CN103630471B - The measuring method of particle median particle diameter in a kind of diesel exhaust gas - Google Patents

Abstract

The present invention relates to field of measuring technique, propose a kind of method of measurements and calculations compression ignition engine exhaust particulate median particle diameter.The measuring method of particle median particle diameter in diesel exhaust gas of the present invention, mainly comprise gather candidate particles sample, candidate particles sample dispersion treatment, obtain discrete particles sem image, judge agglomerated particle degree of scatter, solve M _ithe steps such as the diameter of middle individual particle, finally obtain particle median particle diameter D in diesel exhaust gas ₅₀, contrasting oneself has technology, and the present invention does not need to obtain particle diameter by the conversion of electric current and particle diameter, the feature of the particle in 0.1 μm ~ 0.5 μm particle size range can be obtained intuitively, the process of the present invention's application particle sem image, can differentiate individual particle, improve the measuring accuracy of grain diameter.

Description

The measuring method of particle median particle diameter in a kind of diesel exhaust gas

Technical field

The present invention relates to field of measuring technique, propose a kind of method of measurements and calculations compression ignition engine exhaust particulate median particle diameter.

Background technology

The particle (particulate matter, PM) that automobile is discharged has become one of main source of air environmental pollution thing.2013, automobile " capital V " emission standard was implemented in Beijing, and automobile " state IV " emission standard will be implemented in nationwide.In stricter Abgasgesetz, except to except the quantitative limitation of motor vehicle emission particulate matter, also add the restriction requirement to particle number (particulate number, PN).Engine particle can be divided into thick state (1 ~ 10 μm), aggregative state (100 ~ 300nm) and core state (particle diameter is less than 50nm) according to particle size.Chinese scholars research shows, granular mass particle emission peak concentrates on aggregative state and thick state, and amounts of particles particle emission peak concentrates on core state.Measure engine combustion grain diameter rapidly and accurately, for the quantitative test of different-grain diameter granular mass and quantity discharge, and reduce granular mass and quantity discharge has great importance.

Grain diameter is different by measuring method, can be divided into aerodynamic diameter and electron transfer diameter.Aerodynamic diameter utilizes gravitational method, and electron transfer diameter utilizes number of particles Size Distribution method.For engine combustion particle, at present, the device measuring grain diameters such as scanning/transmission electron microscope (SEM/TEM), electrostatic low pressure ram (ELPI), scan-type electromigration grain graininess instrument (SMPS), amounts of particles and particle size analyzer (EEPS) are mainly adopted both at home and abroad.In measuring principle, SEM/TEM is by shooting particle sem image, and directly measure grain diameter, transformed error is little, can realize the high-acruracy survey of grain diameter in theory.Diesel engine particulate exists with the form of particle swarm usually, many chain, bulk structures in reuniting.Particle swarm contains tens to hundreds of individual particle, overlaps, be difficult to distinguish the profile of individual particle by means of only particle image between individual particle, and sem image obtains is local granule image, statistically poor.ELPI, SMPS and EEPS method mainly utilizes particle charge or electrostatic interaction, wherein, ELPI is made up of multi-stage impinger, utilizes the inertia of charged particle, measure and be deposited on the electric current that on ram, charged particle produces, indirectly obtain the number concentration of different-grain diameter (0.03 ~ 10 μm) particle.These three kinds of measuring methods are all indirectly obtain grain diameter and quantity by the conversion of electric signal, the particle diameter of the particle size results obtained mainly particle swarm, can not reflect the individual particle particle diameter situation that burning is formed, and measuring equipment are complicated, expensive.

For the deficiency of said method, a kind of method of the particle of Measurement in Diesel rapidly and accurately median particle diameter is proposed, the method of invention is conducive to the measuring method simplifying particle median particle diameter, reduce expense needed for testing equipment, for meeting, state five requirement of Abgasgesetz to grain count is significant.

Summary of the invention

The object of the invention is the diesel engine particulate in order to measure 0.1 μm ~ 0.5 μm of particle size range, proposing a kind of measuring method of diesel engine particulate median particle diameter.

For achieving the above object, the technical solution used in the present invention is:

In diesel exhaust gas, a measuring method for particle median particle diameter, comprises the steps:

Step 1: gather candidate particles sample;

Engine combustion particle in employing filter membrane collection engine main exhaust passageway is as candidate particles sample;

Step 2: the dispersion treatment of candidate particles sample;

Adopt ethanol/dichloromethane solution to extract particulate samples to be measured, ultrasonic disperse carried out to the suspending liquid after extraction, the solution after dispersion after filtration, dry after, obtain grain diameter and analyze sample;

Step 3: the sem image obtaining discrete particles;

Gather the image that grain diameter analyzes sample, obtain pending agglomerated particle sem image;

Step 4: the degree of scatter judging agglomerated particle;

Remember that total number of agglomerated particle in pending agglomerated particle sem image is M, adopt M _irepresent i-th agglomerated particle, i=1,2 ... M; According to the base plate lattice dimensions of pending agglomerated particle sem image, lattice method is adopted to measure M _iprojected area note be less than 1 μm ²agglomerated particle number be M ^*if, M ^*< 90%M, returns step 2; If M ^*>=90%M, thinks that particle tentatively disperses, note M _ithe number of middle individual particle is N _i, continue to enter step 5;

Step 5: solve M _ithe diameter of middle individual particle;

Step 5.1, torispherical hypothesis is carried out to individual particle:

Adopt curve fitting method to M _iprofile carry out matching, obtain matched curve, the ordinal number of the number of this matched curve flex point to be X, x be flex point, x=1,2 ... X, works as M _imiddle N _iwhen=1, X=0; Work as M _imiddle N _i=2, and when two individual particles are tangent, X=1; In all the other situations, X>=2, then an xth flex point for matched curve is designated as as X=1, remember that two sections of arc length are respectively with when X>=2, remember that the arc length of the matched curve between adjacent two flex points is y is the ordinal number of arc length;

The particle that step 5.2, eliminating flex point number are too much:

If X > 8, get rid of this agglomerated particle;

If X≤8, retain this agglomerated particle;

Step 5.3, judge M _imiddle individual particle number:

If X=0, i.e. N _i=1, enter step 5.4;

If X=1, i.e. N _i=2, enter step 5.5;

If X=2,3 ... 8, enter step 5.6;

Step 5.4, because N _i=1, then the diameter D of this individual particle ⁱcalculate according to the following formula:

If 0.1 μm of < D ⁱ< 0.5 μm, retains this individual particle diameter, otherwise gets rid of the diameter of this individual particle;

Step 5.5, because X=1, N _i=2, two individual particles are tangent, so the arc length of matched curve with be the girth of two individual particles, then the diameter of two individual particles respectively according to following formulae discovery: $D_I^i=C_I^i/\mathrm{\&pi;},D_{\mathrm{II}}^i=C_{\mathrm{II}}^i/\mathrm{\&pi;};$

If retain this individual particle diameter, otherwise get rid of the diameter of this individual particle;

If retain this individual particle diameter, otherwise get rid of the diameter of this individual particle;

Step 5.6, calculating X=2,3 ... when 8, the diameter of each individual particle:

Step 5.6.1, calculate the arc length of the matched curve between adjacent two flex points and note with air line distance between two corresponding flex points is through type (1) calculates for corresponding particle diameter;

$D_y^i\&times;\sin (180\&times;\frac{C_y^i}{\mathrm{\&pi;}{D}_y^i})=A_y^i---\left(1\right)$

Step 5.6.2, according to each calculate one by one obtain the set of particle diameter corresponding to arc length, for

The particle of step 5.6.3, eliminating same diameter:

To gather in each different numerical value only extract one, form new set; Then in this new set, the number of numerical value is this M _ithe number N of middle individual particle _i;

Remember that new set is b=1,2 ... N _i, represent M _ithe diameter of middle individual particle, b represents M _ithe sequence number of middle individual particle;

Incomplete particle is disperseed in step 5.6.4, eliminating agglomerated particle:

If N _i> 5, gets rid of this agglomerated particle;

If N _i=1 ~ 5, retain this agglomerated particle;

Step 5.6.5, the too high particle of eliminating reunion degree:

Note M _imiddle N _ithe summation of the theoretical projected area of individual individual particle is S _i, S _icalculate by formula (2):

$S_i=\underset{z=1}{\overset{N_i}{\mathrm{\&Sigma;}}}\frac{1}{4}\mathrm{\&pi;}{\left({\mathrm{DD}}_b^i\right)}^2---\left(2\right)$

M is calculated by formula (3) _ithe registration β of middle individual particle _i,

${\mathrm{\&beta;}}_i=\frac{S_i}{S_{M_i}}\&times;100\%---\left(3\right)$

If β _i≤ 50%, get rid of this M _ithe diameter of middle individual particle; If β _i> 50%, retains M _ithe diameter of middle individual particle

Step 5.7, eliminating exceed the individual particle diameter of measurement range:

Differentiate set one by one the diameter of middle individual particle, if meet $0.1\mathrm{\&mu;m}<{\mathrm{DD}}_b^i<0.5\mathrm{\&mu;m},$ Then retain this particle diameter, otherwise get rid of the diameter of this individual particle.

After differentiation, the set of the particle diameter of reservation is designated as represent the rear M of screening _ithe diameter of middle individual particle, z represents M _iin the sequence number of final individual particle, z=1,2 ... NN _i;

the number of middle numerical value is this M _iindividual particle number NN after middle screening _i;

If step 5.8 X=0, note D ⁱfor the diameter of individual particle in agglomerated particle; If X=1, note with for the diameter of individual particle in agglomerated particle; If X=2,3 ... 8, note for the diameter of individual particle in agglomerated particle;

Step 6: screening M _iin all be less than 1 μm ²agglomerated particle, adopt the method for step 5 to solve the diameter of individual particle in agglomerated particle one by one, the set of acquired results is designated as the individual particle diameter of particulate samples;

Step 7: the intermediate value of the individual particle diameter of count particles sample, is particle median particle diameter D in diesel exhaust gas ₅₀.

The invention has the beneficial effects as follows: contrasting oneself has technology, and it is simple and easy that the present invention has measurement mechanism, do not need to obtain particle diameter by the conversion of electric current and particle diameter, the feature of the particle in 0.1 μm ~ 0.5 μm particle size range can be obtained intuitively.The process of the present invention's application particle sem image, can differentiate individual particle, improve the measuring accuracy of grain diameter.

Accompanying drawing explanation

Accompanying drawing is used to provide a further understanding of the present invention, and forms a part for instructions, together with embodiments of the present invention for explaining the present invention, is not construed as limiting the invention.In the accompanying drawings:

Fig. 1: the original sem image of particle of the embodiment of the present invention.

Fig. 2: the effect schematic diagram of topography after the process of the embodiment of the present invention.

Fig. 3: the diameter of individual particle in each agglomerated particle in sample.

Fig. 4: particle median particle diameter calculation process.

Specific embodiments

Below in conjunction with specific embodiment, the present invention is described:

Step 1: gather candidate particles sample;

Engine combustion particle in employing filter membrane collection engine main exhaust passageway is as candidate particles sample; What adopt in the present embodiment is glass fiber filter, and sampling flow controls as 5L/min, and the sampling time is 10min.

Not before dispersion treatment, as shown in Figure 1, particle is chain to engine combustion particle sem image, bulk, floccule mass are got together, and the measurement of individual particle particle diameter is comparatively difficult.

Step 2: the dispersion treatment of candidate particles sample;

Adopt ethanol or dichloromethane solution to extract particulate samples to be measured, the addition of solvent is 5 times of particulate samples quality, and extraction leaves standstill 5min.Ultrasonic disperse is carried out to the suspending liquid after extraction, adopts the solution after being less than 300 object carbon nets/copper mesh filtration ultrasonic disperse, by baker, the carbon net/copper mesh containing particle is evaporated, obtain grain diameter and analyze sample.

Step 3: the sem image obtaining discrete particles;

Adopt scanning/transmission electron microscope to gather the image of grain diameter analysis sample, measurement range and precision can meet the measurement of 0.1 μm ~ 0.5 μm of particle size range particle.After gradation of image, Edge contrast, obtain pending agglomerated particle sem image, Fig. 2 is the effect schematic diagram of topography after process.

Step 4: the degree of scatter judging agglomerated particle;

Remember that total number of agglomerated particle in pending agglomerated particle sem image is M=15, adopt M _irepresent i-th agglomerated particle, i=1,2 ... 15; According to the base plate lattice dimensions of pending agglomerated particle sem image, lattice method is adopted to measure M _iprojected area be respectively: 0.21,0.43,0.15,0.32,0.31,1.12,0.38,0.21,0.35,0.46,0.37,0.19,0.22,0.33,0.27 μm ².Note be less than 1 μm ²agglomerated particle number be M ^*=1, M ^*meet M ^*>=90%M, thinks that particle tentatively disperses, note M _ithe number of middle individual particle is N _i.

With M ₂for example, continue to enter step 5, calculate M ₂the diameter of individual particle.

Step 5: solve M ₂the diameter of middle individual particle;

Step 5.1, torispherical hypothesis is carried out to individual particle:

Adopt curve fitting method to M ₂profile carry out matching, obtain matched curve, the ordinal number of the number of this matched curve flex point to be X=5, x be flex point, x=1,2 ... 5, then an xth flex point for matched curve is designated as remember that the arc length of the matched curve between adjacent two flex points is y is the ordinal number of arc length;

The particle that step 5.2, eliminating flex point number are too much:

M ₂the number X of matched curve flex point meets " X≤8 ", retains this agglomerated particle;

Step 5.3, judge M ₂middle individual particle number:

Because X=5 meets " X=2,3 ... 8 ", enter step 5.6;

When step 5.6, calculating X=5, the diameter of each individual particle:

Step 5.6.1, calculate adjacent two flex points with between the arc length of matched curve be 0.5 μm, with air line distance between two corresponding flex points be 0.12 μm, through type (1) calculates it is 0.2 μm.

$D_1^2\&times;\sin (180\&times;\frac{C_1^2}{\mathrm{\&pi;}{D}_1^2})=A_1^2---\left(1\right)$

Step 5.6.2, according to each calculate one by one obtain the set of particle diameter corresponding to arc length, for $D_1^2=0.2\mathrm{\&mu;m},D_2^2=0.13\mathrm{\&mu;m},D_3^2=0.36\mathrm{\&mu;m},D_4^2=0.47\mathrm{\&mu;m},D_5^2=0.36\mathrm{\&mu;m}.$

The particle of step 5.6.3, eliminating same diameter:

To gather in each different numerical value only extract one, form new set; Then in this new set, the number of numerical value is this M ₂the number N of middle individual particle ₂=4;

Remember that new set is b=1,2 ... N ₂, represent M ₂the diameter of middle individual particle, b represents M ₂the sequence number of middle individual particle; ${\mathrm{DD}}_b^2=\{0.2\mathrm{\&mu;m},0.13\mathrm{\&mu;m},0.36\mathrm{\&mu;m},0.47\mathrm{\&mu;m}\}.$

Incomplete particle is disperseed in step 5.6.4, eliminating agglomerated particle:

N ₂=4 meet " N _i=1 ~ 5 ", this agglomerated particle is therefore retained.

Step 5.6.5, the too high particle of eliminating reunion degree:

Note M ₂middle N ₂the summation of the theoretical projected area of individual individual particle is S ₂, S ₂calculate by formula (2):

$S_2=\underset{z=1}{\overset{N_2}{\mathrm{\&Sigma;}}}\frac{1}{4}\mathrm{\&pi;}{\left({\mathrm{DD}}_b^2\right)}^2---\left(2\right)$

Calculate S ₂=0.32 μm ².

M is calculated by formula (3) ₂the registration β of middle individual particle ₂, wherein,

${\mathrm{\&beta;}}_2=\frac{S_2}{S_{M_2}}\&times;100\%---\left(3\right)$

Calculate β ₂=74.4%, if meet β ₂> 50%, therefore, retains M ₂the particle diameter of middle individual particle

Step 5.7, eliminating exceed the individual particle diameter of measurement range:

Differentiate set one by one the diameter of middle individual particle, if meet $0.1\mathrm{\&mu;m}<{\mathrm{DD}}_b^2<0.5\mathrm{\&mu;m},$ Then retain this particle diameter, otherwise get rid of the diameter of this individual particle.

After differentiation, the set of the particle diameter of reservation is designated as represent the rear M of screening ₂the diameter of middle individual particle, z represents M ₂in the sequence number of final individual particle, z=1,2 ... NN ₂;

the number of middle numerical value is this M ₂individual particle number NN after middle screening ₂;

${\mathrm{FD}}_z^2=\{0.2\mathrm{\&mu;m},0.13\mathrm{\&mu;m},0.36\mathrm{\&mu;m},0.47\mathrm{\&mu;m}\},$ NN ₂=4。

Step 5.8, because X=5 meet " X=2,3 ... 8 ", so note for agglomerated particle M ₂the diameter of middle individual particle;

Step 6: screening M _iin all be less than 1 μm ²agglomerated particle, adopt the method for step 5 to solve the diameter of individual particle in agglomerated particle one by one, the set of acquired results is designated as the individual particle diameter of particulate samples; Final data result refers to Fig. 3.

Step 7: the intermediate value of the individual particle diameter of count particles sample, is particle median particle diameter D in diesel exhaust gas ₅₀=0.34 μm.

Below by reference to the accompanying drawings specific embodiment of the invention scheme is described; but these explanations can not be understood to limit scope of the present invention; protection scope of the present invention is limited by the claims of enclosing, and any change on the claims in the present invention basis is all protection scope of the present invention.

Claims (1)

1. the measuring method of particle median particle diameter in diesel exhaust gas, is characterized in that comprising the steps:

Step 1: gather candidate particles sample;

Engine combustion particle in employing filter membrane collection engine main exhaust passageway is as candidate particles sample;

Step 2: the dispersion treatment of candidate particles sample;

Adopt ethanol/dichloromethane solution to extract particulate samples to be measured, ultrasonic disperse carried out to the suspending liquid after extraction, the solution after dispersion after filtration, dry after, obtain grain diameter and analyze sample;

Step 3: the sem image obtaining discrete particles;

Gather the image that grain diameter analyzes sample, obtain pending agglomerated particle sem image;

Step 4: the degree of scatter judging agglomerated particle;

Remember that total number of agglomerated particle in pending agglomerated particle sem image is M, adopt M _irepresent i-th agglomerated particle, i=1,2 ... M; According to the base plate lattice dimensions of pending agglomerated particle sem image, lattice method is adopted to measure M _iprojected area note be less than 1 μm ²agglomerated particle number be M ^*if, M ^*< 90%M, returns step 2; If M ^*>=90%M, thinks that particle tentatively disperses, note M _ithe number of middle individual particle is N _i, continue to enter step 5;

Step 5: solve M _ithe diameter of middle individual particle;

Step 5.1, torispherical hypothesis is carried out to individual particle:

Adopt curve fitting method to M _iprofile carry out matching, obtain matched curve, the ordinal number of the number of this matched curve flex point to be X, x be flex point, x=1,2 ... X, works as M _imiddle N _iwhen=1, X=0; Work as M _imiddle N _i=2, and when two individual particles are tangent, X=1; In all the other situations, X>=2, then an xth flex point for matched curve is designated as as X=1, remember that two sections of arc length are respectively with when X>=2, remember that the arc length of the matched curve between adjacent two flex points is y is the ordinal number of arc length;

The particle that step 5.2, eliminating flex point number are too much:

If X > 8, get rid of this agglomerated particle;

If X≤8, retain this agglomerated particle;

Step 5.3, judge M _imiddle individual particle number:

If X=0, i.e. N _i=1, enter step 5.4;

If X=1, i.e. N _i=2, enter step 5.5;

If X=2,3 ... 8, enter step 5.6;

Step 5.4, because N _i=1, then the diameter D of this individual particle ⁱcalculate according to the following formula:

If 0.1 μm of < D ⁱ< 0.5 μm, retains this individual particle diameter, otherwise gets rid of the diameter of this individual particle;

Step 5.5, because X=1, N _i=2, two individual particles are tangent, so the arc length of matched curve with be the girth of two individual particles, then the diameter of two individual particles respectively according to following formulae discovery: $D_I^i=C_I^i/\mathrm{\&pi;},$ $D_{\mathrm{II}}^i=C_{\mathrm{II}}^i/\mathrm{\&pi;};$

If retain this individual particle diameter, otherwise get rid of the diameter of this individual particle;

If retain this individual particle diameter, otherwise get rid of the diameter of this individual particle;

Step 5.6, calculating X=2,3 ... when 8, the diameter of each individual particle:

Step 5.6.1, calculate the arc length of the matched curve between adjacent two flex points and note with air line distance between two corresponding flex points is through type (1) calculates for corresponding particle diameter;

$D_y^i\&times;\sin (180\&times;\frac{C_y^i}{\mathrm{\&pi;}{D}_y^i})=A_y^i---\left(1\right)$

Step 5.6.2, according to each calculate one by one obtain the set of particle diameter corresponding to arc length, for

The particle of step 5.6.3, eliminating same diameter:

To gather in each different numerical value only extract one, form new set; Then in this new set, the number of numerical value is this M _ithe number N of middle individual particle _i;

Remember that new set is b=1,2 ... N _i, represent M _ithe diameter of middle individual particle, b represents M _ithe sequence number of middle individual particle;

Incomplete particle is disperseed in step 5.6.4, eliminating agglomerated particle:

If N _i> 5, gets rid of this agglomerated particle;

If N _i=1 ~ 5, retain this agglomerated particle;

Step 5.6.5, the too high particle of eliminating reunion degree:

Note M _imiddle N _ithe summation of the theoretical projected area of individual individual particle is S _i, S _icalculate by formula (2):

$S_i=\underset{z=1}{\overset{N_i}{\mathrm{\&Sigma;}}}\frac{1}{4}\mathrm{\&pi;}{\left({\mathrm{DD}}_b^i\right)}^2---\left(2\right)$

M is calculated by formula (3) _ithe registration β of middle individual particle _i,

${\mathrm{\&beta;}}_i=\frac{S_i}{S_{M_i}}\&times;100\%---\left(3\right)$

If β _i≤ 50%, get rid of this M _ithe diameter of middle individual particle; If β _i> 50%, retains M _ithe diameter of middle individual particle

Step 5.7, eliminating exceed the individual particle diameter of measurement range:

Differentiate set one by one the diameter of middle individual particle, if meet then retain this particle diameter, otherwise get rid of the diameter of this individual particle;

After differentiation, the set of the particle diameter of reservation is designated as represent the rear M of screening _ithe diameter of middle individual particle, z represents M _iin the sequence number of final individual particle, z=1,2 ... NN _i;

the number of middle numerical value is this M _iindividual particle number NN after middle screening _i;

If step 5.8 X=0, note D ⁱfor the diameter of individual particle in agglomerated particle; If X=1, note with for the diameter of individual particle in agglomerated particle; If X=2,3 ... 8, note for the diameter of individual particle in agglomerated particle;

Step 6: screening M _iin all be less than 1 μm ²agglomerated particle, adopt the method for step 5 to solve the diameter of individual particle in agglomerated particle one by one, the set of acquired results is designated as the individual particle diameter of particulate samples;

Step 7: the intermediate value of the individual particle diameter of count particles sample, is particle median particle diameter D in diesel exhaust gas ₅₀.