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Under the background of carbon neutral, hydrogen-fueled Wankel rotary engine (WRE) with high power density and compact layout has the potential to become a substitute for current fossil engines. Ammonia as a carbon-free renewable energy is considered alternative energy used in vehicles, however, its application on WRE is lacking. Therefore, the present work aims to investigate the performance of ammonia-enriched hydrogen-fueled WRE to analyze the feasibility of ammonia applied in hydrogen-fueled WRE. The main conclusions are as follows: Under test conditions, the maximum brake torque and thermal efficiency are obtained at about 30% and 40% volume fraction of ammonia in fuel, and compared with pure hydrogen conditions, achieving relative improvements of 21% and 29%, respectively. Slightly rich combustion is recommended to increase power and decrease NO emissions with an acceptable economic loss. In addition, ammonia enrichment can prevent the occurrence of abnormal combustion. [Display omitted] • Performance analysis of NH3-enriched hydrogen-fueled Wankel rotary engine. • NH3 enrichment can improve dynamics and economy with penalties for NO emission. • Slightly rich combustion is recommended for NH3-enriched hydrogen-fueled WRE. • NH3 enrichment is an effective way to prevent abnormal combustion. [ABSTRACT FROM AUTHOR]

The hydrogen-fueled Wankel rotary engine with excellent power and emission characteristic is under spotlight, while the leakage is still the major problem for Wankel rotary engine, especially the leading spark plug leakage. The peak pressure is increased from 3.34 MPa to 3.52 MPa and the indicated thermal efficiency reaches maximum value of 38.29% when the moving distance of leading spark plug is −6.5 mm, and the mass of leakage fresh mixture is reduced from 0.00311 g to 0 g. When leading spark plug is moved to minor axis, the flow field structure of working chamber is enhanced. However, the peak pressure and indicated thermal efficiency decrease when the moving distance of leading spark plug exceeds −6.5 mm. The excess leakage residual gas has negative effects on combustion. The optimum moving distance of leading spark plug is −6.5 mm at 3000 rpm with λ of 1.6. • The leakage mechanisms of spark plugs are analyzed. • The influence of leading spark plug location on gas leakage is analyzed. • The influence of leading spark plug location on combustion is analyzed. • The influence of leading spark plug location on flow field is analyzed. • The optimum location of leading spark plug is given. [ABSTRACT FROM AUTHOR]

Hydrogen-fueled internal combustion engine is proposed to resist the threat of global warming. Wankel rotary engine (WRE) has been proven to be an excellent hydrogen-fueled power device, which can overcome the shortcomings of hydrogen, such as poor power, serious backfire and large storage volume, to some extent when it is used as fuel in the internal combustion engine. However, due to its unique structure, WRE suffers from severe knock. Therefore, the goal of this work is to investigate the impacts of knock type on the heat release process in hydrogen-fueled WRE. This present work is conducted at 2000 r/min and wide-open throttle. The main results are as follows: In hydrogen-fueled WRE, the peak knock pressure of knock caused by rapid and unstable combustion of hydrogen is usually earlier than CA50 and that of knock caused by spontaneous combustion of end gas is usually later than CA50. The sequence between the crank angle of peak knock pressure and CA50 combined with knock intensity can be used to determine the knock type in hydrogen-fueled WRE. Besides, a means for knock detection is proposed according to the distribution of crank angle corresponding to peak knock pressure. In addition, the distribution of CA0-10, CA50 and CA10-90 of 1000 consecutive cycles under two kinds of knock in hydrogen-fueled WRE are discussed in detail, and regular conclusions are drawn. In particular, the limitation of CA50 as a metric for evaluating knock level is also demonstrated. • The impact of knock type on the heat release of hydrogen Wankel engine is discussed. • The distribution of CA0-10, CA50 and CA10-90 with knock intensity are analyzed. • A method is proposed to estimate the knock occur. • A method is proposed to determine the knock type in hydrogen engines. [ABSTRACT FROM AUTHOR]

The present work proposes the application of CH 4 and H 2 synergy to improve the performance of the Wankel rotary engine (WRE). The whole work was experimentally conducted at 1500 r/min. The results indicate that CH 4 WRE can achieve similar power and significantly higher thermal efficiency than gasoline WRE based on quantitative control, with a maximum absolute efficiency improvement of 11.4%. At the same time, it also can achieve 64% and 77% maximum reduction of CO and NO emissions, respectively. CH 4 –H 2 synergy can further improve the performance of CH 4 -fueled WRE, which can broaden the lean flammability limits and make qualitative control application possible. Compared with CH 4 WRE with quantitative control, qualitative control hybrid fuel WRE can achieve a maximum relative improvement of 6.54% in brake thermal efficiency and significantly reduced NO and CO emissions. However, the extent of qualitative control is limited by cyclic variation. Overall, CH 4 –H 2 synergy can be a potential alternative to elevate the performance of WRE, the key to which is the reasonable match of synergy level and qualitative control extent. • Comparison of performances between CH4 and gasoline Wankel rotary engines. • CH4 has significant advantages in efficiency, CO and NO emission than gasoline. • CH4–H2 synergy can further improve the performance of the CH4 Wankel rotary engine. • Blending H2 coupling qualitative control is a good load control model in CH4 WRE. [ABSTRACT FROM AUTHOR]

The development of hydrogen-fueled Wankel rotary engine is restricted by the leakage problem, especially the apex seal leakage (ASL). In the study, the ASL area is divided into the geometric leakage area (GLA) and the dynamic leakage area (DLA). The models of under-seal pressure prediction and vibration of apex seal are established. The mechanism of GLA and DLA and the effects of key parameters on them are analyzed. Results show that the DLA decreases with the increase of discharge coefficient, clearance between apex seal and slot. There is no DLA when the rotation speed is slower than 2000 rpm or higher than 7000 rpm. Besides, the value of DLA is only 11.23% of GLA and the GLA can be reduced by 88.57% when using a corner-piece structure. The total leakage decreases with the increase of rotation speed. Finally, some measures to reduce the leakage are given. [Display omitted] • The cause of apex seal leakage of the Hydrogen Wankel rotary engine is analyzed. • The prediction model of under-seal pressure of the apex seal is established. • The computational model of the apex seal leakage is established. • The apex seal leakage area and leakage gas mass are calculated. • The suggestions to improve the sealing performance are given. [ABSTRACT FROM AUTHOR]

Syngas is a fuel with a huge market and low carbon emission, which has been proven to be well applied to internal combustion engines. WRE with high power density can effectively improve the power characteristic when syngas is employed as fuel in engines, however, which has not been reported publicly. This work aims to provide insights into the performance of syngas-fueled WRE under different CO/H2 ratios and thus gives theoretical guidance for its application. The test is done at 1500 r/min and part load. It is found that with the increase of the volumetric ratio of CO in syngas (CO%), the efficiency, torque and carbon emissions are deteriorated, however, the NO emission is significantly improved and the knock level is also reduced. In addition, on the premise of constant CO%, a high brake thermal efficiency, low NO emission and knock intensity can be achieved at lean combustion. In particular, when CO% is 10%, the combustion efficiency of CO is independent of the excess air ratio, while when CO% is 20%, that is decreased with increasing excess air ratio. In summary, the syngas-fueled WRE is recommended to adopt the qualitative control and the syngas with low CO%. • Insights into the performance of syngas-fueled Wankel rotary engines. • The trade-off relationship among power, efficiency and NO emission needs to be considered. • Qualitative control and low CO% are recommended in the syngas-fueled WRE. • The combustion efficiency of CO at varied λ is closely related to CO%. [ABSTRACT FROM AUTHOR]

Hydrogen-fueled Wankel rotary engine (WRE) suffers from high NOx emissions, high risk of knock and uneven thermal load. The goal of this work is to investigate the application of quantitative control and qualitative control on a hydrogen-fueled WRE and find a suitable load control strategy for hydrogen-fueled WRE to address above-mentioned problems, which is conducted at 1500r/min. The results show that the combination of qualitative control and quantitative control is an effective way to obtain the excellent performance of hydrogen-fueled WRE, which can achieve higher thermal efficiency while effectively improving some drawbacks of hydrogen-fueled WRE, such as uneven thermal load, high tendency of knock and high NOx emissions. Besides, it also can flexibly select control logic according to the priority of emissions, efficiency, stability and power. Compared to quantitative control, the combined control can realize higher brake thermal efficiency under the same brake torque, and the highest relative and absolute improvements are 38.4% and 4.75%. In addition, it also keeps the engine running in an acceptable cyclic variation range. • Effect of quantitative and qualitative control on hydrogen-fueled WRE is studied. • HWRE has low thermal efficiency, high knock risk and NOx, uneven thermal load. • Combination of two strategies can effectively improve the problem of HWRE. • Combination of two strategies allows flexible control logic based on requirements. [ABSTRACT FROM AUTHOR]

Hydrogen-fueled Wankel rotary engine, with few available research currently, has excellent power and emission characteristics, however, with lower efficiency. With increasing attention to low-carbon emission, it is of great significance to explore methods to improve the efficiency of hydrogen-fueled Wankel rotary engines. This work aims to study the effect of qualitative control coupling variable engine speeds at the wide-open throttle on the power control. The comparative effect of qualitative control coupling engine speeds from 1000 r/min to 1500 r/min under the wide-open throttle and quantitative control at 1500 r/min on the combustion and emission characteristic of hydrogen-fueled Wankel rotary engine is investigated. The results show that compared with quantitative control, qualitative control coupling variable engine speed can achieve excellent performance. The brake thermal efficiency can be maximally increased by 43.5%, an absolute increase of 6.22%, as well the volumetric efficiency with a maximal 105% improvement. The thermal load and risk of knock can be greatly reduced. Moreover, NO emission also can be reduced by more than an order of magnitude or even by zero. Although there is an increase in cyclic variation, the value is no more than 4%. In addition, qualitative control coupling variable engine speed allows flexible matching of appropriate engine speed and excess air ratio based on the actual requirements of efficiency, stability, durability and emission. • The power control method of the hydrogen Wankel rotary engine is investigated. • Qualitative control achieves better engine performance than quantitative control. • Qualitative control coupling engine speed meets the power and high-efficiency demand. • Lower thermal load, knock tendency and NO emission can be obtained. • Much high excess air ratio isn't recommended due to high cyclic variation. [ABSTRACT FROM AUTHOR]

Hydrogen-fueled Wankel rotary engine, with few available research currently, has excellent power and emission characteristics, however, with lower efficiency. With increasing attention to low-carbon emission, it is of great significance to explore methods to improve the efficiency of hydrogen-fueled Wankel rotary engines. This work aims to study the effect of qualitative control coupling variable engine speeds at the wide-open throttle on the power control. The comparative effect of qualitative control coupling engine speeds from 1000 r/min to 1500 r/min under the wide-open throttle and quantitative control at 1500 r/min on the combustion and emission characteristic of hydrogen-fueled Wankel rotary engine is investigated. The results show that compared with quantitative control, qualitative control coupling variable engine speed can achieve excellent performance. The brake thermal efficiency can be maximally increased by 43.5%, an absolute increase of 6.22%, as well the volumetric efficiency with a maximal 105% improvement. The thermal load and risk of knock can be greatly reduced. Moreover, NO emission also can be reduced by more than an order of magnitude or even by zero. Although there is an increase in cyclic variation, the value is no more than 4%. In addition, qualitative control coupling variable engine speed allows flexible matching of appropriate engine speed and excess air ratio based on the actual requirements of efficiency, stability, durability and emission. • The power control method of the hydrogen Wankel rotary engine is investigated. • Qualitative control achieves better engine performance than quantitative control. • Qualitative control coupling engine speed meets the power and high-efficiency demand. • Lower thermal load, knock tendency and NO emission can be obtained. • Much high excess air ratio isn't recommended due to high cyclic variation. [ABSTRACT FROM AUTHOR]

The application of hydrogen direct-injection enrichment improves the performance of gasoline Wankel rotary engine, and the hydrogen injection strategy has a significant impact on combustion, knock, and emissions. The Z160F Wankel rotary engine was used as the investigated compact engine, and the simulation model was developed using CONVERGE software. The combustion, knock and emissions characteristics of the engine were studied with the different mass flow of hydrogen injection, i.e., the trapezoid, wedge, slope, triangle and rectangle type of gas injection rate shape. In the numerical simulations, the in-cylinder pressure oscillations were monitored using monitoring points, and the knock index (KI) was used as an evaluation indicator. The study revealed that the gas injection rate shape significantly affected the mixture of hydrogen and air, thus impacting combustion, knock and emissions. When the injection rate shape was rectangle, the flame speed was faster, the peak pressure in the cylinder was higher, and the corresponding crank angle was earlier, which led to higher pressure oscillations in the cylinder and larger KI. Based on the rectangle injection rate shape, the KI decreased by 75.81%, 33.47%, 26.46% and 76.58% for trapezoid, wedge, slope, and triangle, respectively, and the indicated mean effective pressure increased by 15.68%, 5.07%, 0.56% and 14.98%, respectively. Due to the small difference in maximum temperature, which resulted in very little variation in nitrogen oxides for each injection rate shape, the total hydrocarbon emissions of the trapezoid and triangle injection rate shape was high due to the delayed combustion phase. This paper provides a solution for direct hydrogen injection to improve the combustion, knock and emissions behavior of the rotary engine. [Display omitted] • A rotary engine model with hydrogen direct-injection enrichment was established. • Five different types of hydrogen injection rate shapes were simulated. • The behavior of the combustion, knock and emissions was analyzed. • The optimal indicated thermal efficiency can be achieved by trapezoid type. [ABSTRACT FROM AUTHOR]