CN113187628B - Method for measuring and calculating EGR (exhaust gas recirculation) rate of supercharged engine - Google Patents
Method for measuring and calculating EGR (exhaust gas recirculation) rate of supercharged engine Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 22
- 239000007789 gas Substances 0.000 claims abstract description 86
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 43
- 239000001301 oxygen Substances 0.000 claims abstract description 43
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 43
- 238000004364 calculation method Methods 0.000 claims abstract description 26
- 238000002485 combustion reaction Methods 0.000 claims abstract description 23
- 238000001228 spectrum Methods 0.000 claims abstract description 14
- 238000009795 derivation Methods 0.000 claims abstract description 4
- 239000000295 fuel oil Substances 0.000 claims abstract description 4
- 239000000446 fuel Substances 0.000 claims description 15
- 238000002347 injection Methods 0.000 claims description 9
- 239000007924 injection Substances 0.000 claims description 9
- 239000003921 oil Substances 0.000 claims description 6
- 229910052799 carbon Inorganic materials 0.000 claims description 5
- 230000005540 biological transmission Effects 0.000 claims description 4
- 230000008859 change Effects 0.000 claims description 3
- 238000006073 displacement reaction Methods 0.000 claims description 3
- 238000012360 testing method Methods 0.000 claims description 3
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- 239000001257 hydrogen Substances 0.000 claims description 2
- 230000008569 process Effects 0.000 claims description 2
- 239000000243 solution Substances 0.000 claims description 2
- 239000002912 waste gas Substances 0.000 abstract description 6
- 230000003134 recirculating effect Effects 0.000 description 6
- 238000007906 compression Methods 0.000 description 5
- 239000000203 mixture Substances 0.000 description 4
- 230000006835 compression Effects 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000002283 diesel fuel Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000001052 transient effect Effects 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- NAWXUBYGYWOOIX-SFHVURJKSA-N (2s)-2-[[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]amino]-4-methylidenepentanedioic acid Chemical compound C1=CC2=NC(N)=NC(N)=C2C=C1CCC1=CC=C(C(=O)N[C@@H](CC(=C)C(O)=O)C(O)=O)C=C1 NAWXUBYGYWOOIX-SFHVURJKSA-N 0.000 description 1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
- F02M26/45—Sensors specially adapted for EGR systems
- F02M26/46—Sensors specially adapted for EGR systems for determining the characteristics of gases, e.g. composition
- F02M26/47—Sensors specially adapted for EGR systems for determining the characteristics of gases, e.g. composition the characteristics being temperatures, pressures or flow rates
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B77/00—Component parts, details or accessories, not otherwise provided for
- F02B77/08—Safety, indicating, or supervising devices
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
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- Exhaust-Gas Circulating Devices (AREA)
Abstract
The invention discloses a method for measuring and calculating an EGR rate of a supercharged engine, which comprises the following steps: calculating a total charge mass flow; calculating the mass flow of the waste gas; calculating an EGR rate 1 based on pressures before and after an EGR valve; calculating the isentropic efficiency of the compressor; converting the actual rotating speed of the gas compressor into the folded rotating speed of the gas compressor; calculating the actual mass flow of the compressor; calculating an EGR rate 2 obtained based on the pulse spectrum derivation of the gas compressor; calculating the mass flow of the fuel oil; calculating the mass flow of the waste gas; calculating the oxygen mole number consumed by combustion and the unit mole mass of the exhaust gas when no EGR exists; calculating the unit molar mass of the exhaust gas when EGR exists; calculating an EGR rate 3 based on an exhaust gas oxygen sensor; the final EGR rate is calculated. The method mainly uses an EGR rate calculation method based on the front and rear pressures of the EGR valve, combines an EGR rate calculation method based on an exhaust oxygen sensor and a calculation method for deducing the EGR rate based on the pulse spectrum of the compressor, and can simply and efficiently calculate the EGR rate without using a Venturi tube flowmeter.
Description
Technical Field
The invention relates to the technical field of engines, in particular to a method for measuring and calculating an EGR (exhaust gas recirculation) rate of a supercharged engine.
Background
Exhaust Gas Recirculation (EGR) is a technique of remixing part of exhaust gas after combustion in a cylinder with fresh intake air as a mixture for combustion, and is one of the main measures for reducing NOx emissions of an engine at present. Recirculated exhaust gas has a significant effect on mixture formation, the period of combustion lag, the rate of combustion reaction, and the in-cylinder combustion temperature, so accurate and reliable calculation of EGR rate is critical to control the combustion process and reduce emissions.
At present, the engine mostly adopts a Venturi flowmeter to calculate the EGR rate, but the device has lower precision in transient state, the waste gas contains water vapor and soot, and the pressure guide pipe of the pressure sensor can generate liquid accumulation and carbon deposition in actual use. The accumulated liquid and carbon deposit can often cause the measurement distortion of the sensor, and the output of the sensor fluctuates. In cold winter or high and cold areas, condensed water in the pressure guiding pipe is easy to freeze and block, and finally the flowmeter cannot normally operate. In addition, throttling loss exists at the throat of the Venturi tube, the increase of the EGR rate is influenced, and the fuel consumption is deteriorated.
The existing EGR rate measurement and calculation methods mainly comprise the following steps:
an alternative method is to calculate the EGR rate based on empirical functions of combustion parameters and EGR rate using parameters such as cylinder pressure, ignition delay, premixed combustion ratio, etc., but this method is more difficult to apply to different engines due to differences in the combustion process.
Another alternative is to assume the EGR valve as the ideal nozzle, measure the pressure before and after the valve, calculate the exhaust gas flow by the basic thermodynamic equation, and calculate the EGR rate in combination with the intake air flow. When the pressure difference between the front pressure and the rear pressure of the EGR valve is small, the method is extremely sensitive to the measurement error of the pressure sensor, and the small pressure measurement error can bring large EGR rate calculation error.
The EGR rate can also be calculated by obtaining the mass of the air flow flowing through the supercharger, the pressure ratio is calculated by measuring the outlet pressure and the inlet pressure of the air compressor, the actual operation working condition point of the air compressor is determined based on the rotating speed and the pressure ratio of the air compressor by combining a rotating speed sensor arranged on the supercharger, the reduced flow is obtained, the mass flow of the air flowing through the air compressor is deduced by combining the air inlet temperature, and the EGR rate can be further calculated. The gas compressor is easy to have air resistance in large flow, easy to surge in small flow and unstable in gas flow motion, so that a frequency spectrum cannot be accurately expressed in small flow and low pressure ratio. The method can calculate and deduce the EGR rate under the normal pulse spectrum operation condition of the gas compressor, and can be used as an auxiliary calculation method of the EGR rate in practical application.
It is also a feasible method to measure the exhaust gas oxygen concentration using an oxygen sensor and then calculate the EGR rate. Assuming that diesel oil is completely combusted, combining the oxygen concentration of tail gas actually measured by an oxygen sensor, taking the same diesel oil consumption oxygen with the same mass as an equivalent relation, constructing a simultaneous equation set under the condition of no EGR and EGR, deducing fresh air inflow, waste gas amount, waste gas molar mass and the like through iterative calculation, and further calculating the EGR rate. Since diesel is a mixture, has no definite fuel composition and has a certain influence on the calculation of the EGR rate, the model needs to be calibrated and corrected by experiments.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a method for measuring and calculating the EGR rate of a supercharged engine aiming at the problems of a Venturi flowmeter.
The purpose of the invention is realized by the following technical scheme.
The invention discloses a method for measuring and calculating an EGR rate of a supercharged engine, which comprises the following steps of:
step 1: in a supercharged engine EGR system, a compressor air inlet of a turbocharger is provided with a pre-pressure temperature sensor and a pre-pressure sensor, a compressor air outlet is provided with a post-pressure temperature sensor and a post-pressure sensor, a transmission shaft of the turbocharger is provided with a rotor rotating speed sensor, an engine air inlet is provided with an air inlet temperature sensor and an air inlet pressure sensor, an engine air outlet is provided with an exhaust oxygen sensor, an EGR valve air inlet is provided with an EGR valve pre-temperature sensor and an EGR valve pre-pressure sensor, and an EGR valve air outlet is provided with an EGR valve post-pressure sensor;
step 2: the air inlet temperature T of the engine is measured by an air inlet temperature sensor and an air inlet pressure sensoriAnd intake pressure PiThe total charge mass flow m is calculated as followsch：
In the formula, mchTotal charge mass flow, kg/s; n is a radical ofeEngine speed, RPM; etavol(Ne) Is the rotational speed NeLower inflation efficiency,%; vdIs the engine displacement, m3；RgIs the intake gas constant, J/kg x K; t isiFor introducing airTemperature, K; piIs the intake pressure, pa;
and step 3: EGR valve inlet temperature T measured by EGR valve pre-temperature sensor, EGR valve pre-pressure sensor and EGR valve post-pressure sensoraInlet pressure PaAnd an outlet pressure PbThe mass flow m of exhaust gas is calculated as followsEGR：
Aeff(a)＝A(a)Cd(a)
In the formula, mEGRThe EGR mass flow is kg/s; paEGR valve front pressure, pa; t isaIs the pre-EGR valve temperature, K; pbEGR valve back pressure, pa; rmIs the exhaust gas constant, J/kg x K; a. theeff(a) M is the effective flow cross section area of the valve, and m is 2; psi (P)b,PaAnd κ) is a gas pressure influencing factor; kappa is an isentropic index; a (a) is the effective area of the valve, m ^ 2; d is the diameter of the valve, m; a is the valve opening degree; cd(a) Is the valve flow coefficient;
and 4, step 4: the EGR rate 1 based on the pressure before and after the EGR valve is calculated as follows:
and 5: the inlet temperature T of the compressor is measured by a pre-pressure temperature sensor and a pre-pressure sensor1Inlet pressure P1The temperature T of the outlet of the compressor is measured by a temperature sensor after the compressor is pressed and a pressure sensor after the compressor is pressed2Outlet pressureP2The actual rotating speed N of the gas compressor is measured by a rotor rotating speed sensortCalculating the isentropic efficiency eta of the compressor according to the following formulac：
In the formula etacIsentropic efficiency,%, of the compressor; t is1Is the compressor inlet temperature, K; t is2Is the compressor outlet temperature, K; p1The inlet pressure, Pa, of the compressor; p2The outlet temperature of the compressor is Pa; kappa is an isentropic index;
step 6: the actual rotating speed N of the compressor is calculated according to the following formulatConverted into the compressor reduced rotation speed Nnp：
In the formula, NnpThe compressor is in a reduced rotating speed; n is a radical oftThe actual rotating speed of the compressor; t is01Is the ambient temperature, considered equal to T1；
And 7: according to the pressure end pressure ratio P2/P1Isentropic efficiency eta of gas compressorcGas compressor reduced rotation speed NnpInquiring the MAP of the compressor by the three parameters, determining the operating point of the actual working condition in the pulse spectrum, and obtaining the reduced mass flow m of the compressor under the working conditioncnpFurther, the actual mass flow m of the compressor is calculated according to the following formulac：
In the formula, mcnpObtaining the gas compressor by looking up a table, wherein the gas compressor is obtained by converting (kg/s) into K ^ 0.5/kpa; m iscThe actual mass flow of the compressor is kg/s; p01Is ambient pressure, considered equal to P1；T01Is the ambient temperature, considered equal to T1；
And step 8: the compressor pulse spectrum-based derived EGR rate 2 is calculated as follows:
and step 9: the fuel mass flow m is calculated as followsf：
In the formula, mfThe mass flow of the fuel oil is kg/s; n is a radical ofcylThe number of the cylinders is; q. q offMg/cyl stroke is the single oil injection amount of each cylinder; n is a radical ofeEngine speed, RPM;
step 10: when there is no EGR, all the fresh air enters the cylinder, and the fresh air mass flow m is at this timea1Considered equal to the total charge mass flow mch；
ma1＝mch
Step 11: assuming that the EGR rate changes without causing a change in exhaust gas flow rate when the diesel injection strategy is unchanged, the exhaust gas mass flow m is calculated as followsex：
mex＝mch+mf
Step 12: exhaust gas oxygen concentration [ O ] at the time of no EGR measured by an exhaust gas oxygen sensor2-1]The molar number a of oxygen consumed by combustion in the absence of EGR is calculated by simultaneous solution according to the following two equations1And unit molar mass M of exhaust gasex1：
In the formula, a1Is the unit oxygen mole number, mol, consumed by combustion without EGR; mex1The unit molar mass of the exhaust gas without EGR, g/mol; m and n are respectively diesel equivalent molecular formula CmHnThe number of middle C, H, m and n are given by an oil product test report;
step 13: fresh air mass flow m with EGRa2Is equal to mass flow rate m of the compressorc：
ma2＝mc
Step 14: if the fuel injection strategy is kept unchanged, the mass flow m of fuel per cycle is in two states of EGR and EGR-freefSimilarly, assuming complete combustion of the fuel, the moles of oxygen consumed per cycle are the same, i.e.:
a1＝a2
in the formula, a2Is the unit oxygen mole number, mol, consumed by combustion in the presence of EGR;
step 15: exhaust gas oxygen concentration [ O ] in the presence of EGR measured by an exhaust gas oxygen sensor2-2]The unit molar mass M of exhaust gas in the presence of EGR is calculated by the following formulaex2：
Step 16: the EGR rate 3 obtained based on the exhaust gas oxygen sensor is calculated as follows:
and step 17: obtaining influence factors y1, y2 and y3 of three EGR rate calculation methods, namely an EGR rate calculation method based on pressures of the EGR valve at the front and the back under different working conditions, an EGR rate calculation method based on pulse spectrum derivation of a compressor and an EGR rate calculation method based on an exhaust oxygen sensor, and calculating the final EGR rate according to the following formula:
REGR＝REGR1×y1+REGR2×y2+REGR3×y3
compared with the prior art, the technical scheme of the invention has the following beneficial effects:
(1) the method for measuring and calculating the EGR rate of the supercharged engine has three different EGR rate calculation modes, improves the EGR rate calculation accuracy, and realizes the accurate control of the combustion of the diesel engine.
(2) The method for measuring and calculating the EGR rate of the supercharged engine adopts various sensors to measure parameters and calculate the EGR rate, and has good transient response.
(3) The method for measuring and calculating the EGR rate of the supercharged engine cancels a Venturi flowmeter, reduces throttling loss and is beneficial to reducing the fuel consumption rate.
Drawings
FIG. 1 is a schematic diagram of an engine EGR system.
Reference numerals: 1-an air inlet pipeline; 2-an air filter; 3, an air compressor; 4-an intercooler; 5-an intake throttle valve; 6-recirculating exhaust gas mixing tee joint; 7-an engine; 8-recirculating exhaust gas flow-dividing tee; 9-an EGR valve; 10-EGR intercooler; 11-a turbine; 12-a drive shaft; 13-a post-processor; 14-an exhaust line; 15-pre-nip temperature sensor; 16-a pre-compression pressure sensor; 17-post-compression temperature sensor; 18-post-compression pressure sensor; 19-rotor speed sensor; 20-an intake air temperature sensor; 21-an intake pressure sensor; 22-exhaust gas oxygen sensor; 23-pre EGR valve temperature sensor; 24-EGR valve front pressure sensor; 25-EGR valve back pressure sensor.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The invention provides a method for measuring and calculating an EGR (exhaust gas recirculation) rate of a supercharged engine, which is applied to an EGR system of the supercharged engine. The supercharged engine EGR system is shown in a schematic structural diagram in FIG. 1, and comprises an engine 7 and a turbocharger, wherein the turbocharger is composed of a compressor 3, a transmission shaft 12 and a turbine 11. An air filter 2 is arranged on an air inlet pipeline 1 connected with an air inlet of the air compressor 3, and an intercooler 4, an air inlet throttle valve 5 and a recirculating waste gas mixing tee joint 6 are sequentially connected between an air outlet of the air compressor 3 and an air inlet of the engine 7 through pipelines along the air flowing direction. An exhaust pipeline 14 connected with an exhaust port of the turbine 11 is provided with a post-processor 13, a recirculating exhaust gas shunting tee joint 8 is connected between an air inlet of the turbine 11 and an exhaust port of the engine 7 through a pipeline, and an EGR valve 9 and an EGR intercooler 10 are connected between the recirculating exhaust gas shunting tee joint 8 and the recirculating exhaust gas mixing tee joint 6 through pipelines along the gas flowing direction.
The working process of the supercharged engine EGR system is as follows: fresh air enters from an air inlet pipeline 1, sequentially flows through an air filter 2, an air compressor 3, an intercooler 4 and an air inlet throttle valve 5, and is mixed with recirculated exhaust gas through a recirculated exhaust gas mixing tee joint 6 to enter an engine 7. The engine exhaust gas flows out through the exhaust pipe and then is branched by the recirculating exhaust gas branching tee joint 8, one part of the engine exhaust gas flows through the turbine 11 and the postprocessor 13 in sequence and flows out from the exhaust pipe 14, and the other part of the engine exhaust gas flows through the EGR valve 9 and the EGR intercooler 10 in sequence and flows into the recirculating exhaust gas mixing tee joint 6 to be mixed with fresh air to enter the engine 7 again.
The method for measuring and calculating the EGR rate of the supercharged engine is mainly based on an EGR rate calculation method based on the front and back pressures of an EGR valve 9, and is combined with an EGR rate calculation method based on an exhaust oxygen sensor and a calculation method for deducing the EGR rate based on a pulse spectrum of a compressor to calculate the EGR rate comprehensively. The method specifically comprises the following steps:
step 1: in the supercharged engine EGR system, a pre-pressure temperature sensor 15 and a pre-pressure sensor 16 are arranged at an air inlet of a compressor 3 of a turbocharger, a post-pressure temperature sensor 17 and a post-pressure sensor 18 are arranged at an air outlet of the compressor 3, a rotor speed sensor 19 is arranged on a transmission shaft 12 of the turbocharger, an air inlet temperature sensor 20 and an air inlet pressure sensor 21 are arranged at an air inlet of the engine 3, an exhaust oxygen sensor 22 is arranged at an air outlet of the engine 7, an EGR valve pre-temperature sensor 23 and an EGR valve pre-pressure sensor 24 are arranged at an air inlet of an EGR valve 9, and an EGR valve post-pressure sensor 25 is arranged at an air outlet of the EGR valve 9.
Step 2: the intake temperature T of the engine 7 is measured by an intake temperature sensor 20 and an intake pressure sensor 21iAnd intake pressure PiCalculating the total charge mass flow m according to equation (1)ch：
In the formula, mchTotal charge mass flow, kg/s; n is a radical ofeEngine speed, RPM; etavol(Ne) Is the rotational speed NeLower inflation efficiency,%; vdIs the engine displacement, m3；RgIs the intake gas constant, J/kg x K; t isiIs the inlet air temperature, K; piIs the intake pressure, pa.
And step 3: the EGR valve inlet temperature T is measured by the EGR valve pre-temperature sensor 23, the EGR valve pre-pressure sensor 24 and the EGR valve post-pressure sensor 25aInlet pressure PaAnd outlet pressure PbCalculating the exhaust gas mass flow m according to the formula (2)EGR：
Aeff(a)＝A(a)Cd(a) (3)
In the formula, mEGRIs EGR mass flow, kg/s; paEGR valve front pressure, pa; t isaIs the pre-EGR valve temperature, K; pbEGR valve back pressure, pa; rmIs the exhaust gas constant, J/kg x K; a. theeff(a) M is the effective flow cross section area of the valve, and m is 2; psi(Pb,PaAnd κ) is a gas pressure influencing factor; kappa is an isentropic index; a (a) is the effective area of the valve, m 2; d is the diameter of the valve, m; a is the valve opening degree; cd(a) Is the valve flow coefficient.
And 4, step 4: the EGR rate 1 obtained based on the pressures before and after the EGR valve is calculated according to the formula (6):
and 5: the inlet temperature T of the compressor is measured by a pre-compression temperature sensor 15 and a pre-compression pressure sensor 161Inlet pressure P1The temperature T of the outlet of the compressor is measured by a temperature sensor 17 and a pressure sensor 18 after the pressure2Outlet pressure P2The actual speed N of the compressor is measured by a rotor speed sensor 19tCalculating the isentropic efficiency eta of the compressor according to the formula (7)c：
In the formula etacIsentropic efficiency,%, of the compressor; t is1Is the compressor inlet temperature, K; t is2Is the compressor outlet temperature, K; p1The inlet pressure, Pa, of the compressor; p2The outlet temperature of the compressor is Pa; κ is an isentropic index.
Step 6: according to a formula (8), the actual rotating speed N of the gas compressor is calculatedtConverted into the compressor reduced rotation speed Nnp：
In the formula, NnpThe compressor is in a reduced rotating speed; n is a radical oftThe actual rotating speed of the compressor; t is01Is the ambient temperature, can be considered equal to T1，K。
And 7: according to the pressure end pressure ratio P2/P1Isentropic effect of gas compressorRate etacGas compressor reduced rotation speed NnpInquiring the MAP of the compressor by the three parameters, determining the operating point of the actual working condition in the pulse spectrum, and obtaining the reduced mass flow m of the compressor under the working conditioncnpFurther, the actual mass flow m of the compressor is calculated according to the formula (9)c：
In the formula, mcnpObtaining the gas compressor reduced mass flow (kg/s) K ^0.5/kpa by looking up a table; m iscThe actual mass flow of the compressor is kg/s; p01For ambient pressure, it can be considered to be equal to P1，kpa；T01Is the ambient temperature, can be considered equal to T1，K。
And 8: calculating an EGR rate 2 derived based on the compressor pulse spectrum according to formula (10):
and step 9: calculating the fuel mass flow m according to equation (11)f：
In the formula, mfThe mass flow of the fuel oil is kg/s; n is a radical ofcylThe number of the cylinders; q. q offMg/cyl stroke is the single oil injection amount of each cylinder; n is a radical of hydrogeneEngine speed, RPM.
Step 10: when there is no EGR, all the fresh air enters the cylinder, and the fresh air mass flow m is at this timea1Considered equal to the total charge mass flow mch；
ma1＝mch (12)
Step 11: assuming that the EGR rate changes without a change in the exhaust gas flow rate when the diesel injection strategy is unchanged, the exhaust gas mass flow m is calculated according to equation (13)ex：
mex＝mch+mf (13)
Step 12: the exhaust gas oxygen concentration [ O ] at the time of no EGR is measured by the exhaust gas oxygen sensor 222-1]The molar number a of oxygen consumed by combustion in the absence of EGR is calculated by solving the equations (14) and (15) simultaneously1And unit molar mass M of exhaust gasex：
In the formula, a1Is the unit oxygen mole number, mol, consumed by combustion without EGR; mex1The unit molar mass of the exhaust gas without EGR, g/mol; m and n are respectively diesel equivalent molecular formula CmHnThe number of C, H in, m and n are given by the oil test report.
Step 13: fresh air mass flow m with EGRa2Is equal to mass flow rate m of the compressorc：
ma2＝mc (16)
Step 14: if the fuel injection strategy is kept unchanged, the mass flow m of fuel per cycle is in two states of EGR and EGR-freefSimilarly, assuming complete combustion of the fuel, the moles of oxygen consumed per cycle are the same, i.e.:
a1＝a2 (17)
in the formula, a2Is the moles, mol, of oxygen consumed per mole of combustion in the presence of EGR.
Step 15: the exhaust gas oxygen concentration [ O ] in the presence of EGR is measured by the exhaust gas oxygen sensor 222-2]Calculating the exhaust gas molar mass M in the presence of EGR according to the formula (18)ex2：
Step 16: the EGR rate 3 obtained based on the exhaust gas oxygen sensor is calculated as formula (19):
and step 17: influence factors y1, y2 and y3 of three EGR rate calculation methods, namely an EGR rate calculation method based on pressures around an EGR valve under different working conditions, an EGR rate calculation method based on pulse spectrum derivation of a compressor and an EGR rate calculation method based on an exhaust oxygen sensor, are obtained through experiments, and the final EGR rate is calculated according to a formula (22):
REGR＝REGR1×y1+REGR2×y2+REGR3×y3 (22)
while the present invention has been described in terms of its functions and operations with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise functions and operations described above, and that the above-described embodiments are illustrative rather than restrictive, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined by the appended claims.
Claims (1)
1. A method for measuring and calculating an EGR rate of a supercharged engine is characterized by comprising the following processes:
step 1: in a supercharged engine EGR system, a pre-pressure temperature sensor (15) and a pre-pressure sensor (16) are arranged at an air inlet of a compressor (3) of a turbocharger, a post-pressure temperature sensor (17) and a post-pressure sensor (18) are arranged at an air outlet of the compressor (3), a rotor rotating speed sensor (19) is arranged on a transmission shaft (12) of the turbocharger, an air inlet temperature sensor (20) and an air inlet pressure sensor (21) are arranged at an air inlet of an engine (7), an exhaust oxygen sensor (22) is arranged at an air outlet of the engine (7), an EGR valve pre-temperature sensor (23) and an EGR valve pre-pressure sensor (24) are arranged at an air inlet of an EGR valve (9), and an EGR valve post-pressure sensor (25) is arranged at an air outlet of the EGR valve (9);
step 2: the air inlet temperature T of the engine is measured by an air inlet temperature sensor and an air inlet pressure sensoriAnd intake pressure PiThe total charge mass flow m is calculated as followsch：
In the formula, mchTotal charge mass flow, kg/s; n is a radical of hydrogeneEngine speed, RPM; etavol(Ne) Is the rotational speed NeLower inflation efficiency,%; vdIs the engine displacement, m3；RgIs the intake gas constant, J/kg x K; t isiIs the inlet air temperature, K; piIs the intake pressure, pa;
and step 3: EGR valve inlet temperature T measured by EGR valve pre-temperature sensor, EGR valve pre-pressure sensor and EGR valve post-pressure sensoraInlet pressure PaAnd an outlet pressure PbThe mass flow m of exhaust gas is calculated as followsEGR：
Aeff(a)＝A(a)Cd(a)
In the formula, mEGRIs EGR mass flow, kg/s; paEGR valve front pressure, pa; t isaIs the pre-EGR valve temperature, K; pbEGR valve back pressure, pa; rmIs the exhaust gas constant, J/kg x K; a. theeff(a) M is the effective flow cross section area of the valve, and m is 2; psi (P)b，PaAnd κ) is a gas pressure influencing factor; kappa is an isentropic index; lambda (a) is the effective area of the valve, m ^ 2; d is the diameter of the valve, m; a is the valve opening degree; cd(a) Is the valve flow coefficient;
and 4, step 4: the EGR rate 1 based on the pressure before and after the EGR valve is calculated as follows:
and 5: the inlet temperature T of the compressor is measured by a pre-pressure temperature sensor and a pre-pressure sensor1Inlet pressure P1The temperature T of the outlet of the compressor is measured by a temperature sensor after the compressor is pressed and a pressure sensor after the compressor is pressed2Outlet pressure P2The actual rotating speed N of the gas compressor is measured by a rotor rotating speed sensortCalculating the isentropic efficiency eta of the compressor according to the following formulac：
In the formula etacIsentropic efficiency,%, of the compressor; t is1Is the compressor inlet temperature, K; t is2Is the compressor outlet temperature, K; p1The inlet pressure, Pa, of the compressor; p2The outlet temperature of the compressor is Pa; kappa is an isentropic index;
step 6: the actual rotating speed N of the compressor is calculated according to the following formulatConverted into the compressor reduced rotation speed Nnp：
In the formula, NnpThe compressor is in a reduced rotating speed; n is a radical oftThe actual rotating speed of the compressor is obtained; t is01Is the ambient temperature, considered equal to T1；
And 7: according to the pressure end pressure ratio P2/P1Isentropic efficiency eta of gas compressorcGas compressor reduced rotation speed NnpInquiring the MAP of the compressor by the three parameters, determining the operating point of the actual working condition in the pulse spectrum, and obtaining the reduced mass flow m of the compressor under the working conditioncnpFurther, the actual mass flow m of the compressor is calculated according to the following formulac：
In the formula, mcnpObtaining the gas compressor reduced mass flow (kg/s) K ^0.5/kpa by looking up a table; m iscThe actual mass flow of the compressor is kg/s; p01Is ambient pressure, considered equal to P1；T01Is the ambient temperature, considered equal to T1；
And 8: the compressor pulse spectrum-based derived EGR rate 2 is calculated as follows:
and step 9: the fuel mass flow m is calculated as followsf：
In the formula, mfThe mass flow of the fuel oil is kg/s; n is a radical ofcylThe number of the cylinders is; q. q.sfMg/cyl stroke is the single oil injection amount of each cylinder; n is a radical ofeIs the rotational speed of the engine and,RPM；
step 10: when there is no EGR, all the fresh air enters the cylinder, and the fresh air mass flow m is at this timea1Considered equal to the total charge mass flow mch；
ma1＝mch
Step 11: assuming that the EGR rate changes without causing a change in exhaust gas flow rate when the diesel injection strategy is unchanged, the exhaust gas mass flow m is calculated as followsex：
mex＝mch+mf
Step 12: exhaust gas oxygen concentration [ O ] at the time of no EGR measured by an exhaust gas oxygen sensor2-1]The molar number a of oxygen consumed by combustion in the absence of EGR is calculated by simultaneous solution according to the following two equations1And unit molar mass M of exhaust gasex1：
In the formula, a1Is the unit oxygen mole number, mol, consumed by combustion without EGR; mex1The unit molar mass of the exhaust gas without EGR, g/mol; m and n are respectively diesel equivalent molecular formula CmHnThe number of middle C, H, m and n are given by an oil product test report;
step 13: with EGR, fresh air mass flow ma2Is equal to mass flow rate m of the compressorc：
ma2＝mc
Step 14: if the fuel injection strategy is kept unchanged, the mass flow m of fuel per cycle is in two states of EGR and EGR-freefSimilarly, assuming complete combustion of the fuel, the moles of oxygen consumed per cycle are the same, i.e.:
a1＝a2
in the formula, a2Is provided withMolar number of oxygen consumed by combustion in EGR, mol;
step 15: exhaust gas oxygen concentration [ O ] in the presence of EGR measured by an exhaust gas oxygen sensor2-2]The unit molar mass M of exhaust gas in the presence of EGR is calculated by the following formulaex2：
Step 16: the EGR rate 3 obtained based on the exhaust gas oxygen sensor is calculated as follows:
and step 17: obtaining influence factors y1, y2 and y3 of three EGR rate calculation methods, namely an EGR rate calculation method based on pressures of the EGR valve at the front and the back under different working conditions, an EGR rate calculation method based on pulse spectrum derivation of a compressor and an EGR rate calculation method based on an exhaust oxygen sensor, and calculating the final EGR rate according to the following formula:
REGR＝REGR1×y1+REGR2×y2+REGR3×y3
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