Combustion Pressure Research Articles

Flexible preparation of nanoporous SiO2 aerogel as novel adsorbent for efficient adsorption of Zearalenone

Zearalenone (ZEN) is a form of mycotoxin in the animal feed that is a carcinogen causing pathological changes after entering animal and human body. In the paper, SiO2 aerogels were prepared using sol-gel method adopting atmospheric pressure drying, vacuum drying and combustion drying. The aerogels were characterized and subjected to assess the sorption potential of ZEN. It was found that the atmospheric pressure drying aerogel (ADSA) had the highest surface area and micropore content, while the vacuum drying aerogel (VDSA) was completely mesoporous with the smallest surface area. The combustion drying aerogel (CDSA) was also dominantly mesoporous with fractional micropores. The ZEN equilibrium adsorption capacity for ADSA was the highest while its adsorption rate was the lowest. The adsorption rate of VDSA was the highest, while its equilibrium adsorption capacity was significantly lower than ADSA. The adsorption capacities of VDSA and CDSA were of comparable magnitude owing to the similarity in pore structure. The adsorption isotherms and kinetics were modeled with semiempirical theoretical models. The ZEN adsorption process of all the aerogels was governed by both physisorption and chemisorption. Experimental result suggested a flexible option of SiO2 aerogels as promising low cost absorbent for ZEN removal.

Effect of Aluminum Content on the Combustion Performance of HTPB/AP/Al Propellants under High Combustion Pressure

Effect of Aluminum Content on the Combustion Performance of HTPB/AP/Al Propellants under High Combustion Pressure

Effect of flow number of pilot-stage centrifugal atomizer on idle performance of internally staged combustor

Idle performance is critical to the combustion stability of internally staged combustors. Five pilot-stage atomizers are compared in an internally staged combustor, and the effects of the flow number (FN) on the combustion characteristics and emissions are investigated under idle conditions. Experimental results show that the maximum outlet temperature is 1.02–1.04 times the average outlet temperature, and the maximum temperature is located at the dimensionless radial location of 0.66. The key influencing mechanism of the temperature distribution lies in the matching between the spray angle of the pilot-stage atomizer and the angle of the recirculation zone. When the flow number (FN) of the pilot-stage atomizers was increased from 1.6 to 10, the combustion efficiency (η) showed a “decrease-increase-decrease” trend, whereas the emission of unburned hydrocarbon (UHC) showed a opposite trend. At the meantime, the emission of CO remained unchanged, and NOx remained at the undetectable level. In addition, the low sensitivity of pressure loss (3.3%-4%) and combustion stability (0.66%-0.85%) to idle conditions is attributed to the influence of combustion efficiency and outlet temperature. After a comprehensive evaluation, it is determined that an intermediate FN of 5.0 possesses the most balanced combustion characteristics and emissions under idle conditions in the pilot-stage atomizer.

Tuning the micro‐structure, laser ignition, and isovolumetric burning performance of nitrocellulose propellant via incorporation of graphene oxide

AbstractNanoscale recombination between carbon nanomaterials (CNs) and polymers has been proposed for a variety of industrial and scientific applications. Composite energetic materials consisting of CNs with novel laser ignition property and tunable combustion performance have attracted people's attention. Here, reported is the novel manufacturing process of uniform nitrocellulose (NC)/graphene oxide (GO) nanocomposite propellant and the micro‐structure, laser ignition and isovolumetric burning features of the propellants introduced by GO. The results of microstructure tests indicated that GO (0.25–2 wt%) was stripped and dispersed homogeneously and dense nanocomposite propellants were prepared successfully through water ultrasonic dispersion, twin‐screw mixture, as well as compression molding. The crystallization of NC was forbidden by doping GO, meanwhile, the thermal stability and thermal conductivity of the composite propellants increased slightly with the addition of GO. The results of laser ignition combustion experiments showed that GO was an efficient additive to shorten the ignition delay time from more than 2000–14 ms when 2 wt% of GO was doped, however, the combustion flame intensity was also weakened due to the addition of GO. The combustion tests in a closed bomb vessel were conducted, and the results showed that GO would not affect the stable combustion of NC at high combustion pressure, moreover, the burning rate and dynamic vivacity of the composite propellants decreased with the increase of GO content.

Thermodynamics of hydrogen storage: LOHC system 1-alkyl-indole/octahydro-1-alkyl-indole

The environmental advantages of the hydrogen economy are obvious, but the limiting factor in its development is finding an optimal storage system with high gravimetric and volumetric hydrogen capacities. The most efficient technology for storing and consequently using hydrogen is that with organic compounds that are able to enrich hydrogen by forming bonds with the hydrogen. In this study, we considered 1-alkyl-indoles as suitable LOHC systems because of their high thermal stability and high boiling points. The thermochemical studies of these compounds were performed, including vapour pressure measurements and combustion calorimetry. The experimental data obtained are compared with the results of theoretical quantum chemical methods. In addition, a thermodynamic analysis of the hydrogenation/dehydrogenation of the LOHC systems based on 1-alkyl-indoles was performed.

Combustion characteristics and concentration measurement of ADN-based liquid propellant with electrical ignition method in a combustion chamber

An experimental study was performed to investigate combustion characteristics of ammonium dinitramide (ADN) based liquid propellant with electrical ignition method in a combustion chamber. The experiment was conducted in different gas atmospheres such as argon, air and nitrous oxide under an on-load voltage range of 60–100 V. The influence of the gas atmosphere, on-load voltage on the ignition delay time, peak combustion pressure, ignition energy, total energy and key reaction products mole fractions were studied. The ignition delay time of propellant decreases gradually with the increase of ignition voltage, while the ambient gas has little effect on the ignition delay time because the flame appears inside the propellant earliest. The peak combustion pressure of propellant is highest when the ambient gas is nitrous oxide, whereas lowest in argon atmosphere. The ignition energy and total energy are insensitive to gas atmosphere and decrease gradually with the increasing on-load voltage. The concentration of N2O increases with the increase of on-load voltage. The mole fraction of CO decreases with the increase of on-load voltage in general, especially obviously at relatively high on-load voltage of 100 V.

Characterization of pintle engine performance for GO2/kerosene propellants

Liquid rocket engine with a wide range of thrust variations has drawn much attention in recent years. A GO2/kerosene deep-throttling variable thrust engine using a liquid–gas pintle injector is presented and tested with aim of characterizing engine performance, regulating capability, and heat flux distribution. Three-dimensional numerical simulations are conducted to investigate the flame appearance and spray characteristics of the engine. The SST k-omega model is used for modeling turbulence, the Wave model is used for modeling the secondary breakup, and a multi-step quasi-global combustion mechanism and eddy dissipation concept model are used for modeling combustion. The GO2/kerosene pintle engine achieves stable combustion at 0.18 ∼ 4.35 MPa with a thrust of 21.30 ∼ 864.70 N. The thrust ratio of the pintle engine is 40.6:1 indicating a deep-throttling variable thrust capability. The thrust regulation of the pintle engine using the closed-loop control has high accuracy and response speed, as well as high disturbance suppression capability. The effects of combustor pressure, spray characteristics, and reactants concentration distribution on flame appearance and heat flux distribution of the engine are studied in detail. The engine equipped with a liquid–gas pintle injector could ensure a good atomization effect and high combustion efficiency by actively adjusting the propellant injection pressure drop coefficient. This work will provide a reference for the design of the pintle injector and thermal protection system of deep-throttling variable thrust rocket engines.

Quantification of Poly(vinyl chloride) Microplastics via Pressurized Liquid Extraction and Combustion Ion Chromatography

A reliable analytical method has been developed to quantify poly(vinyl chloride) (PVC) in environmental samples. Quantification was conducted via combustion ion chromatography (C-IC). Hydrogen chloride (HCl) was quantitatively released from PVC during thermal decomposition and trapped in an absorption solution. Selectivity of the marker HCl in complex environmental samples was ensured using cleanup via pressurized liquid extraction (PLE) with methanol at 100 °C (discarded) and tetrahydrofuran at 185 °C (collected). Using this method, recoveries of 85.5 ± 11.5% and a limit of quantification down to 8.3 μg/g were achieved. A variety of hard and soft PVC products could be successfully analyzed via C-IC with recoveries exceeding >95%. Furthermore, no measurable overdetermination was found for various organic and inorganic matrix ingredients, such as sodium chloride, sucralose, hydroxychloroquine, diclofenac, chloramphenicol, triclosan, or polychlorinated biphenyls. In addition, sediments and suspended particular matter showed PVC concentrations ranging up to 16.0 and 220 μg/g, respectively. However, the gap between determined polymer mass and particle masses could be significant since soft PVC products contain plasticizers up to 50 wt %. Hence, the results of the described method represent a sum of all chlorine-containing polymers, which are extractable under the chosen conditions.

Insight into combustion characteristics of micro- and nano-sized boron carbide

The combustion characteristics of micro- and nano-sized boron carbide (B4C) powders were investigated to exploit the role of carbon atoms on combustion. Various combustion parameters had been evaluated for B4C powders. Results demonstrated a direct correlation between the gas oxide of carbon atoms with the morphology of condensed combustion products. The thrust generated when the gas diffused from the B4C matrix to the environment could not only disperse the burning B4C powder, but also break through the liquid oxide layer and leave holes on the surface of micro-sized B4C. The formed holes on the surface were considered oxygen diffusion channels to the interior of B4C particle, which accelerated the mass transfer rate and improved the oxidation efficiency. The evolution images of confined combustion and the characterizations of condensed combustion products suggested that the B4C powder released most of energy potential after stable combustion and transformed into boron oxide. Given the combustion process, the B4C powders exhibited the higher combustion heat and the larger peak area of combustion pressure than boron powders with similar diameter distribution, and the B4C powders in nano-sized generated strongest energy output among all samples.

Using oxy-hydrogen gas to enhance efficacy and reduce emissions of diesel engine

The ever-increasing need for energy, along with diminishing petroleum supplies, has prompted the quest for renewable and sustainable alternative fuels. The goal of this research is to investigate theoretically the impact of using HHO gas on single-cylinder diesel engine characteristics using the simulation software diesel-RK model. Diesel fuel blended with 10% HHO gas is used and tested under different engine speeds. When 10% HHO gas was put into the engine, the thermal efficiency climbed to 31.5 percent and consequently, fuel consumption is reduced by up to 20 percent. The maximum reduction in BSN is 25% which is witnessed at 3500 rpm. The findings are corroborated by the findings of other studies. Among the most important outcomes that were obtained the peak combustion pressure was raised by 10% as compared to diesel fuel without HHO and the brake power enhances from (9% to 16%) when the engine speed is increased from (1500 to 3500) rpm.

Ignition and combustion of Al and ammonium perchlorate-coated Al particles in a double oxidizing air–H2O–Ar atmosphere

Aluminum is a promising energy-containing material that can satisfy both aerospace and underwater thermodynamic propulsion systems. A high-temperature pressurized combustion chamber and a CO2 laser were adopted to investigate the ignition and combustion characteristics of 2, 5, and 40 μm aluminum particles in a 1.0 MPa air–H2O–Ar mixed atmosphere (with varying O2 and H2O concentrations). The combustion-promoting effect of the ammonium perchlorate-coated modification (namely, the AP@Al sample) was evaluated. The results show that Al melts and agglomerates into millimeter-sized droplets (covered with a gas-phase flame) after ignition, and its nonhomogeneous combustion is dominated by diffusion. The flame propagation is greatly enhanced by the AP combustion-promoting effect of oxygen/heat supply and particle dispersion, resulting in a significant decrease in the ignition delay time (ti, approximately 55–85%) and combustion time (tc, approximately 32–96%), whereas an extraordinary increase in the maximum combustion temperature (Tmax, approximately 170–224 K) and pressure changes (approximately 1.7–8.5 kPa, approximately 10.6–136.5 kPa/s) are also observed. Excess water vapor inhibits the flame propagation for AP@Al, viz. the flame area and number of ejected burning particles is decreased. The main factor affecting the combustion temperature is the oxidant rather than the particle size, which may be related to the small difference in the active aluminum content of the samples and the diffusion-controlled combustion mechanism. Due to the advantage of O2 for oxidation and the diffusion rate, the gradual replacement of H2O by air (similar to conversion to a fuel-lean system) leads to a decrease in ti, whereas Tmax is increased for all the samples, and the tc and self-sustaining combustion time are increased for the Al samples, whereas tc is decreased for AP@Al samples for both the equal-molar oxidizing gas concentration and equivalence ratio of O2–H2O control groups in this work. Since O2 creates a new pathway for AlO production, the ignition and combustion performance of Al and AP@Al samples is significantly improved when H2O is replaced by a small amount of air.

Thermal Analysis and Pyrolytic Behavior of Bimetal and Double Oxidant Thermite Al/Mg/MoO3/CuO

AbstractIn order to study the effect of fuel Mg and metal oxide CuO on the reaction of thermite, different proportions of Al‐Mg alloys and MoO3‐CuO metal oxides were prepared by mechanical ball milling, and then the samples of Al1‐xMgx/(MoO3)1‐xCuOx composite thermite were prepared by ultrasonic dispersion method. The samples were characterized by SEM, TG‐DSC, and constant pressure combustion experiments. The results show that in quaternary thermite, adding CuO increases initial exothermic temperature, but increases exothermic heat in high‐temperature regions, and effectively reduces the activation energy of the thermite reaction. On the contrary, adding Mg reduces exothermic heat in the high‐temperature areas, but reduces initial exothermic temperature. After calculation, the quaternary thermite with the best exothermic performance is Al0.8Mg0.2/(MoO3)0.5CuO0.5. Its initial reaction temperature is only 614 °C, but the heat release is up to 2217 J/g. Its activation energy is only 106.7 kJ/mol, but the critical temperature of thermal explosion is up to 927.9 K. At the same time, Al0.8Mg0.2/(MoO3)0.5CuO0.5 has better combustion performance. During combustion, the flame is jet‐like, and the main products are Al2O3, Mo and Cu. This work provides a reference for studying the thermal safety and combustion performance of quaternary thermite.

High-dimensional multi-objective optimization algorithm for combustion chamber of aero-engine based on artificial neural network-multi-objective particle swarm optimization

This paper considers optimizing the performance of high-temperature combustion chamber of an aero-engine based on a concentric and hierarchical model. First, sample data for the design variables are obtained based on Latin hypercube sampling method, and a one-dimensional program is used to obtain the true values of combustion efficiency and total pressure loss corresponding to each group of variables. The obtained data are then pre-processed to establish a dataset. Second, a multi-layer artificial neural network (ANN) architecture is designed and a surrogate model of the combustion-related performance of the combustor is established using a data-driven method. The results of global sensitivity analysis based on variance show that ratio of fuel flow to air flow (fuel–air ratio) and the total inlet pressure are the most important factors influencing the two objective functions. Finally, we optimize the multi-objective combustion-related performance of the surrogate model by applying the particle swarm optimization algorithm to it. The results of experiments show that the ANN-based model could accurately predict the efficiency of combustion and total pressure loss of the chamber, yielding root mean-squared errors of 0.0107 and 0.3032%, respectively. It also had better generalization ability than the cubic polynomial surrogate model. Compared with the cubic polynomial model, it generated an optimal Pareto solution set as prediction that had higher values in both objective functions. The proposed model might require better data that can be obtained using intelligent sampling methods so that deeper neural networks can be designed to reduce error and improve its optimization design.

Influence of pressure on the circumferential diffusion characteristics of fuel vapor and combustion performance in a pressurized burner

To discuss the circumferential diffusion characteristics of the fuel vapor and combustion performance, a 15 kW pressurized burner fueled by diesel is first proposed in this research. And then, combustion experiments and cool-state numerical simulations are conducted at different pressures (P) and thermal loads (Q). The ratio (F) of the aerodynamic to buoyancy forces and the circumferential diffusion uniformity (σ) of the fuel vapor are constructed through pollutant emissions, fuel vapor concentration distribution and velocity field. The results show that under a Q of 3.55 kW, the burner has a relatively low F, and the buoyancy force has a more obvious effect as P increases, further causing circumferential fuel vapor distribution uniformity to suffer. When the burner operates at a Q of 10.64 kW, the undesired circumferential diffusion uniformity of the fuel vapor is only found at 0.3 MPa. For a Q of 15.37 kW, the fuel vapor has a great circumferential diffusion uniformity in the forward end of the liner at each P. A proper F of 89–278 and σ of 0–3.6% are recommended for diesel vapor circumferential diffusion and pollutant emissions, in which the buoyancy force has a relatively lower effect than the aerodynamic force.

Application Characteristics of Bioethanol as an Oxygenated Fuel Additive in Diesel Engines

In this study, pure diesel fuel (E0), 5% bioethanol blended with 95% diesel fuel (E5), 10% bioethanol blended with 90% diesel fuel (E10) and 15% bioethanol blended with 85% diesel fuel (E15) were tested on a diesel engine. The 40, 60 and 80 Nm were the main experimental variables, while the engine speed was kept constant at 1500 rpm. The main results show that the addition of ethanol slightly reduced the maximum combustion pressure and delayed the combustion start, but increased the heat release rate (HRR) to varying degrees. Although the addition of ethanol was not very helpful for reducing hydrocarbon (HC), it could reduce carbon monoxide (CO) under appropriate load conditions (60 Nm and 80 Nm). Additionally, nitrogen oxides (NOx) and smoke emissions were reduced with the addition of ethanol under all test conditions.

Effects of EGR on combustion and emission characteristics of PODE/methanol RCCI mode at high load

In order to extend the high-load operation range of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel reactivity controlled compression ignition (RCCI) combustion mode, a numerical model of in-cylinder combustion was established by coupling PODE/methanol chemical reaction kinetics with CONVERGE software. And then the influence mechanism of exhaust gas recirculation (EGR) addition on in-cylinder combustion process, combustion stability and pollutant formation of the RCCI engine under high load and pilot injection strategy were investigated. The results show that with the increase of EGR ratio, the peak values of the first heat release formed by PODE pilot injection combustion and in-cylinder pressure decrease, the combustion start timing and CA50 phase are gradually delayed. While the peak value of the second heat release formed by PODE main injection combustion at low EGR ratio and the combustion duration remain unchanged. Meanwhile, as the EGR ratio increases from 0 to 30 %, the brake thermal efficiency (BTE) decreases from 46.54 % to 44.40 %. And the in-cylinder equivalent ratio and temperature field distributions become uniform, and both high-temperature region (above 1800 K) and NOx generation area are reduced, which decreases NOx emissions by 42.6 % without increasing soot emissions. The methanol mixture at squish zone is subjected to the high-temperature and high-pressure of pilot injection combustion, resulting in obvious pressure oscillation. While EGR addition decreases the generation of HCO and OH active radicals, ignition points and reaction rate, which effectively inhibits methanol spontaneous combustion and knock phenomenon, and decreases the ringing intensity from 2.82 MW/m2 to 1.50 MW/m2. The pilot injection strategy coupled with 18 % EGR can extend the indicated mean effective pressure to 1.22 MPa. However, the load further extension is mainly limited by the sharp decline of BTE.

Effect of triacetin as an oxygenated additive in algae biodiesel fuelled CI engine combustion, performance, and exhaust emission analysis

In this experimental investigation, oxygenated additive triacetin is used in an algae oil biodiesel-diesel blend (ABD40) to examine the combustion, performance and exhaust emissions from a single-cylinder 3.5 kW diesel engine. Different percentages of additive (2 %, 4 %, 6 % and 8 % by volume) are mixed in ABD40, and the experiments are performed at varying engine loads by maintaining a fixed engine speed. The combustion results at full load (100 %) reveal that 4 % triacetin in ABD40 achieves high combustion pressure than diesel fuel (DF) and other biodiesel blends. Similarly, a high BTE of 30.39 % is achieved for 4 % triacetin in ABD40 than other biodiesel blends. However, it is 7.23 % lesser than mineral diesel fuel. Due to high density and kinematic viscosity, the fuel consumption for biodiesel blends is recorded as higher than DF. Furthermore, low exhaust emissions are acclaimed for 4 % additive triacetin in ABD40 than DF, and a drop of CO (25.51 %), NOx (12.81 %), UHC (70.53 %) and Smoke (14.85 %) is recorded at 100 % load compared to DF. Hence, it is concluded that 4 % triacetin in ABD40 is the better choice as a diesel fuel replacement, and significant performance and emissions results are possible with the addition of oxygenated additive triacetin, which enhanced fuel properties of high heating value and cetane number.

Experimental investigation and Artificial Neural Network modelling of combustion pressure parameters of dual spark plug SI engine

Shortages of petroleum-based fuels due to their rapid consumption rate and their environmental degradation motivates researchers to develop new technologies for the efficient use of petroleum-based fuels as well as the use of environmentally friendly alternate biofuels. Ethanol is one of the promising alternative biofuels for spark ignition (SI) engines. Currently, the Indian union Government aims to mix 20% ethanol by 2030. Therefore, extensive research studies are needed to determine the combustion stability of E20 blend. The purpose of this study was to investigate the combustion pressure fluctuations is dual plug SI engine using ethanol-gasoline blends and to develop Artificial neural network model using back propagation algorithm for the prediction of these fluctuations. The fluctuations of Indicated mean effective pressure (IMEP), maximum cylinder pressure and maximum rate of pressure rise has been measured by conducting experiment in a dual spark plug SI engine under different compression ratios and spark ignition timings using E5, E10, E15 and E20. Then, these experimental data’s have been used for training and testing of BP model to predict the combustion pressure parameters. The % load, blend ratio, compression ratio and spark timings were used as the input parameters whereas IMEP, maximum cylinder pressure and maximum rate of pressure rise were used as the output parameters of the model. The experimental results showed that E20 achieved maximum average IMEP and minimum COVIMEP at a compression ratio of 10:1 and ignition timings of 24° bTDC. The modelling results showed that BP model is capable of predicting the combustion pressure fluctuations with good accuracy.

COMPUTATIONAL ANALYSIS OF THE IMPACT OF BOUNDARY CONDITIONS ON A PARTICLE-LADEN FLOW: A CASE STUDY IN A PRESSURIZED OXY-COAL COMBUSTOR

Designing an effective burner is vital for the development of coal combustion technologies. Because of high pressure, the volumetric fraction of the coal particles in the injected fuel in a pressurized oxy-combustion (POC) burner approaches or even exceeds the limitations allowed by the commercial computational fluid dynamics codes (e.g., Ansys Fluent). Consequently, for such high particle volumetric fractions, the interplay between the particles, the fluid flow, and the burner wall needs to be re-evaluated. The present computational work is a first step in a systematic analysis of the roles of various characteristics involved in the POC process, such as the method of particle release, its location, and the particle size. Specifically, pulverized coal is burned under an elevated pressure of 15 bar in an O<sub>2</sub>/CO<sub>2</sub> environment. A 100 kW, a POC combustor, is modeled with Ansys Fluent using the Reynolds-averaged Navier-Stokes approach. It is revealed that for this pilot-scale, pressurized burner, the gas phase flow velocity in the near-wall region exhibits anomalies. With the major focus on POC, this work aims to eliminate/reduce the impact of high particle loading on the gas-phase flow. To scrutinize the role of particle loading in the near-wall region and eliminate the impact of this velocity on POC downstream, the particle-gas interplay in the boundary layer is investigated by means of the computational simulations incorporating the coupling between the turbulent flow and the particles. It is found that the tuning of the particle release location makes the gas-phase flow velocity in the presence of particles consistent with the pure gas flow velocity profile. The particles size is also found to have a significant impact on the particle trajectory.

A computational analysis of the impact of boundary conditions on a particle-laden flow: A case study in a pressurized oxy-coal combustor

Designing an effective burner is vital for the development of coal combustion technologies. Because of high pressure, the volumetric fraction of the coal particles at the fuel inlet of the POC burner approaches or even exceeds the limitations allowed by the commercial computational fluid dynamics (CFD) codes (e.g., Ansys FLUENT). Consequently, for such high particle volumetric fractions, the interplay between the particles, the fluid flow, and the wall need to be re-evaluated. The present computational work is a first step in a systematic analysis of the roles of various characteristics, specifically, the method of particle release, its location, and the particle size. In the POC process, pulverized coal is burned under elevated pressure in an O2/CO2 environment. Specifically, a 15-bar, 100 kWth, POC combustor is modeled with Ansys FLUENT using the Reynolds-averaged Navier-Stokes (RANS) approach. It is revealed that for this pilot-scale, pressurized burner, the gas phase flow velocity in the near-wall region exhibits some anomalies. In order to scrutinize the role of particle loading in the near-wall region, the particle release location is investigated. The numerical simulations incorporate coupling between the turbulent flow and the particles. It is found that the tuning of the particle release location makes the gas phase flow velocity consistent with the pure gas flow velocity profile. Moreover, the particle releasing location also influences the flame stability. The particle size is also found to have a significant impact on the particle trajectory, flame stability, and temperature.