Injection Strategy Research Articles

Effects of structural parameters of active pre-chamber on the combustion process of methanol/gasoline TJI rotary engine

The application of Turbulent Jet Ignition (TJI) combustion mode in spark ignition engine can improve combustion efficiency and output power. This paper innovatively proposes the application of active pre-chamber (APC) in rotary engine (RE) to realize this mode. And blending a certain percentage of methanol in gasoline to achieve carbon reduction. A three-dimensional computational model of the APC-RE was developed, and the effects of three APC structural parameters including throat section diameter, throat section length and orifice diameter on the component flow and combustion characteristics were investigated. The results showed that the APC-RE exhibited higher sensitivity to the diameter of the throat section than the length variation under the fixed active fuel injection strategy. The low length or small diameter of the throat section causes insufficient energy in the APC jet, and too high values cause unstable combustion. The optimal APC volume is achieved at a throat length of 8 mm and a diameter of 6 mm, with the highest Indicated mean effective pressure (IMEP) and Indicated thermal efficiency (ITE). Next, The APC volume was fixed and the effect of jet orifice size on RE performance was discussed and the optimal size was determined 1.25 mm, which can further optimize the jet velocity and can continue to increase IMEP and ITE by 1.24 % and 1.46 % respectively.

Effect of injection strategy on spray and combustion processes in 2-stroke rod-less opposed piston engine (2S-ROPE)

The 2-stroke Rod-less Opposed Piston Engine (2S-ROPE) is a novel engine design that has garnered attention owing to its high power and low fuel consumption. This study investigated the effects of different fuel injection strategies on the in-cylinder working process of a 2S-ROPE engine, which features a smaller combustion space and lateral injection than conventional diesel engines. A high-precision three-dimensional simulation model was developed to examine the fuel atomization and in-cylinder combustion processes under four distinct injection strategies (S1, S2, S3, and S4). The results demonstrated that the injection strategy significantly influenced the number of oil droplets, particularly for small particles. The number of small droplets in S4 was approximately 6 times that in S1. The double-layer injection strategies (S3 and S4) exhibited a better atomization breakup and oil-air mixing, leading to a faster combustion rate and higher lift power than the single-layer injection strategies (S1 and S2). These findings suggest that the double-layer injection strategy is more suitable for a 2S-ROPE engine, increasing the lift power by up to 23 %. The results can guide the improvement of combustion parameters in most opposed piston engines.

Study on heat release characteristics of the dual composite flame stabilizers for the dual-mode scramjet

The paper studies the heat release (HR) characteristics of a dual-mode scramjet equipped with the dual composite flame stabilizers under simulated free-stream conditions of Mach 6 and dynamic pressure of 30 kPa, through ground direct-connected tests and OpenFOAM numerical simulation. This study focuses on the three-dimensional distribution of subsonic/supersonic HR, local combustion modes, and the variations in HR during the ram-scram mode transition. The results indicate that the high-enthalpy jet transports the high-temperature and fuel-rich gas in the cavity to the mainstream through the ejection effect of the supersonic flow, causing the heat release zone to move to the mainstream. So that the mainstream subsonic-diffusion combustion zone is expanded and is evenly distributed, and then the HR trailing zone downstream of the thermal throat is shortened. The study highlights the different matching characteristics between subsonic flow and HR formed by the dual composite flame stabilizers under high and low equivalence ratio (ER). Optimized injection schemes need to be selected to obtain higher combustion efficiency at different equivalence ratios. In the region of the first-stage composite flame stabilizer, a distinct phenomenon of subsonic/supersonic mixed HR is observed. Subsonic HR predominates under the ramjet mode, while the subsonic HR tends to equal supersonic HR under the scramjet mode. Upstream of the thermal throat, subsonic HR exceeds 80%, and supersonic heat release has a tendency to gradually decrease. Furthermore, when the ER of two-stage dispersed injection is less than 0.5, the heating amount per kilogram of air is less than 1.06 MJ, and the thermal throat cannot be formed, causing the ram-scram mode transition to occur. Conversely, for single-stage concentrated injection, the boundary of ER and heating amount decreases. The study provides support for the design of injection schemes and the regulation of mode transition for dual-mode scramjet based on the HR performance.

Comparison of different longitudinal injection scenarios for achieving optimal performance in SAPS

The Southern Advanced Photon Source (SAPS) is a proposed fourth-generation diffraction-limited storage ring (DLSR) designed with a modified hybrid multibend achromat lattice, achieving a natural emittance as low as 33 pm. Given its limited dynamic aperture, the SAPS is not well suited to off-axis injection, with on-axis injection schemes proving a more favourable option. This paper highlights the advantages of longitudinal injection for SAPS, which employs a fast pulse kicker and multi-frequency RF systems. A systematic comparison is presented of the longitudinal injection schemes for double-frequency and triple-frequency RF systems. The effects of these schemes on circulating beam stretching, the time structure of the fast pulse kicker, RF parameter stability requirements, storage ring acceptance, and injection efficiency are considered. Based on these results, reasonable hardware specifications for the fast stripline kicker and RF system, as well as injector parameter requirements, are provided. These findings are crucial for SAPS to achieve longitudinal injection and can also serve as a reference for similar light sources.

Semantic layout-guided diffusion model for high-fidelity image synthesis in ‘The Thousand Li of Rivers and Mountains’

“The Thousand Li of Rivers and Mountains” (TLRM) is one of the most famous traditional paintings. Even experienced artists face significant challenges in replicating TLRM. Utilizing semantic layout-guided diffusion models offers a novel approach to this task; however, synthesizing high-quality images with consistent semantics and layout is difficult due to TLRM’s unique characteristics. In this paper, we propose a novel diffusion model-based framework guided by semantic layout to generate images tailored to TLRM’s distinct features. We introduce the layout enhanced map and latent layout injection strategies, which improve semantic fidelity and color distribution. These innovations are integrated into our semantic latent diffusion model for effective semantically-guided image generation. To address the training challenges posed by a single large-scale image, we employ specialized data augmentation techniques, facilitating the generation of one-hot semantic layout representations and ensuring continuous training until convergence. Additionally, we developed the TLRM-dataset for semantic image synthesis, which enhances visual quality and semantic consistency. Experimental results and user surveys demonstrate that our model can produce high-fidelity and diversified results, offering significant potential for art education, digital preservation, and cultural heritage. Our code is publicly available at https://github.com/rane7/TLRM-SLDM.

A New Model for Steam Cavity Expansion in Vertical Wells of Heavy Oil Reservoirs

Summary Steamflooding is one of the most effective and mature methods for developing heavy oil. However, existing research has not fully explained the phenomena of steam overburden and heat loss, particularly overlooking the steam velocity loss at the steam cavity front. Therefore, the condensation heat transfer coefficient (CHTC) was introduced to describe the decrease in steam velocity at the steam cavity front. A steam cavity front expansion model, considering shape factor, pseudofluidity ratio, and CHTC ratio (CHTCR), was established and validated by using mine monitoring data. The research results show that the steam cavity of the revised model is in the shape of a “funnel,” and the steam overburden phenomenon is more pronounced at the steam cavity front. Through comparison with the field data of the P6 and P612-1 well groups, it is observed that the average displacement error of the steam cavity front of the two is only 6.58%. As steam injection progresses, the steam cavity is more degraded, and the steam overburden phenomenon is more intensified compared with the initial stage. Taking into account the phenomenon of kinetic energy loss, a higher formation heat loss rate is calculated during the middle and late stages of steam injection in the modified model. The pressure gradient at the steam cavity front is analyzed to determine an optimal displacement radius of 40 m for vertical well steamflooding in heavy oil reservoirs. When parameters such as shape factor, steam injection rate, and CHTC are increased, the development shape of the steam cavity is more ideal, but the convexity of the steam cavity front is increasingly pronounced as the pseudomobility ratio increases. The CHTC was incorporated into the steam cavity expansion model, elucidating the steam overburden phenomenon and advancing the theoretical understanding of steamflooding. By improving the existing model, the analytical formula can be used to rapidly predict the position of the steam cavity front and estimate of the steam-saturated zone, even in the absence of some field data or numerical models. Practical guidance for optimizing steam injection strategies is provided, with the potential to significantly enhance the recovery of heavy oil reservoirs.

Hydrate management strategies for CO2 injection into depleted gas reservoirs

Sequestering CO2 in depleted gas reservoirs using carbon capture, utilization, and storage technologies has emerged as a viable strategy for mitigating global carbon emissions. However, CO2 hydrate formation during injection processes is challenging and poses a risk to the operational integrity and efficiency of sequestration projects. This study investigated CO2 hydrate formation dynamics within silica gel environments that closely mimicked the median pore size of natural sandstone reservoirs, particularly targeting depleted gas fields in the East Sea of Korea. Integrating kinetic insights into experimental hydrate formation assessments and molecular dynamics simulations provided a comprehensive understanding of the CO2 hydrate formation mechanisms, as well as the formation dynamics and stability of the CO2 hydrates. For example, the hydrate formation kinetics were significantly reduced in the small pores, suggesting the feasibility of implementing more economical hydrate inhibitor injection strategies during CO2 injection. Moreover, this study evaluated the inhibitory effects of NaCl and methanol on CO2 hydrate stability by accurately measuring the three-phase (H-Lw-V) equilibria and employing silica gels (6 nm pore size). The presence of methanol and amorphous silica significantly impacted hydrate formation, with methanol potentially influencing the local structure around the hydrate phase and silica hindering hydrate growth through dynamic interactions with CO2 molecules. In addition, we elucidated the complex interplay between CO2, water, and methanol (hydrate inhibitor) within the constrained environments of porous media, offering strategic insights for the development of effective CO2 injection and sequestration strategies. Integrating molecular-level observations with real-world geological modeling presents a novel methodology for enhancing the safety, efficiency, and environmental sustainability of carbon capture and storage operations. The findings of this study provide critical insights into hydrate phase behavior, highlighting the importance of precise equilibrium determination under simulated reservoir conditions to effectively anticipate and mitigate hydrate formation challenges.

A New Algorithm Model Based on Extended Kalman Filter for Predicting Inter-Well Connectivity

Given that more and more oil reservoirs are reaching the high water cut stage during water flooding, the construction of an advanced algorithmic model for identifying inter-well connectivity is crucial to improve oil recovery and extend the oilfield service life cycle. This study proposes a state variable-based dynamic capacitance (SV-DC) model that integrates artificial intelligence techniques with dynamic data and geological features to more accurately identify inter-well connectivity and its evolution. A comprehensive sensitivity analysis was performed on single-well pairs and multi-well groups regarding the permeability amplitude, the width of the high permeable channel, change, and lasting period of injection pressure. In addition, the production performance of multi-well groups, especially the development of ineffective circulation channels and their effects on reservoir development, are studied in-depth. The results show that higher permeability, wider permeable channels, and longer injection pressure maintenance can significantly enhance inter-well connectivity coefficients and reduce time-lag coefficients. Inter-well connectivity in multi-well systems is significantly affected by well-group configuration and inter-well interference effects. Based on the simulation results, the evaluation index of ineffective circulation channels is proposed and applied to dozens of well groups. These identified ineffective circulation channel changing patterns provide an important basis for optimizing oil fields’ injection and production strategies through data-driven insights and contribute to improving oil recovery. The integration of artificial intelligence enhances the ability to analyze complex datasets, allowing for more precise adjustments in field operations. This paper’s research ideas and findings can be confidently extended to other engineering scenarios, such as geothermal development and carbon dioxide storage, where AI-based models can further refine and optimize resource management and operational strategies.

Numerical modelling of CO2-in-water emulsion injection into a water-saturated core

Depressurization method shows promise for methane hydrate (MH) reservoir production, but the reformation of hydrates due to a lack of geothermal heat presents a significant challenge for commercial production. This study proposes a novel approach for MH gas recovery by injecting a CO2-in-water (C/W) emulsion into an MH reservoir aquifer. The exothermic nature of CO2 hydrate formation and liquid CO2 dissolution in water in this method provides heat to the MH layer, effectively preventing hydrate reformation. Subsequently, 1-D numerical models were developed and implemented using the MATLAB Reservoir Simulation Toolbox (MRST). These models were rigorously validated against experimental data under homogeneous conditions and varying injection schemes. The investigation indicated that the average volume fraction of CO2 hydrate within the hydrate particles was found to be 55% of the volume of liquid CO2 droplets. The alternating C/W emulsion injection increased the driving force for CO2 dissolution in water, thereby promoting subsequent hydrate particle decomposition and CO2 hydrate dissolution in water, which effectively mitigated blockage within the porous medium. In conclusion, water alternating C/W emulsion injection, along with the continuous injection of a low volume fraction of liquid CO2 within the C/W emulsion, exhibits promising potential for sustained injection and provides adequate heat to the MH layer, preventing hydrate reformation. Furthermore, the developed numerical model reasonably predicts the behavior of various injection schemes. This developed model can be used for devising long term sub-seabed carbon capture and storage development plan.

Effect of different injection strategies considering intravenous injection on combination therapy of magnetic hyperthermia and thermosensitive liposomes

Abstract The combination therapy of magnetic hyperthermia and thermosensitive liposomes (TSL) is an emerging and effective cancer treatment method. The heat generation of magnetic nanoparticles (MNPs) due to an external alternating magnetic field can not only directly damage tumor cells, but also serves as a triggering factor for the release of doxorubicin from TSL. The aim of this study is to investigate the effects in the degree of tumor cell damage of two proposed injection strategies that consider intravenous administration. Since both MNPs and TSL enter the tumor region intravenously, this study establishes a biological geometric model based on an experiment-based vascular distribution. Furthermore, this study derives the flow velocity of interstitial fluid after coupling the pressure distribution inside blood vessels and the pressure distribution of interstitial fluid, which then provides the convective velocity for the calculation of subsequent nanoparticle concentration. Different injection strategies for the proposed approach are evaluated by drug delivery result, temperature distribution, and tumor cell damage. Simulation results demonstrate that the proposed delayed injection strategy after optimization can not only result in a wider distribution for MNPs and TSL due to the sufficient diffusion time, but also improves the distribution of the temperature and drug concentration fields for the overall efficacy of combination therapy.

Additively-manufactured shear tri-coaxial rocket injector mixing and combustion characteristics

A monolithic tri-coaxial propellant injection scheme for enhanced mixing of methane-oxygen in liquid-propellant rocket systems is enabled by additive manufacturing. Mixing and combustion characteristics of the tri-coaxial design are assessed experimentally from 1–69 bar using laser absorption tomography and chemiluminescence imaging, and are compared to a traditionally-manufactured bi-coaxial design. Quantitative two-dimensional images of temperature and carbon monoxide mole fraction are generated from the laser absorption spectroscopy methods, while OH* chemiluminescence provides an approximate metric for combustion heat release defining flame length and injector standoff distance. At similar pressures and oxidizer-to-fuel ratios, the tri-coaxial injector design is shown to enhance mixing and combustion progress, reducing characteristic mixing length scales and achieving improved combustion performance relative to more conventional bi-coaxial designs. Despite enhanced mixing, the tri-coaxial design exhibits more limited reduction in flame standoff distance from the injector face, suggesting that increased heat flux to the injector face can be managed. The tri-coaxial injector highlights the potential to leverage additive manufacturing to enhance performance and simplify the fabrication of liquid-propellant rocket engines.

Analysis of the impact of geological and engineering parameters on productivity in tight oil reservoirs

AbstractTight oil resources are abundant, but the factors affecting production capacity are complex. In this paper, focusing on tight oil reservoirs, three research works were conducted. First, using the numerical simulation software, a numerical model of tight oil reservoirs was established. Second, the influence of geological parameters such as porosity and permeability on oil production were analyzed. Third, the influence of rock compression coefficient and injection fluid on tight oil production were analyzed. Results show that: (a) When the porosity is 0.05, the cumulative oil production in the first 6 years is the highest, while in the later stage of the simulation, the cumulative oil production with a porosity of 0.1 is the highest. (b) The higher the permeability, the greater the cumulative oil production. The cumulative oil production under different permeability conditions are 1392.044, 2178.805, 2939.1704, and 4038.0878 m3, respectively. (c) Under tight reservoir conditions, the impact of different rock compression coefficients on the daily oil production of oil and gas reservoirs is not very significant. (d) The recovery effect is optimal when using the N2 injection scheme. The effectiveness of the CH4 scheme is second, and there is a certain gap compared to the N2 scheme. The development plan of injecting water has the worst effect. However, compared to the depletion development model, the cumulative oil production by injecting N2, CO2, CH4, and water has all increased.

Numerical simulation for subsidence control in CO2 storage and methane hydrate extraction

Gas hydrates are increasingly viewed as a promising alternative to traditional fossil fuels. However, their extraction process poses risks to structural integrity, potentially causing significant subsidence. In this study, we developed a Thermo-Hydro-Mechanical-Chemical (THMC) model to analyze the impact of gas hydrate extraction on seabed subsidence. Our investigation focused on the influence of bottom hole flowing pressure, initial hydrate concentration, gas saturation, permeability, porosity, and rock thermal conductivity on subsidence during gas hydrate extraction via depressurization.The results show that seabed subsidence is affected by various factors such as bottom hole flowing pressure, initial hydrate concentration, gas saturation, permeability, porosity, and rock thermal conductivity. It was noted that significant subsidence is associated with low initial hydrate concentration, high permeability, porosity, low gas saturation, low rock thermal conductivity, and a notable pressure drop of 79.31%.To address this issue, we propose a seabed subsidence mitigation strategy involving CO2 injection. This approach not only safeguards offshore infrastructure and coastal communities but also helps reduce CO2 emissions, aligning with global climate change mitigation efforts. In our model, CO2 injection occurs in the subsurface reservoir at the interface between the free water zone and hydrate-bearing formations. The CO2 hydrates formation process releases heat, which dissociates methane hydrates, allowing the methane to be replaced by CO2 molecules and move towards the production well.Our analysis reveals that increasing injection temperature and rate significantly reduces subsidence. Additionally, the range of investigated injection pressures, which included pressures equal to and more than double the initial reservoir pressure, showed inconsequential impacts on seabed subsidence.The effectiveness of subsidence reduction is significantly enhanced by injecting a CO2/N2 mixture compared to pure CO2 injection. The most substantial reduction in subsidence occurred when a mixture of CO2 and N2 in a 50/50 vol/vol ratio was injected at a high rate.These findings offer crucial insights for optimizing the efficiency and control of gas hydrate extraction methods. They emphasize the importance of employing balanced injection strategies to minimize environmental risks and ensure sustainable energy extraction.

Doses of Botulinum Toxin in Cervical Dystonia: Does Ultrasound Guidance Change Injection Practices?

Cervical dystonia is widely understood to benefit from botulinum toxin injections. The injection practices may be influenced by specific factors, including the method of injection. Three main guidance methods can be used: palpation of anatomical landmarks, ultrasound, and electromyography. We investigated how target muscles and doses of botulinum toxin were modified after the transition from surface anatomy (non-guided) to ultrasound (US-guided), in patients with cervical dystonia. We also determined the long-term dose trend. We studied a group of 82 patients, who received non-guided injections (median: 16.5 cycles/5.1 years) followed by US-guided injections (median: 12.0 cycles/3.8 years). More muscles, and especially deep muscles, were injected during the US-guided period. The total dose and number of injected muscles were higher when US guidance was used, but the mean dose per muscle was lower. Over the long term, the total dose stabilized, and the mean dose per muscle decreased during the US-guided period. According to our results, the guidance method has a strong impact on the botulinum toxin injection strategy in cervical dystonia (target muscles and dose). Also, the treatment appeared more stable when using US guidance; this could be explained by the good precision of such injections.

Optimising the Particulate Emission Characteristics of a Dual-Fuel Spark Ignition Engine by Changing the Gasoline Direct Injection Strategy

In the current global scenario, it is essential to find more effective and practical solutions to mitigate the problem of particulate emissions from vehicles. In this research, particulate emission characteristics with changing GDI pressure or applying a split GDI strategy with different second injection timings were initially explored in a Dual-Fuel Spark Ignition (DFSI) engine, which employs Ethanol Port Injection (EPI) plus Gasoline Direct Injection (GDI). The experimental results show that by increasing GDI pressure (PGDI) from 5.5 MPa to 18 MPa, ignition delay (θF) shows a small decrease of 0.68 degrees. The parameters, such as maximum in-cylinder temperature (TMI) and exhaust gas temperature (TEG), each increase by 53.75 K and 13.84 K. An apparent reduction of 59.5% and 36.26% was achieved for the concentrations of particulate number (NP) and particulate mass (MP), respectively. Particulate emissions are effectively reduced by a split GDI strategy with an appropriate range of second injection timing (tGDI2). Under tGDI2 = −260 ºCA, NP and MP concentrations exhibit a relatively lower level. However, by delaying tGDI2 from −260 ºCA to −140 ºCA, there is an increase of more than 60% in NP concentration. The research findings help offer new and valuable insights into optimising particulate number and mass emissions from DFSI engines. Moreover, the findings could contribute novel and valuable insights into the optimisation of particulate emission characteristics in DFSI engines.

Postoperative Injection of a Triptolide-Preloaded Hydrogel Prevents the Recurrence of Glioblastoma by Dual-Pathway Activation of Ferroptosis.

Glioblastoma (GBM) recurrence leads to high mortality, which remains a major concern in clinical therapy. Herein, an injectable triptolide (TP)-preloaded hydrogel (TP@DNH) accompanied by a postoperative injection strategy is developed to prevent the recurrence of GBM. With a potential inhibitor of the NRF2/SLC7A11/GPX4 axis, it is demonstrated that TP can deactivate glutathione peroxidase 4 (GPX4) from the source of glutathione (GSH) biosynthesis, thereby activating ferroptosis in GBM cells by blocking the neutralization of intracellular lipid peroxide (LPO). Based on acid-sensitive Fe3+/tannic acid (TA) metal-phenolic networks (MPNs), the TP@DNH hydrogel can induce the effective generation of reactive oxygen species (ROS) through Fe3+/TA-mediated Fenton reaction and achieve controllable release of TP in resected GBM cavity. Due to ROS generation and GPX4 deactivation, postoperative injection of TP@DNH can achieve high-level ferroptosis through dual-pathway LPO accumulation, remarkably suppressing the growth of recurrent GBM and prolonging the overall survival in orthotopic GBM relapse mouse model. This work provides an alternative paradigm for regulating ferroptosis in the postoperative treatment of GBM.

The effects of formation inclination on the operational performance of compressed carbon dioxide energy storage in aquifers

Compressed CO2 energy storage in aquifers (CAESA) is a net-zero energy storage technology. Due to the widespread existence of inclined aquifers in nature, it is of practical significance to study the influence of inclined reservoirs on CO2 migration, safety and energy efficiency of the storage system. We build 3D numerical models with different dips (0°–16°), analyze the hydrodynamic and thermodynamic behavior of the system, and discuss the effects of injection schemes (temperature and pressure) on wellbore pressure, temperature, and energy efficiency. The results show that formation dip affects the energy storage characteristics of the system mainly by affecting the migration and distribution of CO2 in the aquifer. The greater the formation dip, the greater the difference in CO2 distribution, and the farther the CO2 diffuses upward along the dip direction. The farthest migration distances in the low- and high-pressure aquifers, occurring in the case of 16° formation dip, increase by 100 and 53 m, respectively, compared with those of the flat formation. The average daily energy storage efficiency decreases with the increase in formation dip angle. The dip angle of aquifer which is selected for compressed CO2 energy storage should not exceed 8°.

A novel approach of in-cylinder NOx control by inner selective non-catalytic reduction effect for high-pressure direct-injection ammonia engine

As an efficient hydrogen carrier and carbon-free fuel, ammonia shows great promise in realizing zero-carbon propulsions. However, challenges such as poor ignition stability, low combustion efficiency, and fuel-NOx emissions are yet to overcome. In this paper, the high-pressure direct-injection ammonia/diesel dual-fuel combustion mode (HPDF) with post injection strategy is proposed as a solution. The study reveals that HPDF combustion mode enables in-cylinder reduction of NOx, which is attributed to the selective non-catalytic reduction (SNCR) reaction. The results uncover that NH2, NH, and N radicals have a significant reducing effect on NO and NO2, while N2O serves as an important byproduct of the reduction reactions. Subsequently, the generated N2O can be further reduced to N2 through the involvement of O, H, and OH radicals. Building upon these findings, an innovative ammonia post injection method for reducing NOx emissions is explored. The post injection strategy effectively reduces the NOx emissions with only a minor decrease in indicated thermal efficiency, but an over-delayed post injection could also cause significant increase in N2O and unburned NH3 emissions. A post injection proportion of 20%-30% with appropriate post injection timing is found to achieve desired emission reduction. Overall, the HPDF combustion mode is a promising solution for ammonia engine, due to the high thermal efficiency and low nitrogen oxide emissions, as well as the ability to further reduce the NOx emissions through ammonia post injection strategy.

Characterization of pressure oscillations and combustion noise of hydrogen reactivity-controlled compression ignition (RCCI)

Knock and combustion noise are the main reasons limiting the increase in hydrogen (H2) replacement rate in H2 reactivity-controlled compression ignition (RCCI). This study aims to identify the knock-dominated mechanism and elucidate the characteristics of knock and combustion noise of H2 RCCI operated at a broad range of parameters through the combined analysis of the heat release profile and pressure oscillations. The results indicated that under inhomogeneous heat release conditions, the onset of pressure oscillations is mainly attributed to the local fast heat release at the initial combustion stage, but for the conditions with relatively homogeneous and high-reactivity mixture, the pressure oscillations are primarily excited by the end-gas autoignition. Compared with the single injection strategy, the double injection strategy with the first and second start of injection of −60 and −15°CA ATDC (SOI1/2 = −60/-15°CA ATDC) can effectively mitigate the pressure oscillations and shorten the propagation period of pressure waves. However, as the SOI2 is advanced to −30°CA ATDC, the pressure oscillations dramatically increase, because the enhanced fuel reactivity of premixed H2 exacerbates the end-gas autoignition. The results of frequency analysis of in-cylinder pressures show that with the increase in inhomogeneous combustion, the first resonance frequency reduces. As the intake pressure (Pin) is raised from 1.2 to 1.6 bar, the first resonance energy increases, since the elevated in-cylinder temperature associated with the piston compression during the compression stroke enhances the propagation and development of pressure waves. The high-order resonance is closely related to the autoignition of end gas with higher fuel reactivity. Overall, the combustion noise shows a good linear correlation with peak heat release rate for all the points investigated in this work, but the linearity of H2/polyoxymethylene dimethyl ethers RCCI is better than that of H2/diesel RCCI. Moreover, with the increase in Pin, the engine noise associated with the piston compression increases.

The coupling effect of turbulent jet ignition and injection strategy on the combustion performance of a pure methanol rotary engine

Methanol, as an alternative fuel, has significant potential in energy conservation and emission reduction. However, the higher ignition temperature and latent heat of vaporization of methanol fuels also expose engines to the risk of cold-starting difficulties. The turbulent jet ignition (TJI) technology, aimed at enhancing ignition energy, proves effective in improving the ignition and combustion performance of pure methanol. Therefore, this study designed a jet ignition plug to optimize the combustion characteristics of methanol rotary engines. Meanwhile, the influence of injection strategy on the performance of the patterned turbulent jet ignition rotary engine(TJI-RE) was studied for the first time. On this basis, the CFD model of pure methanol TJI-RE was established and validated using relevant experimental data. Results found that the injection angle and position could change in-cylinder fuel distribution during ignition, as well as the quality of fuel entering the pre-chamber, affected by fuel impact position and in-cylinder vortex strength. These factors collectively influenced the combustion characteristics of TJI-RE. Furthermore, the optimal fuel distribution characteristics for TJI-RE included higher fuel concentration in the pre-chamber and increased fuel accumulation in the front of the cylinder Under all calculation conditions, the configuration with the fuel injector positioned 25 mm above the cylinder’s long axis and an injection angle of +50° achieved the highest peak pressure and indicated thermal efficiency for TJI-RE.