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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]

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]

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]

• 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]

• 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]

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]