Increasing Injection Pressure Research Articles

Experimental study on deflagration characteristics of non-uniform oil mist in an enclosed chamber

The deflagration characteristics of oil mist in the marine enclosed chamber are studied. The results show that oil mist deflagration in a non-uniform enclosed chamber is a violent process. When the nozzle size is 1.0 mm, the maximum oil mist deflagration overpressure in the chamber can reach 0.945 MPa. Increasing the nozzle size strengthens the deflagration intensity of oil mist. As the nozzle size increases, the oil mist deflagration flame propagation velocity, peak deflagration overpressure, and gas temperature increase. In addition, the oil mist deflagration process is facilitated by the increase in injection pressure. The maximum flame propagation velocity and maximum deflagration overpressure gradually improve with the increase in injection pressure. This is mainly because the increase in injection pressure leads to better atomization of oil mist droplets, increasing surface area of the oil mist, and the increase in oil mist concentration, which makes the intensity of oil mist deflagration in the enclosed chamber more intense. Nozzle size on the intensity of oil mist deflagration is more influential than the injection pressure.

Experimental investigation of near-field spray characteristics of RP3 aviation fuel based on multivariable sensitivity and uncertainty analysis

The utilization of aviation kerosene RP3 in diesel engines and ground vehicles has attracted more attention due to the implementation of the army's Single Fuel Concept. To explore the characteristics of the RP3 near-field spray primary breakup, experimental studies were carried out via the diffuser back-illumination imaging (DBI) method under single-hole injectors accommodated to varied engine spray circumstance. The critical factors of the variability in RP3 spray characteristics response were figured out by constructing a one-dimensional active subspace to perform multivariable synergistic effects via sensitivity analysis. Moreover, the uncertainties associated with unstable cavitation within nozzle were quantified with a varied array of operating conditions. In comparison to diesel, it is indicated that, there is a range of critical cavitation, in where greater uncertainties in spray cone angles are exhibited, especially for RP3. RP3 tends to form a ‘mushroom’ spray structure, with a smaller spray cone angle compared to diesel, but the disparity gradually diminishes as the fuel injection pressure increases. The gradual transition from ‘needle’ to ‘mushroom’ shape in RP3's near-field spray structure is revealed with increased fuel injection pressure, and the appearance time of the ‘mushroom’ structure advances with higher ambient pressures. Based on the active space construction, the sensitivity analysis discovers that the spray cone angle is dominantly influenced by ambient pressure and cavitation within the nozzle, thus providing a new perspective on analyzing test data without the expense of single variable statistical work.

Combustion modes of kerosene spray in a supersonic combustor

The mixing and combustion characteristics of liquid kerosene spray in a cavity-based supersonic combustor under a Mach 2.52 inflow are experimentally and numerically investigated. The combustion mode transition of kerosene spray includes two aspects: 1. As the injection pressure increases, the combustion mode shows a transition of weak-intensive-transitional(weak to intensive)-weak-blowoff; 2. in the transitional combustion mode, there is a transition from weak to intensive combustion over time. In the weak combustion mode, the combustion chamber pressure increases slightly, and the flame is inside the cavity. In the intensive combustion mode, the pressure rises sharply from the isolation section and the flame is a typical cavity stabilized combustion mode. The weak combustion at low/high injection pressure is due to rich/lean fuel inside the cavity. In the transitional combustion mode, the flame on the downstream wall of the cavity gradually expands and joins with the flame inside the cavity, evolving from weak combustion to intensive combustion. The transition is accomplished in a very short time, on the order of milliseconds. This study deepens the understanding of the combustion mode of scramjet engines and provides a reference for the design of fuel injection schemes for scramjet engines.

Effect of diesel injection pressure for enhancing combustion and reducing mechanical vibration and noise emissions in a non-road diesel engine

In this study, the combustion, performance, emissions, noise, and vibration characteristics of a single-cylinder, four-stroke, air-cooled diesel engine used for non-road purposes were investigated by controlling different injection pressures with a common rail fuel injection system. The aim of this study is to enhance the combustion performance and improve the existing noise and vibration levels of this commonly used non-road diesel engine in fields such as agriculture, wetlands, and the construction sector by optimizing the injection pressure. The experiments were conducted under low and medium load conditions and at a constant engine speed. The single-cylinder, non-road engine's fuel injection system was controlled using a common rail fuel delivery system, and four different diesel injection pressures (250, 300, 350, and 400 bar) were utilized. The experimental results have shown that the combustion performance, emissions, noise, and vibration values of the non-road diesel engine improved with an increase in diesel injection pressure (DIP). Increasing DIP led to higher maximum combustion pressures and resulted in reductions of HC, CO, and smoke emissions by up to 25%, 48%, and 59%, respectively. Vibration values also decreased by up to 25%.

Analysis of influences of injection parameters on combustion process based on 2-stroke rod-less opposed piston diesel engine

Global concerns about environmental pollution and fuel consumption are increasing, and as emissions regulations become more stringent, exploring new power and structural forms to optimise diesel engines is the way forward for future breakthroughs in diesel engines. The 2-Stroke Rod-less Opposed Piston (2S-ROPE) has been extensively studied for its vibration-free and simple construction. Compared to conventional four-stroke engines, it has a smaller bore, shorter cycle time, higher power and lower fuel consumption in the same time, making it an ideal power source for small engines. In this paper, the rod-less structure is applied to a two-stroke opposed-piston diesel engine for the first time. Based on experimental verification by spraying, a dynamic high-precision three-dimensional model of computational fluid dynamics (CFD) is established, using lateral injection, to clarify the various airflow patterns that occur in the cylinder during the intake and exhaust of the 2S-ROPE, and investigates the effects of injection timing and injection pressure on the oil–gas mixing and combustion processes in the 2S-ROPE cylinder. The results show that the in-cylinder turbulent kinetic energy is highest at an injection timing of 15° BTDC (Before Top Dead Center) and that fuel injection has the greatest effect on in-cylinder airflow disturbance at this time. At 17.5° BTDC, the duration of in-cylinder combustion was the longest. The effect of injection timing on the burst pressure is linear, for every 2.5° advance, the maximum pressure in the cylinder increases by about 2 MPa. 20 MPa of injection pressure increases, the stall period is shortened by less than 1°, the combustion duration CA10-90 is shortened with the increase in injection pressure, and for every 20 MPa increase in injection pressure, the burst pressure increases by 1 MPa, which is a significant increase.

The properties of sustainable aviation fuel I: Spray characteristics

This study measures the spray penetration, spray angle and spray volume of sustainable aviation fuel (SAF) experimentally using an optical constant volume combustion chamber under different ambient temperatures, injection pressures, and ambient pressures. The results show that when the ambient temperature increases from 200 °C to 300 °C, the spray penetration decreases by ∽10%–20%, while it further decreases by ∽40%–50% when the temperature increases from 300 °C to 400 °C. Furthermore, the spray penetration of SAF will reach its stable stage fastest at 400 °C. As the ambient temperature increases, the spray angle and spray volume of SAF decreased by 10%–20% and 50%, respectively. In addition, the spray penetration and spray volume of SAF increased by 10% and 20%, respectively, with an increase in injection pressure at 200 °C. An increase in injection pressure at 400 °C causes the decrease in spray penetration and spray volume of SAF by 20%, and both of them showed increasing and decreasing trends at the stable stage. Thus, increase in injection pressure has little effect on the spray angle. Moreover, the spray penetration and spray volume of SAF showed a decreasing trend on increasing ambient pressure, but significant effect was observed at a high temperature of 400 °C than at a low temperature of 200 °C. Conversely, the spray angle of SAF showed an increasing trend with an increase in ambient pressure, but this influence was larger at a low temperature of 200 °C than that at a high temperature of 400 °C.

Experimental research on self-initiation process of rotating detonation wave by high-temperature ethylene-rich gas

This study investigates an experimental process of high-temperature ethylene-rich gas and air for rotating detonation. After abandoning the pre-detonator method, the high-temperature ethylene-rich gas was injected and collided with the outer wall to create a localized high temperature and pressure region that ignited the gas mixture to form the deflagration state. Whether it is a single deflagration flame or double deflagration flame, it is eventually transformed through the deflagration-to-detonation transition (DDT) process into a double detonation wave. With propagation and collision of the double waves, the injection pressure increases, which results in shortening the self-initiation delay time. The equivalence ratio, gas temperature, and mass flow rate affect the success ratio of self-initiation. Rotating detonation engine (RDE) can be successfully initiated in the equivalence ratio range of 0.82 to 1.69. Equivalence ratio and gas temperature increase the propagation velocity of rotating detonation wave (RDW), for maximum RDW velocity of 1324.61 m/s, the gas temperature is 1021.3 °C. At the double wave collision point, a new weak RDW appears that decreases the RDE operating stability and a periodic quenching and re-initiation of RDW phenomenon occurs at that point.

Characterization of diesel spray combustion under micro-hole and ultra-high injection pressure conditions-analyses of diffused back-illumination imaging and OH* chemiluminescence imaging

This study investigated the spray combustion characteristics of diesel fuel using the Diffuse Back-illumination Imaging (DBI), Direct Photographic, and OH* chemiluminescence methods under different injection pressures (100–300 MPa) and different hole diameters (0.07–0.133 mm). The results indicated that at a certain point, the downstream of the spray, which holds a strong turbulent mixing, starts to disappear gradually without bright flames due to the cool flame combustion process. Based on this process, the ignition timing was determined using the space integral of intensity and optical thickness through the DBI method, which was validated by the OH* chemiluminescence method. The utilization of a micro-hole diameter injector and ultra-high injection pressure can effectively reduce ignition delay. Significant oxidation processes were observed both downstream and upstream for the micro-hole injector under ultra-high injection pressure. A parameter utilizing spatially integrated natural luminosity to OH* chemiluminescence ratio showed that increasing injection pressure and reducing hole diameter effectively reduced soot under unit fuel oxidation conditions. And predicted model results of droplet diameter and equivalence ratio (Siebers' and Hiroyasu's model) were used to analyze the experimental results. These findings contribute to the understanding of spray combustion characteristics and inform the development of efficient and low-emission combustion systems.

Laser ignition and flame propagation of methanol-air mixture in a constant volume combustion chamber

ABSTRACT The combustion performance of laser-ignited methanol-air mixture in a constant volume combustion chamber was investigated using the Schlieren photography technique. The experimentation was conducted at 5, 7, 9, and 11 MPa fuel injection pressure and 363 K initial chamber temperature using a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser of 1064 nm wavelength. The gasoline direct injection (GDI) system was used for injecting the fuel at different pressures inside the chamber. The laser beam is focused into the chamber using a 150 mm focal length lens, and laser energy of 200 mJ was used for all experimentation. The Schlieren system was used for capturing flame propagation of methanol-air mixture for different equivalence ratios. The pressure-time history for equivalence ratio (ϕ) of 0.8, 0.9, and 1.0 was plotted and analyzed at different chamber filling pressures. Flame propagation was found faster for ϕ of 1.0 due to higher laminar velocity than 0.8 and 0.9. Flame visualization showed that the flame attains the ellipsoid shape during the early stage of ignition. It generates two lobes in the vertical direction and then again expands in a horizontal direction toward the ignition source. For all equivalence ratios, the flame propagation toward the incoming laser source (X-) was observed faster compared to the flame propagation in the direction and perpendicular to the laser beam direction. For all equivalence ratios, higher laminar flame speed was observed at 5 MPa injection pressure; however, it decreases as the injection pressure increases. At ϕ of 1.0 and 11 MPa injection pressure, the maximum peak pressure of 0.67 MPa and combustion duration of 19.3 ms were noted. At 9 MPa injection pressure and ϕ of 1.0, the peak pressure and combustion duration was found as 0.61 MPa and 19.4 ms, respectively. At ϕ of 0.8, the peak pressure and combustion duration were observed 0.27 MPa with 34.6 ms duration and 0.47 MPa with 36.9 ms duration at 5 MPa and 11 MPa injection pressures, respectively.

Very low soot formation with modulated liquid length and lift-off length of diesel spray flame

The vehicle diesel engine has entered the ultra-high injection pressure era. In order to study the spray and combustion characteristics under ultra-high pressure, the liquid length and combustion characteristics of multi-hole injectors (10 holes) with different hole diameters and different injection pressures were studied via experimental methods. The results show that increasing the injection pressure can effectively increase the slope of liquid length, while the hole diameter has little effect on it. However, during the stable stage, increasing hole diameter increase the liquid length, while the injection pressure has little effect on it. Different from the liquid length, the lift-off length during the stable stage is mainly affected by the injection pressure. F. Dos Santos’ model and the parameters of Siebers can more accurately predict the liquid length and lift-off length, even if the injection pressure has been increased to 300 MPa. Increasing injection pressure and reducing hole diameter can reduce the interference between liquid length and lift-off length. When the liquid length is less than the lift-off length, it can effectively inhibit soot formation. The value of LL/LOL has a fine linear relationship with stoichiometric air percentage. An equation of the relationship between the injection pressure and the hole diameter was established by the predicted model. Using this equation, we can get the range of LL/LOL less than 1 under different hole diameters or different injection pressures. The determination of this equation provides guidance and suggestions for the selection of hole diameters and injection pressure for diesel engines.

Experimental investigation combined with steady-state and transient-state tests on soot characteristics of hydrogenated catalytic biodiesel/n-butanol blends

The utilization of biodiesel and biobutanol offers a promising approach to achieve energy conservation and emission reduction in combustion engines. This study investigates the soot characteristics of hydrogenated catalytic biodiesel mixed with n-butanol (20% by volume) under steady-state and transient-state conditions using diffused background-illumination extinction imaging and two-color method, respectively. Both conditions in constant volume combustion chamber (steady-state) and optical engine (transient-state) exhibit similar soot stages, namely Formation Dominating and Oxidation Dominating. Between the above Dominating stages, the soot development under steady-state conditions is further segmented into Initial Oxidation and Secondary Oxidation, while a Stalemate stage manifests under transient-state conditions owing to wall impingement and strong turbulence. Under steady-state conditions, formation and oxidation processes are mainly controlled by the soot peak of spray head. By decreasing ambient temperature and increasing injection pressure, soot accumulation is notably diminished by 30.27% and 45.72% during the Formation Dominating stage, achieved through the deceleration of precursor reactions and enhancement of air-fuel mixing characteristics within the flame lift-off zone, respectively. Additionally, higher injection pressure notably amplifies the efficacy of the Initial Oxidation, primarily through the reduction of soot residence time. Under transient-state conditions, the Formation Dominating stage for SOI-25 and SOI-20 occur away from the early combustion, resulting in a reduction of 10.26% and 68.36% in soot compared to SOI-30. The Stalemate stage is characterized by a competition between the oxidation of high-temperature flames above 2000 K and the formation of low-temperature flames below 1800 K. A portion of soot originating from the high-temperature flames becomes integrated into the low-temperature flames after cooling, subsequently emerging as the primary hindrance to the ensuing oxidation process.

Droplet characteristics of multi-plume flash boiling spray evaluation using SLIPI-LIEF/Mie planar imaging technique

Flash boiling atomization is a promising approach whose primary breakup heavily relies on the phase change inside the nozzle. Droplet size measurement is crucial for fundamental studies of flash boiling sprays. However, the interference of the vapor phase and multiple scatterings in droplet-dense regions notably impact the accuracy of spray droplet size measurement. In this work, we utilized a three-phase structured laser illumination planar imaging, laser-induced exciplex fluorescence/Mie scattering (3p-SLIPI-LIEF/Mie) method in evaluating the droplet size distribution for a two-hole fuel injector and an ECN Spray G injector. The SMD characteristics of the fuel spray under various temperature and pressure boundary conditions were examined, and flash boiling spray collapse conditions were emphasized. The results show that the proposed SLIPI-LIEF/Mie method is superior to PDI techniques in providing more comprehensive results while maintaining satisfactory accuracy. The SLIPI-LIEF/Mie results show that the near-field plume expansion and SMD distribution strongly correlate with the flash boiling phase transition process. The droplet in the collapsed region was larger than that in the primary plume regions. However, whether or not the spray collapses, the SMD of the spray reduces as the fuel temperature increases, ambient pressure decreases, and injection pressure increases.

Optical characterization of ethanol spray flame on a constant volume combustion chamber

Studying pure ethanol spray flame has the potential to achieve the carbon neutrality vision. This paper studies the effects of fuel injection masses (12, 24, 36 mg) and fuel injection pressures (30, 40, 50 MPa) on ethanol spray flame on an optically visualized constant volume combustion chamber. Further compared with the spray flame of methanol and n-butanol. The combustion characteristics and flame development process were revealed by flame self-illumination high-speed imaging method, and the soot distribution was revealed by wavelength integration two-color method. Results show that ethanol spray flame presents an unstable yellow flame with many wrinkles. Small injection masses exist a partial flame-quenching phenomenon. As injection mass increases, the soot lift-off length decreases, and the flame brightness, soot concentration, and ignition delay increase. The high soot concentration areas locate upstream of the flame, and there is almost no soot downstream. Increased injection pressure increases the soot lift-off length and decreases the flame brightness. The ignition delay is shortened from 8.388 ms to 6.955 ms when injection pressure increases from 30 MPa to 40 MPa. But higher injection pressure has a negligible effect on reducing ignition delay. Finally, an ethanol spray combustion conceptual model is proposed. This paper gives particular guiding significance to the future use of carbon-neutral ethanol in diesel engines.

Spray combustion of fast-pyrolysis bio-oils under engine-like conditions

In the EU funded SmartCHP project, biomass derived fast-pyrolysis bio-oil (FPBO) is used to fuel modified stationary diesel engines for combined heat and power applications. In this study, the spray combustion characteristics of fast-pyrolysis bio-oil and FPBO/ethanol blends are experimentally investigated in a combustion research unit. Due to the special physicochemical properties of fast-pyrolysis bio-oil, major modifications are made to the combustion research unit to facilitate testing this fuel, including the installation of a high-temperature chamber and a heavy-fuel oil injection system. Experimental tests are carried out at a chamber wall temperature of 750 °C and an ambient pressure of 50 bar. The pressure-based heat release analysis is used to evaluate fuel ignition and combustion characteristics, while a high-speed imaging technique is adopted to visualize natural luminosity of spray flames through a borescope.Results show that fast-pyrolysis bio-oil has lower sooting tendency than diesel, and it significantly alleviates the fuel dribble phenomenon. At injection pressure of 300 bar, the poor atomization of fast-pyrolysis bio-oil leads to rather grainy-looking spray flame images, and nozzle orifices becoming clogged within couple of injections. The increase of injection pressure to 900 bar results in an obvious improvement of the atomization quality and nozzle durability for fast-pyrolysis bio-oil. Adding ethanol into fast-pyrolysis bio-oil could improve fuel atomization and further reduce the natural luminosity. The ignition delay of fast-pyrolysis bio-oil is slightly retarded by 10% ethanol addition, while it is advanced by 30% ethanol addition.

Alterations in coal mechanical properties and permeability influenced by liquid CO2 phase change fracturing

Liquid CO2 phase change fracturing (LCPCF) is a promising approach for stimulating coal reservoirs and enhancing gas drainage efficiency of low-permeability coal seams. In this work, low pressure CO2/N2 adsorption, CH4 permeability measurements and UCS tests are combined to quantitatively analyze the changes in coal mechanical properties and permeability before and after LCPCF treatment. The results show that the axial peak strain is increased and ductile failure takes place in treated specimens after 1.26 L of liquid CO2 was used to conduct physical blasting. The UCS and elastic modulus after LCPCF are reduced by 10.82–25.78% and 12.92–28.57%, respectively. Muti-scale pore structures within coal are altered to varying degrees. After LCPCF treatment, mesopore volume and macropore volume are increased by 11.33–41.57% and 33.82–67.5%, respectively, while micropores are slightly affected. Due to the adsorption swelling and Klinkenberg effect, CH4 permeability of all the specimens is reduced with the increase of injection pressure. Comparative analysis of gas permeability has been made between the raw coal and treated specimens. Coal permeability is enhanced by 14.48-29.43% and 10.54-24.82% after LCPCF treatment at the injection pressure of 0.5 MPa and 1.4 MPa, respectively. During the LCPCF process, shock waves and stress waves trigger tensile damage to coal mass, and a large number of new macropores/fractures are generated within coal. This provides more accessible paths for gas flow and coal permeability are greatly promoted. Crack propagation is accelerated by the released high-pressure CO2, and both coal porosity and pore connectivity are further enhanced to facilitate gas seepage in coal seams.

An online physical simulation method for enhanced oil recovery by air injection in shale oil

In order to understand the mechanism of air flooding shale oil, an online physical simulation method for enhanced shale oil recovery by air injection was established by integrating CT scanning and nuclear magnetic resonance (NMR). The development effect of shale oil by air flooding under different depletion pressures, the micro-production characteristics of pore throats with different sizes and the mechanism of shale oil recovery by air flooding were analyzed. The effects of air oxygen content, permeability, gas injection pressure, and fractures on the air flooding effect in shale and crude oil production in pores with different sizes were analyzed. The recovery of shale oil can be greatly improved by injecting air into the depleted shale reservoir, but the oil displacement efficiency and the production degree of different levels of pore throats vary with the injection timing. The higher the air oxygen content and the stronger the low-temperature oxidation, the higher the production degree of pores with different sizes and the higher the shale oil recovery. The higher the permeability and the better the pore throat connectivity, the stronger the fluid flow capacity and the higher the shale oil recovery. As the injection pressure increases, the lower limit of the production degree of pore throats decreases, but gas channeling may occur to cause a premature breakthrough; as a result, the recovery increases and then decreases. Fractures can effectively increase the contact area between gas and crude oil, and increase the air sweep coefficient and matrix oil drainage area by supplying oil to fractures through the matrix, which means that a proper fracturing before air injection can help to improve the oil displacement effect under a reasonable production pressure difference.

Experimental study on spray characteristics of RP-3 kerosene under the near critical condition with different injection conditions

In an aero-engine, the effect of oil-gas mixing directly affects the working condition of the combustion chamber, and the mixing process of RP-3 kerosene near the near-critical point is more complicated because its physical properties are more strongly affected by its own temperature and pressure changes. The injection process of RP-3 kerosene near the near-critical point was photographed under different injection conditions using high-speed ripple shadowing technology. It was found that the increase in air injection pressure and the distance from the nozzle outlet to the cyclone outlet would reduce the jet expansion angle and jet width. The former would reduce the jet’s self-excited oscillation frequency, and the latter would increase it.

Experimental study on the effects of injection pressure on the combustion in a SI aviation piston engine fueled with kerosene

Kerosene becomes an alternative to gasoline in aviation piston engines for its safety and easy replenishment on some special occasions. However, the low octane number of kerosene tends to cause the knock of SI engine, as a result, most of the current SI kerosene engines run in an operation mode of two-stroke, which has the disadvantage of a low compression ratio and high fuel consumption. This study conducted a series of experiments on a two-stroke SI kerosene engine equipped with an air-assisted direct injection system to improve engine performance and fuel economy by increasing injection pressure and combining it with control strategy optimization. First, the effects of injection pressure on the combustion of kerosene engines were studied, including cylinder pressure, combustion rate, and the stability of combustion. The results show that increasing the injection pressure shortens the ignition delay, accelerates the combustion, and substantially improves the combustion stability. Then, the effects of increasing the injection pressure on the control strategies of injection advance angle, ignition advance angle, and fuel injection duration were investigated. Ultimately, based on the investigation of the effects of injection pressure on the control strategies, two optimizations of control strategies were obtained to reduce fuel consumption and increase power, respectively, with the former reducing fuel consumption by 14.9% and the latter increasing power by 6%.

Comparative study of droplet and liquid film velocities in sprays

This study presents a comparative analysis of droplet and conical liquid film velocities in sprays by a pressure swirl injector with Abramovich geometric constant K = 1.986. The velocities were measured simultaneously by schlieren image velocimetry and sequential images of the liquid film, using a high-speed camera with 8192 fps and shutter of 2 μs. Other parameters, such as discharge coefficients, spray cone angles and breakup lengths were also determined, using water as test fluid, for injection pressures from 0.05 to 0.5 MPa. Experimental velocity data were compared to results from different semi-empirical equations. The breakup lengths decreased continuously from around 20 mm to 15 mm for injection pressures from 0.1 to 0.5 MPa, while spray cone angles increased continuously from about 42°–53°, for pressures from 0.2 to 0.5 MPa. Mean axial droplet velocities varied from 4.7 m s−1 to 14.5 m s−1, while the mean total droplet velocities varied from 5 m s−1 to 16.2 m s−1 and the total liquid film velocity increased from 5.7 m s−1 to 20.2 m s−1, approximately, for increasing injection pressure. Liquid film velocities were about 15%–28% higher than the droplet velocities in the pressure range considered, due to the energy required for liquid film breakup and the air drag on the droplets. The current findings underscore that significant discrepancies may arise when relying on inadequate velocity data, particularly when employed in the computation of key parameters such as the Reynolds and Weber numbers.

Response of anthracite microcrystalline structure due to multi-phase CO2 injection

CO2 injection in coal causes permeability reduction, but also affects the microcrystalline structure. To quantify the different response of microcrystalline structure of anthracite after multi-phase CO2 injection, anthracite samples from the Qinshui basin, the samples were demineralized by HF-HCl before CO2 injection, then subjected dry, demineralized samples to CO2 injection experiments at 4 MPa (gaseous), 6 MPa (subcritical) and 8 MPa (supercritical) pressure, the microcrystalline quantification was obtained using X-ray diffraction and image analysis of HRTEM micrographs, the morphological characteristics of ultramicropore were quantitatively characterized by HRTEM image analysis. With increasing injection pressure, the interplanar spacing (d002) and aromaticity (fa) of the coal gradually increased, while the average number of aromatic layers (Nc) and unit stacking height (Lc) gradually decreased; the variation in the unit lateral size (La) also became more complex. Thus, the coal crystal structure was altered after CO2 treatment and the degree of damage increased with pressure. Further, the average length of coal lattice fringes becomes shorter with the increase of pressure, while the length, width and area of ultra-micropores in subcritical and supercritical SH and ZZ coal increase. In addition, the average curvature of the lattice fringes became larger, and the directional ordering decreased after CO2 intrusion. Thus, CO2 injection led to the transformations of crystal structure, generating intermolecular structural defects, and a reduction in order in the striation direction. This study presents the microcrystalline structure and ultra-micropore response of anthracite due to CO2 injection, which also helps with in-depth understanding of the impact of CO2-ECBM.