•Soot particle size evolution of gasoline in a premixed flame was investigated.•Size distribution of gasoline and heptane/toluene blend was qualitatively similar.•Gasoline’s sooting features more persistent nucleation and much faster growth rate.The evolution of soot particle size distribution function (PSDF) in premixed flames of gasoline (34% aromatics by volume) and a n-heptane/toluene blend (66% n-heptane/34% toluene by volume) was investigated in the burner stabilized stagnation (BSS) flame configuration, using the micro-orifice probe sampling and scanning mobility particle sizer (SMPS). The aim of this study is to illustrate the similarities and differences of sooting propensity between the real fuel and the simple hydrocarbon blend in premixed flame conditions. The mole ratio of carbon to oxygen (C/O) in the unburned gas was kept constant at 0.6 and similar maximum flame temperatures and temperature-time histories were kept between the two cases, so that we could focus on the fuel composition effects on sooting propensity. In addition, the size distribution, the total number density, and the volume fraction of soot were also compared to those previously measured for ethylene and propene flames under comparable conditions. It was observed that the particle size distributions of both gasoline and heptane/toluene flames evolve from the unimodal distribution (nucleation mode only) to the bimodal (both nucleation and coagulation mode) distribution. Compared to the heptane/toluene blend, the soot formation in gasoline flame features more persistent nucleation and much faster growth rate.

•Detailed mechanisms of C4H4 + C4H4 + H reaction were investigated.•The first aromatic ring structure can be formed in the C4H4 + C4H4 + H reaction.•Branching ratio of products were got by RRKM theory with solving master equation.•Phenylacetylene is one of the main products.•The energy barrier of H-elimination reaction is sensitive to molecular structure.The free H atom existing in flame plays vital role in combustion chemistry. As a continuation of our previous study, the possibility of forming the first aromatic ring via the self-recombination reaction of but-1-ene-3-yne (C4H4) with H-assistance was investigated in the present study. The potential energy surfaces were calculated with density functional theory and indicate that the C4H4 + C4H4(+H) reaction can generate 6-membered ring, ring-opening and 5-membered ring structures. The zero point energies of the investigated molecules were obtained at CBS-QB3 level, and the reliability of energy calculation was checked with T1 diagnostic. The rate coefficients were calculated using conventional transition state theory (TST) and Rice-Ramsperger-Kassel-Marcus (RRKM) theory with solving master equation. By comparing the rate coefficients and branching ratio of product, we found that the CS10 + H, CS16, CS19 and CS38 are the dominant product of C4H4 + C4H4(+H) reaction in the temperature range of 500–2500 K, and the formation of other products can be ignored. The self-dehydrogenation reaction is the essential step in the formation of the main product CS10 + H. Similar to H-transfer reactions, the self-dehydrogenation reactions are found to be sensitive to the molecular structure in terms of the energy barrier.

•The particle size distribution functions of soot particles in methane-doped ethylene flames behave bimodality.•The number densities in downstream zone of the methane-doped flames are much higher than pure flame.•Small ratio of methane doping can promote the volume fractions, while in large ratio cannot.The impact of methane doping on sooting behavior of ethylene-base burner stabilized stagnation (BSS) flames was investigated by following the evolution of particle size distribution functions (PSDFs) of nascent soot. The M-series of flames with the equivalence ratio of 2.07 was doped by methane with the mixture ratio of 5%, 10% and 40%. All the methane-doping flames showed obvious bimodality in the PSDFs, and more particles in nucleation stage than the C3 reference flame. The synergistic effect appeared in small ratio (5% and 10%) methane doping cases, leading to the increase of the soot number density and soot mobility volume fractions. While the synergistic effect was not found under large methane doping condition (40%), in which the mobility volume fraction was less than that in C3 flame. By calculating the key species and analyzing the reaction pathways of pyrene formation with KM2-Mech, we found that small ratio of methane doping benefits C3H3 and pyrene (A4) formation, which strengthened the sooting tendency. However too much methane doping reduced the yield of C2H2 that is a critical intermediate of PAHs formation, leading to a lower sooting tendency compared with the pure ethylene flame.

•Two-stage injection processes of three fatty acid esters (FAE) were investigated.•The injector inlet pressure and fuel mass injected per cycle were studied.•Fuel effects on the main injection masses are dependent on injection pressure.•Methyl and ethyl oleates have higher speeds of sound at low injection pressure.•The pressure wave of diesel propagates faster than FAE at high injection pressure.The two-stage injection processes of three fatty acid esters, methyl laurate, methyl oleate and ethyl oleate, were investigated and compared with that of fossil diesel using a high-pressure diesel engine common rail injection system. The injection characteristics studied included injector inlet pressure characteristics, and rate and quantity of fuel mass injected per cycle. The effects of fuel properties and injection dwell time between the pilot and main injection events were also considered. Differences in the fuel properties of diesel and fatty acid esters caused modest changes in the main injection quantities and fuel pressure fluctuation characteristics after the end of injection, and the changes were affected by different injection pressures. The injection dwell time was also found to influence the injector inlet pressure characteristics at the start of the main injection event and thus the amount of fuel injected during main injection was slightly changed.

The electronic emission characteristics of 13 gas-phase PAHs, ranging from phenlylacetylene to rubicene, were investigated to diagnose laser-induced fluorescence (LIF) spectra of PAHs in flame by DFT, TD-DFT, and premixed flame modeling methods. It was found that the maximum emission wavelengths of the PAHs with five-membered ring are located in visible region and insensitive to the number of C atoms. However, the fluorescence wavelengths of the PAHs without five-membered rings increase with the number of C atoms due to the reduced HOMO–LUMO gap. In addition, the fluorescence wavelength of the PAHs without five-membered rings with linear arrangement is longer than that of PAHs with nonlinear arrangement. According to the Franck–Condon principle, the vibrationally resolved electronic fluorescence spectra were obtained. The results show that fluorescence bandwidth of the PAHs with five-membered rings is much broader than that of the PAHs without five-membered rings. The concentration of PAHs was calculated by using the premixed flat-flame model with KM2 mechanism. On the basis of the fluorescence bandwidth and the concentration of the PAHs, the potentially fluorescence distribution of PAHs in flame was mapped. One can distinguish the specific PAHs according to the mapped fluorescence distribution of PAHs in this study. It was found that naphthalene should be responsible for the fluorescence located in the 312–340 nm region in the flame. 1-Ethynylnaphthalene is the most possible candidate to emit the fluorescence located in the 360–380 nm region. The fluorescence signals with the wavelength longer than 500 nm are likely emitted by the PAHs with five-membered rings. This study contributes to enhance the selectivity of PAHs in LIF technology, especially in the visible region.

•Two stage injection of diesel–gasoline blends on a common rail system is studied.•Injection dynamics and characteristics are studied with changed parameters.•Diesel/gasoline blends and diesel have similar cycle injection rate and quantity.•Extended pilot injection pulse causes slightly reduced main injection mass.This paper characterizes the two stage injection processes of pure diesel and two diesel–gasoline blends using a diesel common rail injection system. The investigated fuel injection characteristics include the cycle injection quantity, injection rate and injector inlet pressure characteristics, with changes in gasoline proportion and pilot injection energizing pulse. Increased gasoline proportion has negligible influences on the cycle injection rate and mass, as well as the pressure dynamics during the injection process. In addition, the extended pilot injection energizing pulse leads to increased pressure drop at the injector inlet during the main injection and causes reduced main injection mass.

Thermal decompositions of polycyclic aromatic hydrocarbon (PAH) oxyradicals on various surface sites including five-membered ring, free-edge, zigzag, and armchair have been systematically investigated by using ab initio density functional theory B3LYP/6-311+G(d,p) basis set. The calculation based on Hückel theory indicates that PAHs (3H-cydopenta[a]anthracene oxyradical) with oxyradicals on a five-membered ring site have high chemical reactivity. The rate coefficients of PAH oxyradical decomposition were evaluated by using Rice–Ramsperger–Kassel–Marcus theory and solving the master equations in the temperature range of 1500–2500 K and the pressure range of 0.1–10 atm. The kinetic calculations revealed that the rate coefficients of PAH oxyradical decomposition are temperature-, pressure-, and surface site-dependent, and the oxyradical on a five-membered ring is easier to decompose than that on a six-membered ring. Four-membered rings were found in decomposition of the five-membered ring, and a new reaction channel of PAH evolution involving four-membered rings is recommended.

An extensive series of experiments have been conducted using a nonthermal plasma generated by dielectric barrier discharge (DBD) process combined with vanadium pentoxide catalyst to reduce the nitrogen oxides (NOx) from diesel engine exhaust over a broad reaction temperature (100−500 °C). In this system, the effects of input voltage, propylene (C3H6) concentration, and sulfur content, etc. on the plasma facilitated (PF) selective catalytic reduction of NOx with NH3 were examined. In the presence of C3H6 as an additive, the oxidation of NO to NO2 is largely enhanced even with lower input voltages. The PF NH3−SCR system enhanced the overall reaction and showed a remarkable improvement in NOx removal efficiency at temperatures of 100−250 °C. The removal of NOx was found to be largely increased by the input voltage and the addition of propylene. Besides the small amount of nitrous oxide and the significant amount of carbon monoxide, aldehydes-type unregulated byproduct such as formaldehyde and acetaldehyde were also observed at the outlet of the DBD reactor, while formaldehyde and acetaldehyde could be almost completely removed in the NH3−SCR reactor. The NOx conversion decreases at lower temperatures but increases at higher temperatures with SO2 concentration increases. The PF NH3−SCR hybrid system can be used stably with several hundreds of ppm of SO2 in durability tests. Moreover, the presence of SO2 inhibits N2O formation at all employed reaction temperatures.

This study focuses on promoting the low temperature performance of vanadium-based catalysts; for this, the SHS method was applied to synthesize a series of Ti0.9VxM0.1–xO2−δ catalysts. The performances of the catalysts (Ti0.9V0.1O2−δ, Ti0.9Mn0.05V0.05O2−δ, and Ti0.9Ce0.05V0.05O2−δ) were fully investigated with the temperature-programmed-reaction, which proved that these SHS catalysts with nanometer size had high activity over a broad temperature window of 150–400 °C. Compared with Ti0.9V0.1O2−δ, the substituted catalysts, Ti0.9Mn0.05V0.05O2−δ and Ti0.9Ce0.05V0.05O2−δ, showed higher N2 selectivity at high temperatures. The Ce substituted catalyst exhibited good resistance to H2O and SO2 poisoning at low temperatures. The structural and physical-chemical properties of catalysts were characterized comprehensively by BET, XRD, FTIR, TEM, EDX, XPS, and TPD. The XRD results indicated that the active components of V, Mn, and Ce were highly dispersed over the catalysts. The Mn substitution could enhance the Brønsted acid sites on the catalyst surface and accelerate the SCR reaction at low temperatures. The XPS shows that the Ce substitution led to high concentration of chemisorbed oxygen, which diminished the unselective oxidation of NH3 by O2 to N2O, NO, or NO2 and resulted in superior N2 selectivity. The active components of the catalysts, such as V, Mn, and Ce, mostly existed in the form of mixed-valence which was beneficial for the oxidation of NO to NO2. Furthermore, the SCR reaction mechanism over Ti0.9Ce0.05V0.05O2−δ catalyst was also examined using in situ DRIFTS. The results revealed that high active monodentate nitrate and bridging nitrate species as well as abundant ionic NH4+ (Brønsted acid sites) were the key intermediates in the SCR reaction since the ad-monodentate nitrate and bridging nitrate species disappeared quickly in the presence of NH3.

This paper researches on the reduction of NOx (DeNOx) from wet flue gas by a DC corona radical shower system. The experimental results show that the water vapor in the flue gas not only reduces the corona but also reduces the discharge current. The DeNOx efficiency and the quantity of NOx removal per unit energy can be enhanced by raising the concentration of water vapor in the flue gas properly and the maximum quantity of NOx removal per unit energy is more than 25.5 g as the humidity of the flue gas ranges from 10 to 12%. The longer the flue gas resides in the reactor, the higher the DeNOx efficiency is and the lesser NOx will be reduced by per unit power.

Removal of NOx (namely DeNOx) from simulated flue gas with direct current (d.c.) corona radical shower system was investigated. Steady streamer coronas occur when the flow rates of the fed gases are adjusted properly. The experimental results show that both the composition and the flow rate of the gas fed into the nozzles influence the V–I characteristic of corona discharge. The vapor in the flue gas restrains the discharge, reduces the discharge current, but enhances the DeNOx efficiency. Furthermore, removal of NOx from flue gas by radical injection associated with alkali solution (26% by weight of NaOH in water) scrubbing was carried out. Oxygen together with water vapor is fed into the nozzle electrode and the oxygen and water molecules are decomposed in the corona zone. It is found that NO and NO2 can be converted into HNO2 and HNO3, respectively, by radicals formed during the discharge process and the conversion efficiency of NOx in the plasma reactor is more than 60%. The overall DeNOx efficiency of the system reaches 81.7% after the flue gas was scrubbed by the NaOH solution.