Search Results (110)

This study evaluates the risk assessment and hazard identification of hydrothermal liquefaction (HTL)-derived bio-oil from the MARINES project, which converts military organic waste into fuel. The high oxygen content (35–50 wt%), acidic pH (2–4), and viscosity (10–1000 cP) of bio-oils pose unique challenges, including oxidative polymerization, corrosion, and micro-explosions during combustion. Key hazards include storage instability, particulate emissions (20–30% higher than diesel), and aquatic toxicity (LC50 < 10 mg/L for phenolics). Mitigation strategies such as inert gas blanketing, preheating, and spill containment are proposed. While offering renewable fuel potential, HTL bio-oil demands rigorous safety protocols for military/industrial deployment, warranting further experimental validation. Full article

Researchers have tended to blend isopropanol (IPA) with other fuels in diesel engines to reduce emissions and improve performance. However, low-reactivity controlled compression ignition via port injection at a low cetane number results in a well-mixed charge of low-reactivity fuel, air, and recirculated exhaust gas (EGR). This study’s novel approach combines critical elements, such as the mass fraction of port-injected IPA, EGR ratio, and charge temperature, to improve combustion characteristics and lessen emissions from a diesel engine. The results demonstrated that the injection of IPA and the installation of EGR at the inlet reduced NO_x, smoke, and PM_2.5. On the contrary, HC and CO increased with the port-injection of IPA and EGR. Preheating air at the inlet can suppress the emissions of HC and CO. Under 1500 rpm and 60% load, when compared to diesel at the same EGR ratio and charge temperature, the maximum smoke decrease rate (26%) and PM_2.5 decrease rate (21%) occur at 35% IPA, 45 °C, and 10% EGR, while the maximum NO_x decrease rate (24%) occurs at 35% IPA, 60 °C, and 20% EGR. These findings support the novelty of the research. Conversely, it modestly increased CO and HC emissions. However, port-injecting IPA increased thermal efficiency by up to 24% at 60 °C, 1500 rpm, and 60% load with EGR. Full article

Under the strategic objectives of carbon peaking and carbon neutrality, it is inevitable for large-scale integration of renewable energy into thermal power units. Nevertheless, improving the capacity of these units for flexible peak shaving is necessary on account of the intermittent and instability of renewable energy. As a novel combustion technology, self-preheating combustion technology offers enormous merits in this aspect, with increasing combustion efficiency (η) and controlling NO_x emissions simultaneously. Considering production and operation cost, installation difficulty and environmental pollution, this study innovatively proposed a compact fluidized modification device (FMD) on the basis of this technology and explored the influences of buffer tank and operation load on operation stability, fuel modification, combustion characteristics and NO_x emissions on an MW grade pilot-scale test platform. Afterwards, the comparative analysis on performance disparities was further launched between FMD and traditional self-preheating burner (TSB). Adding the buffer tank enhanced operation stability of FMD and improved its modification conditions, and thus promoted NO_x emission control. Optimal modification efficiency was realized at medium and high loads, respectively, for high-volatile and low-volatile coals. As load increased, η increased for high-volatile coal, but with NO_x emissions increasing. In comparison, this condition reduced NO_x emissions with high η for low-volatile coal. Compared to TSB, FMD demonstrated more conspicuous advantages in stable operation and fuel modification. Simultaneously, FMD was more conducive to realizing clean and efficient combustion at high temperatures. In industrial applications, appropriate FMD or TSB should be picked out grounded in diverse application requirements. By optimizing burner structure and operational parameters, original NO_x emissions decreased to a minimum of 77.93 mg/m³ with high η of 98.59% at low load of 30%. Full article

The combustion of ammonia with oxygen presents a promising pathway for global energy transformation using carbon dioxide-neutral energy solutions and carbon capture. Ammonia, a carbon-free fuel, offers several benefits, owing to its non-explosive nature, high octane rating, and ease of storage and distribution. However, challenges such as low flammability and excessive nitrogen oxide (NO_x) emissions must be addressed. This paper explores the recent advances in ammonia oxy-combustion and highlights recent experimental and numerical research on NO_x emission traits, combustion, and flame propagation across various applications, including gas furnaces, internal combustion engines, and boilers. Furthermore, this review discusses the diverse approaches to overcoming the challenges of ammonia combustion, including oxygen enrichment, fuel blending, plasma assistance, preheating, multiple injections, and burner design modifications. By summarizing the advancements in ammonia oxy-combustion investigation, this paper aims to provide valuable insights that can serve as reference information for prospective ammonia oxy-combustion research and applications toward the transition to sustainable energy. Full article

Although various studies on nitrous oxide as a prospective green propellant have been recently explored, a polyethylene nitrous oxide catalytic decomposition hybrid thruster was barely demonstrated due to an inordinately high catalyst preheating time of a heater, which led to the destruction of components. Therefore, hydrogen peroxide was used as a preheatant, a substance to preheat, with a dual-catalyst bed. The thruster with polyethylene (PE) as a fuel, N₂O as an oxidizer, H₂O₂ as the preheatant, Ru/Al₂O₃ as a catalyst for the oxidizer, and Pt/Al₂O₃ as a catalyst for the preheatant was arranged. A preheatant supply time of 10 s with a maximum catalyst bed temperature of more than 500 °C and without combustion and an oxidizer supply time of 20 s with a burning time of approximately 15 s were decided. Because the catalyst bed upstream part for decomposing the preheatant was far from the post-combustion chamber, the post-combustion chamber pressure increased and the preheatant mass flow rate decreased after a hard start during the preheatant supply time. Moreover, because the catalyst bed upstream part primarily contributed to preheating, the maximum catalyst bed temperature was less than the decomposition temperature of the preheatant during the preheatant supply time. Additionally, because the catalyst bed downstream part for decomposing the oxidizer was far from the post-combustion chamber, the post-combustion chamber pressure decreased and then increased during a transient state in the oxidizer supply time. Full article

An experimental investigation into the conversion of ethanol to syngas by partial oxidation in a non-premixed counterflow moving bed filtration combustion reactor was carried out. Regimes of conversion depending on the mass flow rates of fuel and air (separate feeding), as well as a granular solid heat carrier, were studied. Depending on the mass flow rate of the heat carrier, two combustion modes were realized—reaction trailing and intermediate—with different temperature patterns in the gas preheating, combustion, and cooling zones along the reactor. The product gas composition is far from the predictions of the equilibrium model; it contains substation fractions of methane and ethylene. Combustion temperature and conversion are limited by the relatively high level of heat loss from the laboratory-scale reactor. The effect of the heat loss can be reduced by enhancing the absolute flow rate of the reactants. Full article

This paper presents the results of a hot-fire test campaign aimed at characterizing a newly developed ignition system for nitromethane-based green monopropellants. Nitromethane-based propellants are a cost-effective replacement for hydrazine and energetic ionic liquid hydrazine alternatives such as LMP-103S and ASCENT. The developed system uses a glow plug as the ignition source. Additionally, gaseous oxygen is injected simultaneously into the combustion chamber at the beginning of a firing. After closing the oxygen valve, a pure monopropellant operation follows. Three test series were carried out using NMP-001, a previously characterized nitromethane-based monopropellant. During the first test series, the required ROF for ignition was identified to be above 0.3. In the second test series, the low-pressure combustion limit was shown to be 13.9 bar, which is significantly lower than the 30 bar limit of heritage nitromethane-based monopropellants. In the third test series, the oxygen injection timing was optimized to minimize the required amount of oxygen for successful ignition to 1.5 g per ignition in this test setup. This approach to ignition is more cost effective than the catalytic initiation used for other monopropellants because neither costly precious-metal catalytic materials nor lengthy preheating procedures are required. Full article

Excess associated gas from unconventional wells is typically flared while excess produced water is injected underground. In this work, flare gas recovery is integrated with produced water desalination and a solar pre-heater. The solar module with a beam splitter preheats the produced water. Aspen Plus process modeling, economic analysis, and greenhouse gas analysis were performed. The solar flare gas recovery desalination (Solar-FGRD) process can conserve water resources and reduce the brine injection by 77%. The accompanying solar farm results in excess solar electricity for exporting to the grid. The process burner combustion efficiency (CE) is 99.8%, with a destruction and removal efficiency (DRE) of 99.99% for methane as opposed to a flare CE of 80–98% (and a methane DRE of 91–98%). The greenhouse gas (GHG) emissions for CO₂ and methane, in terms of CO₂ equivalent (CO₂e), can be reduced by 45% for US North Dakota and Texas flaring and 13% for North Sea flaring by employing the Solar-FGRD process. Comprehensive financial analysis demonstrates the financial–economic feasibility of the investment project with or without tax credits. Best-case and worst-case scenarios provide a realistic range that investors can consider before making investment decisions. Full article

Individual road mobility comes with two major challenges: greenhouse gas emissions related to global warming and chemical pollution. For the pollution reduction in the spark ignition engine vehicle, the standard and reliable aftertreatment technology is the three-way catalytic converter (TWC). However, the TWC starts to convert once an optimal temperature, usually known as the light-off temperature, is reached. There are many methods to reduce the warm-up period of the TWC, among which is using a burner. The initial question underlying this study was to see if the use of a relatively straightforward extra-combustion device mounted upstream the TWC, without complex elements, was able to serve the purpose of reducing the light-off time. Consequently, an original burner was designed and investigated numerically via the CFD method and experimentally via measurements of the temperature evolution within a TWC, along with the emissions specific to the burner’s operation. The main findings of this study are: (1) the CFD-based examination is a good way to decide on how to achieve the so-called fit-for-purpose internal aerodynamics of the burner (i.e., to obtain a homogeneous mixture) and (2) to reach the light-off temperature, conventionally taken as 500 K, the burner was operated for 5.2 s, i.e., 3.6 g of gasoline injected, 2.7 g of CO₂ and 1.351 g of CO, respectively, emitted. Moreover, this study identified measures for improving the burner’s design as well as an enhanced procedure for the burner’s operating control both aiming to produce a cleaner combustion during the TWC pre-heating. Full article

Glycerol, a byproduct of biodiesel, has moderate energy but high viscosity, making clean combustion challenging. Quickly evaporating fine fuel sprays mix well with air and burn cleanly and efficiently. Unlike conventional air-blast atomizers discharging a jet core/film, a newly developed swirl burst (SB) injector generates fine sprays at the injector’s immediate exit, even for high-viscosity fuels, without preheating, using a unique two-phase atomization mechanism. It thus resulted in ultra-clean combustion for glycerol/methanol (G/M) blends, with complete combustion for G/M of 50/50 ratios by heat release rate (HRR). Lower combustion efficiencies were observed for G/M 60/40 and 70/30, representing crude glycerol. Hence, this study investigates the effect of premixed methane amount from 0–3 kW, and the effect of atomizing gas to liquid mass ratio (ALR) on the dual-fuel combustion efficiency of G/M 60/40-methane in a 7-kW lab-scale swirl-stabilized gas turbine combustor to facilitate crude glycerol use. Results show that more methane and increased ALR cause varying flame lift-off height, length, and gas product temperature. Regardless, mainly lean-premixed combustion, near-zero CO and NOx emissions (≤2 ppm), and ~100% combustion efficiency are enabled for all the cases by SB atomization with the assistance of a small amount of methane. Full article

Oxy-fuel combustion technology replaces air with a mixture of pure O₂ and recycled flue gas for coal combustion, which leads to difficulties in the waste heat recovery of flue gas in the boiler tail of coal-fired power plants. This paper proposes a new integration scheme for waste heat recovery of flue gas in coal-fired power plants with oxy-fuel combustion CO₂ capture. By introducing an oxygen preheater, a recycled flue gas preheater, and a low-pressure economizer, the waste heat of flue gas is fully recovered to preheat oxygen, recycled flue gas, and feed water, respectively. The proposed scheme simultaneously ensures the safe operation of the recycled fan and improves the thermal performance of the coal-fired power plants. Compared to the air combustion configuration, the boiler’s efficiency and gross power efficiency in the oxy-fuel combustion configuration are increased by 0.42% and 1.29%, respectively. Due to power consumption for the added equipment, the net power efficiency is reduced by 10.41%. A techno-economic analysis shows that the cost of electricity for oxy-fuel combustion in coal-fired power plants has increased from USD 46.45/MWh to USD 80.18/MWh, and the cost of the CO₂ avoided reaches USD 43.24/t CO₂. Full article

The current study proposes a novel design configuration of a hydrogen-fueled micro cylindrical combustor. The newly developed design consists of a single-channel inlet and a double-channel outlet with a heat-recirculating structure aimed at enhancing the heat transfer mechanism from the combustion to the walls. Investigations are conducted using three-dimensional numerical simulation means, and emphasis is placed on assessing the effects of the novel design structure on key thermal parameters and nitrogen oxide (NO_x) emissions. The numerical modeling approach is first validated against the experimental and numerical data available in the literature. A parametric study is then conducted by means of varying the length and width of the heat-recirculating channel, inlet velocity, and inlet equivalence ratio. The findings revealed that the novel design configuration significantly improves thermal performance and curtails NO_x emissions in comparison with those of the conventional structure. For example, the proposed design leads the radiation efficiency to increase by roughly 10%. The increase in the width of the preheating channel yields further optimization by boosting the heat transfer process from the flame to the walls. Elevating the inlet velocity exhibits a pronounced increase in the mean wall temperature and a more uniform distribution of the wall temperature. However, the exhaust gas temperature increases with increasing inlet velocity, leading to a reduction in the exergy and radiation efficiencies. The equivalence ratio of unity optimizes key thermal parameters, as the lean and rich conditions suffer from low hydrogen and oxygen contents, respectively. Full article

Green ammonia has become an increasingly popular fuel in recent years because of its combustion process without carbon oxide release. Adding ammonia to methane fuel for co-combustion has become one of the important research topics in the current combustion field. In the present study, the CH₄/NH₃/Air counterflow diffusion flame was taken as the research object, and Chemkin-2019 R3 software was used to explore and analyze the flame extinction limit and chemical kinetics characteristics under different ammonia mixing ratios, initial pressures, and air preheating temperatures. It was obtained that the flame extinction stretch rate was decreased by increasing the NH₃ mole fraction in the CH₄/NH₃ mixed fuel. The increase in pressure or air preheating temperature would accelerate the chemical reaction rate of each component in the combustion process, increase the flame extinction limit, and counteract the “stretching effect” of the flame, thus restraining the flame extinguishing phenomenon. The results of a path analysis show that the formation and consumption of OH had an important influence on flame extinction in the chain reaction. The net reaction rate of OH increases with increasing the initial pressure or air preheating temperature, which leads to an increase in flame intensity, combustion stability, and the extinction limit. Furthermore, the function curve between the reaction influences the RIF factor and the stretch rate of the first-to-ten reactions, affected by the heat release of flame combustion, was drawn and quantitatively analyzed. Eventually, a sensitivity analysis of the flame under different working conditions was completed, which found that promoting the forward reaction R39 H + O₂<=>O + OH also promotes the positive combustion as a whole when the flame was near extinction. The sensitivity coefficient of R39 in the CH₄/NH₃/Air flame increases with the growing initial pressure. The increasing air preheating temperature was capable of switching the reaction of R248 NH₂ + OH<=>NH + H₂O in the CH₄/NH₃/Air flame from an inhibiting reaction to a promoting reaction, while decreasing the sensitivity coefficient of inhibiting the forward reaction R10 O + CH₃<=>H + CH₂O, R88 OH + HO₂<=>O₂ + H₂O, and R271 H + NO + M<=>HNO + M. Thus, the inhibition effect of flame extinction was weakened, and the positive progress of combustion was promoted. Full article

Sensitivity to ambient air temperatures, consuming a large amount of fuel, and wasting a significant amount of heat dumped into the ambient atmosphere are three major challenges facing gas turbine power plants. This study was conducted to simultaneously solve all three aforementioned GT problems using solar energy and introducing a new configuration that consists of solar preheating and inlet-air-cooling systems. In this study, air was preheated at a combustion chamber inlet using parabolic trough collectors. Then, inlet air to the compressor was cooled by these collectors by operating an absorption cooling cycle. At the design point conditions, this novel proposed integration resulted in a 6.87% relative increase in generated power and a 10.53% relative decrement in fuel consumption, achieving a 19.45% relative increment in the plant’s thermal efficiency. This was accompanied by a reduction of 0.026 kg/s, 4.2 kg/s, and 0.278 kg/s in CO₂, CO, and NOx emissions, respectively. Finally, spider diagrams were employed to assess the impact of the operating parameters on the overall system’s performance and its associated environmental implications. Full article

The global energy crisis, forced by fossil fuel shortages and supply chain disruption, stimulates EU policymakers to find alternative energy replacement. Modifying the present polyisoprene footwear production plant into a hybrid system by combining different energy sources raises energy efficiency. The proposed hybrid system incorporates classical and solar-based technology, resulting in energy optimization by utilizing waste heat recovery. By installing an economizer for feeding water preheating using flue gas recovery, it results in the volume of the flue gases lowering from ${\mathrm{v}}_{{\mathrm{FG}}_{\mathrm{P}}}=1.7969{{ \mathrm{m}}^3}_{\mathrm{FG}}/{\mathrm{kg}}_{\mathrm{P}}$ to ${\mathrm{v}}_{{\mathrm{FG}}_{{\mathrm{ECO}}_{\mathrm{P}}}}=1.597 {{\mathrm{m}}^3}_{\mathrm{FG}}/{\mathrm{kg}}_{\mathrm{P}}$, or by 11.13%, while the flue gases’ temperature is lowered from 204 °C (477.15 K) to 50.99 °C (324.14 K). Further improvement in combining feed water and air preheating results in natural gas savings of 12.05%, while the flue gases’ exhaust temperature is decreased to 30.44 °C (303.59 K). The third option, using condensate heat recovery and feeding water preheating using flue gases, showed natural gas savings as much as 17.41% and exhaust flue gases cooling to 112.49 °C (385.64 K). The combination of condensate heat recovery, combustion air and feed water preheating results in the volume of the flue gases being lowered by 20.42% and natural gas savings by 20.24%, while the flue gases’ temperature is reduced to 45.11 °C (318.26 K). The proposed solar application in polyisoprene production predicts the hybrid system showing fuel savings ranging from 77.96% to 87.08% in comparison to the basic process. The greatest fuel savings of 87.08% is shown in a solarized polyisoprene footwear production plant with combustion air and feed water preheating combined with the condensate return system. Integrating the solar heat into the regular industrial process of polyisoprene production showed great potential and showed environmental sustainability through energy optimization in polyisoprene production. Full article