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The rapid development of electric vehicles has drawn extensive attention to using rotary engines as small-scale power generation devices. However, their wide application has been limited by drawbacks such as low combustion efficiency and high emissions. Therefore, to obtain rotary engines with high combustion efficiency and low emissions, this study explored the strengthening effect of natural gas/hydrogen hybrid fuel (NHHF) and Triangular Rotor Piston (TRP) structure on the combustion in the turbulent jet ignition rotary engine (TJI-RE) at different ignition advance angles (IAAs). Additionally, an experimental platform and a three-dimensional computational model for TJI-RE fueled by natural gas/hydrogen hybrid fuel (NHHF) were established in this study. The research results indicated that the TRP structure altered the combustion process by affecting the ignition area in the ignition stage and the turbulence kinetic energy during the combustion stroke. Furthermore, the SC-shaped cylinder exhibited the highest peak pressure for any fixed IAA. When the IAA was fixed at 30°CA (BTDC), the TJI-RE with the SC-shaped cylinder experienced a 12.12% increase in peak pressure and a 4.1% increase in indicated work compared to the FP-shaped cylinder. Additionally, the CO emission was reduced by 13.79%, while the NO emission showed a significant increase. • NHHF was used to reduce the carbon emissions of the RE. • A three-dimensional computational model of the TJI-RE was established. • The effect of piston structure on combustion in TJI-RE was systematically studied. • The optimal combination of piston structure and IAA for the TJI-RE was given. [ABSTRACT FROM AUTHOR]

The aim of this work is to enhance the combustion performance of a turbulent jet ignition Wankel rotary engine (TJI-WRE) fueled by hydrogen/natural gas blends (HNGB) by changing the cylinder shape and adding a turbulence blade (TB). Therefore, the test bench and numerical simulation model for the TJI-WRE are established. Further, the flow field and flame propagation of the TJI-WRE with various cylinder shapes and turbulence blades are investigated. The results demonstrate that a new vortex is formed after the jet flame is injected into the cylinder and impacts the rotor piston surface. This vortex can enhance the combustion speed of the mixture in the back of the cylinder (BOC). The cylinder shape can change the intensity of the new vortex by changing the distance between the jet orifice and the piston surface. Furthermore, TB can change the combustion process by squeezing the in-cylinder unidirectional flow in the combustion stroke. Since the flame mainly propagates to the front of the cylinder (FOC) at the initial combustion stroke, as the TB layout moves from the BOC to the FOC, the squeezing effect of TB on the flame in the FOC becomes increasingly significant, resulting in increased combustion efficiency in the cylinder. [Display omitted] • Hydrogen/natural gas blends fuel was used to reduce carbon emissions. • A computational model of the turbulent jet ignition rotary engine was established. • The mixture formation, combustion, and emissions process were analyzed. • The optimal combination of cylinder structure for the rotary engine was given. • Compared with the original model, optimal cylinder structure PVIP increased by 12.6%. [ABSTRACT FROM AUTHOR]

Natural gas/hydrogen blends (NGHB) fuel is considered as one of the ideal alternative fuels for the rotary engine (RE), which can effectively reduce the carbon emissions of RE. Additionally, applying turbulent jet ignition (TJI) mode to RE can significantly increase the combustion rate. The purpose of this study is to numerically investigate the influence of hydrogen injection position (HIP) and hydrogen injection timing (HIT) on the in-cylinder mixture formation, flame propagation and NOx emission of a TJI hydrogen direct injection plus natural gas port injection RE. Therefore, in this paper, a test bench and a 3D dynamic simulation model of the turbulent jet ignition rotary engine (TJI-RE) fueled with NGHB were respectively established. Moreover, the reliability of the 3D simulation model was verified by experimental data. Furthermore, based on the established 3D model, the fuel distribution and flame propagation in the cylinder under different HIPs and HITs were calculated. The results indicated that the HIP and HIT could change the hydrogen distribution by altering the impact position, impact angle, and the strength of vortexes in the cylinder. To improve the flame propagation speed, more hydrogen should be distributed in the pre-chamber. Additionally, a higher concentration of hydrogen in the cylinder should be maintained above the jet orifice. This was not only conducive to the rapid formation of the initial fire core in the pre-chamber, but also significantly improved the combustion rate of the in-cylinder mixture. Compared with other hydrogen injection strategies, the hydrogen injection strategy by using the HIP at the middle of the cylinder block and the HIT of 190oCA(BTDC) could obtained the highest peak value of in-cylinder pressure and the highest NOx emission. • The natural gas/hydrogen blends fuel was used in rotary engine to reduce its carbon emission. • The turbulent jet ignition (TJI) was used to improve the combustion performance of rotary engine. • The test bench and the numerical simulation model of the TJI rotary engine were established. • The effect of the hydrogen injection position and injection timing on the combustion process were studied. • The optimized hydrogen injection strategies were provided for improving the engine performance. [ABSTRACT FROM AUTHOR]

Hydrogen/natural gas blends fuel is considered one of the ideal alternative fuels for improving the thermal efficiency and reducing carbon emissions of rotary engine. In order to further enhance the combustion and power performance of rotary engine, a new method of the setting of bluff bodies in the cylinder was proposed. The influence of bluff-body settings in the cylinder on the combustion, power performance, and NO generation was numerically studied under different ignition timings. The results indicated that in-cylinder bluff-body settings could influence flame propagation by affecting the turbulent kinetic energy and mixture distribution during the process from the late compression stroke to the combustion stroke. Further, for any fixed bluff-body shape in the cylinder, there is a trade-off relationship between the non-blockage ratio and squish velocity at the cylinder block center section as the ignition timing is progressively advanced or delayed. Consequently, considering the above trade-off relationship, the triangular slotted bluff-body in combination with an ignition timing of 30° CA (BTDC) could be used to achieve the maximum improvement in the combustion and power performance of rotary engine. The peak pressure exhibited a growth of 4.83%, and the indicated mean effective pressure increased by 1.46%. • Using hydrogen/natural gas blend fuel to reduce carbon emissions from the rotary engine. • A novel in-cylinder bluff-body structure in the rotary engine is proposed. • Systematic study of in-cylinder bluff-body effects on the combustion process. • A trade-off relationship influenced by the bluff body is identified. • The optimal structure of the bluff-body is provided for improving performance. [ABSTRACT FROM AUTHOR]

The purpose of the present paper is to investigate the hydrogen injection strategy on the combustion performance of a natural gas/hydrogen rotary engine. Considering that apex seal leakage (ASL) is an inevitable problem in the actual working process of a rotary engine, the action of ASL cannot be ignored for an in-depth study of its combustion performance. Therefore, in this paper, a 3D dynamic simulation model that put the effect of ASL into consideration was established. Furthermore, based on the established 3D model, the combustion process of a natural gas/hydrogen rotary engine under various hydrogen injection angle (HIA) and hydrogen injection timing (HIT) was investigated. The results indicated that the hydrogen jet flow first impacted on the rotor wall after entering the cylinder, and then diffused under the action of the vortexes in the cylinder. Therefore, the HIA and HIT could change the hydrogen distribution by changing the hydrogen impact location and the intensities of the vortexes in the cylinder. In addition, the ideal hydrogen distribution at the ignition timing which could improve the combustion efficiency was given. That is, under the premise of ensuring minimized hydrogen leakage, the hydrogen should mainly distribute in the middle and the front of the cylinder, and a high hydrogen concentration is maintained near the spark plug. • A 3D dynamic simulation model considering the apex seal leakage was established. • The combustion process under varied hydrogen injection strategy were studied. • The ideal hydrogen distribution which can improve the combustion efficiency was given. • The optimized injection strategy was provided for improving the engine performance. [ABSTRACT FROM AUTHOR]

This work aimed to numerically study the effect of hydrogen injection strategy on mixture formation and combustion process in a port injection (PI) rotary engine fueled with natural gas/hydrogen blends. The two main considered factors were hydrogen injection timing (IT) and hydrogen injection duration (ID). Simulation results indicated that for mixture formation, in terms of hydrogen IT, hydrogen IT of 390°CA (BTDC) is a watershed. When the hydrogen IT is before 390°CA (BTDC), the changes in hydrogen IT have little effect on the hydrogen distribution at ignition timing. Hydrogen distribution is uniform across the whole combustion chamber. However, when the hydrogen IT is after 390°CA (BTDC), with the retarded hydrogen IT, there is obvious increase in hydrogen stratification phenomenon, and more hydrogen distributes in the middle and back of combustion chamber at ignition timing. In terms of hydrogen ID, at the fixed hydrogen IT of 360°CA (BTDC), with the extended hydrogen ID, more hydrogen distributes in the back of trailing spark plug (TSP). For combustion process, to obtain a higher overall combustion rate for the PI rotary engine, the hydrogen injection strategy should make more hydrogen located at the front of TSP at ignition timing. In engineering applications, for higher peak cylinder pressure to be obtained, the continued optimization of hydrogen IT should be selected between 390°CA (BTDC) and 330°CA (BTDC). Under the hydrogen IT range of 390°CA (BTDC) to 330°CA (BTDC), the continued optimization of hydrogen ID should select between 8°CA and 24°CA. [ABSTRACT FROM AUTHOR]

The methanol and turbulent jet ignition (TJI) mode were used simultaneously to improve the combustion and emission performance of a gasoline rotary engine (RE) in the study. Further, the experimental bench and numerical model of the TJI-RE fueled with methanol/gasoline blends were established respectively. The reliability of the numerical model was verified by the experiments. Eventually, based on the numerical model, the effects of jet orifice angle (JOA) and jet orifice position (JOP) on the in-cylinder combustion were studied. The results showed that for both the JOA and JOP, they affected the combustion of the TJI-RE through the impingement point of the jet flame on the rotor piston wall and the intensity of the vortex formed by impingement of jet flame on rotor piston wall. For engineering applications, the JOA is recommended to be −30°, and the JOP is recommended to be 16.5 mm on the left side of the vertical axis of the cylinder. Under the above case, compared with the case who has the JOA of +30° and the JOP of 5.5 mm on the right side of the vertical axis of the cylinder, the peak pressure is increased by 32.8%, and the indicated thermal efficiency is increased by 10.26%. • Methanol was used in traditional gasoline rotary engines to reduce carbon emissions. • The turbulent jet ignition (TJI) was used to improve the combustion performance of rotary engine. • The test bench and the numerical simulation model of the TJI rotary engine were established. • The effects of jet orifice angle (JOA) and jet orifice position (JOP) on the combustion were studied. • The JOA was recommended to be −30°. • The JOP was recommended to be 16.5 mm on the left side of the vertical axis of the cylinder. [ABSTRACT FROM AUTHOR]

This work aimed to numerically study the effect of hydrogen injection strategies on mixture formation and combustion process in a hydrogen direct injection plus natural gas port injection (HDI + NGPI) rotary engine. Two major factors, namely hydrogen injection timing (HIT) and hydrogen injection angle (HIA), were considered. Four HITs which were used in simulation, were from the early stages of intake stroke to the late stages of compression stoke. Comparing the fuel movement and combustion process among the four HITs with three HIAs (−60°, 0° and 60°), it was found that for hydrogen movement, when the HIT was at early stages of intake stroke, this advanced HIT led to the fact that the hydrogen distribution areas at ignition timing all spread across the whole combustion chamber for all three HIA cases. When the HIT was at the late stages of the intake stroke and the whole compression stroke, with an increased hydrogen injection angle (HIA) (from −60°, 0° to 60°), the hydrogen accumulation area moved from the front towards the rear of combustion chamber. In addition, with retarded HIT, the hydrogen aggregation degree increased continuously. For combustion process, to obtain a higher overall combustion rate, the hydrogen injection strategy should make as much hydrogen spread between the two spark plugs at ignition timing. In addition, the hydrogen concentration near the LSP and the TSP should be conducive to the flame kernel formation. This is mainly because of the fact that the above hydrogen distributions, not only lead to the rapid formation of the flame kernel near the LSP and the TSP, but also make use of the hydrogen at the early stage of combustion stroke. Under the computational condition, the overall combustion rate for case A: 140 − 60 which had a HIT of 140°CA (BTDC) and a HIA of −60°CA, was the fastest. Compared with case C: 300 + 60 which had a HIT of 300°CA (BTDC) and a HIA of 60°CA, the peak pressure of case A: 140 − 60 was raised by 31.1%. However, compared with other cases, the NO emissions of case A: 140 − 60 at 80°CA (ATDC) was the maximum. Furthermore, for engineering applications, this study also provided a scheme of the change of the optimum HIA under different HITs for improving the performance of the HDI + NGPI rotary engine. [ABSTRACT FROM AUTHOR]

Hydrogen direct injection (HDI) in cylinder is considered as an effective method to improve natural gas engine performance. The present study aims to bridge the gap on the HDI in rotary engine, and to investigate the effect of hydrogen injection timing (IT) and hydrogen injection duration (ID) on mixture formation and combustion process of a hydrogen direct injection plus natural gas port injection (HDI + NGPI) rotary engine. Numerical approach was used in this study for obtaining some critical information, which was difficult to obtain through experiment, such as flow field, fuel distribution and some intermediate concentration fields in cylinder. The research results showed that for mixture formation, the distribution law of the hydrogen and the natural gas at the late stages of the compression stroke (100 ° CA (BTDC)), was as follows: at a fixed ID of 24 ° CA, with retarded hydrogen IT, the stratification phenomenon of hydrogen became obvious increasingly, and the hydrogen distribution area moved towards the back of the combustion chamber continuously. At a fixed IT of 210 ° CA (BTDC), with the extension in ID, the accumulation area of hydrogen reduced significantly, and the hydrogen continued to gather in the middle of the combustion chamber. For combustion process, the overall combustion rate for the hydrogen injection strategy which had an IT of 210 ° CA (BTDC) and ID of 40 ° CA (case ID5), was the fastest. This was due to the fact that compared with the leading spark plug (LSP), the combustion condition around the trailing spark plug (TSP) has a great influence on the combustion process. For case ID5 at ignition timing, the hydrogen concentration near the TSP is high enough for the rapid formation of flame kernel. Compared with case IT1 which had an IT of 390 ° CA (BTDC) and an ID of 24 ° CA, the improved combustion rate of case ID5 had a 11.7% increase in peak pressure, and a 7% decrease in NO emissions. [ABSTRACT FROM AUTHOR]

The application of direct injection (DI) technology is considered as a key solution to the problems of combustion efficiency and emissions on the rotary engine. This work aimed to numerically study the combined effect of injection timing (IT) and injection angle (IA) on mixture formation and combustion process in the 3D flow field of a DI natural gas rotary engine. On the basis of the 3D dynamic simulation model which was established in our previous work [29, 30], some critical information was obtained which was difficult to acquire through experiment. Simulation results showed that to satisfy the ideal fuel distribution for high combustion rate, a small IA should be used when the IT was at the early stages of intake stroke, and a big IA should be used when the IT was at the early stages of compression stroke. However, when the IT was at the middle and later stages of intake stroke, the IA which could satisfy the ideal fuel distribution, was difficult to determine with the changed IT in the middle and later stage of intake stroke. For the above reason, the middle and late stage of intake stroke was not recommended as injection timing in engineering application. [ABSTRACT FROM AUTHOR]

This work aimed to numerically study the influence of injection strategy on mixture formation and combustion process in a port injection natural gas rotary engine. On the base of a 3D dynamic simulation model which was established in our previous work, some critical information was obtained, which was difficult to obtain through experiment, in terms of the flow field, the fuel distribution, the temperature field and the concentration fields of some intermediates. Simulation results showed that for mixture formation, the movements of fuel in injection stage were mainly controlled by the intensity of the vortex I for injection timing, and the value of jet flux for injection duration respectively. With retarded injection timing, the decreasing intensity of the vortex I resulted in less fuel moving toward the back of the combustion chamber. With the extension in injection duration, the decreasing value of jet flux resulted in more fuel staying at the back of the combustion chamber. For combustion process, the overall combustion rate for injection strategy which had an injection timing of 390 °CA (BTDC) and injection duration of 51.5 °CA (case ID4) was the fastest. This was mainly due to the fact that the accumulation area of fuel was at the middle and front of the combustion chamber. Meanwhile, fuel concentration near the leading and trailing spark plugs was conducive for the flame kernel formation. Compared with the injection strategy which had an injection timing of 450 °CA (BTDC) and an injection duration of 55 °CA (case IT1), the improved combustion rate of case ID4 had a 23% increase in the peak pressure, but also a certain increase in NO emissions. [ABSTRACT FROM AUTHOR]

The application of direct injection (DI) technology is considered as an effective way to improve the performance of the rotary engine. This work seeks to numerically dissect the influence of injection strategy on mixture formation and combustion process in a DI natural gas rotary engine. A 3D dynamic simulation model established in our previous work was used to acquire some critical information which was difficult to obtain through experimental investigations. These were the flow field, the fuel distribution, the temperature field and some intermediate concentration fields in the combustion chamber. Simulation results showed that for mixture formation, the motion mechanism of the fuel varies with the injection position. The mass of fuel located at the back of the combustion chamber for injection nozzles A, B and C, was determined by the intensity of vortex I, the coupling function between the value of the impact angle and the intensity of vortex I, and the value of the impact angle respectively. In addition, with retarded injection timing, the accumulation area of fuel for all injection nozzle positions moved from the back to the front of the combustion chamber at ignition timing. For combustion process, the overall combustion rate for the injection strategy (case A4) whose nozzle was 50 mm apart along the engine major axis and whose injection timing was 360°CA (BTDC), was the fastest. Compared with the out-cylinder premixed gas-filling method (case premix method), the improved combustion rate of case A4 had a 29.7% increase in peak pressure, but also a certain increase in NO emissions. [ABSTRACT FROM AUTHOR]

The preparation of methanol can first use renewable energy such as solar energy to produce hydrogen, and then carbon dioxide can be converted into methanol fuel by hydrogenation. Therefore, using methanol as mixed fuel in traditional gasoline rotary engines can effectively reduce the carbon emission of rotary engines. In addition, turbulent jet ignition mode is considered to effectively improve the combustion rate of rotary engines. To deeply study the ignition and combustion process of a methanol/gasoline blends rotary engine using turbulent jet ignition mode, a three-dimensional simulation model and a performance test bench of the rotary engine were established in this paper, respectively. Further, using the experimental data, the reliability of the three-dimensional calculation model was verified. Based on the calculation model, the effects of ignition position and timing on the ignition and combustion process of the methanol/gasoline rotary engine using turbulent jet ignition mode were further studied. The results showed that the ignition position and the ignition timing could significantly change the ignition and combustion process in the cylinder by changing the impact timing between the jet flame and the rotor wall, the intensity of the jet flame and the position where the jet flame enters the cylinder. • Methanol was used as blended fuel to reduce the carbon emission of gasoline rotary engine. • Turbulent jet ignition mode was used to improve the combustion process of rotary engine. • A calculation model of a methanol/gasoline rotary engine using jet ignition mode was established. • The effect of ignition strategy on the ignition and combustion in the cylinder was studied. • The optimized ignition strategy was provided for improving the engine performance. [ABSTRACT FROM AUTHOR]

• The NHBF was used to improve the combustion and emission performance of rotary engine. • A calculation model of a peripheral ported rotary engine considering ASL was established. • The mixture formation and combustion process of NHBF under the action of ASL were analyzed. • The ideal blend fuel distribution which can improve the combustion efficiency was given. • The optimized hydrogen injection strategy was provided for improving the engine performance. Natural gas/hydrogen blended fuel (NHBF) is considered to be one of the ideal alternative fuels for rotary engine, which can effectively reduce the carbon emission of the rotary engine. The purpose of this paper is to numerically study the influence of hydrogen injection timing (HIT) and hydrogen injection angle (HIA) on mixture formation, flame propagation, and NO emission in the cylinder. In addition, considering that the apex seal leakage (ASL) of rotary engine is difficult to avoid, the NHBF in the cylinder will inevitably leak from the apex seal leakage gap to the adjacent cylinders. Therefore, the NHBF leakage under the action of ASL should be considered. In this paper, a 3D dynamic model of the NHBF rotary engine considering the action of ASL was established. Further, the diffusion and combustion processes of NHBF in the cylinder with different HITs and HIAs were calculated. The results showed that the HIT and HIA can significantly change the flame propagation process by changing the fuel stratification pattern in the cylinder. For improving the combustion efficiency of the engine, the HIA of +45° and HIT of 155°CA (BTDC) adopted by Case:155 + 45 should be set as the hydrogen injection strategy. This is mainly because that for Case: 155 + 45, both natural gas and hydrogen are mainly distributed in the FOC, and the concentration of hydrogen and natural gas near the spark plug is also high. However, the defect of Case:155 + 45 is the significant increase of NO emission. [ABSTRACT FROM AUTHOR]

The highly advanced wankel rotary engine is a promising energy system because of its favorable energy to weight ratio, multi-fuel capability and large specific power output. This work aims to numerically study the performance, combustion and emission characteristics of a side-ported rotary engine fueled with natural gas/hydrogen blends under different hydrogen blending modes. Simulations were performed using multi-dimensional software FLUENT 14.0. On the basis of the software, a three-dimensional dynamic simulation model was established by writing dynamic mesh programs, choosing the RNG k - ε turbulent model, the eddy-dissipation concept (EDC) combustion model and a reduced reaction mechanism. The three-dimensional dynamic simulation model based on the chemical reaction kinetics was also validated by the experimental data. Meanwhile, further simulations were then conducted to investigate how to impact the combustion process by the coupling function between hydrogen distribution and the flow field inside the cylinder. Simulation results showed that in order to improve the combustion efficiency, the low-pressure early injection should be used as the hydrogen blending mode. The low-pressure early injection, not only allowed the hydrogen in the combustion chamber to be distributed evenly, but also resulted in the high concentration areas of hydrogen located at the front of the trialing spark plug, which can be used to increase the combustion rate. For the hydrogen low-pressure early injection, the improved combustion rate made in-cylinder pressure and the intermediate OH increase significantly. Compared with no hydrogen induction, it shows a 29% increase in the peak pressures. Meanwhile, the drawback is the increase in NO emissions. [ABSTRACT FROM AUTHOR]

The side-ported rotary engine fueled with natural gas is a new, clean, efficient energy system. This work aims to numerically study the performance, combustion and emission characteristics of a side-ported rotary engine fueled with natural gas under different ignition positions and ignition timings. Simulations were performed using multi-dimensional software ANASYS Fluent. On the basis of the software, a three-dimensional dynamic simulation model was established by writing dynamic mesh programs and choosing a detailed reaction mechanism. The three-dimensional dynamic simulation model, based on the chemical reaction kinetics, was also validated by the experimental data. Meanwhile, further simulations were then conducted to investigate how to impact the combustion process by the coupling function between ignition operating parameter and the flow field inside the cylinder. Simulation results showed that in order to improve the combustion efficiency, the trailing spark plug should be located at the rear of the tumble zone and the ignition timing should be advanced properly. This was mainly caused by the trailing spark plug being located at the rear of the tumble zone, as it not only allowed the fuel in the rear of combustion chamber to be burnt without delay, but also permitted the acceleration of the flame propagation by the tumble. Meanwhile, with advanced ignition timing, the time between ignition timing and the timing of the tumble disappearance increased, which led to an increase of the tumble effect time used to improve the combustion rate. However, the drawback of this improved combustion was the slight increase in NO emissions. Under the computational condition, when the trailing spark plug scheme of case C coupled with an ignition timing of 50 °CA (BTDC) was compared with the spark plug location and the ignition timing of the original engine, it showed a 27.4% increase in the peak pressure. Taking the limited increase of NO exhaust into consideration it was the best ignition allocation scheme under the computational condition. This study provided a theoretical foundation for the determination of best ignition position and ignition timing under different working conditions. [ABSTRACT FROM AUTHOR]

The side-ported rotary engine is a potential alternative to the reciprocating engine because of its favorable performance at low speed. The performance of side-ported rotary engines is strongly influenced by the flow field in the combustion chamber. In this study, an optical side-ported rotary engine test-bed was built and PIV was employed to measure the flow field in the rotor housing central plane. From experiment results, a counterclockwise swirl was detected in the rotor housing central plane. Meanwhile, a three-dimensional dynamic mesh and turbulent flow model was integrated and simulated using the Fluent CFD software. The three-dimensional dynamic simulation model was validated by comparison with experimental results. In addition, the effect of three major parameters on the flow field in the combustion chamber, namely rotating speed, intake pressure and intake angle were numerically investigated. The results show that a swirl forms in the middle and front of the combustion chamber during the intake stroke under low rotating speed. This is in line with the swirl detected in the rotor housing central plane though the PIV experiment at 600 rpm. Furthermore, the flow field, volume coefficient and average turbulence kinetic energy in the combustion chamber were studied in detail by varying rotating speed, intake pressure and intake angle. [ABSTRACT FROM AUTHOR]

The performance of rotary engines is significantly influenced by the flow field. In this study, a detailed mathematical model was integrated into the simulation software FLUENT to investigate the gas flow field in a peripheral ported rotary engine by including a dynamic mesh model and a turbulent flow model. The models were also validated by experimental data. The basic flow mechanism in the combustion chamber was numerically studied. Meanwhile, the effects of the three major parameters on the flow field inside the combustion chamber, namely, rotating speed, intake shape, and intake angle, were also investigated. Results showed that a constantly changing swirl was formed in the combustion chamber during the intake and compression strokes as a result of the combined effects of the pocket of the rotor and the swirls in the combustion chamber. The swirl eventually broke into a unidirectional flow near the top dead center because of the significant decrease in combustion chamber volume. Furthermore, with the change in rotating speed, intake shape, and intake angle, significant differences in flow speed, inertia, and distribution were observed when the fluid entered the combustion chamber, which, in turn, led to obvious differences in the flow field, volume coefficient, and average turbulence kinetic energy in the combustion chamber. [ABSTRACT FROM AUTHOR]

To improve the combustion efficiency of the rotary engine fueled with natural gas/hydrogen blends, the effect of the injection strategy of the blended fuel on the combustion process in cylinder was studied. In addition, considering that apex seal leakage (ASL) is difficult to avoid in the actual working process of rotary engines, the action of ASL was considered in the study. Therefore, a 3D dynamic calculation model of a peripheral ported rotary engine considering the ASL was established. Based on the calculation model, the impact of the blended fuel injection position (BFIP) and the blended fuel injection timing (BFIT) on the combustion process was numerically researched. The results showed that when the fuel injection strategy was Case: B-150, whose BFIP was located at the intersection of the cylinder profile and the long axis with the BFIT of 150°CA (BTDC), the blended fuel was more distributed in the front of cylinder (FOC) and the middle of the cylinder (MOC) at the ignition timing, which effectively avoided the problem of the incomplete combustion in the back of the cylinder (BOC). Therefore, to optimize effectively the combustion performance of the rotary engine, the injection strategy of Case: B-150 was recommended in engineering applications. • A 3D dynamic calculation model of the rotary engine considering ASL was established. • The mixture formation in the rotary engine under the action of ASL was studied. • The ideal blend fuel distribution which can improve the combustion speed was given. • The optimized BFIP and BFIT were provided for improving the engine performance. [ABSTRACT FROM AUTHOR]

• A calculation model of the rotary engine considering ASL was established. • The mixture formation of NHBF in the rotary engine under ASL action was analyzed. • The ideal distribution of NHBF which can improve the combustion efficiency was given. • The optimized IA and IT of NHBF was provided for improving the engine performance. Natural gas/hydrogen blended fuel (NHBF) is considered as one of the most promising alternative fuel for rotary engine. The aim of this paper is therefore to analyse the influence of injection angle (IA) and injection timing (IT) of blended fuel on the combustion performance of a peripheral ported rotary engine fueled with NHBF. Meanwhile, considering that the apex seal leakage is an unavoidable phenomenon during the operation of a rotary engine, the action of the apex seal leakage on flow field and combustion process cannot be ignored. Therefore, a 3D calculation model of the peripheral ported roatry engine, considering the apex seal leakage, was firstly established in this study. Furthermore, under the action of the apex seal leakage, the diffusion and combustion processes of NHBF in the cylinder with different ITs and IAs were calculated. The results indicated that for the distribution of NHBF, when the IT is in the intake stoke, the IA has no obvious effect on the distribution of NHBF. However, when the IT is in the compression stoke, with the increase of IA, the mass of the blended fuel distributed in the back of the cylinder decreases, and the blended fuel continuously accumulates at the middle and front of the cylinder. For combustion process, when the blend fuel injection strategy is Case: 150 + 0, whose installation angle of the blend fuel nozzle is perpendicular to the cylinder block with a IT of 150°CA (BTDC), the blended fuel at spark timing is mainly distributed in the middle and front of the cylinder, which is conducive to the improvement of combustion speed in the cylinder. As a result, compared with other calculation cases, Case: 150 + 0 has the highest combustion speed in the cylinder. Therefore, the IT and IA of Case: 150 + 0 are recommended in the practical engineering application to improve the combustion performace of the peripheral ported rotary engine fueled with NHBF. [ABSTRACT FROM AUTHOR]

The bluff body is commonly used to improve micro combustion. The micro combustor with multiple rectangular bluff bodies in a single row was proposed. The effects of bluff bodies on H 2 /air combustion characteristics were numerically studied. The temperature distributions, ignition position, combustion efficiency and blow-out limit were investigated via changing the total width and number of bluff bodies. The results show that the combined use of multiple bluff bodies can further expand the blow-out limit of H 2 /Air. The effect of high temperature and viscous force on the flow velocity is main factors for the flame morphology. When the total width of bluff bodies is 2 mm, the blow-out limit decreases with the increase of bluff body number. When the total width of bluff bodies is 4 mm and 6 mm, the blow-out limit increases with the increase of the number of bluff bodies. With the increase of inlet velocity, the complete combustion efficiency decreases. The combustion efficiency in the combustor with wider blow-out limit decreases more slowly. It indicates that the combustor with multi-bluff bodies is more suitable for the operation conditions with high flow velocity. • The effects of multiple bluff bodies on H 2 /air micro combustion characteristics. • Viscous resistance and flow velocity are dominant on flame morphology. • Effect of bluff body's number on blow-out limit at different width is different. • Combustor with wider blow-out limit has higher combustion efficiency. [ABSTRACT FROM AUTHOR]

Ammonia is considered one of the most promising fuels, and mixing ammonia with hydrogen as fuel can achieve zero carbon emissions for engines. In this study, an experimental platform for an ammonia/hydrogen rotary engine was constructed, and successful ignition combustion was performed, demonstrating the possibility of the ammonia/hydrogen rotary engine. A 3-dimensional computational model of the ammonia/hydrogen rotary engine coupled with chemical reaction mechanisms was established, and the dependability of the model was confirmed using experimental data. Using numerical simulations, the impact of hydrogen injection position and time on the distribution of the fuel-air mixture, the propagation of flames, and the emissions of NO X in the cylinder under direct hydrogen injection have been studied. The research shows that the injection position and timing of hydrogen can affect airflow movement by changing the impingement angle and cylinder swirl intensity to alter hydrogen distribution in the cylinder under the guidance of the cylinder wall. Furthermore, with a delay in hydrogen injection timing, the turbulence kinetic energy in the cylinder gradually increases and is consistently more significant than that under premixed conditions, with turbulence kinetic energy in Case B-190 approximately 60% higher than that under premixed conditions. When more hydrogen is around the spark plug, the initial flame kernel is formed faster, resulting in a notable acceleration of the fuel-air mixture's combustion rate within the cylinder. In contrast to alternative hydrogen injection strategies, the injection strategy that employs nozzle A and an injection timing of 230°CA (BTDC) can achieve the highest cylinder pressure and lower NO X emissions. • A CFD computational model of ammonia/hydrogen rotor engine was established and validated. • Hydrogen has a greater impact on the flame development compared to ammonia. • Direct injection of hydrogen enhances the turbulent kinetic energy within the cylinder. • Optimizing the direct injection method of hydrogen can effectively reduce the emission of NOx. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to study the detonation re-initiation through multiple reflections upon its entry into a confined space containing liquid fuel within a flow system, which holds significant implications for two-phase pulse detonation engines (PDE) and rotating detonation engines (RDE). Utilizing the Eulerian-Lagrangian method, this study investigates the disparities in the diffraction, quenching, and re-initiation processes of liquid n-heptane/air detonation upstream and downstream. Additionally, it explores the interaction between shock waves and droplets as well as determines the lean flammability limit for re-initiation within a flow system. The findings suggest that the incoming flow significantly contributes to the upstream decoupled detonation re-initiation, as it intensifies the leading shock, thereby expediting droplet fragmentation and evaporation. However, the compressive effect of the incoming flow is insufficient to initiate upstream detonation independently. To achieve re-initiation, it is still necessary for the detonation wave to be reflected by the wall. Moreover, the incoming flow expands the re-initiation boundaries, thereby facilitating the re-initiation of upstream detonation. As the equivalence ratio decreases, a higher inflow Mach number is required to achieve upstream re-initiation. • Upstream and downstream detonation re-initiation are compared. • Interaction between droplets and leading shock upstream and downstream are illustrated. • The detonation re-initiation boundaries beneath an incoming flow are found. [ABSTRACT FROM AUTHOR]

• Investigating hydrogen heterogeneous reaction takes place in catalytic combustor with a blunt body. • Introducing the blunt body into the catalytic combustor enhances the hydrogen conversion ratio. • Strengthening heat and mass transfer characteristics is observed as the blockage ratio increases. • By exploring field synergy effects, the optimal performance parameters of the combustor with a blunt body are determined. A numerical investigation has been conducted to explore the effect of an inserted blunt body on the heterogeneous reaction (HTR) characteristics in a micro-catalytic combustor operating with premixed hydrogen/air. The two-dimensional numerical model incorporates a comprehensive heterogeneous reaction mechanism of hydrogen employed by experimental verification. The influences of blockage ratio at various inlet velocities have been investigated to obtain optimized design parameters of the combustor. The findings of this research highlight analysis of the positive influence of an inserted blunt body within the combustor, including enhancement of chemical reaction rate and hydrogen conversion ratio. Numerical results shows that the gaseous mixture between the blunt body and catalytic surface noticed a considerable velocity increase, leading to a greater adsorption–desorption of bulk species on the catalytic surface. At the same inlet velocity, the hydrogen conversion ratio gradually increases with higher blockage ratios. When the blockage ratio is less than or equal to 0.6, the average inner wall temperature is positively affected by the increased blockage ratio. However, the effect becomes negative at higher blockage ratios (0.8). The Pr (Prandtl number) number near the gas–solid interface adjacent to the blunt body initially decreases and then increases, while Nu/Nu0 (Nusselt number) and Pe (Peclet number) exhibit an initial increase followed by a decrease. The presence of the blunt body leads to a reduction in the cross-sectional area of the channel, causing an acceleration in fluid velocity near the blunt body and exerting an impact on the boundary layer near the gas–solid interface. This indicates that the addition of the blunt body reduces the boundary layer thickness and enhances the mass and heat transfer characteristics in the region. The study reveal that as the blockage ratio increases, the overall field synergy of the combustor initially increases and then decreases. The peak field synergy is attained at an optimal blocking ratio of 0.6. The findings of this study have important implications for the design of micro-scale combustors. [ABSTRACT FROM AUTHOR]

Energy conservation is important in this modern era because of its high demand in transportation systems coupled with the depletion of fossil fuels. Biodiesel is thus an alternative fuel to replace conventional diesel. This study investigates the effect of chamber pressure (Pamb) and chamber temperature (Tamb) on biodiesel spray penetration length (SL) and spray pattern (SP) characteristics in a constant-volume vessel, under rotary engine working conditions, using spray visualization and image processing techniques. Furthermore, a three-dimensional (3D) direct-injection rotary engine model was developed and used for computational fluid dynamics (CFD) simulation studies of biodiesel distribution, mixture forming, and combustion process at different injection timing (IT) in the cylinder. Results indicate that increasing Pamb decreases SL and broadens SP , while increasing Tamb decreases SL and narrows SP. At advanced IT, biodiesel diffuses and disperses, and at retarded IT, which is the suitable rate for combustion, biodiesel concentrates and narrows. Compared with the original scheme [80° crank angle before top dead center (CA BTDC)], Pmax increases by 16.79%, ϕmax decreases by 28.75%, NO and CO change a little, and CO2 decreases. Its drawback is a 15.65% increase in soot formation. [ABSTRACT FROM AUTHOR]

• Spray characteristic of aviation kerosene under RE working conditions was studied. • A reliable 3D dynamic model of aviation kerosene fueled DI-RE was set up. • Evaporation of fuel accelerated evidently when ambient temperature reached 600 K. • Relationship between injection strategy and in-cylinder flow field was dissected. • Distribution of fuel under various injection strategies was studied and obtained. In view of the gradual promotion of Single Fuel Concept in the military field and also the rotary engine (RE) which has been widely applied in specialized equipment, it is necessary to study the basic spray characteristics of aviation kerosene under RE operation conditions and optimize the fuel injection strategies. In this research, an optically visible constant volume combustion chamber platform for Mie-scattering and a validated three-dimensional dynamic simulation model of aviation kerosene fueled direct injection rotary engine (DI-RE) were established. The experimental results show that the ambient temperature and pressure affect the spray process differently. There is no linear relationship between ambient temperature and penetration length. The ambient temperature of 600 K is a watershed, when it is below 600 K, the penetration length increases as the temperature rises. When the temperature reaches 600 K, the penetration length decreases rapidly which means a prominent improvement of atomization quality. On the basis of experimental results, the simulation was carried out and the results show that different injection strategies have important effect on distribution of fuel in cylinder, the larger injection angle will promote the atomization of fuel due to the collision between the spray and air flow field. In Case A3, B2 and C2, the fuel mainly distributes near the spark plugs in the center of the combustion chamber, which is supposed to be more conducive to the ignition and diffusion combustion process of the fuel. [ABSTRACT FROM AUTHOR]

Paleoelevation reconstructions of the Himalayan mountains and Tibetan Plateau have been a focus of geoscientists, as they can improve our understanding of the temporal evolution of climate, biodiversity, and ecosystems. Although a few approaches for paleoelevation reconstruction have been developed in the past decades, each method has inherent strengths and weaknesses, and the uplift histories of the Tibetan Plateau based on different proxies differ considerably. Therefore, developing novel approaches and applying multidisciplinary methods to reconstruct paleoelevation is badly needed. Plant leaf wax δ2H (δ2H wax) and brGDGTs-derived indices (MBT, MBT' or MBT' 5ME) show potential for tracking environmental changes along elevation transects. However, few studies have verified the reliability of the coupled δ2H wax -brGDGTs-derived proxies for paleoelevation reconstructions. In addition, many elevation transects studied so far were dominated by different water vapor sources, which may influence the relationship between these two proxies and elevation. In this study, δ2H wax and brGDGTs were analyzed in topsoil along an elevation transect between 971 m and 5307 m asl (above sea level) near Mt. Annapurna, on the southern slopes of the Himalaya. With the large elevation contrast of 4336 m, and the small horizontal span (40 km), this transect is an ideal place to further evaluate the potential of δ2H wax , MBT' 5ME , and coupled δ2H wax -MBT′ 5ME proxies for local paleoelevation reconstruction. The results showed that both δ2H wax and MBT' 5ME proxy indices decreased significantly with increasing elevation, suggesting that both proxies were reliable in paleoelevation estimates. Moreover, the coupled δ2H wax -MBT′ 5ME proxy showed greater potential for paleoelevation estimates than the single δ2H wax or MBT' 5ME proxies. This study highlighted the great potential of the coupled δ2H wax -MBT′ 5ME proxy in paleoelevation estimates, as this dual proxy can improve the correlation coefficients (R2) and reduce the uncertainties (RMSE) in paleoelevation estimates over a wide area of the globe. In addition, in order to effectively constrain the influence of environmental factors on these proxies, it is necessary to have a thorough understanding of the climatic and environmental background when applying the two proxies for paleoelevation. • Studied transect with single water vapor source, large elevation gradient, small horizontal span. • Coupled δ2H wax -MBT′ 5ME proxy is more reliable than a single proxy in elevation estimates. • Paleoelevation reconstruction from this proxy requires constraints on climate and environment. • This supports the application of the coupled δ2H wax -MBT′ 5ME proxy in paleoaltimetry. [ABSTRACT FROM AUTHOR]

Abstract Enteromorpha is a kind of waste algae that can cause marine ecological disaster. Actively exploring some effective ways for resource utilization of Enteromorpha has important economic and environmental significance. In this article, NH 4 Cl and NH 4 Br modified Enteromorpha chars (E8C5 and E8B5) were prepared by pyrolysis and simple impregnation method for capturing gas phase elemental mercury (Hg0) for the first time. The effects of pyrolysis temperature, loading value, reaction temperature and concentrations of main flue gas components (e.g. O 2 , NO, SO 2 , H 2 O) on Hg0 capture were studied. Mercury removal mechanism and kinetics were also investigated. The results show that Hg0 removal efficiency increases with the increase of pyrolysis temperature, and the optimal pyrolysis temperature is 800 °C. Hg0 removal is significantly enhanced by NH 4 Cl or NH 4 Br modification, and the chars modified by NH 4 Br show better performance than those modified by NH 4 Cl. Optimal loading values and reaction temperature for E8C5 and E8B5 are 5 wt.% and 130 °C, respectively. Presence of O 2 and NO promotes Hg0 removal, whereas presence of SO 2 inhibits Hg0 removal. Lower concentration of H 2 O is beneficial to Hg0 removal, but higher concentration of H 2 O shows an obvious inhibitory effect on Hg0 capture. Hg0 adsorption over E8C5 and E8B5 are endothermic processes. Chemisorption plays a key role in Hg0 removal. Both Hg0 removal processes over E8C5 and E8B5 meet pseudo-second-order kinetic model. Highlights • A kind of seaweed, enteromorpha, is used to prepare bio-chars by pyrolysis. • Prepared bio-chars are modified by NH 4 Cl and NH 4 Br, and are used to remove Hg0. • Halide covalent groups/active oxygen species are major chemisorption sites for Hg0. • Hg0 removals are controlled by chemisorption process. [ABSTRACT FROM AUTHOR]

Highlights • A novel natural gas-diesel rotary engine was proposed and studied. • Effects of dual-fuel injection timings on engine performance were analyzed. • Delaying fuel injection timing resulted in richer mixture in the combustion chamber. • Preferred fuel injection timings were 340°CA BTDC and 70°CA BTDC. • Peak combustion pressure of preferred injection schemes increased 16.34% and 27.38%. Abstract This study aimed at further improving the combustion efficiency of the diesel rotary engine (DRE), and in this regard a novel natural gas-diesel rotary engine (NG-DRE) was numerically studied. Based on the experimental validated computational fluid dynamics (CFD) model, a 3D-dynamic numerical study of the NG-DRE was carried out by adopting NG port injection plus diesel direct injection mode. The influence of natural gas injection timing (NGIT) and diesel injection timing (DIT) on air-fuel mixing, combustion and emission characteristics were explored. Simulation results showed that NG-DRE performance was better than DRE. During the entire air-fuel mixing process, NG movement was easily affected by the vorticity density due to its good diffusion characteristics, however its influence on diesel movement was relatively minimal. At assisted ignition timing, NG concentrated at the rear of the combustion chamber, and diesel concentrated at the front and middle of the combustion chamber. Delaying NGIT and DIT, the mixture became more concentrated due to a shorter mixing time. Moreover, the delayed NGIT and DIT resulted in improvement of the pressure and combustion rate, while for a further delayed DIT the pressure was decreased due to the pressure negative work. Considering the engine power and emission performance, for dual-fuel injection schemes, 340°CA BTDC and 70°CA BTDC were the preferred application schemes for NG and diesel respectively. Their peak combustion pressure (P max) increased by 16.34% and 27.38% respectively, but due to the richer mixture, soot value increased by 0.023% and 0.054% and CO (carbon monoxide) value also increased by 0.026% and 0.039% respectively. [ABSTRACT FROM AUTHOR]

Heterogeneous reaction characteristics of premixed H 2 /Air mixture are numerically investigated in micro combustor with coating platinum (Pt) catalyst on the inner wall. The well-designed combustor with the inserted baffle is committed to improving the transport of bulk species on the catalytic surface, therefore enhancing the fuel conversion ratio. A two-dimensional numerical model with detailed heterogeneous reaction mechanism is developed and verified. In this work, the numerical results reveal that the heterogeneous reaction rate and fuel conversion ratio are significantly improved in the combustor with inserted baffle. The velocity of gaseous mixture swiftly increases between the baffle and catalytic surface, resulting in the increasing adsorption-desorption of bulk species on the catalytic surface. The main influencing factors of inserted baffle body comprise of slit width between two ribs in the same row (W), rib length (L), distance between adjacent baffles row (D), number of baffle row (n) which are studied to obtain a set of optimized parameters of baffle in the well-designed combustor. The optimized parameters of the baffle are W = 0 mm, L = 0.4 mm, D = 4 mm and n = 4, which are employed in the combustor to obtain a high hydrogen conversion ratio. Moreover, the effect of different inlet velocities and equivalent ratios of the mixture on the heterogeneous reaction characteristics are carried out in the designed combustor. As the designed combustor performs well, and the improvement effect of the optimized baffle gradually increases together with the inlet velocity, particularly for high inlet velocity (7 m/s). The promotion effects of baffle in the designed combustor are presented when the rich and lean fuel are adopted at inlet velocity of 7 m/s. Finally, the relative parameters of this work can serve as a reference and guidance for the design of micro scale combustor. • A digital model for a catalytic micro combustor with baffles is established. • Optimization of baffle parameters is found to improve the combustor performance. • Effect of varying inlet conditions on the well-designed combustor performance is investigated. • The principle of enhanced heterogeneous reaction in a micro combustor is explored. [ABSTRACT FROM AUTHOR]

This paper aims at improving the combustion efficiency of direct injection diesel rotary engine (DI-DRE) by adjusting the injection strategy. An experimental validated 3D-dynamic simulation model coupled with chemical kinetics mechanism was established. A high-pressure direct injection mode was used to investigate the effect of diesel fuel injection timing (IT) and injection angle (IA) on fuel-air mixing and combustion process in a DI-DRE with spark ignition. Results showed that increasing IA changed the fuel distribution position from front to back of the combustion chamber, delayed IT and the fuel distribution area also became narrower and more concentrated. For combustion process, the fuel concentrated at partial central position towards the back of the combustion chamber was better for ignition. The distribution of more continuous mixture between the two spark plugs and concentration of more fuel near the trailing spark plug (TSP) was conducive to the improvement of combustion efficiency. The preferable combustion rate and emission performance were obtained when the IT was 80°CA (BTDC) and IA was 90°. Compared to the original scheme, maximum combustion pressure increased by16.82% while crank angle for maximum combustion pressure reduced by 8.19%. Soot and CO emissions reduced by 41.48% and 32.87% respectively. However, NO and CO 2 emissions increased slightly. [ABSTRACT FROM AUTHOR]

• 3-D dynamic simulation model based on chemical kinetics reaction is established. • Simulation models based on biodiesel fuel is validated by experimental data. • Equivalence ratio, injection and spark timing effect on rotary engine are analyzed. • Preferred injection and spark timing are 80°CA(BTDC) and 35°CA(BTDC) respectively. • Preferred equivalence ratio is 0.8 under the computational condition. Rotary engine has a flat combustion chamber that results in high unburned fuel leading to fuel inefficiency and emissions. Biodiesel regarded as a clean source of energy is an alternative fuel due to its ability to minimize environmental pollution resulting from unwanted emissions. In this regard, the improvement of combustion efficiency of a direct injection rotary engine fueled with biodiesel was numerically investigated. Experimental data was used in validating the established three-dimensional computational fluid dynamics (3D-CFD) model. On this basis, investigation of various biodiesel injection timing (IT) (100, 80, 60) °CA before top dead center (BTDC), spark timing (ST) (35, 30, 25, 20) °CA BTDC and equivalence ratios (∅) (0.6, 0.8, 1.0, 1.2) on mixture formation and combustion process was carried out. Results revealed that when IT retarded fuel distribution narrows and the mixture formed is concentrated. Conversely when ST retarded there is broad and dispersed fuel distribution. For lean condition the mixture formed is less concentrated compared to rich condition. For combustion process, when biodiesel was concentrated at the middle of in-cylinder at 30 mm (X-axis) and 15 mm (Z-axis) from the centerline in opposing directions it was better for spark-on. Also, the in-cylinder pressure and temperature reduced with advanced IT, retarded ST and decreased ∅. When ∅ leaned, flame development and propagation periods decreased. The suitable rate for combustion considering emissions was obtained when IT was 80°CA (BTDC) and ST 35°CA (BTDC) at a ∅ of 0.8 because when compared to the original scheme (case B4), maximum combustion pressure increased by 28.57% and increase of CO 2 , CO, soot and NO emissions were reasonable due to increase in temperature and fuel evaporation. [ABSTRACT FROM AUTHOR]

• Spray combustion characteristics and ignition limit was experimentally studied. • Optical CVCC platform as well as reliable 3D simulation model was applied. • Ignition delay and lift-off length decrease with the increased ambient conditions. • Better engine dynamic and emission performance was obtained in Case A3. Investigating the adaptability of aviation kerosene in the direct injection rotary engine is of great significance and practical value. In this paper, an optically visible constant volume combustion chamber platform with various optical diagnostic techniques was firstly set up to study the spray combustion characteristics of the fuel. Secondly, a reliable three-dimensional dynamic simulation model of direct injection rotary engine was established to investigate the combustion process of aviation kerosene under optimized injection strategies. The experimental results show that the ambient temperature of 800 K and ambient pressure of 20 bar is the ignition limit of aviation kerosene under the condition of rotary engine. With the increase of ambient conditions, the ignition delay and the flame lift-off length shorten continuously. At 850 K ambient temperature, when the ambient pressure reaches 25 bar, the lift-off length will no longer shorten and remains at about 6 mm. The simulation results indicate that under the Injection position A-Injection angle 90° (Case A3), higher combustion efficiency before top dead center can be achieved due to more appropriate distribution, concentration and atomization quality of fuel at ignition timing. The peak pressure in cylinder reaches 38.89 bar, which means a better engine dynamic performance. Meanwhile, acceptable CO and Soot emissions are obtained by the complete combustion of fuel in Case A3, however, the higher combustion temperature makes the production of pollutant NO slightly higher than other injection strategies. [ABSTRACT FROM AUTHOR]

Highlights • A novel natural gas-diesel dual-fuel rotary engine was proposed and studied. • Fuel spray characteristics under rotary engine working conditions were obtained. • Dynamic simulation model was validated in detail for diesel rotary engine. • Mixture formation process and combustion characteristics were analyzed. • Blending natural gas could effectively improve the total combustion rate. Abstract To further improve the performance of diesel rotary engine, a novel natural gas-diesel rotary engine was proposed and studied in this paper. Based on a spray experimental setup, the diesel spray characteristics under diesel rotary engine working conditions were obtained and analyzed. Thereafter it was used to validate the spray model for diesel rotary engine modeling and simulation. The effect of different natural gas blending ratios on mixture formation and combustion process in the natural gas-diesel rotary engine were investigated. Simulation results showed that for fuel-air mixing process, the natural gas movement process was susceptible to the airflow motion. However, the diesel distribution range was obviously enlarged under the influence of high-speed unidirectional flow. At assisted ignition timing, the stratified distributed diesel made the combustion process mainly occured at the front and middle of the combustion chamber. Besides, the flame propagation speed was accelerated with natural gas blending ratio increasing, which effectively improved the total combustion rate. Compared to single-fuel mode, when natural gas blending ratio increased to 20%, the maximum combustion pressure increased by 24.17%. Meanwhile, soot and CO decreased obviously, but NO and CO 2 also increased. [ABSTRACT FROM AUTHOR]

• A numerical model of flame impinging on a hemispherical surface was established. • The flame structure, temperature and heat flux of target surface was compared under various operation conditions. • The heat transfer efficiency was presented to quantify the thermal performance of impinging flame jet and the optimum thermal performance under each operation condition was obtained. • The centerline velocity and temperature were obtained to analyze the effect of impingement surface on flame flow and heat transfer. A combined experimental and numerical investigation was conducted to study the heat transfer characteristics of premixed methane-air flame jet impinging on a hemispherical surface. The effects of the mixture equivalence ratio (ϕ = 0.9–1.5), burner to plate distance (H/d = 1–6), the mixture Reynolds number (Re = 300–800) and curvature ratio (d/D = 0.1–0.133) on the heat transfer characteristics were investigated. CFD software was used to simulate the laminar methane-air flame impinging on a hemispherical surface for different operation conditions, and the heat flux distribution and average heat flux on the impingement surface were obtained. The heat transfer efficiency is presented to quantify the thermal performance of impinging flame jet. It was found that the equivalence ratio has an important effect on the flame height, which in turn affects the heat transfer efficiency, and the stoichiometric mixture has the lowest heat transfer efficiency because its lowest flame height. The burner-to-plate distance plays a decisive role in the heat transfer characteristics of impinging flame jet, and when the flame premixed cone just touches the impingement surface, it has the best thermal performance. Higher mixture Reynolds number has higher flame height, temperature and heat flux distribution, but lower heat transfer efficiency. The configuration of impinging flame jet with smaller curvature ratio has better thermal performance. [ABSTRACT FROM AUTHOR]

In order to project future changes in climate and their corresponding environmental and social impacts, it is of utmost importance to understand the spatiotemporal patterns of past climate changes on the Tibetan Plateau (TP). Although numerous records of late Holocene climate changes have been developed across the TP, the spatiotemporal patterns of changes in temperature and precipitation/moisture are unclear and a comprehensive review of this topic is urgently needed. Here, we present such a synthesis using currently available temperature and precipitation/moisture records from across the TP to understand spatial and temporal variations over the past two millennia. The main conclusions are as follows: 1) Temperature variations on the TP during the past two millennia are not homogeneous and show strong seasonality. Although patterns of mean annual temperature change on the TP during the past two millennia remain contradictory, summer temperature variations are generally consistent. The summer temperature reconstructions indicate that the warmest period during the past two millennia was in the middle ages, as opposed to the recent 20th century. 2) Precipitation/moisture patterns on the TP are spatially complex. The most striking feature is that an inverse pattern of precipitation/moisture variation can be detected over most parts of the TP between 600-1400 AD and 1400-1900 AD. Specifically, the eastern TP, southwestern TP, and part of the northeastern TP were generally wetter, whereas the southeastern TP, the southern TP, the northwestern TP, and part of the northeastern TP were generally drier during 600–1400 AD as compared to during 1400–1900 AD. However, such anti-phased hydroclimatic variability is not found in either the cold period of 1–600 AD or in the current warm period of the past century. This indicates that temperature and precipitation/moisture changes appear in multiple combinations. 3) Fluctuations in the intensity and seasonal movement of the westerlies and the Indian summer monsoon (ISM) over the Tibetan Plateau, as well as the associated climate variability modes (e.g., North Atlantic Oscillation (NAO), Indian Ocean dipole (IOD), ENSO, and Intertropical Convergence Zone (ITCZ)), might be responsible for the spatially complex patterns of climate anomalies over TP during the past 2000 years. 4) The results highlight the need for more high-quality paleoclimatic and paleoenvironmental reconstructions that span the past two millennia on the TP. Such reconstructions must have unambiguous climate significance, clear seasonality, site-specific calibration, and robust dating. • First comprehensive review of the late Holocene temperature and precipitation/moisture records for TP. • Summer temperature on TP are generally consistent, but mean annual temperature are contradictory. • An inverse pattern of precipitation/moisture variation between 600–1400 AD and 1400–1900 AD across the TP. [ABSTRACT FROM AUTHOR]

• Hetero-/homogeneous combustion characteristics are observed in a micro reactor. • Gaseous flame is against the heterogeneous reaction in the micro catalytic channel. • Heat feedback from homogeneous reaction on catalyst promotes heterogeneous reaction rate. • Released heat from heterogeneous reaction improves the homogeneous reaction rate. • The effects of catalytic surface are more pronounced for micro combustion schemes. The heterogeneous-homogeneous combustion characteristics of premixed H 2 /Air mixture in a micro combustor with 2 mm platinum (Pt) catalyst segmentation are investigated by numerical simulation. The detailed chemical reaction mechanisms of gas-phase reaction and surface reaction of H 2 are employed in a 2D CFD model by the verification. The characteristics in the catalytic combustor, such as temperature distribution, species concentration, kinetics reaction rate and heat transfer, are examined by varying inlet flow velocities. There is an interesting fact that an obvious demarcation line splits the channel into two regions at high velocities, which are dominated by heterogeneous reaction (Htr) and homogeneous reaction (Hr). In addition, there is a coupling heterogeneous-homogeneous reaction (HHr) in the 2 mm downstream of the catalytic region. These should be thoroughly deliberated using thermal and chemical analyses to determine that the gaseous flame is against the Htr in the catalytic combustor. The results can be shown that the heat flux into the upstream catalytic wall is primarily due to exothermicity induced by Htr. A low amount of heat feedback via the solid wall to inlet wall which is released by Hr. The heat fluxes from the gas–solid interface preheat the fresh gaseous mixture in the channel, thereby promoting the occurrence of Hr, increasing the heat release rate and kinetic reaction rate of Hr. Moreover, heat feedback from the heat release of Hr through the solid wall increases the reaction rates of Htr. The hydrogen conversion rate is improved by the effect of Htr in the catalytic combustor. In summary, the effect of introducing catalytic surface to induce the Htr could be well suitable for micro combustion schemes. [ABSTRACT FROM AUTHOR]

• Effects of fuel injection angle on diesel Wankel engine performance are explored. • Stratified combustion process under forward flow fuel injection angle is studied. • Forward flow fuel injection angle strategy can realize fuel stratified distribution. • Fuel injection angle for better combustion performance is analyzed and obtained. • The forward flow fuel injection angle of 65° is the preferred application scheme. High-pressure direct injection (HPDI) combined with stratified combustion technology can further enhance the combustion performance of the diesel Wankel engine (DWE). Consequently, based on our experimentally validated three-dimensional (3D) dynamic simulation model, this study proposes to adopt the fine-designed forward flow fuel injection angle (FIA) to realize mixture distribution in the front region of the rotary combustion chamber (RCC). Then the stratified fuel movement and combustion processes under different FIAs of a high-pressure direct injection diesel Wankel engine (HPDI-DWE) are investigated. The numerical results show that for mixture formation, the ideal distribution rule should make the fuel distribute near the spark ignition chamber (SIC) and avoid excessive mixture concentration since flame presents forward propagation characteristics. During the combustion process, combustion reaction occurs in the front zone of the RCC, while flame front shapes show symmetry structure due to the stratified distribution of fuel and generation of symmetric vortexes in this region. Increasing FIA, better power performance is obtained overall, meanwhile, mixture combustion rate and heat release process are accelerated. Considering the trade-off between power and emission, the preferred FIA is 65°. Compared to FIA of 60° (original scheme), its peak pressure (Pmax) is increased by 1.8%, total combustion duration (TCD), central heat release angle (CA50) and flame propagation period (CA10-90) are shortened by 11.1%, 20.4% and 14.1%, respectively. Moreover, soot and carbon dioxide (NO) are significantly reduced by 39.5% and 52.5%, respectively. [ABSTRACT FROM AUTHOR]

• Stratified combustion process of natural gas/diesel Wankel engine was explored. • Effect of key assisted-ignition factors on combustion characteristics was studied. • Optimized schemes under natural gas/diesel combustion mode were determined. • Using dual assisted-ignition spark plugs could improve fuel burning rate. • Assisted-ignition timing at 35°CA BTDC was the ideal application scheme. It is important to improve the combustion performance of the diesel Wankel engine for its further engineering applications. Therefore, the main objective of this study was to study the dual-fuel mixture formation and stratified combustion process in the novel natural gas blended diesel Wankel engine. Meanwhile, the effects of assisted-ignition timing and assisted-ignition position on engine combustion characteristics were investigated. The results indicated that when the assisted-ignition timings and positions were changed, natural gas distribution near assisted-spark plugs changed slightly, while the variation of diesel distribution was conspicuous. Moreover, adopting dual assisted-ignition spark plugs could accelerate the fuel burning rate and improve engine combustion performance. Besides, it was found that more mixture concentrated near the assisted-spark plugs was beneficial to increase the pressure in-cylinder and combustion rate. The symmetrical arranged dual assisted-ignition spark plugs that were respected to the X-axis (Case 4) and assisted-ignition timing of 35°CA BTDC (Case 6) were the preferred practical application schemes. Compared to the schemes of single spark plug ignition (Case 1) and 20°CA BTDC ignition timing (Case 9), the peak pressure in-cylinder of the preferred application schemes increased by 42.96% and 10.91%, respectively. [ABSTRACT FROM AUTHOR]

• Stratified combustion process under assisted ignition strategy was analyzed. • Effect of key assisted ignition factor on combustion characteristics was explored. • 35°CA BTDC ignition timing and (0, −88.5, ±15 mm) ignition position were optimal. • Case5 and Case7 were the preferred application assisted ignition strategy scheme. • The combustion performance of optimized spark schemes was effectively improved. This work aimed to further improve the combustion performance in a diesel Wankel engine by optimizing the assisted ignition strategy. Based on the established and verified dynamic simulation model, the effects of some key assisted ignition parameters, such as the number of assisted spark plug, assisted ignition position (AIP) and assisted ignition timing (AIT) on combustion performance were analyzed systematically. Simulation results indicated that the reaction process occurred in the mid-anterior region of the rotary chamber due to the stratified-charge mixture and forward-propagate flame. The combustion performance of the double assisted spark plug schemes was better than that of the single assisted spark plug scheme. The double assisted spark plugs symmetrically distributed relative to the major axis (X-axis) of the rotary chamber, the combustion process was more reasonable. When changing AIP, peak combustion pressure (P max) and combustion zone varied greatly, while they changed little when advancing AIT. For the optimized assisted ignition strategies, the optimal AIP scheme was Case5 (0, −88.5, ±15 mm) and the optimum AIT scheme was Case7 (35°CA BTDC). Comparing with the original scheme (Case1), their P max increased by 16.68% and 17.83%, respectively. Meanwhile, the CA50 and CA10-90 were shortened obviously. [ABSTRACT FROM AUTHOR]