Could you please click on the top right corner of the old manFollowIt not only facilitates your discussion and sharing, but also brings you a different sense of participation. Thank you for your support!Wen|Qiwu JunEdit|Qiwu JunprefaceOzone is a molecule composed of three oxygen atoms with strong oxidizing ability

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Wen|Qiwu Jun

Edit|Qiwu Jun

preface

Ozone is a molecule composed of three oxygen atoms with strong oxidizing ability. It plays an important role in the atmosphere, as both an important oxidant and a harmful pollutant.

When ozone interacts with hydrocarbon compounds, it triggers a series of chemical reactions, producing various products, including ozone oxides and secondary organic aerosols. These reaction processes are of great significance for atmospheric chemistry, environmental pollution, and combustion science.

This article focuses on the study of the chemical changes and combustion properties of ozone injected into hydrocarbon compounds, and explores the reaction mechanism, product generation, and combustion properties of ozone and hydrocarbon compounds.

Materials, methods, and experimental preparation

Discharge reactor: Discharge is generated on the surface of a grid pattern discharge element placed in the discharge reactor. This component is designed to generate surface discharge, with a discharge voltage generated by a high AC voltage source (LogyElectric Co., LHV-13AC), ranging from 8.0 kV to 13.0 kV (with a frequency of approximately 9 kHz to 11 kHz).

Ozone concentration is measured as the standard for reactive oxygen species and is generated between 0.62 g/m3 and 8.8 g/m3 through dry air or pure oxygen.

Reactor containers and hydrocarbons: Petroleum and light diesel are used to react with dry air or oxygen exposed to discharge. We used commercial gasoline and light diesel oil in the test. The octane number of gasoline and the cetane number of light diesel oil are 90 to 92 and 53 to 55 respectively.

Hydrocarbons represented by gasoline and light diesel are composed of many chemical substances. Isooctane (2.2.4-trimethylpentane, C8H18), which is a component of gasoline and light diesel, will also be used as the experimental reactant.

These hydrocarbons evaporate in the reactor vessel (Figure 1) and are injected with air or oxygen exposed to discharge at the inlet to study the chemical reaction between the active species and the evaporated hydrocarbons. The entire experimental conditions were not controlled and were conducted at atmospheric pressure and a temperature of approximately 23 degrees Celsius.

Figure 1

Analysis of mixed gases

The gas mixture composition of dry air exposed to discharge and evaporated hydrocarbons was detected by Fourier transform infrared spectroscopy (FTIR, FTIR-8900) and gas chromatography-mass spectrometry (GC-MS, GCMS-QP2010).

For FTIR, a 22 meter reflective long-range gas cell (Permanently Aligned GasCell 162-2530) was installed to detect gas details. The wavenumber range of the mixed gas is between 4000cm-1 and 1000cm-1, and the FTIR spectrum of the mixed gas is accumulated 40 times.

The evaporation chamber temperature of GC (gas chromatography) is set to increase from 30 degrees Celsius to 250 degrees Celsius, with an increase of 10 degrees Celsius per minute. The entire measurement time is 24 minutes. The column flow rate is maintained at 2.43 milliliters per minute, and the column pressure is maintained at 97.9 kPa. The mass charge ratio in mass spectrometry was detected from 35 to 250m/z.

Fourier transform infrared analysis

Firstly, a transparent glass cover (approximately 18 liters) was mixed with dry air and hydrocarbons exposed by discharge. Pour 50 milliliters of commercially available gasoline (octane number 90-92) into a beaker and place it in the center of the glass cover. The gas flow rate injected into the glass cover is always maintained at 12 liters/minute.

After injecting dry air exposed by discharge, the evaporated hydrocarbons immediately become turbid and gradually form thick smoke (Figure 2). This indicates that the active substances in the gas have decomposed the structure of some hydrocarbons and generated water molecules. Therefore, the generation of turbid mixed gases may be caused by saturated water vapor.

Figure 2

As the basic component of gasoline, isooctane (2.2.4-trimethylpentane, C8H18) is mixed with dry air through a discharge chamber. In the testing, ozone concentration was used as a measure of several parameters and maintained at 2.7 grams per cubic meter.

The FTIR spectrum of the mixed gas is shown in Figure 3. In the FTIR spectrum, a peak at 1725cm-1 was clearly detected. This is believed to be a reaction product generated by hydrocarbons and active substances in discharged dry air.

There is a relatively sharp feature near 1058cm-1 and 2120cm-1 in the FTIR spectrum, attributed to additional ozone. CO2 near 2360cm-1 and N2O near 2237cm-1 were also detected.

Especially after injecting discharge dry air, the wide characteristics of hydrocarbons around 3000cm-1 are significantly weakened. These disappeared or weakened spectra, such as those near 3000cm-1, transform into other chemical structures.

However, due to the fact that the spectrum of H2O may be much weaker than other spectra, the presence of water was not observed in the spectrum. Through FTIR spectroscopy analysis, it was clearly found that injecting discharge dry air resulted in partial chemical changes in isooctane.

Analyzed the spectra that clearly appeared at 1725cm-1 in two FTIR spectra as reaction products. We mainly searched for oxidation products of hydrocarbons and found some candidates with strong peaks close to 1725cm-1, such as heptaldehyde (C7H14O), 2-hexanone (C7H14O), acetone (C3H6O), octanal (C8H16O), cis cyclohexane (C8H16O2), and dodecanal (C12H24O).

The FTIR spectrum of one of them, octanal, is shown in Figure 4. Ozone may be the main element generating hydrocarbon oxidation products, as other reactive oxygen species (such as oxygen atoms, singlet oxygen molecules, and hydroxyl groups) have much shorter lifespans than it.

In Figure 4, a typical FTIR spectrum of a mixture of evaporated gasoline and dry air exposed by discharge is shown. Although these spectra were not observed before the injection of dry air through the discharge reactor, reaction products similar to isooctane (2.2.4-trimethylpentane) were also detected at around 1725cm-1.

Figure 4

As the concentration of ozone increases, the generation rate of reaction products gradually saturates (Figure 5). The generation rate of newly detected spectra and weakened peaks of hydrocarbons strongly depends on the ozone concentration in the discharged dry air.

The typical peaks of additional ozone gas appear at 1058cm-1 and 2120cm-1, which do not react with hydrocarbons. In this study, peak values of reaction products and additional ozone gas were detected when injecting the thinnest 0.62 grams/cubic meter of ozone.

FTIR spectra above 3200cm-1 often show lower transmittance. Short wavelength infrared light tends to scatter around small particles in long-distance gas pools (such as water molecules generated in the reaction between ozone and hydrocarbons).

The spectrum of evaporated light diesel mixed with ozone is similar to other FTIR spectra (Figure 6). A peak of the reaction product was also observed at around 1725cm-1. Compared with gasoline, the specific gravity of light diesel is higher, so the production rate of reaction products near 1725cm-1 in the case of gasoline is lower.

Ozone is one of the necessary active gases for chemical changes in the chemical composition of evaporated hydrocarbons. It can be inferred that ozone partially decomposes the CH bonds of hydrocarbons and generates ozonated hydrocarbons as reaction products at 1725cm-1.

In summary, it was found that even the reaction products generated by the lowest concentration of ozone during testing were generated by injected ozone and hydrocarbons. These ozonated hydrocarbons may directly or indirectly contribute more effectively to improving the combustion of internal combustion engines.

Figure 6

By GC-MS analysis (gas chromatography-mass spectrometry analysis)

The experimental personnel conducted research on the detailed information of the reaction products, especially searching for the composition of strong peaks detected by FTIR near 1725cm-1. Gasoline evaporates at room temperature (23 degrees Celsius) and is injected into the sample inlet of GC-MS. The retention time data of GC is shown in Figure 7.

Figure 7

In addition, gasoline is evaporated and mixed with oxygen passing through the discharge reactor in a closed container. The mixed gas is directly introduced into GC-MS, and its spectrum is shown in Figure 8.

The spectral lines of GC-MS are identified through a spectral library, and the chemical substances are mainly indicated in Table 1. Search for chemical substances when the relative intensity is greater than 5 arbitrary units. The shaded cells in the "without zone" column of Table 1 represent the substances that undergo chemical changes after ozone injection.

In addition, the shaded cells in the "with Zone" column of Table 1 represent the oxidation products of hydrocarbons mainly generated after ozone injection. It was found that hydrocarbons bind to oxygen atoms or molecules after ozone injection.

Figure 8

The evaporated gasoline consists of approximately 300 hydrocarbons, and several high concentrations of compounds were detected by GC-MS from the evaporated gasoline, such as butane (C4H10), pentane (C5H12), and hexane (C6H14) (Table 1; ozone free).

After ozone injection, several reaction products were detected, such as acetaldehyde (C2H4O), heptaldehyde (C7H14O), 2-hexanone (C7H14O), and octanal (C8H16O).

The number of carbon atoms injected with ozone tends to be higher than that of evaporated gasoline without ozone treatment. It is expected that after the partial decomposition of CH bonds by ozone, the decomposed hydrocarbons will recombine.

A search was conducted on the FTIR spectra of reaction products of hydrocarbons bound to oxygen atoms or molecules using the scientific database of the National Institute of Standards and Technology (NIST Standard Reference Database) in the United States.

Many reaction products were found to have FTIR spectra near 1725cm-1, such as acetaldehyde (C2H4O), acetone (C3H6O), heptaldehyde (C7H14O), octanal (C8H16O), and dodecanal (C12H24O).

Combustion Properties of Vapor Phase Combustion Reaction between n-Octane and Ozone

Figure 10n-

The sampling point is located at the end of the flow reactor for analyzing the combustion reaction properties in the electric furnace. Using dry air as the air source for the ozone generator, the ozone concentration was maintained at 6.4 grams per cubic meter in the experiment.

Analyze carbon dioxide, carbon monoxide, oxygen, and nitrogen in the exhaust gas generated during the vapor phase combustion reaction of n-octane using gas chromatography thermal conductivity detector (GC-TCD). Analyze organic compounds in the gas at the sampling point using gas chromatography flame ionization detector (GC-FID).

Figure 10

The GC column has a radius of 4.0 to 6.0 millimeters and a length of 2.0 to 6.0 meters, made of copper or stainless steel. The GC column is equipped with packing materials for measuring gases in the exhaust gas; Porpak QS is used for analyzing carbon dioxide, while MS-5A is used for analyzing nitrogen, oxygen, and carbon monoxide.

Reversal rate of n-octane: In a saturated evaporator, dry air or ozone dry air is mixed with n-octane, and then the gas mixture is burned in an electric furnace at a temperature range of 200 to 800 degrees Celsius for one hour.

The combustion product gas is captured and then analyzed using diethyl ether as the internal standard substance through GC-FID. Evaluate the reversal rate of n-octane in vapor phase combustion reactions by analyzing the concentration of n-octane in the exhaust gas.

The concentration of n-octane is estimated through a calibration curve, which determines the ratio of n-octane peak area to the peak area and mass ratio of the internal standard substance (diethyl ether) in the gas chromatography. In addition, as mentioned above, other major combustion product gases (such as nitrogen, oxygen, carbon dioxide, and carbon monoxide) were analyzed using GC-TCD, and known concentrations were appropriately quantified using peak area calibration curves in gas chromatography.

The reversal rate of n-octane is derived from equation (1) related to the vapor pressure of n-octane (Antoine equation in equation (2)) and the amount of n-octane (equation (3)).

Ir: Conversion rate of n-octane (%) Co: Concentration of unreacted n-octane in liquid reaction product (mol) Ci: Initial concentration of n-octane (mol)

P: Vapor pressure (mmHg) A: 6.924 (Antoine constant of n-octane) B: 11355.126 (Antoine constant of n-octane) C: 209.517 (Antoine constant of n-octane) T: Temperature

Fn octane: flow rate of n-octane (milliliters/minute) Pn octane: vapor pressure of n-octane (atmospheric pressure) Fair: flow rate of air (milliliters/minute) Pair: vapor pressure of air (atmospheric pressure)

Figure 12100800n-30020%

Ozone gas may react with n-octane at lower reaction temperatures. At high temperatures, the reversal rate of n-octane becomes similar because the half-life of ozone tends to be shorter and ozone is prone to decomposition.

Concentration of combustion product gas

n-/Figure 13

When there is/is no ozone flowing into the saturated evaporator, the concentration of carbon monoxide generated during incomplete combustion gradually increases until 600 degrees Celsius. Then, at a reaction temperature of 700 degrees Celsius, the concentration of carbon monoxide rapidly decreases, while in the case of combustion with dry air, carbon dioxide rapidly increases.

In addition, when burned in ozone rich air, the concentration of carbon dioxide rapidly increases at 600 degrees Celsius. It is speculated that in n-octane combusted with ozone, complete combustion was achieved at temperatures almost 100 degrees Celsius lower than those without ozone combustion. Therefore, the results indicate that combustion reactions with/without ozone exhibit the same reaction and occur simultaneously in different reactions.

Figure 13

n-/300600Figure 14

Compared to dry air (without ozone), the combustion heat containing ozone is about 10 degrees Celsius lower at each reaction temperature. One of the reasons for the low combustion heat may be the intermediate products caused by ozone.

In addition, in the case of injecting ozone, the time required for uniform combustion heat in the electric furnace is about 10 minutes, while the time required for uniform combustion heat without ozone exceeds 30 minutes. Ozone injection may help stabilize combustion, as the time required to achieve uniform furnace temperature is also shorter than when ozone is not used.

Figure 14

summary

The FTIR spectra of vaporized hydrocarbons (commercial gasoline and light diesel) mixed with exhaust dry air were analyzed to study the intake stroke. After ozone injection, it was found that the FTIR spectrum of reaction product -1 and its generation rate were closely related to ozone concentration at around 1725cm.

In addition, it was found that thin ozone (0.76g/m3) contributed to the production of reaction products, with excess ozone detected at around 1058cm -1 and 2120cm-1. GC-MS detected the binding of hydrocarbons to oxygen atoms or molecules, and many of the reaction products had FTIR spectra close to 1725cm-1. The excess ozone was logically decomposed in the cylinder under high pressure and high temperature conditions.

It is speculated that hydrocarbons gradually undergo ozonation in the cylinder, and these reaction products contribute to effective combustion.

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