CN107289460B - A kind of oil-poor direct-injection air atomizer spray nozzle of pre- membranous type - Google Patents

Abstract

The invention discloses a pre-film type lean oil direct injection air atomization nozzle, which adopts the method of pre-expanding the fuel oil to form a film and air auxiliary atomization to realize rapid atomization of the fuel oil. It is composed of a direct injection fuel nozzle, a central channel, a tangential incident channel of the pre-coated tube, a pre-coated tube, an axial swirler and a sleeve with a throat: the air required for combustion can be obtained from the central channel, the pre-coated tube and the Passing through the axial swirler, the percentages of the effective area of the three to the total effective area of the unit nozzle are: 3%-5%, 7%-15% and 80%-90%. Due to the large amount of air passing through the swirler, the two swirl flows are mixed to form a single-directional swirl flow that is consistent with the direction of the axial swirler. The swirling flow will form a recirculation zone downstream of the nozzle, using high-temperature combustion products to heat the fresh mixture to achieve stable combustion. The central channel has a small amount of air flow, which prevents the backflow formed by the swirling flow from reaching the upstream of the throat.

Description

A Pre-film Type Lean Oil Direct Injection Air Atomizing Nozzle

technical field

The invention relates to a swirl atomizing nozzle, in particular to a pre-film type lean oil direct injection air atomizing nozzle.

Background technique

In aero-engines, the improvement of NOx emission performance is mainly achieved by reducing the reaction temperature and residence time of combustion, but at the same time, the emission levels of CO and UHC also need to be considered. Because in a common combustion chamber, it is usually by increasing the combustion temperature and prolonging the residence time by using the recirculation zone formed by the air swirl to improve the combustion efficiency and reduce the emission of pollutants such as CO and UHC. To reduce the formation of NOx pollutants, it is necessary to reduce the residence time and lower the reaction temperature. Therefore, designing a combustor design scheme that can reduce NOx generation while ensuring the stability and high efficiency of the combustor is a hot research topic at present. For aeroengine combustors that use lean combustion to reduce pollutant generation, the uniformity of fuel and air mixing is a key factor to reduce local high temperature areas and achieve emission reduction targets. Lean premixed pre-evaporative combustion technology (LPP) has received a lot of attention and research in recent decades, and successfully achieved the goal of reducing NOx emissions. However, in order to increase the working efficiency of the aero-engine, its boost ratio is constantly increasing, which also means that the inlet temperature and pressure of the combustion chamber are also increasing, which greatly shortens the fuel ignition delay time. The LPP combustion chamber technology Spontaneous combustion and flashback have become urgent problems to be solved. At the same time, according to some studies, it is known that the LPP low-pollution combustion chamber is more likely to excite the thermoacoustic oscillation in the combustion chamber. In order to overcome the shortcomings of LPP technology, researchers have carried out many related studies and technical improvements. Among them, Lean Direct Injection (LDI) skillfully avoids these problems by injecting fuel directly into the combustion chamber. The problem of spontaneous combustion prevents the continued application of LPP combustors in the next generation of high-pressure ratio aeroengines, which also makes people turn their attention to LDI, a new combustion organization.

Lean Direct Injection (LDI) combustion technology directly injects fuel and air into the combustion chamber for combustion. Since there is no pre-mixing and pre-evaporation process, the problems of spontaneous combustion and flashback are avoided. However, how to quickly and evenly mix air and fuel is the key to reducing emissions of this type of technology, which also puts forward higher requirements for the capability of fuel injection structures. The LDI low-emission combustion chamber must be able to quickly atomize, evaporate and mix with air before the fuel enters the combustion chamber and is not burned, so as to avoid local high temperature areas in the combustion chamber and achieve the same emission level as LPP. At present, there are mainly two structural forms of LDI low-emission combustors, one is a multi-swirl LDI combustor with a central stage, and the other is a multi-point injection LDI combustor with multiple unit nozzles.

The multi-point injection LDI combustion chamber replaces the traditional large swirler structure with multiple nozzle arrays, and distributes fuel to each small nozzle and then directly injects it into the combustion chamber. This greatly increases the contact area between fuel and air, and promotes the rapid mixing of fuel and air into a uniform lean state, thereby reducing the combustion temperature and inhibiting the formation of NOx. Each small nozzle adopts the way of swirl to stabilize the fire, and the recirculation zone formed by it is smaller than that formed by the traditional swirler, which reduces the length of the flame and the residence time of combustion, and can also effectively reduce the generation of NOx.

The LDI unit nozzle is the basic unit of the multi-point injection LDI combustion chamber. It is the most critical part of the combustion chamber to achieve lean fuel and low pollution combustion. The fuel atomization and rapid mixing technology performance of the unit nozzle directly determines the emission level of the combustion chamber, which is the key Sexual technical problems. Therefore, the present invention designs a unit nozzle capable of realizing rapid and uniform atomization for the requirement of the LDI combustion chamber.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a pre-film unit nozzle capable of meeting the atomization performance requirements for the rapidity and uniformity of liquid fuel atomization in the existing LDI combustion chamber. The nozzle adopts a structure similar to a cyclone separator to spread the fuel entering the channel into a thin film, and the liquid film of the fuel at the outlet is destabilized under the action of aerodynamic force, and the fuel is broken into droplets after the initial atomization. At the same time, increase the swirling flow formed by the internal and external air at the outlet to strengthen the aerodynamic force acting on the liquid film, so that the average diameter of the droplets formed after the initial atomization of the fuel is smaller. In addition, a swirl-free flow channel is designed in the center of the nozzle, which can be used to adjust the shape of the downstream flow field, which is conducive to better organization of combustion, and can also prevent the flame from propagating upstream into the pre-film tube.

The technical solution adopted by the present invention to solve its technical problems: a pre-film type lean oil direct injection air atomization nozzle, which adopts the pre-film atomization method, and at the same time adds swirling air with opposite internal and external rotation directions to rapidly spray the fuel. Uniform atomization. The structure is composed of a direct injection fuel nozzle, a central channel, a tangential channel at the inlet of the pre-coated tube, a pre-coated tube, an axial swirler and a sleeve with a throat; the central channel, the pre-coated tube and the sleeve are concentric , wherein: the front section of the central channel is slightly expanded; the tail of the pre-film tube is connected with a tangential hole; the axial swirler vane is between the pre-film tube and the sleeve; the sleeve is contracted and expanded downstream of the swirler structure. The air required for combustion can pass through the central passage, the pre-film tube and the axial swirler respectively. The percentages of the effective areas of these three to the total effective area of the unit nozzle are: 3%-5%, 7%-15% and 80%-90%. A small amount of air passing through the central channel can be used to adjust the flow field structure of the combustion zone downstream of the nozzle and improve the combustion performance of the nozzle. The fuel required for combustion downstream of the nozzle enters the pre-film tube from the tangential hole at the end of the pre-film tube, and 7%-15% of the combustion air enters the tube through the tangential hole at the end of the pre-film tube, forming a swirling airflow while assisting the liquid The fuel unfolds into a film. The ratio of air to fuel flow in the pre-film tube is between 2-4, this range can prevent spontaneous combustion in the tube while ensuring the atomization quality. A large amount of air passes from the axial swirler through the rotating airflow in the opposite direction to the swirling direction of the pre-film tube, and the two airflows in the opposite direction of rotation jointly shear the liquid fuel film at the exit of the pre-film tube, and the shearing effect is achieved by strengthening the shrinking channel Rapid atomization of fuel. The angle between the expansion section after the throat of the sleeve and the central axis is between 40°-50°, which is used to form an oil mist field with a moderate spray angle and a reasonable spatial distribution to achieve stable combustion.

Wherein, the material of the direct injection fuel nozzle is stainless steel, the flow number FN of the nozzle is about 25, and the aspect ratio of the nozzle is between 0.5-1. The nozzle outlet is facing the center of the tangential incident channel of the pre-film tube, and the distance between the nozzle exit plane and the tangential incident channel of the pre-film tube is about 2mm.

The material of the central channel is stainless steel, which is a slightly expanded circular straight channel at the outlet, the diameter of the small hole used to control the effective area of the channel at the inlet is 2-3 mm, and the angle between the expanded section of the outlet and the central axis is 2 °-4°, the diameter of the outlet is 5-6mm.

The material of the tangential incident channel of the pre-film tube is stainless steel, which is a circular straight channel with an inner diameter of 4-6mm. The distance between the inlet end face of the channel and the axis of the pre-film tube is 8-10mm, and its central axis is relatively The tube centerline is offset by a distance of 3.5-5mm.

The material of the pre-film tube is stainless steel, which is an annular pipe whose diameter decreases step by step and one end is closed, and an incident hole is opened at the closed end to connect with the tangential incident channel. The outer diameter of the outlet of the pre-film tube is 7-8mm, the inner radius is 5.2-6.2mm, and the length of the pre-film tube is 25-35mm.

The material of the axial swirler is stainless steel, the maximum outer diameter of the blade is 22-24mm, and the inner diameter is 11-13mm. The axial swirler has 10-16 straight blades evenly distributed along the circumference, the thickness is about 0.8-1.2mm, and the angle between the blade centerline and the axis is 35°-45°. The axial width at the top of the blade is 8-10mm, and the axial width at the bottom is 5-6mm.

The material of the sleeve is stainless steel, which is a circular channel with a throat. The angle between the contraction section and the central axis is about 30°, the diameter of the throat is 18-20mm, the maximum diameter of the outlet expansion section is 24-26mm, and the angle between the expansion section and the central axis is 40°-45°.

The working principle of the present invention is to realize rapid atomization of fuel by adopting the method of pre-expanding the fuel into a film and assisting air atomization. The fuel is directly injected into the annular channel of the pre-film tube through the tangential incident channel of the pre-film tube, generating tangential momentum to expand and form a film on the inner wall of the pre-film tube. At the same time, 7%-15% of the air also enters the pre-film tube through the tangential channel to form a swirling flow, and the swirling airflow drives the liquid fuel to move to the outlet of the pre-film tube and helps the fuel to spread better on the inner wall. A large amount of airflow passes through the axial swirler to form a swirling airflow, and the direction is opposite to the swirling direction of the pre-film tube. The fuel liquid film realizes rapid atomization under the shear action of internal and external reverse swirl. Due to the large amount of air passing through the swirler, the two swirl flows are mixed to form a single-directional swirl flow that is consistent with the direction of the axial swirler. The swirling flow will form a recirculation zone downstream of the nozzle, using high-temperature combustion products to heat the fresh mixture to achieve stable combustion. The central channel has a small amount of air flow, which prevents the backflow formed by the swirling flow from reaching the upstream of the throat.

Compared with the prior art, the present invention has the following advantages:

(1) The pre-membrane air atomizing nozzle invented by me uses a method similar to a cyclone separator to form a swirling flow, and at the same time, the fuel is spread along the wall. This can effectively spread the fuel from the liquid column into a circumferentially uniform thin film of very small thickness, thereby achieving rapid and uniform atomization.

(2) The pre-membrane air atomizing nozzle invented by me adopts the direct flow channel in the center to adjust the structure of the downstream flow field and adjust the position of the recirculation zone, which can effectively prevent the occurrence of tempering.

(3) The pre-film air atomizing nozzle invented by me can effectively meet the requirements of fuel-lean direct injection combustion chambers for rapid and uniform atomization of fuel; at the same time, the structural size is small, and it can meet the requirements of multiple small nozzles for multi-point injection LDI combustion chambers It replaces the characteristics of a traditional large cyclone structure; it is easy to install and easy to maintain, the oil circuit is simple and easy to operate, it is suitable for a variety of liquid fuels, and has greater fuel expansion.

Description of drawings

Fig. 1 is the structural representation of a kind of pre-film type lean oil direct injection air atomizing nozzle of the present invention;

Fig. 2 is a positive triaxial view of a pre-film type lean oil direct injection air atomizing nozzle of the present invention;

Fig. 3 is the schematic diagram of the direct injection fuel nozzle of the present invention;

The meanings of the reference signs in the figure are: 1 is the direct injection fuel nozzle, 2 is the central channel, 3 is the tangential incident channel of the pre-coated tube, 4 is the pre-coated tube, 5 is the axial swirler, 6 is the nozzle with throat sleeve.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, a pre-film type lean oil direct injection air atomizing nozzle described in this example adopts the method of pre-expanding the fuel to form a film and air-assisted atomization, and the whole is made of stainless steel, including: direct injection Fuel nozzle 1, central channel 2, pre-coated tube tangential injection channel 3, pre-coated tube 4, axial swirler 5, sleeve with throat 6. The direct injection fuel nozzle 1 injects the liquid fuel into the tangential injection channel 3 of the pre-filmed tube. Since the axis of the tangential incident channel 3 is offset based on the axis of the pre-film tube 4, the liquid fuel incident into the pre-film tube 4 has a tangential momentum relative to the axis of the pre-film tube 4, and the fuel will flow along the pre-film tube 4. inner wall flow. Through this physical process, the liquid fuel can be expanded from the liquid column into a thinner liquid film, which is conducive to the subsequent atomization to form smaller fuel droplets. 7%-15% of the air will also enter the pre-film tube 4 from the tangential incident channel 3 of the pre-film tube, and use the same principle to form a swirl flow to help the fuel to expand and form a film faster and better. At the same time, the axial flow of air in the pre-film tube is used to drive the fuel to flow downstream in the axial direction of the pre-film tube and enter the flow field. A large amount of airflow passes through the axial swirler 5 to form a rotating airflow, and the direction is opposite to that of the airflow in the pre-film tube. The fuel liquid film on the inner wall of the pre-film tube 4 receives the shear action of internal and external reverse swirling flow at the outlet of the pre-film tube 4 to achieve rapid and uniform atomization. However, due to the large amount of air passing through the axial swirler 5, the two opposite swirl flows mix with each other to form a swirl flow in the same direction as the axial swirler. The swirl strength of the swirl flow will be weaker than the swirl flow formed by the axial swirler 5, but it can meet the requirement of forming a recirculation zone downstream of the nozzle. When the fuel is burning, the recirculation zone in the flow field can use the high-temperature combustion products to heat the fresh mixture to achieve stable combustion. There is a small amount of air passing through the central channel 2 of the nozzle, and this air flow can effectively prevent the backflow formed by the swirl flow downstream from going deep into the upstream of the throat, preventing the problem caused by the flame spreading to the upstream of the throat. The contraction and expansion structure in the sleeve 6 can increase the angular velocity of the swirling flow, reduce the average diameter of the droplet particles and improve the mixing degree of oil and gas; at the same time, the throat can also increase the axial velocity and prevent the flame from propagating upstream.

As shown in Figure 1, the center of the direct injection fuel nozzle 1 is aligned with the center of the tangential incident channel 3 of the pre-film pipe, and the distance between the outlet of the direct injection fuel nozzle 1 and the inlet of the injection pipe is 1-3 mm. 1. The diameter is 0.3-0.6mm, and the inner diameter of the entrance of the tangential incident channel 3 is 5-7mm, which can effectively ensure that all fuel oil enters the pre-film pipe 4. The center of the direct injection fuel nozzle 1 is aligned with the center of the tangential incident channel 3 of the pre-film tube, and the offset distance between the center of the tangential incident channel 3 and the center of the pre-film tube 4 is 1.5-3 mm. The axial distance between the outlet plane of the pre-film tube 4 and the throat of the sleeve is 1-3mm.

As shown in FIG. 2 , the axial distance between the axial swirler 5 and the center of the tangential incident channel is 12-15 mm, which reduces the influence of the tangential incident channel 3 on the air intake of the swirler 5 .

As shown in Figure 3, one end of the direct injection fuel nozzle is connected to the pressure oil supply device, and the other end is opened with a small hole with an aspect ratio between 0.5-1 to inject fuel.

Claims (7)

1. A pre-film type lean oil direct injection air atomizing nozzle is characterized in that: the pre-film atomization method is used, and the swirling air with the opposite internal and external rotation is added at the same time to quickly and evenly atomize the fuel. The structure consists of a direct injection fuel nozzle (1), a central channel (2), a tangential incident channel of the pre-coated tube (3), a pre-coated tube (4), an axial swirler (5) and a sleeve with a throat (6) composition; central channel (2), pre-film tube (4) and sleeve (6) are three concentric, wherein: the front section of central channel (2) expands slightly; The afterbody of pre-film tube (4) is connected with cut To the hole; between the pre-film pipe (4) and the sleeve (6) is the vane of the axial swirler (5); the sleeve (6) is a contraction and expansion structure downstream of the axial swirler (5) , the air required for combustion can pass through the central channel (2), the pre-film tube (4) and the axial swirler (5) respectively. The percentages of the effective areas of these three to the total effective area of the unit nozzles are: 3 %-5%, 7%-15% and 80%-90%, a small amount of air passing through the central channel (2) can be used to adjust the flow field structure of the combustion zone downstream of the nozzle, and increase the combustion performance of the nozzle. The fuel required for combustion enters the pre-film tube (4) from the tangential hole at the end of the pre-film tube (4), and 7%-15% of the combustion air enters the tube through the tangential hole at the end of the pre-film tube (4), While forming the swirling airflow, it assists the liquid fuel to expand and form a film. The ratio of air to fuel flow in the pre-film tube (4) is between 2-4. This range can prevent spontaneous combustion in the tube and ensure the atomization quality. A large amount of air passes through the swirling air flow opposite to the swirling direction of the pre-film tube (4) from the axial swirler (5), and the two air streams in the opposite direction of rotation shear the liquid fuel film at the exit of the pre-film tube (4), and Rapid atomization of fuel is achieved by enhancing the shearing effect of the shrinking channel. The angle between the expansion section behind the throat of the sleeve (6) and the central axis is between 40°-50°, which is used to form a moderate spray angle and spatial distribution. Reasonable oil mist field to achieve stable combustion. 2. A pre-film type lean oil direct injection air atomizing nozzle according to claim 1, characterized in that: the material of the direct injection fuel nozzle is stainless steel, the flow number FN of the nozzle is about 25, and the nozzle's The aspect ratio is between 0.5-1, the nozzle outlet is facing the center of the tangential incident channel of the pre-film tube, and the distance between the nozzle exit plane and the tangential incident channel of the pre-film tube is about 2mm. 3. A pre-film type lean oil direct injection air atomizing nozzle according to claim 1, characterized in that: the material of the central channel is stainless steel, which is a slightly expanded circular straight channel at the outlet, and the inlet The diameter of the small hole used to control the effective area of the channel is 2-3mm, the angle between the expansion section of the outlet and the central axis is 2°-4°, and the diameter of the outlet is 5-6mm. 4. A kind of pre-film type lean oil direct injection air atomizing nozzle according to claim 1, characterized in that: the material of the tangential incident channel of the pre-film tube is stainless steel, which is a circular straight channel with an inner diameter of 4-6mm, the distance between the channel inlet end surface and the axis of the pre-film tube is 8-10mm, and the offset distance of the central axis relative to the center line of the pre-film tube is 3.5-5mm. 5. A pre-film type lean-oil direct-injection air atomizing nozzle according to claim 1, characterized in that: the material of the pre-film tube is stainless steel, which is an annular ring whose diameter decreases step by step and one end is closed The pipeline has an incident hole connected to the tangential incident channel at the closed end, the outer diameter of the outlet of the pre-coated tube is 7-8mm, the inner radius is 5.2-6.2mm, and the length of the pre-coated tube is 25-35mm. 6. A pre-film type lean oil direct injection air atomizing nozzle according to claim 1, characterized in that: the material of the axial swirler is stainless steel, the maximum outer diameter of the blade is 22-24mm, and the inner The diameter is 11-13mm, the axial swirler has 10-16 straight blades evenly distributed along the circumference, the thickness is about 0.8-1.2mm, the angle between the blade centerline and the axis is 35°-45°, the blade The top axial width is 8-10mm, and the bottom axial width is 5-6mm. 7. A pre-membrane type lean oil direct injection air atomizing nozzle according to claim 1, characterized in that: the material of the sleeve is stainless steel, which is a circular channel with a throat, and the constriction section and The included angle of the central axis is about 30°, the diameter of the throat is 18-20mm, the maximum diameter of the outlet expansion section is 24-26mm, and the included angle between the expansion section and the central axis is 40°-45°.