CN107524514B - The high power to weight ratio heavy oil piston engine air inlet buffer of two strokes of one kind and its design method - Google Patents

Abstract

The invention provides an air intake buffer applied to a two-stroke high-power heavy-gravity oil piston engine and a design method thereof. There are no other mechanical and moving parts inside the cavity. Through the structural design of the structural section between multiple sets of cavities, the engine can effectively control the pollution of the fresh inlet air caused by the backflow gas in the cylinder during scavenging, and push the backflow gas into the air again. In the cylinder, the scavenging efficiency is higher, the scavenging coefficient is larger, and the engine power per cycle is larger.

Description

A two-stroke high-power heavy-gravity oil piston engine intake buffer and its design method

technical field

The invention relates to the field of design of an intake buffer structure of a piston engine, in particular to a design method of an intake buffer of a two-stroke high-power heavy-gravity oil piston engine.

Background technique

With the development of general aviation, the two-stroke heavy oil piston engine has gradually attracted people's attention. The performance of the two-stroke piston engine is greatly affected by the air exchange quality. An ideal air exchange system is to obtain as large a scavenging coefficient as possible on the premise of a small excess scavenging coefficient, and reduce the scavenging completion. Residual exhaust gas in the cylinder afterwards.

For aviation piston engines with high power-to-weight ratio requirements, the structural weight to achieve the target power of the engine should be as low as possible. Compare.

The existing anti-backflow technologies mostly use one-way valve body devices of various designs and structures to realize the one-way flow of fluids. These structures are mechanically linked by several components, such as the micro-resistance spring structure, which is complex in structure and difficult to design. Not only will it increase the structural weight of the machine, but it will also interfere with the flow of the fluid.

SUMMARY OF THE INVENTION

In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide a scavenging air intake buffer and a design method thereof for a two-stroke high-power heavy-gravity oil piston engine, which is used to solve the problem of the backflow of cylinder gas and the pollution of fresh intake air. At the same time, a higher scavenging coefficient can be obtained with the same fresh intake air volume. The present invention obtains the structural size parameters of the buffer by performing theoretical calculation, and the buffer structure and the cylinder of the engine are designed in an integrated manner, and are cast together with the crankcase, so that the process is simpler and the processing cost is lower. Easier to implement in production.

The complete technical solution of the present invention includes:

An engine air intake buffer, the buffer is located between the scavenging pump outlet and the cylinder air inlet, and has at least one structural cavity, the structural cavity is used to accommodate the cylinder when the engine is ventilated Backflow gas.

The engine is a two-stroke heavy oil piston engine.

The buffer has a plurality of structural cavities, and the intersecting interfaces of adjacent cavities are provided with holes as the inlet and outlet of the gas in the cavities, and the cross-sectional area of each cavity along the gas flow direction is larger than the inlet and outlet of the cavities. area, so that there is a sudden change in the cross-section of the buffer and the air inlet and the cross-section of each adjacent cavity in the buffer.

The buffer includes a first cavity, a second cavity and a third cavity, wherein the third cavity and the second cavity are in direct communication with the outlet of the scavenging pump, and the third cavity and the second cavity are in direct communication with the outlet of the scavenging pump. The second cavity is also communicated with the first cavity through the hole. One end of the first cavity is connected to the second cavity, and the other end is used as an outlet for crankcase gas.

When the cross-sectional area of the first cavity is scavenged, the gas backflow direction gradually expands.

The intake buffer and the crankcase are integrally designed, and the intake buffer and the crankcase of the engine are integrally cast.

The volume of the structural cavity is 2.5 times the volume of the backflow gas of the cylinder gas.

Two-stroke heavy oil piston engine with said buffer.

In the method of using the intake buffer of the two-stroke high-power heavy-gravity oil piston engine for intake buffering, during the normal intake process of the engine, the gas in the cylinder flows backwards, and the gas flows along the intake port whose section gradually expands. When it flows out of the cylinder, the speed of the gas gradually decreases during the flow;

After the gas flows through the outlet connecting the crankcase and the cylinder into the crankcase, it first flows through the first volume of the buffer, and the section of the first volume gradually expands, so that the speed of the backflow gas continues to decrease; the gas flows through the first volume. Then it flows into the second cavity through the hole between the first cavity and the second cavity, and the throttling effect is generated through the small hole, the pressure of the gas is reduced, the flow loss is increased, and the gas velocity is reduced;

Subsequently, when the gas flows from the second cavity into the third cavity, a throttling effect is also produced, which further reduces the pressure and velocity of the gas;

The fresh air flows out from the outlet of the scavenging pump and enters the crankcase through the third cavity and the second cavity. The fresh air in the third cavity and the second cavity flows through the first cavity together, and enters the cylinder through the outlet of the crankcase. The intake port on the upper, and finally enters the cylinder as a working fluid for circulation.

The design method of the air intake buffer of the two-stroke high-power heavy-gravity oil piston engine includes the following steps:

(1) According to the design requirements of the engine, determine the in-cylinder pressure when the intake valve of the engine cylinder is opened and the gas pressure at the outlet of the engine supercharger, and determine the gas pressure difference p ₁ -p on both sides of the gas port when the intake valve of the cylinder is opened ₂ , where p ₁ is the pressure inside the cylinder, and p ₂ is the pressure outside the cylinder;

(2) Simplify the differential formal equation along the fluid streamline direction for incompressible fluid and steady flow, as shown in the following formula:

According to the simplified conditions: V=const, ρ=const,

The incompressible fluid equation along the streamline direction is obtained as follows:

In the formula, ρ is the gas density, V ₁ is the gas velocity in the cylinder, V ₂ is the gas velocity outside the cylinder, z ₁ and z ₂ are the gas heights on both sides of the air inlet; set z ₁ and z ₂ to be equal;

Combined with the pressure difference p ₁ -p ₂ on both sides of the air inlet described in step (1), since the airflow velocity inside the cylinder is 0, set V ₁ equal to 0, according to the equation to find V ₂ is the backflow gas average backflow velocity;

(3) According to the gas expansion law in the engine cylinder, mathematically describe the isentropic expansion process of the gas, as shown in the following formula:

In the above formula, v ₁ is the gas specific volume when the intake valve is opened, v ₂ is the gas specific volume at the end of the gas backflow, and the value of n ranges from 1.32 to 1.36.

According to the two gas specific volumes, the downward distance of the piston during the gas backflow process is obtained, and the backflow time of the gas is obtained by combining the parameters of the cylinder bore, stroke and speed of the engine; Suppose, the average velocity of the reverse flow is obtained based on the assumed reverse flow and the calculated reverse flow time.

(4) By correcting the backflow, the average backflow velocity obtained in step (3) is consistent with the calculation result in (2); according to the estimation result described in step (3), the revised cylinder backflow gas is obtained quality;

(5) Calculate the distance of gas backflow from the duration of gas backflow obtained by combining the gas specific volume in step (3) with the parameters of the cylinder bore, stroke and rotational speed of the engine and the average backflow speed obtained in step (2), and use this as a buffer The initial length of the buffer is calculated from the backflow gas mass obtained after the correction in step (4); the initial cross-sectional area of the buffer;

(6) According to the intake port area of the buffer and the engine cylinder, and the mass continuity equation of the incompressible fluid:

q _m =ρV ₂ A=const

Correct the backflow speed of the backflow gas, and then repeat steps (3)-(5) to correct the length and cross-sectional area of the buffer; where q _m is the mass flow rate during backflow, that is, the gas flowing back from the cylinder per unit time Mass, A is the cross-sectional area of the buffer.

(7) After determining the overall outline size of the buffer, divide the length of the three internal cavities to ensure that the gas from the scavenging pump outlet enters the crankcase as evenly as possible. The lengths of the gas flow directions are equal.

The design method of the intake buffer of the two-stroke high-power heavy-gravity oil piston engine uses the aerodynamic principle, combines the design parameters of the intake and exhaust of the engine, and obtains the structural parameters of the buffer by solving the equation. Through theoretical calculation and structural design, the pollution amount of the backflow gas in the engine cylinder to the fresh intake air can be effectively controlled, and the air exchange quality of the engine can be effectively improved, which is conducive to improving the performance of the engine and realizing the high power and weight of the aviation piston engine. Compare.

As described above, a method for designing an intake buffer of a two-stroke high-power heavy-weight oil piston engine of the present invention has the following beneficial effects:

1. Effectively control the pollution of the backflow gas in the cylinder to the fresh inlet air and improve the intake air quality.

2. Push the backflowing gas into the cylinder again. Under the same excess scavenging coefficient, the mass of the gas participating in the scavenging increases, and the scavenging coefficient of the cylinder is larger.

3. In the case of the same excess scavenging coefficient, the scavenging efficiency of the cylinder is higher, the residual exhaust gas in the cylinder is less, the fresh air in the cylinder is more when the air is re-intaken, and the power of the engine per cycle is greater.

4. Without greatly increasing the weight of the engine structure, the air exchange quality of the engine is improved, the performance of the engine is improved, and the power-to-weight ratio of the engine is improved.

To sum up, the design method for the intake buffer of a two-stroke high-power heavy-gravity oil piston engine of the present invention can enable the engine to effectively control the pollution of the fresh intake air caused by the backflow gas in the cylinder, ensure the quality of the intake air of the cylinder, and ensure the quality of the intake air in the cylinder. After backflowing into the buffer, this part of the gas will be pushed into the cylinder again to be scavenged together with the scavenging gas. Under the same excess scavenging coefficient, the mass of the gas participating in the scavenging increases, and the scavenging coefficient of the cylinder is higher. If the cylinder is larger, the scavenging efficiency of the cylinder is higher, the residual exhaust gas in the cylinder is less, the fresh air in the cylinder is more when the air is re-intaken, and the engine can do more power per cycle. Since the buffer of the present invention is a group of rectangular cavities, it does not contain other mechanical moving parts, and its design size is in the range of ten to several tens of millimeters, and its structural weight is very light. In the case of structural weight, the ventilation quality of the engine is improved, the performance of the engine is improved, and the power-to-weight ratio of the engine is improved.

Description of drawings

Figure 1 is a schematic diagram of the outlet of the scavenging pump.

FIG. 2 is a schematic diagram of the intake buffer on the crankcase according to the present invention.

FIG. 3 is a schematic cross-sectional view of the intake buffer on the crankcase according to the present invention.

Figure 4 is a schematic diagram of the contact surface between the crankcase and the cylinder.

Figure 5 is a schematic diagram of the cylinder structure.

In the figure: 1- scavenging pump outlet, 2- buffer third chamber, 3- buffer second chamber 2, 4- buffer first chamber 3, 5- crankcase gas outlet, 6- cylinder intake Road, 7-cylinder.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1 , the intake buffer according to the present invention is located after the outlet 1 of the scavenging pump.

As shown in FIGS. 2 and 3 , the air intake buffer involved in the present invention includes three gas chambers, namely a first chamber 4 , a second chamber 3 and a third chamber 2 . The third cavity 2 and the second cavity 3 are in direct contact with the outlet of the scavenging pump, and the third cavity 2 and the second cavity 3 are connected through an opening, and the second cavity 3 and the first cavity 4 Also connected through a hole. One end of the first gas chamber 4 is connected to the second chamber 3 , and the other end serves as an outlet for crankcase gas.

As shown in Figures 4 and 5, the crankcase outlet 5 is connected to the cylinder 7 through the intake port 6 of the cylinder to realize the inflow of gas.

During the normal intake process of the engine, fresh air flows out from the scavenging pump outlet 1 and enters the crankcase through the third cavity 2 and the second cavity 3, and the fresh air in the third cavity 2 and the second cavity 3 together It flows through the first chamber 4, enters the intake port 6 on the cylinder through the outlet 5 of the crankcase, and finally enters the cylinder 7 as a working fluid for circulation.

When the engine is working, if you want to get a better cylinder scavenging effect, it is a very effective method to increase the valve overlap angle. When the opening time of the intake valve is advanced, the pressure ratio in the cylinder when the intake valve of the cylinder is opened will be increased. When the intake pressure is high, the gas in the cylinder will flow backwards. If the buffer is not used, the gas in the cylinder 7 enters the crankcase through the intake port 6, and then continues to pollute the fresh air forward. The air intake buffer involved in the present invention utilizes the multiple expansion and contraction of the flow channel during the gas flow process, so as to rapidly reduce the pressure and speed of the backflow gas, and restrict the outflow gas within a certain area through a cavity of a certain volume , slow down the speed of the gas to pollute the intake air forward, thereby controlling the pollution degree of the fresh intake air.

When the gas in the cylinder 7 flows backwards, the gas flows out of the cylinder along the intake port 6 whose cross-section gradually expands, and the speed of the gas gradually decreases during the flow. After the gas flows through the outlet 5 connecting the crankcase and the cylinder into the crankcase, it first flows through the first chamber 4 of the buffer. As shown in Figure 3, the section of the first chamber 4 is also gradually expanded, which will cause The speed of the backflow gas continues to decrease. After the gas flows through the first chamber 4, it flows into the second chamber 3 through the hole between the first chamber 4 and the second chamber 3. As shown in FIG. 3, the gas flows from the first chamber 4 into the second chamber. In cavity 3, a throttling effect is produced through the small holes, the pressure of the gas is reduced, the flow loss is increased, and the gas velocity is reduced. Similarly, when the gas flows from the second chamber 3 into the third chamber 2, a throttling effect will also occur, which further reduces the pressure and velocity of the gas. When the gas flows through the three chambers, the speed and pressure will decrease step by step.

The following describes a design method for the intake buffer of a two-stroke high-power heavy-gravity oil piston engine described in this paper through specific design steps. Those skilled in the art can easily understand other advantages and benefits of the present invention from the content disclosed in this specification, the present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be based on different From the viewpoint of application, various modifications or changes can be made without departing from the spirit of the present invention.

Please refer to FIGS. 1-5 . It should be noted that the diagrams provided in this document only illustrate the design results according to the design method discussed in the present invention in a schematic manner.

A design method for an intake buffer of a two-stroke high-power heavy-gravity oil piston engine of the present invention comprises the following steps:

The design method of the intake buffer of the two-stroke high-power heavy-gravity oil piston engine is characterized in that it comprises the following steps:

(1) According to the design requirements of the engine, determine the in-cylinder pressure when the intake valve of the engine cylinder is opened and the gas pressure at the outlet of the engine supercharger, and determine the gas pressure difference p ₁ -p on both sides of the gas port when the intake valve of the cylinder is opened ₂ , where p ₁ is the pressure inside the cylinder, and p ₂ is the pressure outside the cylinder;

(2) Simplify the differential formal equation along the fluid streamline direction for incompressible fluid and steady flow, as shown in the following formula:

Simplified conditions: V=const, ρ=const,,

The incompressible fluid equation along the streamline direction is obtained as follows:

In the formula, ρ is the gas density, V ₁ is the gas velocity in the cylinder, V ₂ is the gas velocity outside the cylinder, z ₁ and z ₂ are the gas heights on both sides of the air inlet; set z ₁ and z ₂ to be equal;

Combined with the pressure difference p ₁ -p ₂ on both sides of the intake port described in step 1, since the airflow velocity inside the cylinder is 0, set V ₁ equal to 0, according to the equation, V ₂ can be calculated as the average of the backflow gas backflow speed;

(3) According to the gas expansion law in the engine cylinder, mathematically describe the isentropic expansion process of the gas, as shown in the following formula:

In the above formula, v ₁ is the gas specific volume when the intake valve is opened, v ₂ is the gas specific volume at the end of the gas backflow, and the value of n ranges from 1.32 to 1.36.

During the exhaust period of the engine, the gas pressure in the cylinder is continuously decreasing. According to the formula given in step (3), from the initial state of the intake valve opening to the end of the gas backflow, the gas pressure in the cylinder gradually decreases to equal to the sweep air pressure. Corresponding to the two states of the opening of the intake valve and the end of the reverse flow, there are corresponding gas specific volumes in their respective states, and the gas specific volume is related to the cylinder volume, that is, related to the downward distance of the piston. According to the gas specific volume in the two states, the downward distance of the piston during the gas backflow process can be obtained,

Combining the parameters of the cylinder bore, stroke and speed of the engine, the backflow time of the gas can be obtained. Combined with the preliminary assumptions of the gas reduction in the cylinder during the gas backflow stage, the duration of the gas backflow and the average backflow speed are estimated; specifically, the backflow of an engine cylinder is assumed, such as 10% of the total gas volume, and then the This amount is corrected. According to the assumed backflow and the calculated backflow time, the average backflow velocity can be obtained.

(4) By making multiple assumptions about the reverse flow, the average reverse flow velocity obtained in the third step is consistent with the calculation result in the second step. According to the estimation result described in step (3), carry out preliminary calculation to the backflow gas quality of the cylinder;

(5) Calculate the distance of gas backflow from the duration of gas backflow obtained by combining the gas specific volume in step (3) with the parameters of the cylinder bore, stroke and rotational speed of the engine and the average backflow speed obtained in step (2), and use this as a buffer The initial length of the buffer is calculated from the backflow gas mass obtained after the correction in step (3); the initial cross-sectional area of the buffer;

(6) According to the intake port area of the buffer and the engine cylinder, and the mass continuity equation of the incompressible fluid:

q _m =ρV ₂ A=const

Correct the backflow speed of the backflow gas, and then repeat steps (3)-(5) to correct the length and cross-sectional area of the buffer; where q _m is the mass flow rate during backflow, that is, the gas flowing back from the cylinder per unit time Mass, A is the cross-sectional area of the buffer

(7) After determining the overall outline size of the buffer, divide the length of the three internal cavities to ensure that the gas from the scavenging pump outlet enters the crankcase as evenly as possible. The lengths of the gas flow directions are equal.

Through the above technology, the air exchange quality of the engine cylinder can be effectively controlled, and the overall performance of the engine can be improved by improving the air exchange quality of the engine, so that the structure of the engine is simple and lightweight, which is beneficial to the engine to achieve a high power-to-weight ratio.

The above are only preferred embodiments of the present invention and do not limit the present invention. Any simple modifications, changes and equivalent structural changes made to the above embodiments according to the technical essence of the present invention still belong to the technology of the present invention. within the scope of the program.

Claims (9)

1. a kind of engine charge buffer, which is characterized in that the buffer is located at the gentle cylinder air inlet of scavenging pump discharge Between, and there is at least one structure cavity, the structure cavity is flow backwards in cylinder in engine breathing to accommodate Combustion gas, the buffer have multiple structure cavities, and hole is provided on the intersection interface of adjacent cavity as appearance intracavity gas Inlet and outlet, area of section of each cavity in gas flow direction be greater than cavity disengaging open area so that buffer with into The section of port intersection, there is mutation in the section of each adjacent cavity intersection in buffer.

2. engine charge buffer described in claim 1, which is characterized in that the engine is the high power to weight ratio of two-stroke Heavy oil piston engine.

3. engine charge buffer described in claim 1, which is characterized in that the buffer includes the first cavity, the Two cavities and third cavity, wherein third cavity and the second cavity are directly connected to scavenging pump discharge, and third cavity and second Through hole is connected between cavity, is connected between the second cavity and the first cavity also by hole, first cavity one end connection second Cavity, outlet of the other end as crank case gases.

4. engine charge buffer as claimed in claim 3, which is characterized in that when the sectional area of first cavity is along scavenging Gas reflux direction is gradually expanded.

5. engine charge buffer described in claim 1, which is characterized in that the air inlet buffer and crankshaft are case integrated Design, the crankcase integrally casting shaping of air inlet buffer and engine.

6. engine charge buffer described in claim 1, it is characterised in that: the volume size of the structure cavity is cylinder 2.5 times of the volume of gas reflux gas.

7. having the high power to weight ratio heavy oil piston engine of two-stroke of the described in any item buffers of claim 1-4.

8. utilizing the method for engine charge buffer air inlet described in any one of claims 1-6 buffering, it is characterised in that: In the normal intake process of engine, the combustion gas in cylinder is flow backwards, and combustion gas is backflowed out of along the air intake duct that section gradually expands Cylinder, the speed of combustion gas gradually decreases in flow process；

Combustion gas is flowed through after the outlet that crankcase is connected with cylinder enters crankcase, first flows through the first cavity of buffer, and first The section of cavity gradually expands, and reduces the speed for flowing backwards combustion gas persistently；Combustion gas passes through the first cavity after flowing through the first cavity Hole between the second cavity flows into the second cavity, generates throttle effect, the pressure reduction of gas by aperture, and flow damage It loses and increases, gas velocity reduces；

Subsequent gas equally generates throttle effect when flowing into third cavity by the second cavity, keeps the pressure of gas and speed further It reduces；

Fresh air goes out from scavenging pump outlet flow, enters crankcase, third cavity and second by third cavity and the second cavity Fresh air in cavity flows through the first cavity together, and the air intake duct of cylinder is entered by the outlet of crankcase, finally enters gas It is recycled in cylinder as working medium.

9. a kind of design method of engine charge buffer described in any one of claims 1-6, it is characterised in that including such as Lower step:

(1) according to the design requirement of engine, in-cylinder pressure and engine booster when engine air cylinder intake valve is opened are determined The gas pressure of device outlet, and determine the gas pressure difference p of port two sides when cylinder intake valve is opened₁-p₂, wherein p₁For cylinder Interior pressure, p₂For cylinder external pressure；

(2) simplification that incompressible fluid and Steady Flow are carried out to the differential form equation along fluid flow line direction, such as following formula institute Show:

According to simplified condition: V=const, ρ=const,

The incompressible fluid equation along grain direction is obtained, is shown below:

In formula, ρ is gas density, V₁For cylinder interior air-flow speed, V₂For air velocity outside cylinder, z₁And z₂For air inlet two sides Gas height；If z₁And z₂It is equal；

The pressure difference p of the air inlet two sides in conjunction with described in step (1)₁-p₂, since the air velocity of cylinder interior is 0, if V₁ Equal to 0, V is found out according to equation₂As flow backwards the average refluence speed of combustion gas；

(3) according to the gas expansion rule in cylinder, mathematical description is carried out to gas isentropic expansion process, such as following formula institute Show:

In above formula, v₁Gas specific volume when being opened for inlet valve, v₂Value range for the gas specific volume that gas reflux terminates, n is 1.32~1.36,

The Bottom Runby of piston during gas reflux is obtained according to two gas specific volumes, cylinder diameter, row in conjunction with engine Journey and rotary speed parameter obtain the refluence time of combustion gas；And it is carried out in gas reflux stage gas in the jar reduction amount, that is, refluence amount Tentatively it is assumed that the average speed flow backwards according to the refluence amount of hypothesis and the refluence time being calculated；

(4) by being modified to refluence amount, so that the calculated result one in refluence average speed and (2) that step (3) obtains It causes；According to calculated result described in step (3), and obtains revised cylinder and flow backwards combustion gas quality；

(5) gas reflux that is obtained by cylinder diameter, stroke and the rotary speed parameter of gas specific volume combination engine in step (3) continues The average refluence speed that time and step (2) obtain calculates the distance of gas reflux, in this, as the initial length of buffer, By the initial cross-section area for flowing backwards combustion gas quality and calculating buffer obtained after being corrected in step (4)；

(6) according to the quality continuity equation of the air inlet open area and incompressible fluid of buffer and cylinder:

q_m=ρ V₂A=const

The refluence speed for flowing backwards combustion gas is modified, later repeatedly length and area of section of step (3)-(5) to buffer It is modified；Q in formula_mThe gaseous mass that mass flow when to flow backwards, i.e. unit time are backflowed out of from cylinder, A is buffer Area of section；

(7) it determines and the division in length is carried out to three internal cavities after the overall profile size of buffer, guarantee scavenging pump The gas of outlet enters uniform as far as possible when crankcase, designs cavity third cavity and the second cavity along the length phase of gas flow Deng.