Injection Angle Research Articles

Toroidal injection angle dependence of EC assisted plasma initiation at DIII-D

Abstract An experimental scan of the electron cyclotron waves (EC) toroidal injection angle in plasma breakdown is performed at the DIII-D tokamak. The second harmonic, extraordinary mode EC is used for the study. The dependence of n e and T e on the EC injection angle cannot be conclusively drawn from this study due to the large error bars in the n e and T e measurements. On the other hand, high T e data points are observed in some discharges which can be explained by nonlinear heating. The D α emission measurement shows a clear relation between the breakdown time and the injection angle. An experimental investigation of the cause of the dependence of breakdown delay on the EC injection angle suggests that when the injection angle is oblique, the EC heating after the reflection at the inboard wall may become ineffective and cause the breakdown delay even when the EC heating before and directly upon injection remains effective. A preliminary run of the heat and transport balance code DYON indicates that the obtained dataset is suitable for a quantitative validation of EC absorption models.

Initial results from neoclassical tearing mode stabilization experiment in KSTAR high normalized beta plasmas

Abstract Active stabilization of neoclassical tearing modes (NTMs) is critical for high beta plasma operation in the KSTAR tokamak. In recent device operation, an experiment was conducted to develop a m/n = 2/1 NTM stabilization in high normalized beta (βN) plasmas having βN > 3 by using electron cyclotron current drive (ECCD). The experiment is designed to first demonstrate the direct mode stabilization effect of the device EC system by varying the ECCD deposition location around the mode rational surface to prepare for future NTM stabilization in KSTAR using feedback schemes. In the experiment, the toroidal magnetic field strength, BT, is reduced to 1.5–1.6 T to create a highly localized ECCD profile on a large island width expected to produce a high stabilization effect. To align the ECCD with the mode, BT is varied between discharges by keeping the EC wave injection angles fixed to move the current deposition location across the q = 2 mode rational surface in ~1 cm steps along the plasma midplane. The result shows a prompt reduction of the mode amplitude by ~60% with a partial recovery of the loss of stored energy when the ECCD with 0.7 MW power is applied promptly after the mode onset at BT = 1.54 T. This abrupt reduction of the mode amplitude is significantly weaker or disappears in other discharges having slightly different BT in which the ECCD is deposited a few centimeters away. This result indicates a direct interaction between the driven EC current and the radially localized island structure first observed in the device. The EC ray-tracing analysis using the TORAY code shows that the applied EC-driven current aligns with the mode rational surface when the mode amplitude is observed to decrease. The stability of the observed 2/1 NTM is examined by constructing the modified Rutherford equation (MRE). The calculated EC power requirement for complete mode stabilization by assuming perfect alignment of ECCD on the mode is 0.8-1.7 MW by considering the uncertainties in the equation. This MRE-computed mode stability agrees with the experiment. The result projects that the present KSTAR EC system can stabilize the 2/1 NTM disrupting high βN plasmas, and provides the requirement of the mode-ECCD alignment for complete mode stabilization in future experiments in which an accurate alignment is planned to be made by feedback schemes being developed.

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.

Experimental study of fuel distribution and combustion characteristics under subatmospheric pressure in an afterburner

The fuel distribution and ignition characteristics of an afterburner with typical components under subatmospheric inlet conditions are important references for improving the performance of the afterburner at high flight altitudes. In this work, lean ignition limits, outlet temperature distributions, fuel droplet size distributions and flame propagation processes in the afterburner were obtained experimentally. The results show that with increasing fuel injection angle, the fuel atomization characteristics improve, but the flame intensity fluctuation increases, and the ignition performance deteriorates; thus, a proper ratio of liquid-phase fuel to vapor-phase fuel is one of the key elements for successful ignition. On the one hand, the increased stabilizer blockage ratio results in a localized flow velocity increase near the trailing edge of the stabilizer, which effectively promotes fuel atomization in the shear layer, resulting in a fuel droplet size reduction of 25–30 μm. On the other hand, the extent of the recirculation zone increases, and a large low-pressure and low-turbulence recirculation zone is not conducive to fuel atomization in the flow direction. During the ignition process in an afterburner with all the typical components, the flame kernel first propagates along the flow direction for a certain distance and then propagates and anchors toward the shear layer. At subatmospheric pressures, the decrease in the intensity of the combustion reaction causes a reduction in the heat released by combustion, and the fuel droplet size increases by 10–25 μm, which requires more heat for evaporation. Therefore, the flame propagates an increased distance along the flow as the pressure decreases. Furthermore, the difficulty of ignition increases, and the ignition equivalence ratio increases by 0.1–0.15.

Al-based amorphous coatings by warm spraying: Numerical simulation and experimental validation

Al-based fully amorphous coatings with low porosity were successfully produced via warm spraying, combining numerical simulation and experimental validation. A warm spray gun model, employing computational fluid dynamics, was developed to simulate the warm spraying process. The study delved into the effects of reactant flow rate, oxygen/fuel (O/F) ratio, coolant flow rate, spray distance, particle size, particle shape, particle injection velocity, and particle injection angle on the gas flow field parameters (pressure, temperature, and velocity) and particle in-flight behaviors (temperature, velocity, and in-flight trajectory). The optimum spraying parameters (OSP) predicted by the simulation results were determined: 0.008740 kg/s for reactant flow rate, 2.7 for the O/F ratio, 0.007356 kg/s for coolant flow rate, 142 mm for spraying distance, 10–35 μm for particle size range, spherical for particle shape, 10 m/s for particle injection velocity, and 0° for particle injection angle. Subsequently, warm spraying experiments based on the OSP yielded Al-based fully amorphous coatings with a porosity of 0.08 %. This work provides valuable insights for the production of Al-based fully amorphous coatings with minimal porosity through warm spraying.

Numerical study on the effect of injection strategy on combustion and NO emission from different sources in a diesel/ammonia RCCI engine

Diesel/ammonia operation is one of the ways to efficiently utilize ammonia and reduce carbon emissions, however, the increase in fuel NO introduces serious emission problems. To explore the generation mechanisms of fuel NO and oxidant source NO, a multi-component diesel/ammonia chemical reaction mechanism was constructed in this study, and based on 3D CFD simulation and N-element tracking method, the combustion and different source NO emission characteristics of diesel/ammonia reactivity controlled compression ignition (RCCI) engine at low loads were investigated by pilot injection timing (SOI1) and pilot injection ratio (PIR). In addition, the effect of different first injection spray angle (SA1) and double injection spray angle (SAtotal) on the engine operation was investigated. The results showed that high PIR and delayed SOI1 enhanced the engine IMEP but led to high PRRmax. At a PIR of 15 %, total NO emissions increased as SOI1 advanced, and the trend was reversed when the PIR was higher than 15 %. Fuel NO was produced earlier than the oxidant source N∗O. In terms of 1 spatial distribution, high concentrations of both NO and N∗O were distributed in and around the secondary diesel fuel ignition location, and fuel NO began to be reduced where the oxidant source N∗O was rapidly formed. The reduction mechanism of NO in the cylinder was a multi-path reduction mechanism incorporating Thermal DeNOx, NO Reburning, and inverse reaction pathways for NO formation from the oxidant source. Appropriate reduction of the SAtotal can significantly reduce the total NO emission while maintaining no significant reduction in IMEP. When SAtotal was 82°, the total NO emission was only 16.3 % of the original spray angle and PRRmax was further reduced. After optimization, when a narrow SAtotal of 82°, SOI1 of −15° CA, and PIR of 35 % were used, the IMEP of the engine increased by 5.9 %, and the total NO emission was reduced by 86 %, while PRRmax did not exceed the PRR upper limit.

NUMERICAL AND EXPERIMENTAL RESEARCH ON THE DI-CI ENGINE PERFORMANCE CHARACTERISTICS UNDER LPG - DIESEL DUAL FUEL COMBUSTION MODE

Properties of Liquefied Petroleum Gas (LPG) are suitable as an alternative fuel for internal combustion engines. This work aims to combine both numerical optimization analysis of LPG injector placement angle and subsequent experiment with selected mounting injector angle to investigate the effects of using LPG as a parallel-partial substitute fuel with diesel fuel under dual-fuel combustion mode. An electronic injection fuel control system was applied to the modified intake manifold to generate the appropriate LPG injection. Three mounting angle injector positions including 450, 900 and 1350 in the upstream direction of intake air have been defined by Ansys Fluent to take into account efficient LPG-air mixing. Then, the experiment was conducted with LPG-diesel dual-fuel combustion mode (DFC mode) and compared to entirely diesel combustion mode as baseline data. Different load conditions ranging from idle to 4.0 kW were imposed at a constant engine speed of 1700rpm. The obtained results revealed that the injector’s mounting angle position by 45 opposite to the intake air flow showed the correlation with the calculated LPG-air ratio in dual fuel combustion reaction. In DFC mode, the brake thermal efficiency (BTE) decreased on average by 4.6% and the LPG substitution rate gradually decreased while brake-specific fuel consumption (BSFC) increased for all engine loads. The exhaust temperature in the dual-fuel combustion mode was found to be higher than that of full diesel fuel mode at low loads (less than 2.5 kW) and began to decrease at higher loads.

Numerical investigation on secondary injection and thrust vector control in a planar double divergent nozzle

In this work, the performance of secondary injection thrust vector control of an altitude adaptive planar double divergent supersonic nozzle is numerically investigated. The compressible turbulent flow is solved using the kT−kL−ω transition-sensitive eddy-viscosity model. An analytical model to predict the separation distance and penetration height due to secondary fluid injection is developed based on the blunt-body theory, and it shows good agreement with the numerical estimation. The computational results indicate that injection pressure, injector location and injection angle significantly impact the thrust vector control performance. The core flow is disrupted by the momentum injection from the secondary fluid, causing the flow field structure to become asymmetrical. The wall pressure imbalance between the upper and lower nozzle increases as the secondary jet pressure elevates. Further, the thrust vectoring amplification factor is improved when the injector is placed downstream near the outlet since the shock reflection is circumvented. Indeed, that resulted in the generation of a large lateral thrust force. Most importantly, for a high injector slot angle, the primary downstream vortex disappears, and a strong secondary upstream vortex is generated, which shifts the primary upstream vortex opposite to the core flow, subsequently the shock separation is advanced. In addition, a secondary injector fitted near the exit with high inclination angles and injection pressure generated a lateral thrust of 20%.

A Large Eddy Simulation Study on Hydrogen Microjets in Hot Vitiated Crossflow

Abstract In this paper, the results of a large eddy simulation (LES) study on hydrogen microjets (dj ~ 0.5 mm) injected into a hot (1600 K) vitiated crossflow at different angles?namely, normal (90°) and inclined jet (30°), are presented. The goal is to explore the effects of injection angle on coherent turbulent structure formations, flame-vortex interactions, and wall heat flux contributions. The LES identifies the presence of the horseshoe vortex, the shear layer vortices (SLV), and the counter-rotating vortex pair (CVP), along with the shedding of spanwise-symmetry hairpin vortices in both the normal and inclined jets. The structures in the latter, however, appear more convoluted. In the near field, SLV-induced flow is crucial for mixing and flame propagation on the windward side of the jet, stabilized by autoignition near the jet exits. A flame-shear layer offset is observed here. In the far field, CVP dominates hot vitiated crossflow entrainment, driving flame propagation and heat and species transfer to the leeward side near the injection wall. In the wake region, combustion remains closer to the normal jet exit due to a stronger recirculation zone, resulting in higher wall heat fluxes. The mean wall heat flux values of both the normal and inclined jets decrease and approach each other with moving away from the jet exit in the streamwise direction. The present LES study results are compared to experimental data from the literature by considering instantaneous hydroxide (OH) fields and mean wall heat fluxes.

Enhancing the usability range of acetylene in CI engines through split injection of high-reactive fuel under RCCI operation: Optimized operability using an MCDM approach

Reactivity Controlled Compression Ignition (RCCI) has emerged as a promising solution to address the challenges of advanced combustion techniques in diesel engines, balancing combustion control and emission reduction. This study investigates the impact of split-injection high-reactivity fuel (HRF) dosing in RCCI to enhance charge homogeneity at lower injection timing advancements. It systematically explores progressive advancements in HRF injection timing, distinguishing between main and pilot injections. The main injection varied from 20° bTDC to 70° bTDC, while the pilot injection, relative to the main injection, spans 25°-40° CA ahead with a 5° progression. As an LRF, Port-injected Acetylene supplements the process with variable premixed ratios. Further, using a multi-criteria decision-making method (AHP), the study optimizes operating conditions, proposing a main injection at 20° bTDC, a pilot injection 40° CA ahead, and 70 % LRF participation. This optimized condition yields significant benefits such as 32.99 % higher brake thermal efficiency (BTE), 160 % longer premixed duration, 18.65 % lower maximum temperature, 89.41 % lower NO emissions, 91.83 % lower hydrocarbon (HC) emissions, 91.24 % lower CO emissions and 97.20 % lower smoke opacity compared to conventional diesel combustion (CDC) operation. The results highlight the advantages of multiple fuel injections in RCCI, improving blending characteristics at lower injection angles.

The impact of stray magnetic fields on the KSTAR NBI performance

The stray magnetic fields generated by a plasma discharge impact the performance of neutral beam injection (NBI), leading to a decline in the plasma performance of the Korea Superconducting Tokamak Advanced Research (KSTAR). To evaluate the impact of the stray magnetic field on the NBI performance, a Monte Carlo simulation tool was developed. The simulation tool integrates the stray magnetic fields, NBI beam line components, and charge exchange processes comprehensively, allowing for quantitative analysis of the NBI performance reduction due to the stray magnetic fields. The high pressure of the beam chamber, along with the stray magnetic fields, causes a significant reduction of the beam power, emphasizing the need to maintain low vacuum pressure. However, the stray magnetic field does not significantly affect the injection angle of the beam particles reaching the tokamak. Predictive integrated simulations show that the decrease in beam performance due to stray magnetic fields can affect a degradation in plasma performance during long pulse discharge in KSTAR.

A comprehensive comparison of film cooling characteristics of shaped holes on the leading edge of rotating blade

This study numerically investigates the cooling characteristics and flow features of various hole geometries on the rotating blade leading edge. A comprehensive comparison of cooling effectiveness, heat transfer coefficients, net heat flux reduction, and discharge coefficients is conducted among laidback fan-shaped, fan-shaped, laidback, cone holes, and cylindrical holes with two different diameters. Detailed flow and thermal field analysis reveals the impact of geometry on cooling performance. The blade rotational speed is 600 rpm, with a Reynolds number of 12.4 × 104, blowing ratios from 0.5 to 2.0, and fixed injection and spanwise angles at 90° and 30°. Shaped holes share a uniform hole exit-to-inlet area ratio, and cylindrical holes match their inlet or exit areas. The RANS equations were closed using the SST k-ω turbulence model coupled with the Gamma Theta transition model, and an unstructured grid of 13.0 million cells was employed to attain relatively accurate predictive results. Results show that the lateral expansion on the leading edge significantly enhances cooling performance, with fan-shaped holes outperforming others, especially at high blowing ratios. Additionally, cooling effectiveness and discharge coefficient on the leading edge correlate strongly with hole geometric parameters. Shaped holes with equal area ratios show similar discharge coefficients. Cooling effectiveness at high blowing ratios is proportional to the effective exit width, provided that the coolant flows smoothly without severe lift-off.

Experimental investigation and numerical analysis on high-efficiency shock vectoring control serpentine nozzles

The high-efficiency Shock Vectoring Control Serpentine Nozzle (SVCSN) takes into account both thrust vectoring and infrared stealth, and significantly improves the comprehensive performance of the aero-engines through an additional auxiliary duct. In this paper, the schlieren photographs at the exit of the high-efficiency SVCSN and the wall static pressure distributions were obtained by experiments, and the numerical results were used to enrich the thrust vectoring characteristics. The effects of the auxiliary injection were analyzed first to reveal the advantages of the high-efficiency SVCSN compared to the conventional SVCSN. Then, the aerodynamic parameters and the structural parameters of the high-efficiency SVCSN were investigated, including the Nozzle Pressure Ratio (NPR), the Secondary flow Pressure Ratio (SPR), the secondary flow relative area and the secondary flow injection angle. Finally, the coupling performance of the high-efficiency SVCSN is studied by using the approximate modeling technology. Results show that the auxiliary injection increases the range between the two shock legs of the “λ” shock wave induced by the secondary flow, then causes the separation zone and high-pressure boss of the down wall to expand upstream, and finally results in a prominent increase in the thrust vectoring performance. The thrust vectoring angle and Vectoring Efficiency (VE) of the high-efficiency SVCSN are about 61.6% and 75.7%, respectively, higher than those of the conventional SVCSN at NPR = 6. The effects of the NPR and the SPR on the thrust vectoring performance of the high-efficiency SVCSN are coupled with each other. A larger NPR matched with a smaller SPR shows better thrust vectoring performance. The maximum fluctuations in thrust vectoring angle and VE caused by the NPR and SPR are about 22% and 64%. The VE decreases monotonously with the increase of the secondary flow relative area. Smaller secondary flow injection angle shows better thrust vector performance, and the thrust vectoring angle and VE of the secondary flow injection angle of 90° are about 20% higher than those of the secondary flow injection angle of 110° at NPR = 6. Therefore, the secondary flow relative area of 0.06 and the secondary flow injection angle of 90° are recommended.

FACTFINDERS FOR PATIENT SAFETY: Minimizing risks with cervical epidural injections

This series of FactFinders presents a brief summary of the evidence and outlines recommendations to minimize risks associated with cervical epidural injections.Evidence in support of the following facts is presented.Minimizing Risks with Cervical Interlaminar Epidural Steroid Injections – 1) CILESIs should be performed at C6-C7 or below, with C7-T1 as the preferred access point due to the more generous dorsal epidural space at this level compared to the more cephalad interlaminar segments. This reduces the risk of the minor complication of dural puncture and the major complication of spinal cord injury due to inadvertent needle placement. 2) LF gaps are most prevalent in the midline cervical spine. This can result in diminished tactile feedback with loss of resistance (LOR), increasing the risk for inadvertent dural puncture or spinal cord injury. Based on current evidence, needle placement in the paramedian portion of the interlaminar space is safest to avoid LF gaps. 3) An optimal AP trajectory view and the physician's ability to discern engagement in the LF and subsequent LOR are crucial. Confirmation of minimal needle insertion depth relative to the ventral margin of the lamina with either a lateral or contralateral oblique (CLO) safety view is critical to minimize the risk of inadvertently inserting the needle too ventral. 4) There have been closed claims and case reports of patients who have suffered catastrophic neurologic injuries while receiving CILESIs under deep sedation. If sedation is administered, the least amount necessary should be utilized to ensure the patient can provide verbal feedback during the procedure. 5) CILESIs are an elective procedure; therefore, necessity and likelihood of benefit must be foremost considerations. Current guidelines recommend holding ACAP therapy before CILESIs due to the potentially catastrophic complications associated with epidural hematoma (EH) formation. However, there is also a risk of severe systemic complications with ceasing ACAP in specific clinical scenarios. The treating physician is obligated to determine if the procedure is indicated and can ultimately decide to delay the intervention or not perform the procedure if the benefit does not outweigh the risks.Minimizing Risks with Cervical Transforaminal Epidural Steroid Injections – the Role of Preprocedural Review of Advanced Imaging -- Variations in vascular anatomy may warrant a modified approach to CTFESI. Preprocedural review of cross-sectional imaging can provide critical information for safe injection angle planning specific to individual patients and may help to decrease the risk of unintended vascular events with potentially catastrophic outcomes.Safety of Multi-level or Bilateral Fluoroscopically-Guided Cervical Transforaminal Epidural Steroid Injections -- Safe performance of a CTFESI procedure requires the ability to detect inadvertent arterial injection. Contrast medium placed into the epidural space and/or along the exiting spinal nerves during an initial CTFESI may obscure the detection of inadvertent cannulation of a radiculomedullary artery by a subsequent CTFESI. While no available literature directly addresses the potential risk that exists with a multi-level or bilateral CTFESI, caution is still warranted.

Effect of orientation angle for needle-free jet injection

In this paper, we report on the delivery efficiency of needle-free jet injections using injectors with typical jet speed vj≈140m/s, orifice diameter do=157μm, and volume V=0.1 mL. The target substrates were either hydrogel tissue phantoms or porcine tissues combined with excised human skin. The novelty of this study is two-fold: First, we investigate the influence of injection angle relative to the skin surface, and second, we also study the influence of the jet path relative to the orientation of muscle fibers. While most commercial jet injectors employ a fitting that would render the device normal to the skin surface, recent studies have proposed oblique injections, which may be beneficial for intradermal or subcutaneous tissue injection. Furthermore, for deeper intramuscular injections, we propose that an angled jet path taking the muscle fiber orientation into account may result in a bolus or dispersion zone that is conducive to increased cellular uptake of the drug.

Experimental and numerical investigation on middle passage gap leakage with different mass flow rate and injection angle on turbine endwall

Regarding the actual installation feature of the blades and disk using tenon and mortise, the middle passage gap exists between the adjacent blades and the leakage flows out of the gap, cooling the endwall. To explore the balance between the aerodynamic and cooling performance on blade endwall in turbine cascade, this paper investigated the effect of middle passage gap leakage under various mass flow rate and injection angle configurations. Film cooling effectiveness measurement was performed with pressure-sensitive paint technique in a five-passages linear cascade. The mass flow ratio of middle passage gap leakage ranged from 0.5 % to 1.5 % with the injection angle (αm) ranging from −20° to 20°. A combined approach utilizing numerical simulations to elucidate detailed aerodynamic loss mechanisms and experimental results of middle passage gap leakage was employed. The results show that increasing the mass flow rate of middle passage gap leakage does not suppress mainstream intrusion phenomenon. Cases with injection angle generally show improved cooling performance compared to the non-injection case (αm = 0°). The least improvements are 19 % and 27.9 % for mass flow rates of 0.5 % and 1.0 %, respectively. The case with an injection angle of 20° demonstrates the best comprehensive performance, achieving higher area-averaged cooling effectiveness and lower aerodynamic loss (1.2 % and 18.9 % decrease for mass flow rates of 0.5 % and 1.0 %).

Research on ignition matching for magnesium-based water ramjet engines

This paper addresses the ignition compatibility issues of the water ramjet engine (WRE). It studies the impact of several engine parameters on the ignition process and performance, including the primary water injection angle, primary water-fuel ratio, igniter mass, and igniter position. Based on the specified parameters, a multiphase flow computational model for the ignition process of the WRE developed. The obtained results show that the ignition performance of the engine is significantly affected by the primary water-fuel ratio, igniter mass, and igniter location. When the primary water-fuel ratio increases, the equilibrium temperature in the combustion chamber tends to initially increase and then decrease, reaching a maximum value for a ratio of 0.55. Criteria are then proposed to determine whether the WRE can transition into the self-sustained combustion phase. These ignition criteria are established by considering the relationship between the mass of the igniter charge, its location, and the surface area of the burning surface of the propellant. The results obtained by the proposed model demonstrate that the engine will not extinguish when this value is greater than 46.65.

Optimizing diesel engine performance and emissions with diesel-hydrogen mixtures: Impact of injector configuration, angle, and pressure

Several factors affect engine performance, including fuel injection pressure, injection angle, and injector orifice diameter. Any deviation from normal conditions in any of these aspects can disrupt optimal engine performance, resulting in inefficient combustion and increased exhaust emissions. To investigate the effect of injector hole number, injection hole angle, and injection pressure on the performance and emissions of a diesel engine operating on a diesel/hydrogen blend (10 % hydrogen and 90 % diesel), a single-cylinder direct injection diesel engine was used. Three injector nozzle configurations just for diesel injector with different hole diameters (0.6, 0.3, and 0.2 mm) were used at injection angles of 0, 15, and 30 degrees, respectively. Three injection pressures (200, 400, and 600 bar) were tested, with results monitored for brake-specific fuel consumption (BSFC), brake thermal efficiency (BTE), smoke, and NOx emissions.Optimal results were achieved with a maximum injection pressure of 400 bar and a nozzle angle of 15 degrees, resulting in improved engine performance and BTE, along with a 6.5 % reduction in BSFC. Increasing the number of injector holes, injection pressure, and injection angle resulted in reduced BSFC and smoke emissions, but with a significant increase in NOx emissions. Notably, this study deviates from traditional combustion methods by introducing air from a 1.1-atmosphere tank instead of relying solely on natural intake. In addition, hydrogen fuel is introduced into the air manifold via a separate injector with an injection pressure of 20 bar, while diesel fuel is injected directly into the combustion chamber.

Combustion characteristics analysis and performance evaluation of a hydrogen engine under direct injection plus lean burn mode

Direct injection plus lean burn technology can effectively control combustion processes and reduce carbon emissions of hydrogen engines. Hence, hydrogen direct injection strategy optimization is a key means to improve engine performance and achieve low emissions. Thus, a three-dimensional transient calculation model coupled chemical reaction mechanism is established, and its reliability and accuracy are systematically evaluated using experimental data. Then, the effects of hydrogen direct injection strategies on the hydrogen-air mixing and combustion process are investigated. The results indicate that the ideal mixture stratification law is that the gas fuel concentration is gradually stratified from the ignition center to the periphery region. The maximum indicated work is obtained for the B-60° scheme which its injection position is near the intake side and 7.5 mm from the cylinder center on the X-axis. The optimal hydrogen injection angles vary with different injection positions by evaluating engine performance, specifically, 60° is optimal for injection position B, while 30° is best for injection position C which is between intake and exhaust and 40 mm from the cylinder center on the Y-axis. Finally, the achieved maximum thermal efficiencies of 41% and indicated power of 4.29 kW for the B-60° scheme, and its nitric oxide can meet the Europe V emission standards (7.5 g/kWh). This research can offer theoretical guidance for designing and optimizing fuel injection strategies for hydrogen energy engines, and it is relevant for promoting carbon neutrality and cleaner production.

Effects of diesel injector nozzle angle and split diesel injection strategy on combustion and emission characteristics of an ammonia/diesel dual-fuel engine

Pre-injection can effectively improve combustion and thermal efficiency while reducing unburned ammonia (uNH3) and N2O emissions in ammonia/diesel dual-fuel engines. Nevertheless, the pre-injected diesel often impacts the cylinder liner or piston pinch area, adversely affecting combustion and emissions. In this study, various narrow injector nozzle angles (90°/60°) of diesel fuel are applied on investigating engine performance and emissions. Experiments are conducted at 1200 r/min, IMEP 1.2 MPa, and AEF (ammonia energy fraction) 50 %, consisting of varying INA (injector nozzle angle) of 145°/90°/60°, PIR (pre-injection ratio) from 20 %–80 %, PIT (pre-injection timing) from −70 °CA ATDC to −30 °CA ATDC, and sweeping MIT (main injection timing). Results show that larger INA prefer a lower PIR and delayed PIT to reduce the pre-injected fuel hitting the liner, and smaller INA prefer a higher PIR to reduce the main-injected fuel hitting the piston wall. ITE of INA145° peaks at a moderate PIR and delayed PIT while ITE of INA90° and INA60° peaks at a high PIR and early PIT. Decreasing INA combined with high PIR and early PIT helps to reduce uNH3, N2O, and GHG emissions, at the cost of a slight decrease in ITE.