CN102287260A - Double-swirl combustion system with swirls - Google Patents

Abstract

The invention relates to a double-swirl combustion system with gas inlet swirls (S-DSCS). When the double-swirl combustion system is adopted, on one hand, fuel oil forms the swirls in opposite directions inside and outside a combustion chamber through a double-swirl combustion chamber structure, the uniformity of oil-gas mixed gas in the axial space of the combustion chamber is improved, and on the other hand, the fuel oil is more uniformly distributed in the circumferential space of the combustion chamber through the gas inlet swirls, so the fuel oil is more uniformly distributed in the circumferential space of the combustion chamber under the duplex effects of double swirls and vortexes, the air utilization rate is improved, the heat releasing through combustion is accelerated, the power is improved, the oil consumption is reduced, and simultaneously, the discharge performance is also improved. The double-swirl combustion system is realized through adding the gas inlet swirls on the basis of the double-swirl combustion chamber, and simplicity, convenience and easy implementation are realized.

Description

A double swirl combustion system with swirl

The invention relates to a diesel engine double swirl combustion system with intake swirl. The system superimposes the intake swirl on the basis of the double swirl formed by the double swirl combustion chamber, so that the fuel can not only flow along the axis of the combustion chamber The distribution in the plane is more uniform, and due to the existence of vortex, the fuel is distributed more uniformly in the circumferential direction of the combustion chamber, thereby improving the uniformity of the mixture and the utilization rate of air, making the combustion heat release faster, reducing fuel consumption, While increasing power, emission performance has also been improved.

Background technique

The oil-air mixing process of modern diesel engines directly affects the combustion performance and emission characteristics. Therefore, making the fuel oil more widely distributed in the entire combustion chamber space, increasing the mixing speed with air, and reducing the uneven distribution of fuel oil in the combustion chamber can significantly improve the power, economy and emission performance of the diesel engine.

Various methods of matching oil, gas and chamber in the combustion chamber are used in modern diesel engines to improve engine combustion and emission performance, but these technical routes lead to uneven distribution and low air utilization rate to a certain extent. For a better explanation, several typical combustion system defects are analyzed separately below in conjunction with Figure 1 and Figure 2. Figure 1 is the shape of the ω-shaped combustion chamber, and Figure 2 is the top view of the ω-shaped combustion chamber. Areas 1, 2, and 3 in Figure 1 and Area 4 in Figure 2 are different spatial positions of the combustion chamber, and S is the oil spray Note. The oil-air mixing form in the ω-shaped combustion chamber is a typical jet mixing in a confined space. Generally, a multi-hole injector is used, and the angle of the oil beam is small. The axis of fuel injection is roughly parallel to the generatrix of the central cone of the combustion chamber. Generally, high-pressure fuel injection technology can improve the quality of atomization and air entrainment, which is beneficial to the mixing of oil and gas near the oil beam S. However, it can be seen from Figure 1 that in area 1 near the center of the combustion chamber and area 2 on the upper side of the combustion chamber The distribution of fuel in the zone and the 3rd zone of the top gap is less, the air utilization rate is low, and it is easy to cause the accumulation of fuel near the throat of the combustion chamber. Although the intake vortex can be used to improve the uniformity of fuel distribution in zone 4 in Figure 2, no matter what measures are taken by this type of combustion system (changing fuel injection pressure, nozzle diameter and number of holes, fuel injection timing, etc.), it cannot Improve the air utilization in Zones 1, 2, and 3. However, in the existing double-plump system, the air utilization rate in zones 1, 2, and 3 is improved due to the existence of the double-plump flow, as shown in FIG. 3 . But without matching the intake swirl, the air in Zone 4 is still not well utilized. To sum up, at present, these combustion systems only focus on the mixing of oil and gas in a part of the combustion chamber space, and there is no way to realize the uniform distribution of fuel oil and the full utilization of air in the entire combustion chamber space. The purpose of the present invention is to add an intake vortex on the basis of the double-plume combustion chamber, so that the fuel can be distributed more evenly in the axial plane and circumferential direction of the combustion chamber under the double action of the double-plume combustion and the vortex, so that it can be more uniform. Make full use of the air in the entire space of the combustion chamber, promote the rapid mixing of oil and gas, make the combustion more complete, and improve the economy, power and harmful emissions of the diesel engine.

The dual-plume combustion system of the diesel engine with swirl flow involved in the present invention, on the one hand, as shown in Figure 3, the high-pressure fuel is ejected from the nozzle and touches the arc ridge of the double-plume combustion chamber, and under the action of the arc ridge, part of it enters the combustion chamber. The indoor chamber is mixed with the air, and part of it enters the combustion chamber to mix with the air, which is beneficial to the oil-gas mixing in Zone 1, Zone 2 and Zone 3, and expands the distribution of fuel oil on the axial section of the combustion chamber; on the other hand, as shown in Figure 4, through The vortex is organized in the cylinder, and under the action of the fuel, the contact area between the fuel and the fresh air can be expanded in the circumferential direction, so that the air in the 4th zone can be fully utilized, thereby improving the air utilization rate. The design of the combustion system makes effective use of the air in the entire space of the double plume combustion chamber, and the fuel is more evenly distributed in the combustion chamber space, so the combustion speed is faster and the heat release near the top dead center is increased. Efficiency and workability, emission performance is also improved. The combustion system is easy to process, and can be realized by adding an intake vortex vortex on the basis of the existing double swirl flow combustion chamber by using a vortex air channel.

Contents of the invention

The object of the present invention is to provide a dual-plume combustor system for a diesel engine with swirling flow, which can make the fuel mix with air more uniformly in the axial section of the combustor under the action of the arc ridge of the double-plume combustor , At the same time, under the action of vortex, the fuel is mixed more evenly in the circumferential direction of the combustion chamber, that is, the fuel is distributed more evenly in the entire combustion chamber space. This improves the mixing effect of fuel and air, improves the air utilization rate, improves the combustion process, and improves the economy, power and emission performance indicators.

In order to realize the purpose of the present invention, a kind of circumferential flow that can add air in the cylinder on the basis of a combustion chamber with a special structure is proposed, that is, a swirl flow. Wherein, the combustion chamber is a double swirl flow combustion chamber. At an appropriate crank angle, the high-pressure fuel is ejected through the nozzle and collides with the arc ridge of the double-plume combustion chamber. The oil beam is divided into two, the inner chamber forms a clockwise fuel scroll, and the outer chamber forms a counterclockwise direction. The fuel is scrolled, so that the fuel forms a plume flow in two directions, and the air utilization effect on the axial section of the combustion chamber is good, which is the advantage of the double plume combustion chamber.

On the basis of the double swirl combustion chamber, the intake vortex is guided during the intake process, and the fuel is fully mixed with the air in the circumferential direction of the combustion chamber under the action of the vortex. The intake vortex can be formed by air passages of different structures, such as tangential air passages, spiral air passages, and air shields. After the oil beam is sprayed out for a certain distance, under the action of the vortex, the evaporated fuel and some small fuel oil droplets move along the direction of the vortex rotation, and the area of the oil mist increases, thereby expanding the oil beam in the circumferential direction of the combustion chamber. Distribution. The contact surface between fuel and air increases, and the mixing effect is better, that is, the circumferential air utilization effect is good. This is the advantage of adding the intake swirl. Fuel and air are fully mixed in the axial and circumferential directions of the cylinder, making the fuel-air mixture in the entire space of the combustion chamber more uniform.

In the present invention, the design of the double swirl combustor and the matching of the swirl ratio are key. In order to achieve the purpose of making full use of the air in the combustion chamber of the double plume combustor, the arc radius of the combustion chamber and the outer chamber, the volume ratio of the inner and outer chambers, the position of the arc ridge and the matching of the angle of the fuel oil beam should all be considered. The best working condition of the double swirl combustor is when the fuel oil sprays out at the proper engine crank angle position and hits the arc ridge, and there is a reasonable ratio of fuel distribution between the inner and outer chambers. The size of the swirl ratio determines the distribution of the oil beams in the circumferential direction of the combustion chamber. If the swirl ratio is too small, the mixing effect will not be obvious. If the swirl ratio is too large, two adjacent bundles of fuel will be superimposed, and the local fuel concentration will be uneven. , the mixing effect deteriorates.

By adopting the invention, the oil and gas mixing of the diesel engine can be made more uniform and the combustion speed can be accelerated. During the intake process, the intake vortex is generated in the cylinder. On the one hand, the fuel is mixed evenly in the axial direction under the action of the arc ridge of the double swirl combustion chamber; The fuel oil is evenly distributed in the entire space of the combustion chamber, which is an improvement, expansion and extension of the double-plume combustion system. The present invention can be matched on the basis of the original double plume combustion chamber, and is simple and easy to implement.

Description of drawings

Figure 1 is the diagram of the oil and gas partition in the axial section of the ω-type combustor.

Figure 2 is a diagram of the oil and gas partition in the circumferential direction of the ω-shaped combustor under the condition of no intake vortex.

Figure 3 is a diagram of the oil and gas partition in the axial section of the double swirl combustor.

Figure 4 is a diagram of the circumferential oil and gas partition of the double swirl combustor under the condition of intake swirl.

Fig. 5 is a three-dimensional model of an ω-shaped combustion chamber corresponding to one injection hole in a specific embodiment.

Fig. 6 is a three-dimensional model when the double plume combustor corresponds to one injection hole in the specific embodiment.

Fig. 7 is the mesh modeling of the ω-shaped combustion chamber corresponding to one injection hole in the CFD software.

Fig. 8 is the grid modeling when the double plume combustor corresponds to one nozzle hole in the CFD software.

Figure 9 shows the calculation results of effective power corresponding to different swirl ratios for ω-type combustors.

Figure 10 shows the simulation results of the effective power of the double swirl combustor corresponding to different swirl ratios.

Figure 11 shows the simulation calculation results of the effective power when the ω-type combustor has no swirl, the ω-type combustor has the optimal swirl ratio, the double-swirl combustor has no swirl, and the double-swirl combustor has the optimal swirl ratio.

Fig. 12 is an axial slice diagram of the fuel-air equivalence ratio corresponding to SR=0 of the ω-type combustor at 376°CA.

Fig. 13 is an axial slice diagram of the velocity field corresponding to SR=0.8 in the double plume combustor at 376°CA.

Fig. 14 is a circumferential slice diagram of the fuel-air equivalence ratio corresponding to SR=0 of the ω-type combustor at 376°CA.

Figure 15 is a circumferential slice of the fuel-air equivalence ratio corresponding to SR=0.8 in a double-plume combustor at 376°CA.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing:

Figure 3 is the boundary of the double plume combustor. In the figure, the high-pressure fuel reaches the arc ridge soon after being sprayed out, and the fuel enters the inner chamber space 1 and the outer chamber space 2 respectively under the action of the arc ridge. When the fuel injection angle matches the fuel injection advance angle and arc ridge position, the fuel can hit the arc ridge at an appropriate engine crank angle, and the fuel is divided into two parts, one part moves clockwise in the inner chamber, and the other part moves outside. The chamber moves in a counterclockwise direction, which creates a two-way fuel swirl, hence the name of the double-swirl combustor. Therefore, through the function of the arc ridge, the fuel can be distributed to the inner and outer chambers of the combustion chamber in a certain proportion, the air utilization rate in the axial direction of the combustion chamber is greatly improved, and the mixing speed and combustion rate of oil and gas are improved.

The intake vortex is induced on the basis of the double swirl combustion chamber, as shown in Figure 4, the fuel is deflected along the direction of the vortex under the blowing of the vortex, and the coverage area of the fuel in the circumferential direction of the combustion chamber increases, that is, the area in Figure 4 4 area reduction. The fuel is in full contact with fresh air, which improves the air utilization rate. In this way, on the basis of the double swirl combustion system (DSCS), the vortex (Swirl) is induced in the short-term process, and the double swirl combustion system with intake swirl (S-DSCS) is formed. Under the combined effect, it can be evenly distributed in the entire range of the combustion chamber, which improves the uniformity of the oil-gas mixture.

Specific examples:

The CFD three-dimensional mesh models of the ω-shaped combustor and the double swirl combustor with intake swirl under the same compression ratio were respectively established, and the simulation calculations were compared.

The design parameters of the combustion chamber are: cylinder diameter 132mm, stroke 145mm, connecting rod length 262mm, clearance height 1.3mm. Calculated according to the compression ratio of 17, the volume of the ω combustion chamber and the double swirl combustion chamber should be 106224mm ³ . In the actual modeling, the volumes of the ω combustion chamber and the double plume combustion chamber are 106448mm ³ and 106056mm ³ respectively, and the deviation rates are 0.21% and 0.16%, respectively. In the geometry, the diameter of the throat of the ω-shaped combustion chamber is 99mm, the diameter of the throat of the outer chamber of the double plume combustion chamber is 99mm, and the diameter of the inner chamber is 64mm. The depth of the double plume arc ridge is 10.45mm, the arc radius of the inner chamber is 7.2mm, and the arc radius of the outer chamber is 9.9mm.

Figure 5 and Figure 6 are the modeling diagrams of the ω-shaped combustion chamber and the double-plume combustion chamber corresponding to the single injection hole in the Pro/E software. Figure 7 and Figure 8 are the mesh models of the ω-shaped combustion chamber and the double-plume combustion chamber in the 3D simulation software. Since the calculation uses an 8-hole injector, according to the symmetry of the calculation results, only 1/8 The combustion chamber is meshed. According to the previous calculation experience, if the grid is too large, the calculation accuracy will decrease; if the grid is too small, the calculation time will be greatly increased under the condition of the same calculation accuracy, which will reduce the calculation efficiency. Therefore, in the model, the grid scale is about It is 1mm, which shortens the calculation time while ensuring the calculation accuracy.

The initial conditions and calculation model selection of the two combustion chambers are the same. The initial calculation conditions are as follows: the rotational speed is 2500 rpm, the average pressure in the cylinder at the calculation starting point is 3.9 bar, the intake air temperature is 333K, and the excess air coefficient is 1.8. The fuel injection start point is 346°CA, the fuel injection end time is 384°CA, and the fuel injection duration is 38°CA. The circulating oil supply of single hole is 33.4mg/cyc. The spray angle is 155°. The calculation formula of the swirl ratio: SR ratio=rotating airflow velocity in the cylinder/engine speed, therefore, the swirl ratio can be adjusted by setting the swirling airflow velocity in the cylinder during the calculation, and the swirl ratio is set to 0, 0.4, and 0.8 in turn , 1.2, 1.6.

Figure 9 corresponds to the simulation calculation results of the effective power Pe of the ω-type combustor under different swirl ratios. It can be seen from the figure that the effective power Pe increases first and then decreases with the increase of the eddy current ratio. When SR=1.2, the effective power Pe reaches the maximum, which is 69.35kW.

Figure 10 corresponds to the simulation calculation results of the effective power Pe of the double swirl combustor under different swirl ratios. It can be seen from the figure that the effective power Pe increases first and then decreases with the increase of the eddy current ratio. When SR=0.8, the effective power Pe reaches the maximum value, reaching 85.43kW. Therefore, adding swirl will improve the performance of the double swirl combustion combustion system, but it has an optimum value SR=0.8, which makes the performance optimal.

Figure 11 shows the effective power when the ω-shaped combustor, the double-plump combustion without adding swirl, the ω-shaped combustor corresponds to the optimal swirl ratio, and the double-plump combustor corresponds to the optimal swirl ratio. It can be seen from the figure that after adding swirl, the performance of the ω-shaped combustion chamber is improved compared with that without swirl, indicating that adding swirl can help improve the performance of the engine, but the improvement is limited, and the effective power is increased from 65.06kW to 69.35kW , which only increased by 6.6%. At the same time, it can be seen that even if the optimal swirl ratio is selected, the performance of the ω-shaped combustor is still inferior to that of the double swirl combustor without swirl. It has been improved, but due to the limitations of its own structure, the performance of the engine cannot be greatly improved, that is, the potential for performance improvement is limited. When the double swirl combustion chamber takes the best swirl ratio, the performance is also improved compared with that without swirl, and the effective power Pe reaches 85.43kW, which is 21.8% higher than that without swirl, and 31.3% higher than that of the ω-type combustor. The power increase is significant. This shows that after adding vortex to the double swirl combustion chamber, not only the fuel mixing effect is good in the axial direction, but also the circumferential oil-gas mixing is also improved, which can significantly improve the engine performance.

Fig. 12 is the axial slice nephogram of fuel-air equivalence ratio at 376°CA for the example of ω-type combustor. Fig. 13 is an axial slice diagram of the velocity field at 376°C CA of the double swirl combustor under the condition of no swirl ratio. Combining these three pictures, it can be seen that the fuel oil in the ω-shaped combustion chamber is concentrated in the deep pit at the far end of the combustion chamber, without sufficient diffusion, and the air in Zone 1, Zone 2 and Zone 3 is not fully utilized, and the fuel gas The mixing effect is poor, which reduces the burning rate. In the double swirl combustion chamber model, under the action of the arc ridge, part of the fuel rotates clockwise into the inner chamber, and part of it enters the outer chamber counterclockwise, which is beneficial for the fuel to use the air in the inner and outer chambers. Fig. 14 is a slice diagram of the fuel-air equivalence ratio circumferential direction at 376°CA when the double-plump combustor has no swirl. slice graph. It can be seen from Fig. 14 and Fig. 15 that after the vortex is added to the double swirl combustor, the fuel moves and bends under the action of the vortex, the fuel distribution area increases, and the mixing effect is better. At the same time, it can also be explained from Figure 15 why the effective power Pe decreases when the swirl ratio SR>0.8 in the double swirl combustor. Deflection, adjacent oil jets overlap, causing local mixers to be too rich, thereby deteriorating combustion performance. Therefore, for the dual-swirl combustion system with swirl, the angle of the injector oil beam, the timing of fuel injection, the size of the combustion chamber and the matching relationship with the size of the intake swirl are the key points of the present invention.

Claims (2)

1. A diesel double plume combustion system with intake swirl is used to improve the air utilization rate in the entire space range of the combustion chamber, characterized in that: the in-cylinder swirl is made on the basis of the original double swirl combustion chamber. Among them, the double swirl combustion chamber can ensure that the fuel hits the arc ridge to form two airflows in opposite directions, and the vortex can expand the contact area between the fuel and the air in the circumferential direction of the combustion chamber, thereby making the fuel distribution in the entire space of the combustion chamber More uniform combustion, more complete combustion, and improved engine performance. 2. The in-cylinder vortex according to claim 1, characterized in that it can be produced by various structures, such as tangential air passages, spiral air passages, and air guide screens.

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