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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 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]

• 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]

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]