CN115112379A - Method for determining exhaust pressure of engine - Google Patents
Method for determining exhaust pressure of engine Download PDFInfo
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- CN115112379A CN115112379A CN202110301343.1A CN202110301343A CN115112379A CN 115112379 A CN115112379 A CN 115112379A CN 202110301343 A CN202110301343 A CN 202110301343A CN 115112379 A CN115112379 A CN 115112379A
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- 238000000034 method Methods 0.000 title claims abstract description 33
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 77
- 238000004364 calculation method Methods 0.000 claims abstract description 25
- 239000002245 particle Substances 0.000 claims description 20
- 239000000446 fuel Substances 0.000 claims description 18
- 239000007789 gas Substances 0.000 claims description 17
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 15
- 229910052799 carbon Inorganic materials 0.000 claims description 15
- 239000007921 spray Substances 0.000 claims description 12
- 239000002737 fuel gas Substances 0.000 claims description 7
- 239000003054 catalyst Substances 0.000 claims description 6
- 239000012041 precatalyst Substances 0.000 claims description 5
- 239000004071 soot Substances 0.000 claims description 4
- 239000003921 oil Substances 0.000 description 5
- 230000003197 catalytic effect Effects 0.000 description 4
- 238000007906 compression Methods 0.000 description 4
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- 239000003502 gasoline Substances 0.000 description 4
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- G01M15/04—Testing internal-combustion engines
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- G01M15/102—Testing internal-combustion engines by monitoring exhaust gases or combustion flame by monitoring exhaust gases
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Abstract
The present invention provides a method for determining exhaust pressure of an engine, comprising the steps of: and acquiring the flow rate, the flow area and the flow coefficient of the equivalent nozzle, and the pressure ratio of the upstream temperature, the downstream pressure and the upstream pressure of the equivalent nozzle, wherein the equivalent nozzle is a nozzle model established according to the structure of the exhaust pipe. The upstream pressure of the equivalent nozzle is determined based on the flow through, the upstream temperature, the flow area, the flow coefficient, and the pressure ratio. The exhaust pressure is determined based on the upstream pressure of the equivalent nozzle. By introducing influence factors including a flow cross section and a flow coefficient, correct calculation of hot exhaust gas in an engine cylinder is guaranteed, correct calculation of a fresh charge is further guaranteed, and accurate input is provided for oil consumption, emission, safety and dynamic performance of the engine.
Description
Technical Field
The invention relates to the field of automobiles, in particular to a method for determining exhaust pressure of an engine.
Background
The accuracy of the exhaust pressure of the engine directly determines the calculation accuracy of residual exhaust gas in an engine cylinder, so that the accuracy of fresh charging in the cylinder is influenced, the control of parameters such as ignition and oil injection of the engine is further influenced, and the oil consumption, the emission and the safety of the engine are finally influenced. For a supercharged engine, the accuracy of the exhaust pressure will also affect the accuracy of the supercharging control and thus the dynamic response of the engine. Therefore, accurate exhaust pressure calculation is a guarantee of engine oil consumption, emission, safety and dynamic performance.
The exhaust pressure mainly comprises a pressure Pcat before a catalytic package and a pressure Pexh before a turbine, and the exhaust pressure of a non-supercharged engine mainly refers to the pressure before the catalytic package. The present invention is described by way of example, but not by way of limitation, with respect to a supercharged engine.
The current mainstream calculation strategy of the exhaust pressure simplifies the pre-catalytic pressure into a function of exhaust flow and exhaust temperature, wherein the function is shown as formula (1), and the pre-catalytic pressure is calculated in a table look-up mode of flow and temperature; and the calculation of the preswirl pressure is simplified into the preswirl pressure, the exhaust flow and the supercharging pressure ratio pi in As in equation (2).
P cat ＝f(m,T) (1)
P exh ＝f(P cat ,m,π in ) (2)
The algorithm has good precision for gasoline engines of emission regulations in the fifth and past, but as emission and oil consumption regulations become more and more strict, particulate traps (GPF) and variable cross-section turbocharging (VGT) are more and more applied to gasoline engines, and the traditional mainstream exhaust pressure algorithm is over simplified to generate larger errors.
Disclosure of Invention
The invention aims to solve the problem that a mainstream exhaust pressure algorithm in the prior art generates a large error. A method for determining the exhaust pressure of an engine is provided, which improves the measurement and calculation precision of the exhaust pressure by introducing the influence factors of the flow cross section and the flow coefficient.
A method is provided for determining exhaust pressure of an engine, comprising the steps of:
acquiring the flow-through flow, the flow area and the flow coefficient of the equivalent spray pipe, and the pressure ratio of the upstream temperature, the downstream pressure and the upstream pressure of the equivalent spray pipe, wherein the equivalent spray pipe is a spray pipe model established according to an exhaust pipe structure; determining the upstream pressure of the equivalent nozzle according to the flow, the upstream temperature, the flow area, the flow coefficient and the pressure ratio; the exhaust pressure is determined based on the upstream pressure of the equivalent nozzle.
According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining an exhaust pressure of an engine, the determining the upstream pressure comprising:
in the formula:
P 1 the upstream pressure of the equivalent nozzle;
dm/dt is the flow rate;
f(T 1 ) Is an upstream temperature function obtained according to the upstream temperature and the gas constant of the fuel gas;
f (mu 1) is a flow coefficient function obtained according to the flow coefficient;
f(F res ) Is a flow area function obtained according to the flow area;
psi is a piecewise pressure ratio function derived from the pressure ratio.
According to another specific embodiment of the invention, the embodiment of the invention discloses a method for determining the exhaust pressure of an engine, a comparison table is prepared in advance according to the corresponding relation between the segmented pressure ratio function and the pressure ratio of the upstream and downstream of the equivalent nozzle, and the numerical value of the segmented pressure ratio function corresponding to the pressure ratio is obtained according to the table lookup of the comparison table when the engine is actually controlled.
Wherein, the segment pressure ratio function satisfies the relationship:
in the formula:
P 0 is the downstream pressure;
k is an isentropic index.
According to another embodiment of the present invention, a method for determining exhaust pressure of an engine, a flow coefficient function, is disclosedThe number f (mu) 1 )＝1/μ 1 In the formula, mu 1 Is the flow coefficient of the equivalent nozzle.
According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining exhaust pressure of an engine, a flow coefficient is obtained from a pressure ratio, and the flow coefficient satisfies a relationship with the pressure ratio:
μ 1 ＝a 1 +a 2 *π-a 3 *π 2 where pi is P 0 /P 1 Coefficient a 1 、a 2 、a 3 And carrying out calibration fitting according to the performance of the actual engine.
According to another embodiment of the present invention, a method for determining exhaust pressure of an engine is disclosed, the flow area function being F (F) res )＝1/F res In the formula F res Is the flow area; and is
If the engine does not have a particulate trap, the flow area function is a fixed value.
If the engine is provided with the particle trap, the flow area function is obtained by searching an accumulated carbon amount table according to the accumulated carbon amount of the particle trap, and the accumulated carbon amount table is obtained in advance through calculation according to the running time of the engine and the generated soot.
If the engine has a turbocharger, the flow area function is obtained by looking up a table according to the nozzle ring angle of the turbine.
According to another embodiment of the present invention, a method for determining exhaust pressure of an engine is disclosed, the upstream temperature function
In the formula:
r is a gas constant of fuel gas;
T 1 is the upstream temperature.
According to another embodiment of the present invention, a method for determining exhaust pressure of an engine is disclosed, wherein if the engine is in a steady state operating condition, the flow rate is intake air flow plus fuel mass flow, wherein the intake air flow is measured by a flow meter installed in an intake pipe, and the fuel mass flow is calculated according to the intake air flow, an air-fuel ratio and an excess air ratio;
if the engine is in dynamic conditions, the flow through is determined by dividing the available cycle intake mass plus the fuel mass by the time per cycle.
According to another embodiment of the invention, a method for determining exhaust pressure of an engine is disclosed, wherein if the engine has a particulate trap, a pipe model is established for the first equivalent pipe using the particulate trap, and the exhaust pressure comprises a pre-catalyst pack pressure, the pre-catalyst pack pressure being an upstream pressure of the first equivalent pipe.
If the engine is provided with the particle trap and the turbocharger, respectively establishing a nozzle model by the particle trap and the turbocharger as a first equivalent nozzle and a second equivalent nozzle, and the exhaust pressure comprises the pressure before a catalyst bag and the pressure before a turbine, wherein the pressure before the catalyst bag is the upstream pressure of the first equivalent nozzle, and the pressure before the turbine is the upstream pressure of the second equivalent nozzle.
According to another embodiment of the present disclosure, a method for determining an exhaust pressure of an engine is disclosed, wherein a pressure downstream of a first equivalent nozzle is atmospheric pressure. The downstream pressure of the second equivalent nozzle is directly obtained by a sensor. Alternatively, if the engine has a particulate trap and a variable area turbocharger, the pressure downstream of the second equivalent nozzle is the pressure upstream of the first equivalent nozzle.
The invention has the beneficial effects that:
the temperature of the mixed gas in the cylinder after the intake valve is closed is influenced by the amount of hot exhaust gas in the cylinder, and the temperature of the mixed gas is too high, so that the ignition type gasoline engine is possibly subjected to compression ignition in a compression stroke, the pressure rise rate is rapidly increased, and a crankshaft connecting rod mechanism is damaged. The invention aims to provide a more accurate exhaust pressure calculation strategy, which introduces influence factors of a flow cross section and a flow coefficient to ensure correct calculation of hot exhaust gas in an engine cylinder, further ensure correct calculation of a fresh charge and provide accurate input for oil consumption, emission, safety and dynamic performance of an engine.
Drawings
FIG. 1 is a schematic diagram of a model architecture of an equivalent nozzle for use in a method of determining exhaust pressure of an engine in an embodiment of the present invention;
FIG. 2 is a look-up table of a segmented pressure ratio function for a method of determining exhaust pressure of an engine in an embodiment of the present invention;
fig. 3 is a control flow block diagram of a method for determining exhaust pressure of an engine in an embodiment of the present invention.
Description of reference numerals:
10: a first equivalent nozzle;
11: upstream of the first equivalent nozzle; 12: downstream of the first equivalent nozzle;
20: a second equivalent nozzle;
21: upstream of the second equivalent nozzle; 22: downstream of the second equivalent nozzle.
Detailed Description
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure. While the invention will be described in conjunction with the preferred embodiments, it is not intended that features of the invention be limited to these embodiments. On the contrary, the invention is described in connection with the embodiments for the purpose of covering alternatives or modifications that may be extended based on the claims of the present invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be practiced without these particulars. Moreover, some of the specific details have been left out of the description in order to avoid obscuring or obscuring the focus of the present invention. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
It should be noted that in this specification, like reference numerals and letters refer to like items in the following drawings, and thus, once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings.
In the description of the present embodiment, it should be noted that the terms "upper", "lower", "inner", "bottom", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings or orientations or positional relationships that are conventionally placed when the products of the present invention are used, and are only used for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the devices or elements indicated must have specific orientations, be configured in specific orientations, and operate, and thus, should not be construed as limiting the present invention.
The terms "first," "second," and the like are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance.
In the description of the present embodiment, it should be further noted that, unless explicitly stated or limited otherwise, the terms "disposed," "connected," and "connected" are to be interpreted broadly, e.g., as a fixed connection, a detachable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present embodiment can be understood in specific cases by those of ordinary skill in the art.
To make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Examples
The present embodiment provides a method for determining exhaust pressure of an engine, comprising the steps of:
and obtaining the flow rate, the flow area and the flow coefficient of the equivalent spray pipe, and the pressure ratio of the upstream temperature, the downstream pressure and the upstream pressure of the equivalent spray pipe, wherein the equivalent spray pipe is a spray pipe model established according to an exhaust pipe structure. The upstream pressure of the equivalent nozzle is determined based on the flow through, the upstream temperature, the flow area, the flow coefficient, and the pressure ratio. The exhaust pressure is determined based on the upstream pressure of the equivalent nozzle.
Specifically, the equivalent nozzle refers to a tapered nozzle model established by an exhaust pipe system according to the engineering thermodynamic principle, wherein the front end (left end in fig. 1) and the rear end (right end in fig. 1) of the minimum section of the equivalent nozzle are respectively upstream and downstream of the equivalent nozzle. Taking an exhaust pipe system with a particle trap and a turbocharger as an example, an equivalent nozzle as shown in fig. 1 is established in the present embodiment, wherein the turbocharger is taken as a second equivalent nozzle 20, the left and right ends of the second equivalent nozzle 20 are respectively a second equivalent nozzle upstream 21 and a second equivalent nozzle downstream 22, the particle trap is taken as a first equivalent nozzle 10, and the left and right ends of the first equivalent nozzle 11 are respectively a first equivalent nozzle upstream 11 and a first equivalent nozzle downstream 12. At this time, the discharge pressure includes the upstream pressure of the first equivalent nozzle 10 and the second equivalent nozzle 20. In this model, the pressure downstream of the first equivalent nozzle 10 is atmospheric pressure and the pressure downstream of the second equivalent nozzle 20 is the pressure upstream of the first nozzle.
The flow rate is the flow rate passing through the equivalent nozzle and is the sum of the air intake quantity of the engine and the fuel injection quantity, the air intake quantity of the engine can be measured by a flow meter arranged in an air inlet pipe, and the fuel injection quantity can be calculated by the air intake quantity, the air-fuel ratio and the excess air coefficient (lambda).
The upstream temperature may be measured by a sensor or calculated from an exhaust temperature model of the engine.
Regarding the acquisition of the flow cross-section, if the item is a item with a particle trap, the fitting is performed according to the accumulated carbon amount of the particle trap, and if the particle trap is not present, the flow cross-section is constant.
The flow coefficient of the equivalent nozzle can be calculated and set according to an empirical formula or calibrated according to a specific engine.
It should be understood that the flow rate, upstream temperature, flow area, flow coefficient and pressure ratio to be obtained by determining the upstream pressure of the equivalent nozzle may be obtained directly at the corresponding position using sensors, or indirectly through computer conversion. The method for calculating the upstream pressure of the equivalent nozzle after obtaining the data may be calculating through a functional relationship, or performing a table look-up after a preliminary experiment, or calculating through other methods according to the parameters, and this embodiment emphasizes that the influence factors of the flow cross section and the flow coefficient are introduced into the exhaust pressure calculation strategy, and the specific calculation formula and calculation method are not specifically limited in this embodiment, and the preferred embodiment is described later, and will not be described herein again.
By adopting the scheme, the temperature of the mixed gas in the cylinder after the intake valve is closed is influenced by the amount of hot exhaust gas in the cylinder, and the temperature of the mixed gas is too high, so that the ignition type gasoline engine is possibly subjected to compression ignition in a compression stroke, the pressure rise rate rises rapidly, and a crankshaft connecting rod mechanism is damaged. The invention aims to provide a more accurate exhaust pressure calculation strategy, which introduces influence factors of a flow cross section and a flow coefficient to ensure the correct calculation of hot exhaust gas in an engine cylinder, further ensure the correct calculation of a fresh charge and provide accurate input for the oil consumption, the emission, the safety and the dynamic property of an engine.
In a preferred embodiment, the flow rate, the upstream temperature, the flow area, the flow coefficient and the pressure ratio satisfy the following functional relationship, and the upstream pressure of the equivalent nozzle is determined according to the following functional relationship.
In the formula:
P 1 the upstream pressure of the equivalent nozzle;
dm/dt is the flow rate;
f(T 1 ) Is an upstream temperature function obtained according to the upstream temperature and the gas constant of the fuel gas;
f (mu 1) is a flow coefficient function obtained according to the flow coefficient;
f(F res ) Is a flow area function obtained according to the flow area;
psi is a piecewise pressure ratio function derived from the pressure ratio.
It is to be understood that in the above formula, subscript 1 represents the equivalent nozzle upstream and subscript 0 represents the equivalent nozzle downstream.
Specifically, based on the flow equation (a) flowing through the equivalent nozzle, a back pressure calculation formula can be derived, and then an exhaust pressure calculation strategy is established.
Wherein, the segment pressure ratio function psi satisfies the relationship:
in the formula:
P 0 is the downstream pressure;
k is an isentropic index.
More specifically, in the above-mentioned segment pressure ratio function ψ, k is an isentropic index, and for pure combustion products, the equation of the especially linear property is: ke is 1.365-0.55/10000 × T, and when T changes by 100K, ke changes only by 0.0055, so ke can be approximately considered as a constant. That is to say (2/k +1) k/k-1 When P is equal to 0.528 0 /P 1 When the content is more than or equal to 0.528,
when P is present 0 /P 1 When the content is less than or equal to 0.528,
it should be understood that one skilled in the art can also write a calculation program into the controller or the terminal to calculate the k value at each temperature, so as to further improve the k value precision, (2/k +1) k/k-1 The value of 0.528 is an example, and this is not specifically defined in the present embodiment.
Wherein, P is calculated as a single function of the pressure ratio between the upstream and downstream of the equivalent nozzle 0 Then, canTo obtain P 1 Is a single valued function. The relationship between the pressure ratio and the pressure ratio is shown in FIG. 2.
Since the corresponding relation between the pressure ratio and the ke is uniquely determined after the ke is determined, the corresponding relation can be written into a table and the table can be looked up by the pressure ratio. Therefore, when the device is used, a comparison table shown in fig. 2 can be made in advance according to the corresponding relation between the segmented pressure ratio function and the pressure ratio of the upstream and downstream of the equivalent nozzle, and the numerical value of the segmented pressure ratio function corresponding to the pressure ratio is obtained according to the comparison table when the engine is actually controlled.
Further, in the above flow equation (a), ρ is a gas density, ρ 1 P 1 Subscript 1 in (1) represents the upstream of the equivalent nozzle, and similarly 0 represents the downstream of the equivalent nozzle, and dm is the flow rate flowing through the equivalent nozzle in dt times.
Based on the above equation (a), and PV ═ mRT and the density, the formula ρ ═ m/V can be derived:
the (b) is substituted and simplified by the formula (a), and comprises the following components:
in formula (c), R is the gas constant of the fuel gas, and has a value of 287.11J/(kg × K), and T1 is the upstream temperature of the effective nozzle. Therefore, the pressure P1 upstream of the equivalent nozzle is a function of the equivalent nozzle flow dm/dt, the upstream temperature T1, the flow coefficient μ, the flow area Fres, and the segment pressure ratio function, which is abbreviated as:
the following functional formula (e) which is satisfied among the flow rate, the upstream temperature, the flow area, the flow coefficient and the segment pressure ratio function is obtained:
further, the flow coefficient function is f (μ) 1 )＝1/μ 1 In the formula, mu 1 Is the flow coefficient of the equivalent nozzle. The flow coefficient is obtained as a function of a pressure ratio, and the flow coefficient and the pressure ratio satisfy the relationship:
μ 1 ＝a 1 +a 2 *π-a 3 *π 2 ，
wherein pi ═ P 0 /P 1 (ii) a Coefficient a 1 、a 2 、a 3 And carrying out calibration fitting according to the performance of the actual engine.
It should be understood that, in order to save effort, the fitting result may also be made into a calibration table, and the calibration table made in advance may be queried according to the pressure ratio when the flow coefficient is required to be obtained during the operation of the vehicle.
Taking a conventional engine as an example, the relationship between the flow coefficient and the pressure ratio is as follows:
μ 1 ＝0.49+0.46π-0.08π 2 in which pi is P 0 /P 1 。
That is, f (μ 1) can be determined by a pressure ratio lookup table as well, and the flow coefficient table can be obtained by making a table in advance and then looking up the table, in the same manner as the method of the segmented pressure ratio function ψ described above.
The coefficients a1, a2 and a3 are subjected to calibration fitting according to the performance of the actual engine, in order to save calculation power, the fitting result can also be made into a calibration table, and the table is looked up according to the pressure ratio
In a preferred embodiment, the engine is also calibrated directly to obtain the flow coefficient.
In the present embodiment, the empirical formula of the flow coefficient has its application range, so that it is more practical to perform calibration according to a specific engine.
Further, the flow area function is F (F) res )＝1/F res In the formula F res Is the flow area.
In particular, if the engine does not have a particulate trap, the flow area function is a fixed value, and the constant can be measured by one skilled in the art based on actual measurements.
If the engine is provided with the particle trap, the value of the flow area function is obtained by searching an accumulated carbon amount table according to the accumulated carbon amount of the particle trap, and the accumulated carbon amount table is obtained in advance according to the running time of the engine and the generated soot by calculation. The accumulated carbon quantity is obtained by an engine accumulated carbon model, and integral calculation can be carried out according to the running time of the engine and the generated soot. The accumulated carbon amount is inversely related to f (fres), the larger the accumulated carbon amount is, the smaller the flow area is, and a person skilled in the art can calculate a corresponding table of the accumulated carbon amount and the flow area according to the actual condition before loading.
If the engine is provided with a turbocharger, the value of the flow area function is determined by the angle of the turbine nozzle ring, and the flow area function can be fitted according to the angle of the turbine nozzle ring and obtained by looking up a table according to the angle of the turbine nozzle ring when the engine is used.
When the engine has both the turbocharger and the particulate trap, referring to fig. 1, the calculation is performed in two stages, the pressure at the upstream of the particulate trap is calculated by the above formula (e) as the input of the pressure at the downstream of the turbocharger, and then the pressure at the upstream of the turbocharger is calculated by the above formula (e).
Further, upstream temperature function
In the formula:
r is a gas constant of fuel gas;
T 1 is the upstream temperature.
The upstream temperature T1 may be measured by a sensor or may be calculated by an exhaust temperature model of the engine.
Further, if the engine is in a steady state condition, the flow dm/dt is the intake air flow plus the fuel mass flow, wherein the intake air flow is measured by a flow meter installed in the intake pipe, and the fuel mass flow is calculated according to the intake air flow, the air-fuel ratio and the excess air coefficient.
If the engine is in dynamic conditions, the flow through dm/dt is determined from the available cycle charge mass plus the fuel mass divided by the time per cycle.
Specifically, dm/dt is the flow rate through the equivalent nozzle, i.e., the sum of the engine intake air amount (intake air flow rate) which can be measured by a flow meter installed in the intake pipe, and the fuel injection amount (fuel mass flow rate) which can be calculated from the intake air amount, the air-fuel ratio, and the excess air ratio lambda. The dynamic working condition refers to the working conditions of acceleration, deceleration and the like.
Taking an equivalent nozzle modeled by a turbocharger as an example, a control diagram for obtaining the upstream pressure of the equivalent nozzle according to the flow rate, the upstream temperature, the flow area, the flow coefficient and the segmented pressure ratio function is shown in fig. 3.
According to another embodiment of the invention, a method for determining exhaust pressure of an engine is disclosed, according to which, if the engine has a particulate trap, a pipe model is established for the first equivalent pipe using the particulate trap, and the exhaust pressure includes a pre-catalyst pack pressure that is a pressure upstream of the first equivalent pipe. If the engine is provided with the particle trap and the turbocharger, respectively establishing a nozzle model by the particle trap and the turbocharger as a first equivalent nozzle and a second equivalent nozzle, and the exhaust pressure comprises the pressure before a catalyst bag and the pressure before a turbine, wherein the pressure before the catalyst bag is the upstream pressure of the first equivalent nozzle, and the pressure before the turbine is the upstream pressure of the second equivalent nozzle.
Specifically, the pressure downstream of the first equivalent nozzle is atmospheric pressure. The downstream pressure of the second equivalent nozzle is directly obtained by a sensor. If the engine is provided with a particle catcher and a variable-section turbocharger, the pressure downstream of the second equivalent nozzle can be directly obtained by a sensor, and the pressure upstream of the first equivalent nozzle can be the pressure downstream of the second equivalent nozzle.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing is a more detailed description of the invention, taken in conjunction with the specific embodiments thereof, and that no limitation of the invention is intended thereby. Various changes in form and detail, including simple deductions or substitutions, may be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (10)
1. A method for determining exhaust pressure of an engine, comprising the steps of:
acquiring the flow rate, the flow area and the flow coefficient of an equivalent spray pipe, and the pressure ratio of the upstream temperature, the downstream pressure and the upstream pressure of the equivalent spray pipe, wherein the equivalent spray pipe is a spray pipe model established according to an exhaust pipe structure;
determining an upstream pressure of the equivalent nozzle from the flow through, the upstream temperature, the flow area, the flow coefficient, and the pressure ratio;
determining the exhaust pressure based on an upstream pressure of the equivalent nozzle.
2. The method for determining exhaust pressure of an engine of claim 1, wherein determining the upstream pressure comprises:
in the formula:
P 1 is the pressure upstream of the equivalent nozzle;
dm/dt is the flow rate;
f(T 1 ) Is an upstream temperature function obtained according to the upstream temperature and the gas constant of the fuel gas;
f (mu 1) is a flow coefficient function obtained according to the flow coefficient;
f(F res ) Is a flow area function obtained according to the flow area;
ψ is a segmented pressure ratio function obtained from the pressure ratio.
3. The method for determining the exhaust pressure of the engine according to claim 2, wherein a look-up table is prepared in advance according to the correspondence between the segmented pressure ratio function and the pressure ratios upstream and downstream of the equivalent nozzle, and the numerical value of the segmented pressure ratio function corresponding to the pressure ratio is obtained according to the look-up table when the engine is actually controlled; wherein,
the segment pressure ratio function satisfies the relationship:
in the formula:
P 0 is the downstream pressure;
k is an isentropic index.
4. The method for determining exhaust pressure of an engine according to claim 2, wherein said flow coefficient function is f (μ [) 1 )＝1/μ 1 ，
In the formula, mu 1 Is the flow coefficient of the equivalent nozzle.
5. The method for determining exhaust pressure of an engine according to claim 4,
the flow coefficient is obtained from the pressure ratio, and the flow coefficient and the pressure ratio satisfy a relationship:
μ 1 ＝a 1 +a 2 *π-a 3 *π 2 ，
wherein pi ═ P 0 /P 1 ；
Coefficient a 1 、a 2 、a 3 And carrying out calibration fitting according to the performance of the actual engine.
6. The method for determining exhaust pressure of an engine of claim 2, wherein the flow area function is F (F) res )＝1/F res In the formula F res Is the flow area; and is
If the engine does not have a particulate trap, the flow area function is a fixed value;
if the engine is provided with the particle trap, the flow area function is obtained by searching an accumulated carbon amount table according to the accumulated carbon amount of the particle trap, and the accumulated carbon amount table is obtained in advance according to the running time of the engine and the generated soot in a calculation mode;
if the engine is provided with a turbocharger, the flow area function is obtained by looking up a table according to the angle of the nozzle ring of the turbine.
7. The method for determining exhaust pressure of an engine of claim 2, wherein the upstream temperature function
In the formula:
r is a gas constant of fuel gas;
T 1 is the upstream temperature.
8. The method for determining exhaust pressure of an engine according to claim 2,
if the engine is in a steady-state working condition, the flowing-through flow is intake flow and fuel mass flow, wherein the intake flow is measured by a flow meter arranged in an intake pipe, and the fuel mass flow is obtained by calculation according to the intake flow, an air-fuel ratio and an excess air coefficient;
if the engine is in a dynamic condition, the flow through is determined according to the available cycle intake mass plus the fuel mass divided by the cycle time.
9. The method for determining exhaust pressure of an engine according to any one of claims 1-8,
if the engine is provided with a particle catcher, establishing a nozzle model of the particle catcher as a first equivalent nozzle, and enabling the exhaust pressure to comprise the pressure before a catalyst bag, wherein the pressure before the catalyst bag is the upstream pressure of the first equivalent nozzle;
if the engine is provided with a particle trap and a turbocharger, respectively establishing a nozzle model by the particle trap and the turbocharger as a first equivalent nozzle and a second equivalent nozzle, and the exhaust pressure comprises a pre-catalyst bag pressure and a pre-turbine pressure, wherein the pre-catalyst bag pressure is the upstream pressure of the first equivalent nozzle, and the pre-turbine pressure is the upstream pressure of the second equivalent nozzle.
10. The method for determining exhaust pressure of an engine according to claim 9,
the downstream pressure of the first equivalent nozzle is atmospheric pressure;
the downstream pressure of the second equivalent nozzle is directly obtained through a sensor; or
If the engine has a particulate trap and a turbocharger, the pressure downstream of the second equivalent nozzle is the pressure upstream of the first equivalent nozzle.
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