, we inspected the flame propagation direction, flame area, and flame centroid. Flame propagation direction showed different tendency between with/without SCV, and flame area with SCV was faster and larger than that of conventional engine. Finally, the representative flame images at each crank angle were acquired by PDF method to verify flame growth process. It is found that strengthened swirl flow is more beneficial for faster and stable combustion.

A Study of Variable Swirl Intake Port on 4-valve High Speed DI Diesel Engine. Flow Characteristics in Twin Variable Swirl Intake Ports.

To improve engine power and reduce exhaust emissions of 4-valve, high-speed DI diesel engines, the intake swirl ratio must be controlled according to the engine operating conditions. This paper discusses a variable swirl intake port consisting of helical port and tangential port with a swirl control valve. The swirl flow characteristics were analyzed on the basis of steady-state air flow tests and 3-dimensional computations. An automesh generator for numerical analysis of twin intake ports was developed to facilitate these computations. The results indicate that the total performance of twin ports can be estimated from that of a single port and that there were no adverse effects from interaction of the port flows in the cylinder.

Development of a technique for quantifying in-cylinder A/F ratio distribution using LIF image processing

Abstract Mixture formation in the cylinder greatly influences combustion. In this study, a system was developed for analyzing mixture formation by using LIF to visualize the formation process and image processing to quantify the air/fuel ratio distribution. Iso-octane was used as the fuel, DMA as the fluorescent tracer and a KrF excimer laser (wavelength of 248 nm) as the excitation light source. This system was used to visualize mixture formation in an engine with a tumble-type swirl control valve, and the effect of varying the fuel injection timing on mixture behavior and the A/F ratio distribution was examined.

The correlation between in-cylinder air motion and engine performance in two intake valve engine.

Recently, two intake valve engines have come into wide use because of their high output performance. However, there exists some difficulties in strengthening the air motion in combustion chamber in order to achieve stable combustion on partial load in a lean mixture operation. In this study improvements in engine performance that result in a stable combustion of lean mixture are examined. These improvments are brought about by the installation of a swirl control valve in the siamesed-type intake port of a two intake valve engine. Characteristics of air motion inside a combustion chamber are also examined using a laser doppler velocimeter. As a result of this study it is clarified that lean stable limit was not always extended in proportion to the strength of tangential swirl and combustion velocity. It is also found that an enlargement of lean stable limit was related to a decrease of cycle by cycle variation.