Gas Phase Mixture Research Articles

Laboratory simulations of ice growth in space: An expected nonuniform ice mantle composition

Context. In dense, cold molecular regions, gas-phase chemical species freeze out onto grain surfaces. These icy condensates become an important reservoir of volatile elements and feedstock for molecular diversity. Aims. While there is a fairly general agreement on the chemical composition of icy mantles, there are differences in how the various molecular components are perceived to be present. Should the materials composing the ice be mixed or are they segregated into distinct chemical zones? Methods. To answer such a question, we performed a few exploratory experiments that allowed the adsorbing surface (mimic dust grains) to slowly relax to very low temperatures while gas-phase mixtures of H2O, NH3, and CO embed onto it. Results. We find that mantles are far from being uniform, and they could evolve into completely mixed ices only if the ambient temperature undergoes a catastrophic collapse. Conclusions. Under the typical conditions of an interstellar dense cloud, ices present a high degree of molecular segregation, with possible consequences on the ice chemistry and the desorption mechanisms.

Investigation of thermodynamic state evolution, phase transition and mixing of the hydrocarbon droplet in convective supercritical environments

Liquid alkane droplets transit to supercritical fluids under supercritical conditions. However, the subsequent thermodynamic state evolution, phase transition, and mixing in this case, which directly influences combustion in actual diesel engines, need further investigation. We studied the thermodynamic state evolution, phase transition, and mixing of n-heptane droplets in supercritical laminar nitrogen streams through a set of conservation equations. Non-ideal thermodynamic and transport properties were calculated to incorporate the dramatic variation of physical properties in the supercritical regime. We focus on the effects of Reynolds number, ambient pressure, and droplet size on the thermodynamic state evolution, phase transition and mixing of droplets. Results showed that increasing the Reynolds number can accelerate the evolution of thermodynamic states, which leads to the faster transition of droplets from the liquid phase and supercritical fluids to gas-phase mixtures. With the increased Reynolds number, the phase transition rate is increased and the mixing homogeneity is improved due to the enhanced mass transfer. Caused by the negative correlation between mass transfer and ambient pressure, in higher pressure, droplets after the supercritical transition require more time to transition from supercritical fluids to vapor-phase mixtures. Increasing ambient pressure inhibited the droplet phase transition process and deteriorated the mixing homogeneity, but no significant influence was shown on the droplet dynamic evolution process. Smaller droplets transition faster from liquid phase and supercritical fluids to vapor-phase mixtures. The faster thermodynamic state evolution and faster dynamic evolution process of the smaller droplet leads to its more rapid homogeneous mixing with ambient gasses, but the mode of dynamics is independent of the droplet size.

Exploring Gas-Phase Chemical Reactions in NH3/B2H6 Systems for Chemical Vapor Deposition Using Reactive Molecular Dynamics.

Hexagonal boron nitride (hBN) has attracted significant attention as a two-dimensional (2D) material due to its unique structure and properties. In this paper, we investigated the gas-phase reactions between B2H6 and NH3 and the reaction pathways potentially leading to the synthesis of hBN by using ReaxFF-based reactive molecular dynamics (MD) simulations. From the hundreds of chemical reaction pathways observed in these MD simulations, we extracted a highly reduced chemical kinetic model to describe the gas-phase mixture evolution in chemical vapor deposition of hBN using B2H6 and NH3 as precursors. The intent is to integrate this chemical model into future computational fluid dynamics (CFD) simulations of actual hBN deposition testing and production reactors to provide enhanced insights for experimental synthesis processes and reactor optimization. The chemical model of this study will serve as a stepping stone for large-scale simulations.

Two-stage thermocatalytic conversion of waste XLPE to diesel-like fuel

Cross-linked polyethylenes (XLPE) are not preferred in industrial pyrolysis applications and mechanical recovery methods due to great thermochemical resistance to heat and deformation. The studies on pyrolysis of XLPE up to 600?C on obtaining fuel have generally yielded high levels of wax and have not been of interest to the energy sector. In this study, two-stage pyrolysis of XLPE was carried out catalytically and also without catalyst (thermal, T- -pyr) under 500?C with heating rates of 5 and 10?C min-1. In the pyrolysis experiments, three different catalytic studies were performed by adding MCM- -41 + HZSM-5 catalyst mixture to the polymer phase only (PPC-pyr), by filling Cu(I)-MAS + HZSM-5 catalyst mixture to the gas outlet column only (GPC- -Pyr) and adding catalyst mixtures in both polymer phase and gas phase (MPC- -pyr). The highest diesel-like fuel (91.40 wt. %) was obtained in multiphase catalytic pyrolysis experiments at 460?C with a heating rate of 5?C min-1. The calorific value, kinematic viscosity, density, flash point and cetane number of the fuel were found as 45.97 MJ kg-1, 2.72 cSt, 832.5 kg m-3, 57 and 59?C, respectively. The results of the two-stage catalytic cracking and the heating rate profile will be a guide for industrial pyrolysis applications. The simple feasibility for industrial applications showed that it would be a very profitable investment.

Optimization effect of propylene oxide (PO) on evaporation, combustion, and pollutant emissions of high-energy–density JP-10 fuel

JP-10 is a high-energy–density fuel that is widely used in aerospace propulsion systems due to its wide range of synthetic raw materials and low production costs. However, it faces challenges related to difficult ignition, low combustion efficiency and high pollutant emissions. To address this, blending JP-10 with propylene oxide (PO), a highly volatile substance, provides a practical solution. This study investigates the propagation and evolution characteristics of JP-10/PO binary fuel in large horizontal pipelines. The results demonstrate a synergistic enhancement effect achieved by the JP-10/PO hybrid fuel. PO, with its lower boiling point, quickly evaporates from the mixed droplets, creating a continuous primary flame. As the droplet temperature increases, JP-10, known for its high combustion heat, starts to evaporate, actively participating in the explosion process and forming a secondary flame that spreads in two directions. The combustion of the JP-10/PO mixed droplets involves both physical and chemical processes, including droplet evaporation and gaseous combustion. A binary droplet evaporation model is developed to quantitatively assess the impact of PO fuel ratio on spray evaporation. Additionally, the study examines steam explosion parameters and reaction product characteristics under different PO fuel ratios. It is observed that the evaporation of JP-10/PO mixed droplets occurs in three stages: transient heating, binary equilibrium evaporation, and single component equilibrium evaporation. Increasing the PO fuel ratio leads to a higher temperature rise rate of the droplets and an increased evaporation reaction rate constant. Moreover, the ignition delay time of JP-10/PO gas-phase mixture fuel decreases, while the adiabatic flame temperature gradually reduces. Furthermore, higher PO fuel ratios help reduce the emissions of unstable products in both mixed fuels due to the inherent oxygen content of PO molecules. The current research results can provide scientific references for the improvement of high-energy density fuels and the development of new propellants.

Products and yields for the NO3 radical initiated atmospheric degradation of 2-methylfuran (2-MF, CH3–C4H3O)

Furans represent a group of oxygenated, heterocyclic, organic compounds that are emitted during biomass burning (BB). Notably, these compounds undergo rapid oxidation, a process observed both during the day and at night. Methylated furanoids comprise a large fraction of total furan emissions. Recent kinetic studies suggest that the NO3 initiated degradation of methylated furans is the dominant reaction pathway during nighttime, and with significant contribution on daytime. The aim of this study is to investigate the degradation products and the reaction mechanism of 2-methylfuran (2-MF) reaction with NO3 radicals using two atmospheric simulation chambers: CHARME (Chamber for the Atmospheric Reactivity and the Metrology of the Environment, Dunkerque, France) and THALAMOS (Thermally Regulated Atmospheric Simulation Chamber, Douai, France). All experiments were carried out at ambient temperature, (294 ± 2) K and atmospheric pressure (760 Torr, zero air). Oxidation products were qualitatively and quantitatively characterized using multiple, complementary detection techniques. Gas phase major and minor products were detected via offline GC-EI-MS (Gas chromatography - Electronic Impact - Mass Spectrometry) after trapping the gas-phase mixture on different adsorption media. PTR-ToF-MS (Proton Transfer Mass Reaction – Time of Flight – Mass Spectrometer, CHARME) and SIFT-MS (Selected Ion Flow Tube Mass Spectrometry, THALAMOS) were used on-line to monitor reactants and major products and to determine the end-product yields. 4-Oxo-2-pentenal (H(O)CCHCHC(O)CH3), and 2(5H)-furanone, 5-methyl, 5-nitrooxy ((CH3)C(ONO2)(C4H2O2)) were detected as major products with yields (62 ± 15) % and (26 ± 3) %, respectively. In-situ FTIR (Fourier Transform Infrared Spectroscopy) along with quantum mechanical molecular calculations revealed that organic nitrates and dinitrates were also formed. Secondary organic aerosols (SOA) formation, in the presence of ammonium sulfate seed, was also monitored using SMPS-CPC (Scanning Mobility Particle Sizer-Condensation Particle Counter). The size distribution and the mass concentration of the particles were determined for 2-MF concentration between 80 and 531 ppbv leading to SOA yields 1.03–2.23 %. Finally, SOA formed were chemically characterized using ESI-LC-QToF-MS/MS (Electrospray Ionization Liquid Chromatography – Quadrupole - Time of Flight - Tandem Mass Spectrometer) revealing that oligomers, e.g. highly oxygenated molecules (HOMs) were also formed. Based on our experimental observations, a reaction mechanism is proposed. NO3 radical is predominately added to the C2/C5 double bond of 2-MF, while the H atom abstraction channel, is estimated to be of minor importance. Results from this work provide detailed information about the NO3 radical initiated oxidation of 2-MF that can be used in chemical transport models to simulate the ageing processes occurring in biomass burning plumes.

Satellites of the Dipole-Forbidden Transitions to the Low-Lying 2S1/2 and 2D3/2,5/2 Excited States of K, Rb, and Cs Atoms in the Spectra of Gas-Phase Mixtures with CF4

Satellites of the Dipole-Forbidden Transitions to the Low-Lying 2S1/2 and 2D3/2,5/2 Excited States of K, Rb, and Cs Atoms in the Spectra of Gas-Phase Mixtures with CF4

Gas phase multicomponent detection and analysis combining broadband dual-frequency comb absorption spectroscopy and deep learning

In absorption spectroscopy, analysis of multicomponent gas mixtures becomes challenging when absorption features overlap (blended spectra). Here we propose a gas sensor which can accurately identify the species and retrieve the concentrations of components in a gaseous mixture in a broad spectrum. The sensor integrates a mid-infrared dual-frequency comb laser source for spectrum acquisition and a deep learning algorithm for spectral analysis. The sensor was tested on gas phase mixtures of methane, acetone and water vapor. A prototype sensor was assessed in realistic scenarios in real time. We also systematically analyzed and presented explicit visualizations to explain the underlying working mechanism of the algorithms.

Potential of Carbon Nanotube Chemiresistor Array in Detecting Gas-Phase Mixtures of Toxic Chemical Compounds.

Toxic industrial chemicals (TICs), when accidentally released into the workplace or environment, often form a gaseous mixture that complicates detection and mitigation measures. However, most of the existing gas sensors are unsuitable for detecting such mixtures. In this study, we demonstrated the detection and identification of gaseous mixtures of TICs using a chemiresistor array of single-walled carbon nanotubes (SWCNTs). The array consists of three SWCNT chemiresistors coated with different molecular/ionic species, achieving a limit of detection (LOD) of 2.2 ppb for ammonia (NH3), 820 ppb for sulfur dioxide (SO2), and 2.4 ppm for ethylene oxide (EtO). By fitting the concentration-dependent sensor responses to an adsorption isotherm, we extracted parameters that characterize each analyte-coating combination, including the proportionality and equilibrium constants for adsorption. Principal component analysis confirmed that the sensor array detected and identified mixtures of two TIC gases: NH3/SO2, NH3/EtO, and SO2/EtO. Exposing the sensor array to three TIC mixtures with various EtO/SO2 ratios at a fixed NH3 concentration showed an excellent correlation between the sensor response and the mixture composition. Additionally, we proposed concentration ranges within which the sensor array can effectively detect the gaseous mixtures. Being highly sensitive and capable of analyzing both individual and mixed TICs, our gas sensor array has great potential for monitoring the safety and environmental effects of industrial chemical processes.

Gas-phase etching mechanism of silicon oxide by a mixture of hydrogen fluoride and ammonium fluoride: A density functional theory study

We report the selective etching mechanism of silicon oxide using a mixture of hydrogen fluoride (HF) and NH4F gases. A damage-free selective removal of native oxide has been used in semiconductor manufacturing by forming and removing the ammonium fluorosilicate [(NH4)2SiF6] salt layer. A downstream plasma of NF3/NH3 or a gas-phase mixture of HF and NH4F was used to form (NH4)2SiF6. We modeled and simulated the fluorination of silicon oxide and the salt formation by density functional theory calculation. First, we simulated the successive fluorination of silicon oxide using SiO2 slab models. The fluorination reactions of SiO2 surfaces by the mixture produced a volatile SiF4 molecule or a surface anion of –OSiF4−* with an NH4+ cation with low activation energies. Unlike HF, NH4F produced surface salt species consisting of a surface anion and an ammonium cation. Next, we simulated the (NH4)2SiF6 formation from the two reaction products on fluorinated SiO2 surfaces. (NH4)2SiF6 can be formed exothermally with low activation energies (0.27 or 0.30 eV). Finally, we compared silicon with SiO2 to demonstrate the inherently selective etching of silicon oxide. The fluorination reactions of silicon by the mixture showed the activation energies significantly higher than the SiO2 cases, 1.22–1.56 eV by HF and 1.94–2.46 eV by NH4F due to the less stable transition state geometries. Therefore, the selective salt formation on silicon oxide, not on silicon, is expected in near-room temperature processing, which enables selective etching of silicon oxide.

Removal of gas phase methanol and acetonitrile mixture in an air membrane bioreactor (aMBR) under steady and transient-state operations

A laboratory scale air membrane bioreactor (aMBR) was used to treat a gas-phase mixture of methanol (MeOH) and acetonitrile (ACN), with an inoculum comprising of a mixed culture of microorganisms. The aMBR was tested under both steady-state and transient modes, with inlet concentrations ranging from 1 to 50 g/m3 for both compounds. Under steady-state conditions, the aMBR was operated at various empty bed residence times (EBRT) and MeOH:ACN ratios, while intermittent shutdown was tested during transient-state operations. The results showed that, the aMBR demonstrated > 80% removal efficiencies for both MeOH and ACN. An EBRT of 30 s was found to be the best treatment time for the mixture, providing>98% removal, with<20 mg/L of the pollutant accumulation in the liquid-phase. The microorganisms also showed preferential utilization of ACN compared to MeOH from the gas-phase and good resilience capacity after three days of shutdown/re-start operation.

Plasma enhanced atomic layer deposition of crystallized gallium phosphide on Si with tri-Ethylgallium and tri-tert-Butylphosphine

25 ∼ 30 nm thick polycrystalline gallium phosphide (GaP) films with high P / Ga atomic ratios were deposited on Si (100) using a plasma enhanced atomic layer deposition (PE-ALD) process with triethyl gallium (TEG), tri-tertiary butyl phosphide (tri-TBP), and atomic hydrogen. The key is chemical functionalization of the Si (100) surface since the wet-cleaned Si surface is nearly inert to TEG and tri-TBP. In-situ Auger spectroscopy was employed to identify the most successful functionalization which employed a gas phase mixture of atomic hydrogen and tri-TBP consistent with formation of a surface phosphide layer on Si(100); this layer efficiently nucleated the PE-ALD of GaP. The crystallinity and surface roughness of GaP films were tuned by controlling the pulse length of atomic H plasma, showing the self-limiting ALD film growth with 2.7 Å/cycle. The optimal crystallized GaP thin film on 6°-miscut Si showed local epitaxy growth of homogeneous GaP epi-layers in transmission electron microscopy (TEM).

Electric Dipole Moments from Stark Effect in Supersonic Expansion: n-Propanol, n-Butanol, and n-Butyl Cyanide.

The orientation and magnitude of the molecular electric dipole moment are key properties relevant to topics ranging from the nature of intermolecular interactions to the quantitative analysis of complex gas-phase mixtures, such as chemistry in astrophysical environments. Stark effect measurements on rotational spectra have been the method of choice for isolated molecules but have become less common with the practical disappearance of Stark modulation spectrometers. Their role has been taken over by supersonic expansion measurements within a Fabry-Perot resonator cavity, which introduces specific technical problems that need to be overcome. Several of the adopted solutions are described and compared. Presently, we report precise electric dipole moment determinations for the two most stable conformers of the selected molecules of confirmed or potential astrophysical relevance: n-propanol, n-butanol, and n-butyl cyanide. All dipole moment components have been precisely determined at supersonic expansion conditions by employing specially designed Stark electrodes and a computer program for fitting the measured Stark shifts, inclusive of cases with resolved nuclear quadrupole hyperfine structure. The experimental values are compared with suitable quantum chemistry computations. It is found that, among the tested levels of computation, vibrationally averaged dipole moments are the closest to the observation and the molecular values are, as in the lighter molecules in the series, largely determined by the hydroxyl or nitrile groups.

Selective adsorption to benzene-cyclohexane gas-phase mixture over ion exchange Y zeolites

The selective adsorption to benzene-cyclohexane gas-phase mixture was performed over several parent zeolites (NaY, NaZSM-5, and NaMOR) and over ion exchanged Y zeolites. NaY showed a greatly higher adsorption selectivity & capacity to benzene than NaZSM-5 and NaMOR, primarily attributed to the high density of surface Na+ sites, the high specific surface area, and the better pore diffusion ability of the former. Moreover, a reasonable Zn2+ ion exchange treatment not only significantly enhanced the adsorption selectivity to benzene but also improved the benzene adsorption capacity of Y zeolite. This may be due to the uneven surface charge on the surface of Zn2+ exchanged Y zeolite, where the electrostatic attraction effect between surface Zn2+ and benzene molecules may powerfully promote the preferential adsorption to benzene which even replaces surface cyclohexane molecules. While the exchanged Y zeolites with Cu2+, Cr3+ or Fe3+ displayed the declined performance for selective adsorption. Especially, severe pore blockage occurred after Cr3+ or Fe3+ exchange. Furthermore, based on the optimization on the aspects of the solution concentration and the exchange time during Zn2+ ion exchange treatment, the selectivity to benzene of 93% & 98% and the benzene adsorption capacity of >3.0 mmol/g were obtained over 0.2-Zn-Y (2 h) and 0.1-Zn-Y (4 h) samples, respectively.

Performance and neural modeling of a compost-based biofilter treating a gas-phase mixture of benzene and xylene

Biofilter (BF) has been regarded as a versatile gas treatment technology for removing volatile organic compounds (VOCs) from contaminated gas streams. In order for BF to be utilized in the industrial setting, it is essential to conduct research aimed at removing VOC mixtures under different inlet loading conditions, i.e. as a function of the gas flow rate and inlet VOC concentrations. The main aim of this study was to apply artificial neural networks (ANN) and determine the relationship between flow rate (FR), pressure drop (PD), inlet concentration (C), and removal efficiency (RE) in the BF treating gas-phase benzene and xylene mixtures. The ANN model was trained and tested to assess the removal efficiency of benzene (REB) and xylene (REX) under the influence of different FR, PD and C. The model's performance was assessed using a cross-validation method. The REb varied from 20% to >60%, while the REx varied from 10% to 70% during the different experimental phases of BF operation. The causal index (CI) technique was used to determine the sensitivity of the input parameters on the output variables. The ANN model with a topology of 4-4-2 performed the best in terms of predicting the RE profiles of both the pollutants. Furthermore, the effect was more pronounced for xylene because an increase in the benzene concentration reduced xylene removal (CI = −25.7170) more severely than benzene removal. An increase in the xylene concentration had a marginally positive effect on the benzene removal (CI = +0.1178).

Simultaneous acidic air biofiltration of toluene and styrene mixture in the presence of rhamnolipids: Performance evaluation and neural model analysis

Biotrickling filters (BTFs) supplied with di-rhamnolipids have been proven to improve biodegradability and bioavailability of singly fed hydrophobic volatile organic compounds (VOCs). However, BTFs performance could be significantly impacted for multi-component mixtures. Herein, the performance of lab-scale fungal-BTF was evaluated for the co-treatment of toluene-styrene gas-phase mixture and compared to previous single runs of both VOCs. For equal ratios of the VOCs, the total removal efficiencies (REtotal) ranged from 89.1% to 74% by varying the total inlet loading rates (LRtotal) from 199.1 to 295.2 g m−3 h−1 at empty bed residence times (EBRT) of 90 and 60 s. Both VOCs were efficiently removed (up to RE 90%) at 199.1 g m−3 h−1 inlet LRtotal and 90 s EBRT. Shortening EBRT to 60 s revealed that styrene degradation was kinetic-limited, whereas toluene was less impacted, indicating styrene inhibition and preferential toluene utilization. Increasing toluene:styrene ratio to 2:1 (v./v.) improved styrene biodegradation and mineralization. Neural network model was developed for the binary mixture which highlighted the interaction effects between input and output variables. The model provided high predictive accuracy (R2-0.993) and revealed significant information towards improving future BTFs design.

Ignition, Combustion, and Detonation of Gas-Phase and Heterogeneous Mixtures (Review)

Ignition, Combustion, and Detonation of Gas-Phase and Heterogeneous Mixtures (Review)

Identifying chronic rhinosinusitis without nasal polyps by analyzing aspirated nasal air with an electronic nose based on differential mobility spectrometry

Background The diagnosis of chronic rhinosinusitis (CRS) is a complicated procedure. An electronic nose (eNose) is a novel method that detects disease from gas-phase mixtures, such as human breath. Aims/Objectives To determine whether an eNose based on differential mobility spectrometry (DMS) can detect chronic rhinosinusitis without nasal polyps (CRSsNP) by analyzing aspirated nasal air. Materials and methods Adult patients with CRSsNP were examined. The control group consisted of patients with septal deviation. Nasal air was aspirated into a collection bag and analyzed with DMS. The DMS data were classified using regularized linear discriminant analysis (LDA) models with 10-fold cross-validation. Results The accuracy of the DMS to distinguish CRSsNP from patients with septal deviation was 69%. Sensitivity and specificity were 67 and 70%, respectively. Bonferroni-corrected statistical differences were clearly noted. When a subgroup with more severe inflammatory disease was compared to controls, the classification accuracy increased to 82%. Conclusions The results of this feasibility study demonstrate that CRSsNP can potentially be differentiated distinguished from patients with similar nasal symptoms by analyzing the aspirated nasal air using DMS. Further research is warranted to evaluate the ability of this novel method in the differential diagnostics of CRS.

Viscosity measurements of CO2-rich; CO2 + N2 and CO2 + H2 mixtures in gas or supercritical phase at temperatures between 273 and 473 K and pressures up to 8.7 MPa

New experimental viscosity data of three binary CO2-rich mixtures with approximate mole fractions of 0.93 CO2 + 0.07 H2, 0.80 CO2 + 0.20 H2, and 0.90 CO2 + 0.10 N2 are reported. The measurements were performed at four different isotherms between 273 K and 473 K. Two independent rotating body viscometers with different pressure range were utilized, suitable for measurement of pressures up to 2 MPa and 20 MPa, respectively. The maximum expanded combined relative uncertainty (k = 2) in viscosity was 0.25% for the data obtained from the low-pressure viscometer and 0.6% for the data measured by the high-pressure viscometer. The experimental data were compared to the data estimated by the extended corresponding states (ECS) model implemented in the NIST REFPROP 10.0 database. The maximum deviation between the model and the new data is 1.86%. The data measured with the two apparatuses agree within the estimated uncertainty.

Deflagration evolution characteristic and chemical reaction kinetic mechanism of JP-10/DEE mixed fuel in a large-scale tube

As a high energy density hydrocarbon fuel, JP-10 is widely used in various types of engines. However, JP-10 also has problems such as not easy to ignite and incomplete combustion. DEE with good flammability and volatility can make up for the above shortcomings. In present work, a series of experiments were carried out to study the deflagration propagation characteristics of JP-10/DEE mixtures with different fuel ratios in a large-scale tube. The initial pressure wave induced by ignition and the deflagration flame front divide the flow field into an unreacted zone, a disturbance zone and a product zone. The propagation velocity of the flame front in the observation window is obtained by the Canny edge extraction procedure, and a secondary flame phenomenon is found as JP-10 slowly evaporates and ignites. With the increase of DEE concentration, the propagation speed of primary flame increases, the induction time of secondary flame is advanced. In addition, JP-10/DEE mixed fuel deflagration has a synergistic enhancement effect, and the maximum deflagration intensity is achieved when fuel ratio is 0.6. The maximum flame temperature of JP-10/DEE mixed fuel deflagration is 1660 °C, and the fastest flame propagation speed is about 97 m/s. Moreover, the adiabatic flame temperature of the JP-10/DEE gas-phase mixture decreases with the increase of DEE concentration, but the system is more easily ignited, and the emission of incomplete combustion products decreases.