NOx Formation Research Articles

Performance, emission and combustion characteristics of liquid fuel produced through catalytic co-pyrolysis of waste LDPE and Pongamia pinnata seeds: An experimental investigation in CI engine

As there is an urgent need to address the global problem of increasing plastic waste and decreasing petroleum-based fuels, it is possible to convert waste plastic and unused biomass seeds into fuels that can be utilized in transportation sector. The current study deals with blending pure diesel (D100) with the liquid fuel (PB2) obtained from the co-pyrolysis of Pongamia pinnata seeds and waste low-density polyethylene (LDPE) with Calcium oxide (CaO) as the catalyst. Three blends of D100, namely, PB2@10 (with 10 % blend), PB2@20 (with 20 % blend) and PB2@30 (with 30 % blend) were tested for performance, emission and combustion in an unmodified CI engine for an analytical comparative analysis using standard methods. The results showed that the BSFC was almost same (0.3 kg/kWh) at higher loads for all three blends, while the BTE was found to be equal or increased compared to D100 in the range of 27–30 % at higher loads for higher blends. NOx formation was found to decrease by 19.4 % and 13 % at the highest load for PB2@30 andPB2@30. The smoke formation also decreased for all blends (maximum 22.5 %) while the maximum difference of lambda was determined to have decreased in comparison to D100, close to 1 at higher loads. The maximum cylinder pressure and temperature were also found to have increased during combustion by approximately 1 % for PB2@10 while that of PB2@20 and PB2@30 remained quite close to D100. The obtained renewable liquid fuel could certainly be utilized in blends with pure diesel for use in vehicles.

Optimizing air distribution in floor and wall burners of an industrial steam cracking firebox: a CFD study

A 3D computational fluid dynamics model for an industrial scale steam cracking firebox is combined with a 1D reactor model for the cracking process within the reactor coil. This framework is validated using industrial tunable diode laser absorption spectroscopy (TDLAS) measurements in a naphtha steam cracking furnace. Industrial O2, H2O, CO and temperature data show good agreement with simulation results at different locations within the firebox. The influence of varying the primary-to-secondary air flow distribution to the floor and wall burners separately is investigated using the validated framework. Altering the primary-to-secondary air flow distribution of the floor burners from 75/25 to 25/75 results in a 66% increase in furnace run length and a 35% decrease in NOx formation. This shift in air ratio ensures a lower rollover height of the flame and a large recirculation zone of the flue gas, spreading the radiative heat flux on the reactor coil more evenly. Altering the primary-to-secondary air flow distribution of the sidewall burners from 50/50 to 100/0 results in a 13% increase in run length and a 30% decrease in NOx formation. More primary air towards the sidewall burners is found to lead to more evenly spread out flames along the wall, resulting in flame interactions between the different burners and a combined flow towards the center of the firebox. These interactions result in a more uniform tube metal temperature profile along the different passes of the coil.

An integrated 0D/1D/3D numerical framework to predict performance, emissions, knock and heat transfer in ICEs fueled with NH3–H2 mixtures: The conversion of a marine Diesel engine as case study

In the maritime transportation, e-fuels represent a valid alternative to fossil energy sources, in order to accomplish the European Union goals in terms of climate neutrality. Among the e-fuels, the ammonia-hydrogen mixtures can play a leading role, as the combination of the two allows to exploit the advantages of each one, simultaneously compensating their gaps.The main goal of the present publication is the proposal of a robust numerical framework based on 0D, 1D and 3D tools for CFD analyses of internal combustion engines fueled with ammonia-hydrogen mixtures.The 1D engine model provides boundary conditions for the multi-dimensional investigations and estimates the overall engine performance. 3D in-cylinder detailed analyses are proficiently used to predict combustion efficiency (via the well-established G-equation model supported by laminar flame speed correlations for both ammonia and hydrogen) and emissions (with a detailed chemistry based approach). Heat transfer and knock tendency are evaluated as well, by in-house developed models. As for the 0D/1D chemical kinetics calculations, firstly they support 3D analyses (for example via the generation of ignition delay time tables). Moreover, they allow insights on aspects such as NOx formation, to individuate mixture qualities able to strongly reduce the emissions.The present paper offers also indications for designers on the effectiveness of NH3–H2 as valid substitutes of traditional fuels in marine applications. In fact, the proposed framework is preliminary tested to convert an existing marine Diesel engine to ammonia-hydrogen mixtures. Different proportions (among the two fuels) are investigated, included pure ammonia and pure hydrogen and the NH3–H2 80mol%-20mol% mixture is selected as the best compromise. Thanks to both the anti-knock quality of the ammonia and the (limited) addition of hydrogen as combustion enhancer, the engine supplied with NH3–H2 mixtures is able to operate free of knock and keep the same performance as the original one. Simultaneously (neglecting the presence of lubricant oil in the combustion chamber) unburned hydrocarbons, carbon monoxide and carbon dioxide are eliminated. Still in comparison with the Diesel version, the heat transfer is similar, the NOx formation is much greater and the engine range (here evaluated in terms of working hours) noticeably reduces.

Theoretical Kinetics Predictions for Reactions on the NH2O Potential Energy Surface.

Recent modeling studies of ammonia oxidation, which are motivated by the prospective role of ammonia as a zero-carbon fuel, have indicated significant discrepancies among the existing literature mechanisms. In this study, high-level theoretical kinetics predictions have been obtained for reactions on the NH2O potential energy surface, including the NH2 + O, HNO + H, and NH + OH reactions. These reactions have previously been highlighted as important reactions in NH3 oxidation with high sensitivity and high uncertainty. The potential energy surface is explored with coupled cluster calculations, including large basis sets and high-level corrections to yield high-accuracy (∼0.2 kcal/mol 2σ uncertainty) estimates of the stationary point energies. Variational transition state theory is used to predict the microcanonical rate constants, which are then incorporated in master equation treatments of the temperature- and pressure-dependent kinetics. For radical-radical channels, the microcanonical rates are obtained from variable reaction coordinate transition state theory implementing directly evaluated multireference electronic energies. The analysis yields predictions for the total rate constants as well as the branching ratios. We find that the NO + H2 channel contributes 10% of the total NH2 + O flux at combustion temperatures, although this channel is not included in modern NH3 oxidation mechanisms. Modeling is used to illustrate the ramifications of these rate predictions on the kinetics of NH3 oxidation and NOx formation. The present results for NH2 + O are important for predicting the chain branching and formation of NO in the oxidation of NH3 and thermal DeNOx.

Effect of oxygen enrichment on the combustion characteristic and pollutant emissions of kerosene-biogas mixtures on a mini jet engine combustion chamber

There are many alternative fuel studies in gas turbine engines, which are widely used in aviation and energy production. Biogas has also become popular among alternative fuels, especially since it can be obtained from waste. Biogas not only provides a renewable energy source, but also helps to manage organic waste, reduce greenhouse gas emissions and promote sustainable practices in waste management and energy production. The most important issue for alternative fuel studies in gas turbine engines is maximum emission reduction with minimum efficiency loss. In this study, oxygen enrichment and alternative fuel simulation were performed on a mini gas turbine engine. The biogas/kerosene mixture was used together with the oxygen enrichment method, which is known to increase the flame temperature in the literature, due to the lowering effect of the biogas on the combustion chamber outlet temperature.As an alternative fuel, biogas was mixed with kerosene up to 50% in 10% increments. The geometry of the GTM-120 engine used in the study was simplified and validated with the combustion chamber outlet temperatures at 3 different rpms created with the fuel and air inlet conditions taken from the literature. While kerosene fuel is injected from 12 nozzles with Discrete Phase Method, k-e turbulence model and Discrete Ordinates radiation model are used. Alternative fuel was given from the nozzle surfaces as a mass flow inlet by calculating the flow rate so that the thermal power remains constant. All simulations were made with steady-state and 1600 iterations. As a result, it was observed that oxygen enrichment increased the flame temperature and NOX formation, while decreasing the CO emission.On the other hand, it has been observed that the CO2 in the biogas reduces both the temperature and NOX emissions due to its diluting effect, while at the same time increasing the CO emissions in the front region. Furthermore, the decrease in the total C/H mass also led to a reduction in the CO emission at the outlet. Another effect of the biogas was the reduction in the CO2 at the outlet. Thanks to this study, the use of alternative fuels and a decrease in pollutant emissions have been achieved by keeping the loss of engine efficiency at a minimum.With this study, it has been demonstrated that biogas can be used as an alternative fuel with kerosene by keeping the engine efficiency loss to a minimum and a decrease in pollutant emissions.

Flame stabilization characteristics of turbulent hydrogen jet flame diluted by nitrogen

Hydrogen is already widely produced and used in the industry. NOx formation during the combustion of hydrogen can be reduced by adding nitrogen. Nonetheless, this comes at the cost of decreased flame stability, which constrains the applicability of hydrogen. Therefore, the flame stabilization characteristics of nitrogen-diluted hydrogen jet flame at varying dilution concentrations (10%–50%) were investigated using thin-lipped nozzles with diameters of 2, 3, and 5 mm. The experimental results show that the nitrogen-diluted jet flame becomes bluer and the flame height and width decrease with the dilution concentration. Due to the incomplete combustion at downstream of the diluted jet flame, the classical prediction model using the dimensionless flame Froude number (Frf) overpredicts the flame height of nitrogen-diluted hydrogen jet flame. The model, ρeSLhμe=50(ueSL)g(ρeρ∞), can effectively predict the flame lift-off distance of diluted hydrogen jet flames, where SL is the corresponding laminar combustion speed in the lean mixture zone (Φ = 0.91). A unified prediction model of blowout limit based on the Damköhler number for diluted hydrogen and hydrocarbon jet flames was proposed for the first time. This study helps to better understand the instability mechanism of diluted hydrogen.

Effects of oxygen addition on thermal and pollutant emission characteristics of a cylindrical furnace fueled with 1-Hexanol–biodiesel–diesel blends

This study aims to investigate the combined effects of oxygen addition to inlet air and utilization of 1-Hexanol, biodiesel, and diesel blends on the thermal and emission characteristics of a cylindrical furnace. The design of experiments was used based on the presence of three-composite fuels and the oxygen inlet flow as independent variables. The experimental tests were conducted on a cylindrical furnace equipped with a diesel burner. The results showed that the combustion temperature increased by up to 11 °C with the increase in the flow rate of oxygen addition. Moreover, the results indicated that with an increase in oxygen addition flow rate, the HC and CO emissions decreased by almost 33% and 18%, respectively. However, there was no significant effect on CO2 emissions. On the other hand, the amount of NOx emissions increased with oxygen addition flow rate by approximately 12.5%. According to the results, the increase in the percentage of biodiesel and hexanol caused an increase in NOx emissions and a reduction in CO and HC emissions. And, the fuel mixture with 50% diesel, 30% biofuel, and 20% 1-Hexanol (D50B30H20) had the maximum NOx emissions and the minimum HC and CO emissions in comparison with other fuel mixtures for all oxygen addition flow rates. The results also indicated that increasing the percentage of biofuels in the fuel mixture, along with an increase in the rate of oxygen addition, leads to a higher reduction rate of HC and CO emissions. Furthermore, oxygen flow rates higher than 5 liters per minute did not significantly affect the formation of CO2 emissions, but prevented the formation of NOx.

Thermal efficiency and boundary analysis of compression ignition internal combustion Rankine cycle engine

The compression ignition internal combustion Rankine cycle (CI-ICRC) is a novel combustion cycle that integrates oxy-fuel combustion, direct water injection (DWI), and waste heat recovery into diesel cycle to achieve ultra-high thermal efficiency and zero emissions. NOX formation is eliminated by utilizing oxygen instead of air, and water is injected into the cylinder to improve thermal efficiency. To achieve over 50% indicated thermal efficiency in the CI-ICRC engine, a thermodynamic model of the CI-ICRC engine is established in this paper to explore the potential thermal efficiency and boundary under different DWI strategies. Theoretical results demonstrate that the thermal efficiency of CI-ICRC engine is mostly affected by DWI mass and temperature, the thermal efficiency is dramatically enhanced as DWI mass and temperature increase. Under a water-to-fuel ratio of 20 and DWI temperature of 423K, the calculated thermal efficiency reaches 76.8%. Moreover, exhaust waste heat is mainly recovered through DWI, which increases the working fluid within the combustion chamber, thereby increasing the expansion work and improving cyclic thermal efficiency. Additionally, specific heat ratio of the mixture within the cylinder can be enhanced by 0.04 through DWI, improving the thermal efficiency by 9% at an in-cylinder temperature of 800 K.

Suppression of NOx emissions by intensive strain in lean premixed hydrogen flamelets

NOx formation in premixed, highly-strained, pure hydrogen-air flamelets is investigated at lean conditions. Detailed-chemistry, one-dimensional and two-dimensional simulations are performed on a reactants-to-products configuration with varying applied strain rate. The results highlight for the first time for lean pure-hydrogen flamelets that NOx emissions are suppressed as strain rate is increased. The most substantial decrease is observed across the thermal NOx formation pathway. Here the suppression of NOx is triggered by a redistribution across the flamelet of the radicals involved in the pathway reactions. A comparison with methane flamelets is further performed to understand to what extent the observed trends with strain can be specifically linked to hydrogen burning features. Similar NOx suppression trends with strain are also observed for increased pressure and different equivalence ratios, although with different rates of decrease. A correlation is proposed based on the observed results and further theoretical considerations, to predict NOx emissions according to applied strain rate and equivalence ratio.

A deep graph convolutional network model of NOx emission prediction for coal‐fired boiler

AbstractTo deal with environmental problems caused by NOx production in thermal plants, it is imperative to establish a reliable model to predict NOx concentration in the combustion process. NOx formation in a coal‐fired boiler is complex, and many variables affect NOx emissions. The effective information fusion of these variables can improve the accuracy of NOx concentration prediction. However, the existing NOx prediction algorithms based on thermal parameters rarely consider the mechanical knowledge of the boiler operation, and it is not easy to incorporate the topological information of production into modelling. Therefore, a graph convolutional network is proposed for NOx emission prediction. First, the key variables affecting NOx generation are selected according to the knowledge and the random forest‐based variable importance. Then, the model structure is designed by exploring the topological information among thermal variables to capture the complex spatial dependence. The model inputs are constructed by coding different operation variables, and the adjacency matrix is generated according to the correlation information between variables, which can fuse data information and reduce redundancy. On this basis, the prediction model of NOx concentration is established. Historical data from a 660 MW coal‐fired boiler are used in the experiment. The prediction results show that the proposed model can effectively fuse the information of characteristic variables and fully exploit the non‐linear mapping relationship between process variables and NOx emission. When compared with three typical models in NOx modelling, the proposed model has better performance with a determination coefficient of 0.906.

(Invited) The SOFC Program at the DOE’s Office of Fossil Energy and Carbon Management (FECM) and National Energy Technology Laboratory (NETL)

The Solid Oxide Fuel Cell (SOFC) Program, managed by the U.S. Department of Energy (DOE) Office of Fossil Energy (FE) and administered by the FE’s National Energy Technology Laboratory (NETL) is currently developing low-cost SOFC power generation systems. SOFC power systems have the potential to achieve greater than 60 percent efficiency. The SOFC’s operating temperature is lower than combustion-based processes and precludes NOx formation. In addition, there are near-zero emissions of CO2, criteria pollutants, and particulates. Furthermore, SOFC power systems require approximately one-third the amount of water relative to conventional combustion-based power systems. The Program includes the testing of SOFC with natural gas in distributed applications, including data centers. In addition to SOFC, there are several projects on various aspects of high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water. The development of efficient systems for hydrogen production is very interesting, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants.

Investigation of the drop-in capabilities of a renewable 1-Octanol based E-fuel for heavy-duty engine applications

This article presents the results of an investigation of neat 1-Octanol and its blends with Diesel, which can be potential drop-in fuels for heavy-duty compression ignition engines. Fuel blends consisting of 10 %, 20 %, and 30 % 1-Octanol by volume in Diesel, including neat 1-Octanol, were investigated for ignition and combustion performances. The ignition behavior was assessed using a constant-volume combustion-chamber-based ignition tester. The experimental investigation was conducted on a heavy-duty single-cylinder engine by varying the combustion center. In addition, injection-rate shaping was performed to understand the effects of various injection-rate shapes, namely square, ramp, and boot rate shapes, on the performance of neat 1-Octanol.The ignition tester results indicated an increased ignition sensitivity of neat 1-Octanol towards the chamber pressure and temperature compared to that of Diesel. At an elevated chamber temperature (650 °C) and pressure (20 bar), the ignition delay of neat 1-Octanol approaches closer to that of Diesel. Engine experiments revealed an improved thermal efficiency with neat 1-Octanol and its blends by up to 1.2 %, owing to their improved mixture homogenization capabilities. Furthermore, neat 1-Octanol and its blend led to a drastic reduction in smoke and carbon monoxide. In addition, it results in the highest peak during the premixed heat release, and with a square injection-rate shape, an additional minor improvement in thermal efficiency was observed. The relative changes in carbon monoxide and hydrocarbon emissions between the injection-rate shapes were negligible. At higher load, the boot-rate shape results in lower NOx formation than the square-rate shape at an almost identical thermal efficiency. Overall, the 10 % 1-Octanol, 20 % 1-Octanol and 30 % 1-Octanol blends, which fulfill the Cetane number requirements for the given fuel norms, can be used as drop-in fuels, as they exhibit a comparable or even better performance than Diesel.

Experimental Study on NOX Formation Characteristics in Flue Gas Recirculation Combustion Process of S-CO2 Coal-Fired Boiler

ABSTRACT Flue gas recirculation technology and air-staged combustion technology are both effective methods for reducing the production of NOX in coal-fired boilers. However, the synergistic effect of air-staged combustion technology and flue gas recirculation technology on NOX generation characteristics in S-CO2 boilers needs further study. The formation characteristics of NOX in the main combustion zone of coal combustion were studied experimentally when flue gas recirculation and air-staged combustion were combined. The results indicate that as the recirculation flue gas is injected at deeper levels, there is a gradual decrease in the concentration of NOX along the path, And the concentration of O2 also decreases gradually. The concentration of NOX decreases as the excess air coefficient decreases. The concentration of O2 increases as the excess air coefficient increases. Additionally, the NOX concentration at the furnace outlet increases with the increase of the excess air coefficient. Along the axial direction of the one-dimensional flame combustion furnace, the NOX production along the way and the NOX concentration at the outlet decrease with the increase of the flue gas recirculation position. Flue gas recirculation in air-staged combustion is an effective method for reducing NOX emissions. The positioning of flue gas recirculation significantly impacts NOX emissions. The NOx concentration is lowest when the flue gas recirculation rate is 27% and the mixing position of the recirculated flue gas is 300 mm with an excess air coefficient of 0.8.

Kinetics modeling of NOx emission of oxygen-enriched and rich-lean-staged ammonia combustion under gas turbine conditions

Though the oxygen enrichment combustion and fuel-rich/quick-mix/fuel-lean (RQL) combustion are respectively effective to improve burning velocity and reduce NOx emissions respectively, their combination feasibility and characteristics for burning ammonia (NH3) need further investigation as oxygen enrichment could increase NOx production. Thus, a kinetic modeling study was conducted on the NOx emission characteristics of an oxygen-enriched and RQL-staged NH3-fired combustor under gas turbine conditions by using the chemical reaction network (CRN) method. The results revealed that NOx emission could be minimized as long as the equivalence ratio (ϕ) in the fuel-rich stage was kept at a certain value according to the oxygen enrichment degree (Ω) in the fuel-rich stage oxidizer, regardless of the Ω in the fuel-lean stage oxidizer. At a higher Ω, low NOx emission was achieved in a wider ϕ range, while the optimal ϕ in the fuel-rich stage became higher and the corresponding NOx emission was lower. This mainly benefited from the stronger NH3 consumption in the fuel-rich stage due to the higher temperature and higher concentration of OH/H radicals. However, a higher Ω in the fuel-rich stage enhanced the thermal NOx formation in the fuel-lean stage. Based on the results of the present study, oxygen-enriched NH3 combustion with a proper ϕ setting in the fuel-rich stage could simultaneously improve the burning intensity and reduce NOx emission for burning NH3 in a gas turbine.

LES Investigation of Kerosene Spray Flame Emission Characteristics in a Staged Combustor

ABSTRACT Staged combustion technology is widely applied in modern low-emission energy and power systems. This study employs large eddy simulations (LES) to investigate the flame dynamics and emission characteristics in a staged two-phase partially premixed model combustor. To improve the suitability of the thickened flame model (TFM) for turbulent flames in the thin-reaction-zone regime, a new model for efficiency function is formulated such that the effects of small-scale turbulence on flame propagation are taken into account. The enhanced LES-TFM approach is then integrated with an efficient NOx model, in which an additional NOx transport equation is solved with pre-tabulated NOx formation source terms. Five LES runs are performed to investigate the evolution of flame dynamics and emission characteristics with staging ratios at the scaled cruise operating conditions, in which the optimal staging ratio is critical for NOx reduction. Results show that the trend of flame morphology and NOx emission predictions with staging ratios are consistent with the experimental results. The flame zones in the staged model combustor shift from a pilot-stage-only flame to a pilot-primary-stage flame, then to a primary-stage-only flame with decreasing fuel staging ratio. Due to the redistribution of the equivalence ratio and the NOx emission characteristics trade-off between the two-stage flows, there is an optimal staging ratio for NOx reduction in the staged model combustor. The proposed LES-TFM-NOx approach, which has both the benefits of efficient flame dynamics modeling with the global reaction mechanism and the advantages of prediction accuracy with the detailed mechanism for NOx emission, demonstrates its advantages in simulating flame and emission characteristics in low-emission combustion devices.

Effect of the swirl angle on calcium carbide gas combustion characteristics of lower burner under annular shaft kiln

In order to solve the problem of high CO concentration in the emitted flue gas after adopting the flue gas recirculation technology in the annular shaft kiln, in this paper, the combustion characteristics of calcium carbide gas in swirl burners under the annular shaft kilns were studied by numerical simulation, the influence of fuel and primary air swirl intensity on combustion characteristics were studied, and the gas temperature distribution, pressure distribution and combustion products including CO, CO2 and NO was analyzed. The results show that the fuel gas swirl intensity has a great influence on the improvement of fuel burn-out ratio. The angle of the fuel gas blade increases, the maximum temperature of the combustion flame and the fuel combustion rate increase, and the CO content at the outlet of the burner decreases. When the angle of the fuel gas blade increased from 30o to 55o, swirl number increased from 0.41 to 1.02, the CO content at the inner sleeve position decreased from 8929 mg/m3 to 2467 mg/m3. The results also show that the effect of the primary air swirl intensity on reduce CO emissions and NOx formation was not obvious.

Understanding non-equilibrium [formula omitted]/[formula omitted] chemistry in plasma-assisted low-temperature [formula omitted] oxidation

Ammonia represents one of most promising zero-carbon energy solutions to address the increasingly urgent climate change problem. However, the existing utilization of ammonia faces significant challenges from low chemical reactivity and high N2O/NOx emissions, which cause severe inefficiency issues such as cold start and cycle variability of power generation, and detrimental effects on air quality, respectively. A sustainable and energy-efficient approach to tackle the above challenges is low temperature plasma which enables non-equilibrium energy and chemical utilization of ammonia such as oxidation using renewable electricity. As such, this work, for the first time, explores plasma assisted ammonia oxidation at room temperature with a focus on unveiling non-equilibrium NOx/N2O reaction pathways by combining in-situ laser diagnostics with plasma modeling. We found that the non-equilibrium plasma controls the NOx formation by supplying O/H/N atoms via electron-impact dissociation and collisional quenching of excited species. The N2O formation follows a two-step mechanism, where electron-impact reactions first provide amine radicals which further react with NOx to generate N2O. These pathways facilitate a high-efficiency and environment-friendly operation of plasma assisted ammonia oxidation with enhanced reactivity and reduced NOx/N2O emissions through manipulating mixture compositions and plasma discharge parameters.

Degradation and chemical stability of graphitic carbon nitride during ultraviolet light irradiation

Graphitic carbon nitride (g-C3N4) was synthesized by pyrolysis of urea at 450 °C for 2 h. X-ray diffraction and transmission electron microscopy confirmed the formation of the stacked hexagonal layers and platelet-like structure of g-C3N4. The sample was irradiated by ultraviolet (UV, 370 nm) light for about 62 h and X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), Nitrogen adsorption–desorption isotherm, and photoluminescence spectroscopy (PL) were used to investigate the degradation. XPS spectra of C 1s electrons revealed four components associated with adventitious carbon, the –C≡N group, heptazine/triazine and carboxyl/carbonate species. Quantitative XPS analysis indicated an increase in the peak areas associated with the –C≡N group and carboxyl/carbonate species, accompanied by a decrease in the areas of the components associated with the heptazine/triazine and adventitious carbon. XPS spectra of N 1s were fitted using four components which were assigned to pyridinic nitrogen (C–N=C), nitrile group (N≡C), amine groups (NHx) and tertiary nitrogen (N-(C)3). The relative areas of peaks associated with the amine and nitrile groups have slightly increased after UV irradiation whereas the peak associated with pyridinic nitrogen decreased. FTIR spectra suggested a reduction in the C–N and C=N heterocycle bonds and slight variation in the C≡N bonds after UV irradiation. BET analysis revealed that the surface area and pore volume have decreased after irradiation. ToF-SIMS analysis indicate the formation of NOx, CNO, NHx, and C4H3NO2 species after irradiation. PL spectra of the g-C3N4 showed a broad blue-green emission which was fitted using three bands and ascribed to the δ*-LP, π-LP, and π-π* transitions within the bandgap. During UV irradiation, the g-C3N4 powder lost about 22% of its blue-green emission intensity after nearly 45 h and then remained stable for further irradiation time. This study confirmed the degradation of g-C3N4 under UV irradiation, which should be further studied for better integration of this material in photoexcited applications.

Effects of tri-ethylene glycol mono methyl ether and alumina on the performances of enriched hydrogen dual fuel diesel engine

The present study is focused on the combustion behavior, performance and emissions of a modified diesel engine working on dual fuel mode with hydrogen as a gaseous fuel by the inclusion of tri-ethylene glycol mono methyl ether and alumina nanoparticles as fuel additives. The inclusion of tri-ethylene glycol mono methyl ether, alumina and hydrogen separately and simultaneously improved the net heat release with reduced cylinder pressure at high loads as compared with neat diesel. The brake thermal efficiency increased by 22.5% and 11.6% by the inclusion of tri-ethylene glycol mono methyl ether and hydrogen respectively at 50% load, when combined together, it was improved remarkably by 28.15%. The addition of alumina was responsible for a slight reduction in NOx formation at all loads, while it was incremented by hydrogen enrichment at the highest load as compared to pure diesel. The CO formation was incremented by the addition of alumina, while the CO2 and HC formations were reduced up to 50% load, increased at 70% load. The CO, CO2, HC and smoke opacity were reduced with TGME and hydrogen enrichment, while the NOx formation was reduced up to 50% load, then increased at the higher load.

Nitrogen migration and transformation from ammonia to char during ammonia-coal/char co-pyrolysis

Ammonia (NH3)-coal co-firing is a promising technology to reduce CO2 emission. The strong interaction between ammonia and coal during the co-pyrolysis has a considerable impact on nitrogen migration and transformation and will further affect the NOx formation. In this paper, to investigate the effect of the volatile fraction on the migration of N, Shenhua (SH) and Wanxiang (WX) bituminous coals were devolatilized to different levels in the first pyrolysis step and were then co-pyrolyzed with NH3 in the second pyrolysis step. It is found that the migration of N from the gas to solid is more significant than the release of N with the volatile, especially when the temperature in the first pyrolysis step is low. Given the same pyrolysis condition, WX coal/char has more oxygen-containing functional groups than SH, thus the increase of N content during the NH3/coal co-pyrolysis is more significant for WX. The absolute contents of pyridinic N (N-6), pyrrolic N (N-5), and protonated pyridinic N or quaternary N (N-Q) are calculated before and after the co-pyrolysis step according to the results of elemental analysis and X-ray photoelectron spectroscopy. An obvious increase of N-6 is observed in chars with lower degree of devolatilization for both coals. A transformation of N-5 to other types of N is observed for SH coal/char. In contrast, the transformation of N-5 is less obvious for WX, which is due to the presence of alkali metal chlorides in WX. Moreover, WX coal/char has less aromatic structure and more aliphatic groups, which promotes the transformation of N from NH3 to N-5. Based on these results, possible reaction pathways of N migration and transformation during NH3/coal co-pyrolysis are proposed.