The high power to weight ratio heavy oil piston engine air inlet buffer of two strokes of one kind and its design
Method
Technical field
The present invention relates to piston engine air inlet buffer structure design fields, and in particular to a kind of high power to weight ratio weight of two strokes
Oil piston engine charge buffer design method.
Background technique
With the development of General Aviation, two stroke heavy oil piston engines are gradually valued by people.Two-stroke piston
The performance of engine is affected by ventilation quality, a kind of ideal air exchange system, is as far as possible in small excessive scavenging system
Under the premise of number, coefficient of scavenging as big as possible is obtained, reduces the residual gas in the exhaust hood of scavenging completion.
For the aviation piston engine that high power to weight ratio requires, the construction weight for reaching engine target power should be use up
May be low, this requires optimizing engine performance in the case where engine structure weight is not significantly increased, it is advantageously implemented hair
The high power to weight ratio of motivation.
Existing anti-down Flow Technique mostly uses the check valve body device of various designs, structure to realize the one-way flow of fluid,
These structures are by several components by mechanical linkage, such as micro- resistance spring structure, and structure is complicated, and difficult design not only can
Increase mechanical construction weight, the flowing of fluid can also be interfered.
Summary of the invention
In view of the foregoing deficiencies of prior art, the purpose of the present invention is to provide one kind to be directed to two-stroke Gao Gongchong
Specific gravity oil piston engine blow-through air air inlet buffer and its design method, for solving cylinder gas reflux pollution new charge
Problem, while higher coefficient of scavenging is obtained in the case where identical new charge amount.The present invention is obtained by carrying out theoretical calculation
The parameters of structural dimension of buffer out, and the cylinder of the buffer structure and engine is the integrated design, with crankcase one
It is easier in technique with casting processing, it is cheaper in processing cost, it is easier to realize in production.
The complete technical solution of the present invention includes:
A kind of engine charge buffer, the buffer is located between the gentle cylinder air inlet of scavenging pump discharge, and has
There is the structure cavity of at least one, the structure cavity is in engine breathing to accommodate the combustion gas flow backwards in cylinder.
The engine is two-stroke heavy oil piston engine.
The buffer has 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
The section of air inlet intersection, there is mutation in the section of each adjacent cavity intersection in buffer.
The buffer includes the first cavity, the second cavity and third cavity, wherein third cavity and the second cavity with
Scavenging pump discharge is directly connected to, and through hole is connected between third cavity and the second cavity, between the second cavity and the first cavity
It is connected also by hole, first cavity one end is connected to the second cavity, outlet of the other end as crank case gases.
Gas reflux direction is gradually expanded when the sectional area scavenging of first cavity.
The crankcase integrally casting of the air inlet buffer and crankcase integrated design, air inlet buffer and engine at
Type.
The volume size of the structure cavity is 2.5 times of volume of cylinder gas reflux gas.
Two-stroke heavy oil piston engine with the buffer.
The method for carrying out air inlet buffering using the piston-engined air inlet buffer of the high power to weight ratio heavy oil of two-stroke,
In the normal intake process of engine, the combustion gas in cylinder is flow backwards, the air intake duct that combustion gas is gradually expanded along section to stream
Cylinder out, the speed of combustion gas gradually subtracts reduction in flow process;
Combustion gas is flowed through after the outlet that crankcase is connected with cylinder enters crankcase, and the first cavity of buffer is first flowed through,
The section of first cavity gradually expands, and reduces the speed for flowing backwards combustion gas persistently;Combustion gas passes through first after flowing through the first cavity
Hole between cavity and the second cavity flows into the second cavity, generates throttle effect, the pressure reduction of gas by aperture, and flow
Dynamic loss increases, and gas velocity reduces;
Subsequent gas equally generates throttle effect when flowing into third cavity by the second cavity, make gas pressure and speed into
One step reduces;
Fresh air goes out from scavenging pump outlet flow, enters crankcase by third cavity and the second cavity, third cavity and
Fresh air in second cavity flows through the first cavity together, is entered the air intake duct on cylinder by the outlet of crankcase, finally
It is used as working medium to be recycled into cylinder.
The design method of the piston-engined air inlet buffer of the high power to weight ratio heavy oil of the two-stroke, including walk as follows
It is rapid:
(1) according to the design requirement of engine, in-cylinder pressure and engine when engine air cylinder intake valve is opened are determined
The gas pressure of supercharger outlet, and determine the gas pressure difference p of port two sides when cylinder intake valve is opened1-p2, wherein p1For
Inner pressure of air cylinder, p2For cylinder external pressure;
(2) simplification of incompressible fluid and Steady Flow is carried out to the differential form equation along fluid flow line direction, it is as follows
Shown in formula:
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 cylinder outer gas flow rate speed, z1And z2For air inlet
The gas height of mouth two sides;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 V1Equal 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, it is as follows
Shown in formula:
In above formula, v1Gas specific volume when being opened for inlet valve, v2For the gas specific volume that gas reflux terminates, the value model of n
Enclose is 1.32~1.36.
The Bottom Runby of piston during gas reflux is obtained according to two gas specific volumes, in conjunction with the cylinder of engine
Diameter, stroke and rotary speed parameter obtain the refluence time of combustion gas;And in gas reflux stage gas in the jar reduction amount, that is, refluence amount
It carries out preliminary 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 calculating knot in refluence average speed and (2) that step (3) obtains
Fruit is consistent;According to estimation 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)
The average refluence speed that duration and step (2) obtain calculates the distance of gas reflux, in this, as the initial of buffer
Length, 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:
qm=ρ V2A=const
The refluence speed for flowing backwards combustion gas is modified, later repeatedly length and section of step (3)-(5) to buffer
Area is modified;Q in formulamThe gaseous mass that mass flow when to flow backwards, i.e. unit time are backflowed out of from cylinder, A is slow
Rush the area of section of device.
(7) it determines and the division in length is carried out to three internal cavities after the overall profile size of buffer, guarantee to sweep
The gas of air pump outlet enters uniform as far as possible when crankcase, designs cavity third cavity and the second cavity along the length of gas flow
It is equal.
The high power to weight ratio heavy oil piston engine air inlet buffer design method of the two-stroke, using pneumatic principle, in conjunction with hair
The design parameter of motivation intake and exhaust obtains the structural parameters of buffer by the solution to equation.Pass through theoretical calculation and structure
Design, can efficiently control the refluence combustion gas in cylinder to the contaminant capacity of new charge, can effectively improve hair
The ventilation quality of motivation, the high power to weight ratio for being conducive to the performance for improving engine and realizing aviation piston engine.
As described above, the high power to weight ratio heavy oil piston engine air inlet buffer design method of the present invention two strokes of one kind, tool
Have it is following the utility model has the advantages that
Pollution of the combustion gas to fresh inlet air is flow backwards in cylinder 1. efficiently controlling, and improves air mass.
2. the combustion gas backflowed out of is again pushed into cylinder, in the case where identical excessive coefficient of scavenging, scavenging is participated in
Gaseous mass increase, the coefficient of scavenging of cylinder is bigger.
3. the scavenging efficiency of cylinder is higher, and the residual gas in cylinder is more in the case where identical excessive coefficient of scavenging
Few, fresh air when air inlet in cylinder is more again, and the amount of work of per engine cycle is bigger.
4. promoting the ventilation quality of engine in the case where engine structure weight is not significantly increased, making engine
Performance boost, be conducive to the raising of engine power to weight ratio.
In conclusion the high power to weight ratio heavy oil piston engine air inlet buffer design method of two strokes of the invention, can make
Engine, which efficiently controls, flows backwards pollution of the combustion gas to fresh inlet air in cylinder, guarantee the air mass of cylinder, Er Qie
Gas reflux is into after buffer, this portion gas can be pushed into cylinder again and carry out scavenging together with scavenging gas, in phase
In the case where same excessive coefficient of scavenging, the gaseous mass for participating in scavenging increases, and the coefficient of scavenging of cylinder is bigger, the scavenging of cylinder
More efficient, the residual gas in cylinder is less, and fresh air when air inlet in cylinder is more again, the acting of per engine cycle
It measures bigger.Since buffer of the invention is one group of rectangle cavity, inside is without containing other mechanical moving elements, Er Qieqi
For design size under the scale of ten a few to tens of millimeters, construction weight is very light, and engine structure weight is not significantly increased this
In the case where amount, the ventilation quality of engine is promoted, the performance boost of engine is made, is conducive to mentioning for engine power to weight ratio
It is high.
Detailed description of the invention
Fig. 1 is scavenging pump discharge schematic diagram.
Fig. 2 is the enterprising pneumatic buffer schematic diagram of crankcase according to the present invention.
Fig. 3 is the enterprising pneumatic buffer schematic cross-section of crankcase according to the present invention.
Fig. 4 is crankcase and cylinder contact surface schematic diagram.
Fig. 5 is structural representation of air cylinder.
In figure: 1- scavenging pump discharge, 2- buffer third cavity, the second cavity of 3- buffer 2, the first cavity of 4- buffer
3, the outlet of 5- crank case gases, 6- inlet cylinder, 7- cylinder.
Specific embodiment
The present invention will be further described with reference to the accompanying drawings and detailed description.
As shown in Figure 1, air inlet buffer according to the present invention is located at after scavenging pump discharge 1.
As shown in Figure 2,3, air inlet buffer according to the present invention includes three gas cavities, i.e. the first cavity 4,
Two cavities 3 and third cavity 2.Wherein third cavity 2 and the second cavity 3 are directly contacted with scavenging pump discharge, and 2 He of third cavity
It is connected between second cavity 3 by an aperture, the second cavity 3 is connected with the first cavity 4 also by a hole.The first cavity of gas
4 one end are connected to the second cavity 3, outlet of the other end as crank case gases.
As shown in Figure 4,5, crankcase outlet 5 is connect with cylinder 7 by the air intake duct 6 of cylinder, realizes the inflow of gas.
In the normal intake process of engine, fresh air is flowed out from scavenging pump discharge 1, passes through third cavity 2 and the
Two cavities 3 enter crankcase, and the fresh air in third cavity 2 and the second cavity 3 flows through the first cavity 4 together, passes through crankshaft
The outlet 5 of case is entered the air intake duct 6 on cylinder, is finally entered in cylinder 7 and is recycled as working medium.
When the engine is working, if expecting preferable cylinder scavenging effect, it is highly effective for increasing valve overlap
Method, after the opening time of preadmission door, pressure ratio admission pressure when cylinder intake valve can be made to open in cylinder is high, in cylinder
Combustion gas can flow backwards.If not using buffer, the combustion gas in cylinder 7 enters crankcase by air intake duct 6, and then continues dirty forward
Contaminate fresh air.Air inlet buffer according to the present invention is made using the multiple expansion and contraction of runner in gas flow
The pressure and speed for flowing backwards combustion gas reduce rapidly, and will be limited in certain area to the combustion gas of outflow by the cavity of certain volume
In domain, slow down the speed that air inlet is polluted forward in combustion gas, thus pollution level of the control to new charge.
When the combustion gas in cylinder 7 is flow backwards, the air intake duct 6 that combustion gas is gradually expanded along section is flowed to outflow cylinder
The speed of combustion gas gradually subtracts reduction during dynamic.It is first after the entrance of outlet 5 crankcase that crankcase is connected with cylinder is flowed through in combustion gas
The first cavity of buffer 4 is first flowed through, as shown in figure 3, the section of the first cavity 4 is also in gradually expand shape, can make to flow backwards in this way and fire
The speed of gas persistently reduces.Combustion gas, which is flowed through, flows into the by the hole between the first cavity 4 and the second cavity 3 after the first cavity 4
In two cavities 3, as shown in figure 3, throttle effect is generated by aperture when gas flows into the second cavity 3 by the first cavity 4, gas
Pressure reduction, and flow losses increase, gas velocity reduces.Similarly, when gas flows into third cavity 2 by the second cavity 3
Throttle effect can be generated, the pressure of gas and speed are further decreased.When gas flows through three cavities, speed, pressure can be by
Grade reduces.
Illustrate the high power to weight ratio heavy oil piston engine of a kind of two stroke as described herein below by way of specific design procedure
Air inlet buffer design method.Those skilled in the art can be understood easily of the invention by content disclosed by this specification
Other advantages and benefit, the present invention can also be embodied or applied by other different embodiments, this specification
In every details can also based on different viewpoints in application, without departing from the spirit of the present invention carry out it is various modification or change
Become.
Please refer to Fig. 1-5, it should be noted that diagram presented herein only illustrates in a schematic way according to the present invention
The design method of middle discussion be designed after result.
The high power to weight ratio heavy oil piston engine air inlet buffer design method of two strokes of one kind of the invention, including following step
It is rapid:
The design method of the piston-engined air inlet buffer of the high power to weight ratio heavy oil of two-stroke, it is characterised in that including as follows
Step:
(1) according to the design requirement of engine, in-cylinder pressure and engine when engine air cylinder intake valve is opened are determined
The gas pressure of supercharger outlet, and determine the gas pressure difference p of port two sides when cylinder intake valve is opened1-p2, wherein p1For
Inner pressure of air cylinder, p2For cylinder external pressure;
(2) simplification of incompressible fluid and Steady Flow is carried out to the differential form equation along fluid flow line direction, it is as follows
Shown in formula:
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 cylinder outer gas flow rate speed, z1And z2For air inlet
The gas height of mouth two sides;If z1And z2It is equal;
The pressure difference p of the air inlet two sides in conjunction with described in step 11-p2, since the air velocity of cylinder interior is 0, if
V1Equal to 0, V can be 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, it is as follows
Shown in formula:
In above formula, v1Gas specific volume when being opened for inlet valve, v2For the gas specific volume that gas reflux terminates, the value model of n
Enclose is 1.32~1.36.
In the exhaust period of engine, the gas pressure in cylinder is constantly being reduced, according to the public affairs provided in step (3)
Formula, the original state opened from inlet valve terminate to gas reflux, and the gas pressure in cylinder is gradually reduced to equal than scavenging pressure.
Corresponding to IO Intake Valve Opens and two states terminated are flow backwards, there is corresponding gas specific volume under respective state respectively, and gas ratio
Appearance is related with volume of cylinder, i.e., related with piston Bottom Runby.It is available in combustion gas according to the gas specific volume under two states
The Bottom Runby of piston during refluence,
In conjunction with the cylinder diameter, stroke and rotary speed parameter of engine, the refluence time of combustion gas can be obtained.It is fallen in conjunction in combustion gas
Stream stage gas in the jar reduction amount preliminary is it is assumed that duration to gas reflux and averagely flowing backwards speed and estimating;Tool
Body is first to assume that the refluence amount of a cylinder is later again modified the amount such as the 10% of combustion gas total amount.According to vacation
If refluence amount and be calculated refluence time available refluence average speed.
(4) by carrying out repeatedly refluence amount it is assumed that in the refluence average speed and second step for obtaining third step
Calculated result is consistent.According to estimation result described in step (3), primary Calculation is carried out to the refluence combustion gas quality of cylinder;
(5) gas reflux that is obtained by cylinder diameter, stroke and the rotary speed parameter of gas specific volume combination engine in step (3)
The average refluence speed that duration and step (2) obtain calculates the distance of gas reflux, in this, as the initial of buffer
Length, by the initial cross-section area for flowing backwards combustion gas quality and calculating buffer obtained after being corrected in step (3);
(6) according to the quality continuity equation of the air inlet open area and incompressible fluid of buffer and cylinder:
qm=ρ V2A=const
The refluence speed for flowing backwards combustion gas is modified, later repeatedly length and section of step (3)-(5) to buffer
Area is modified;Q in formulamThe gaseous mass that mass flow when to flow backwards, i.e. unit time are backflowed out of from cylinder, A is slow
Rush the area of section of device
(7) it determines and the division in length is carried out to three internal cavities after the overall profile size of buffer, guarantee to sweep
The gas of air pump outlet enters uniform as far as possible when crankcase, designs cavity third cavity and the second cavity along the length of gas flow
It is equal.
Pass through above-mentioned technology, cylinder can be efficiently controlled ventilation quality, and changing by raising engine
Makings amount makes the overall performance of engine get a promotion, to make the simple and light of engine, is conducive to engine reality
Existing high power to weight ratio.
The above is only presently preferred embodiments of the present invention, is not intended to limit the invention in any way, it is all according to the present invention
Technical spirit any simple modification to the above embodiments, change and equivalent structural changes, still fall within skill of the present invention
In the protection scope of art scheme.