1 Experimental part

 

Experimental section

 

111 sample collection and pre-processing

 

Both the experimental lubricating oil and diesel are produced by Shanghai Oil Refinery. The lubricating oil specification is 15E/ 40CF24. The diesel is standard light diesel for engine testing of No. 0. It is made by blending and refining straight-run diesel fraction and catalytic cracking diesel fraction It is equivalent to the European Community Standard Diesel Reference Fuel CEC RF2032A284. The experimental procedures of the diesel engine bench were carried out strictly in accordance with the 13 working condition method in GB17691? 2005, and the particulate sampling adopts a split-flow constant-volume sampling system.

 

The sample and the blank filter paper (for comparison) were wrapped with glass fiber membrane and put into a 150 mL Sox-type extractor. After extraction with 75 mL dichloromethane (chromatographically pure) in a constant temperature water bath at 48°C for 14 h, the extract was KD concentration (Kuderna2Danish evaporation concentration device is referred to as KD concentration and cryopreservation for analysis (organic analysis).

 

Use a pipette to add 3 mL of diesel sample to the activated alumina chromatography column moistened with dichloromethane, and wash with 100 mL of 20% (volume fraction) n-hexane plus 80% (volume fraction) dichloromethane mixture Take off, take the eluate and concentrate for later use.

 

Cut the dried sample into a plastic bottle, accurately add 50 mL (pipette) of ultrapure water, shake it evenly, and put it in an ultrasonic cleaner for ultrasonic extraction for 30 minutes. After ultrasonic extraction is completed, take out the plastic bottle and let it stand still After diluting the supernatant, filter it twice with a disposable syringe filter to obtain the liquid to be analyzed (for inorganic ion analysis).

 

112 instrument conditions

 

Instruments: ICS22000 ion chromatograph, GC/MS (Agi2 lent 6890GC25975MSD).

 

Reagents: potassium hydroxide, methanesulfonic acid (manufactured by Di'an, USA).

 

Standard material: SO 4 2 -, NO 2 -, NO 3 -, F -, Cl-mixed standard samples produced by Agilent; the water used to prepare the mixed standard samples is ultrapure water.

 

Ion chromatography column: cation is IonpacCG (5 mm×50 mm) guard column, IonpacCS (5 mm×250 mm) separation column; anion is IonPacAⅡ2HC (4 mm×50 mm) guard column, IonPacAⅡ2HC (4 mm×250 mm) separation column. Suppressor current: anion is 75 mA; cation is 94 mA. Eluent: anion is 30 mmol/L potassium hydroxide solution; cation is 32 mmol/L methanesulfonic acid solution. Flow rate: 1 mL/min. Detector: conductivity detector.

 

Suppressor: anion ASRS24 mm; cation CSRs24 mm. Column temperature, conductivity cell temperature: cation 40℃, anion 30℃.

 

The chromatographic column of the GC-MS is AgilentHP25MS 5% PhenylMethyl Siloam (30 m×250μm×0125μm) capillary column. Sampling method: automatic injection of 1μL; vaporization chamber temperature: 250°C; programmed temperature increase: initial temperature 60°C, hold for 3 minutes, increase at 4°C/min to 160°C, hold for 2 minutes, and then increase at 5°C/min to 200 ℃, then rise to 300℃ at 4℃/min; Carrier gas: high purity helium; Scan mode: full scan, mass number 50～550; Solvent delay: 5 min; EI ion source temperature 230℃, quadrupole 150 ℃; mass spectrum tuning standard material: perfluorotributylamine (PFTBA); mass spectrum search library: N IST05 (American National Bureau of Standards).

 

113 Preparation of standard solution for experimental process: Weigh 21542 g of sodium chloride (NaCl), 11908 g of potassium chloride (KCl), 21770 g of anhydrous calcium oxide (CaCl 2), and sulfuric acid that have been dried at 120°C for 2 h. Magnesium (MgSO 4) 41953 g, weigh 21967 g of ammonium chloride (NH 4 Cl), dissolve them separately, transfer them to a 1L volumetric flask and dilute to the mark. The mass fraction of the mixed standard sample is 110×10-3.

 

Respectively take a certain amount of the standard stock solution mentioned above and put it into a volumetric flask and dilute with ultrapure water to a constant volume, and prepare a mixed standard solution of 5 concentrations as a standard curve. The mass concentration is 011 mg/L, 110 mg/L, 310 mg/L, 510 mg/L, 10 mg/L.

 

Anion: Transfer the purchased F -, Cl -, NO 2 -, SO 4 2 -, NO 3-mixed standard samples to polyethylene plastic bottles, respectively, take a certain amount of standard solution and put it into a volumetric flask with ultra pure Dilute with water to a constant volume, and prepare a mixed standard solution of 5 concentrations as a standard curve. The mass concentration is 0105 mg/L, 110 mg/L, 210 mg/L, 510 mg/L, 10 mg/L.

 

Dilute the filtrate obtained from the above pretreatment with distilled water, and use the American Diane ion chromatograph for quantitative detection. The injection volume is 25μL. The linear regression equation of the standard curve has a correlation coefficient r> 01999, and there is a good linear relationship between ion concentration and peak area. .

 

2 Results and discussion

 

After deducting the background of the inorganic ion content of the blank control sample A0, it is known that the exhaust particles do not contain magnesium ions, fluoride ions and chloride ions. The contents of various anions and cations in 15 samples are shown in 2.

 

According to the results, the mass fractions of sodium ion and ammonium ion in diesel engine exhaust particulate samples are relatively high, with averages of 31093% and 21507%, respectively, while the mass fractions of calcium and potassium ions are low, with an average of 21010% , 11727%. The cation content of each sample has no significant change with the engine model.

 

It can be seen that the mass fractions of sulfate radicals in 15 samples are all high, the largest value is the A11 sample, reaching 131989%, and the low value is 91252% for the A14 sample. The main reason for this result is the high sulfur content of the fuel used. . The diesel used in the bench test is the refined 0 light diesel, and its sulfur content is actually measured to be 1112×10-3 (mass fraction). However, to meet the requirements of the National III emission limit, the sulfur content of the diesel must be lower than 0135× 10- 3, obviously the fuel currently provided does not meet the requirements of the national emission standards. It is understood that the current vehicle fuel quality sold on the market cannot fully meet the emission requirements, resulting in a serious decline in the emission level of in-use vehicles that meet emission regulations. Taking No. 0 diesel as an example, the mass fraction of sulfur in commercial diesel in most parts of the country is 1150×10-3.

 

Analysis of 211 organic component determination results

 

Take the pretreated organic extract and analyze it. The total ion chromatograms of the 15 samples analyzed in the experiment are not listed here. Choose the total ion chromatogram of one of the samples (1).

 

Export the integration report and the N IST05 library search report, analyze and determine the detection order, name and molecular formula of each component of SOF (Soluble Organic Fraction), and use the area normalization method for quantification. See the results.

 

The analysis results show that the SOF component in diesel particulates is mainly composed of C13 to C34 normal alkanes and branched alkanes, of which alkanes below C 24 account for the main part of SOF, and their mass fraction is 6015%; in addition to alkanes, it is also detected There are a considerable number of polycyclic aromatic hydrocarbons (naphthalene, fluorene, phenanthrene, anthracene, etc.), mainly naphthalene and phenanthrene, with a mass fraction of 1413%; in addition, isobutyramide, 2, 62 Tert-butyl p-methylphenol (BHT) 311%, 22 methyl hexyl propionate, diisobutyl phthalate (DIBP), dibutyl phthalate (DBP), two phthalate Isooctyl ester (D IOP), tert-hexadecyl mercaptan, 6, 10, 142 trimethyl 222 pentadecanone and other phenols, esters, alcohols, ketones and derivatives, accounting for 2512% of the total components Among them, IBP, DBP, D IOP can be classified as phthalate esters (PAEs) 1718%, and others account for 413%.

 

212 source analysis of particulate matter

 

2. 2. Sources of alkanes in 1SOF

 

According to the analysis results, in the SOF component of diesel engine exhaust particles, the carbon number distribution of straight and branched alkanes is mainly concentrated around C 21, tetradecane, pentadecane, hexadecane, and heptadecane The proportion of SOF components is small, only 31858%. The main reason is that these 4 kinds of alkanes are relatively flammable in fuel oil and most of them are burned. It can be seen that the experimental diesel has a chain length of C10?C30 and a peak distribution of C18. Most of the alkanes in diesel exhaust particles are the same as the alkanes of the diesel component, indicating that the main source of SOF is incompletely burned diesel. However, diesel engine exhaust particles contain high-carbon paraffin C34, which is not detected in diesel () components. Literature <7> points out that the unburned lubricating oil entering the combustion chamber is also one of the sources of SOF. The existing domestic research on lubricating oil components is mainly concentrated in the petroleum smelting industry, because industry standards generally only include the components of lubricating oil base oil It is divided into three parts: saturated alkanes, aromatic hydrocarbons and gums, without in-depth analysis of specific components. But lubricating oil is generally composed of high-boiling, high-molecular-weight hydrocarbons, and the number of carbon atoms is generally C 15 to C45. Therefore, the C 34 in the particles detected in this paper is most likely to come from unburned lubricating oil that flees into the combustion chamber.

 

2. 2. 2 Source analysis of other components

 

Comparing the components of the particulate matter with the components of diesel, we can see that the types of polycyclic aromatic hydrocarbons (naphthalene, fluorene, phenanthrene, anthracene, etc.) in the particles are similar to those in diesel, and most of them are 223-ring PAHs and their derivatives. One result shows that the low-ring aromatic hydrocarbons in SOF are derived from unburned diesel.

 

Isobutyramide, 2,62 di-tert-butyl p-methylphenol (BHT), 22 methyl hexyl propionate, diisobutyl phthalate (DIBP), dibutyl phthalate (DBP) , Diisooctyl phthalate (DI2 OP), tert-hexadecyl mercaptan, 6, 10, 142 trimethyl 222 pentadecanone and other compounds were not detected in diesel. Since the mass fractions of BHT, D IBP, DBP and D IOP in diesel engine exhaust particulate samples account for more than 70% of other organic impurities, according to existing studies, it is known that the above-mentioned harmful substances are not detected in the lubricating oil base oil, and these can be judged The components are derived from lubricating oil additives. This test result should arouse the attention of environmental protection departments and the oil smelting industry.

 

Isobutyramide, 22 methyl hexyl propionate, tert-hexadecyl mercaptan, 6, 10,142 trimethyl 222 pentadecanone, these less impurities are neither detected in diesel, nor lubricating oil additives No such compounds have been detected in lubricating oil base oils in the literature, and it is inferred that they may be intermediate products of combustion under complex conditions. According to the above conclusions, the main sources of diesel engine exhaust particles are diesel 75138%, lubricant additives 21107%, and combustion intermediate products 3155%.