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The study aims to numerically investigate the combustion and emissions formation processes in a spark-ignition rotary engine fueled with hydrogen-gasoline blends. The Renormalization Group k-ε turbulence coupled with a skeletal primary reference fuel mechanism were adopted to simulate the engine working process under 0%, 2% and 4% hydrogen volume fractions in CONVERGE software. The flow field variation and detailed combustion processes were analyzed and discussed. Results showed that a mainstream flow field along with the rotor movement was formed during the compression stroke and sustained in the combustion chamber until the exhaust valve opening. The center of the burned zone would move in same direction with the mainstream flow. Meanwhile, due to the effect of the mainstream flow, the flame propagation in direction of the mainstream flow was expedited. While the flame propagation in contrary direction was retarded, consequently, the unburned mixtures at rear region of combustion chamber suffered incomplete combustion. The distributions of nitric oxide and carbon monoxide emissions were also dominantly affected by the flow field in the combustion chamber. After hydrogen addition, the increased OH, H and O radicals concentrations combined with the intense flow flied accelerated the combustion process, which resulted in the improvement and advancement of in-cylinder pressure and temperature. Compared with original gasoline case, the peak in-cylinder pressure was increased by 9.1% and 13.7% with 2% and 4% hydrogen blends, respectively. With hydrogen enrichment, the increased in-cylinder temperature promoted the formation of nitric oxide emission. Besides, Carbon monoxide emission was decreased with the increase of hydrogen addition fraction. [ABSTRACT FROM AUTHOR]

• Knock of hydrogen-fueled Wankel rotary engine is investigated in this work. • Effect of ignition timing, spark plug location and number, λ and speed are studied. • Knock intensity with distribution, knock duration and cyclic variation are analyzed. • All of aspects studied in this work have significant effects on the knock. Hydrogen-fueled Wankel rotary engine (HWER) is an excellent power device with superior power and emission performances. Besides, unlike hydrogen-fueled reciprocating piston engines, HWRE is less prone to backfire due to its structural advantages. However, limited by its long combustion chamber, knock, one of abnormal combustion in engines, still hinders the development of HWER. Hence, based on this consideration, the goal of this work is to investigate the knock of HWRE from different aspects, including ignition timing, spark plug number, spark plug location, excess air ratio and engine speed, to provide relevant information for the design of hydrogen-specific WRE. The results show that the knock intensity gradually increases as the ignition timing is advanced, the excess air ratio is decreased and the engine speed is increased, but the knock duration shows different variations. Adopting dual spark plugs tends to lead to stronger knock caused by unstable combustion of hydrogen, while only adopting leading spark plug tends to lead to the knock caused by auto-ignition. When dual spark plugs are used, the leading spark plug is more responsible for the knock caused by unstable combustion and the trailing spark plug is more responsible for the knock caused by auto-ignition. [ABSTRACT FROM AUTHOR]

• The model of HFRE with active pre-chamber TJI was established. • The combustion characteristic of HFRE-SC was analyzed. • The optimum HIT and HID was obtained. Hydrogen can be used as fuel to replace gasoline, with the benefit of reducing harmful emissions of rotary engine (RE). The swirl chamber (SC) coupling spark plug and nozzle will achieve diffusion combustion and higher power as compared to the conventional spark plug. In the current work, a CFD model of a hydrogen-fueled rotary engine with swirl chamber (HFRE-SC) is established to study the impacts of hydrogen injection timing (HIT) and hydrogen injection duration (HID) on combustion characteristics of HFRE-SC. Results reveal that SC combustion system may achieve more combustion efficiency and higher indicated power when compared to port injection (PI). Moreover, lean hydrogen in the rear of combustion chamber (ROCC) can result from retarding HIT and extending HID. In addition, when the rich zone in SC moves toward the spark plug, making it difficult for flames to develop and spread. The best performance can be obtained when using the HIT at 75 °CA BTDC and the HID during 35 °CA, with an 8.42 % up in indicated power compared to the PI. [ABSTRACT FROM AUTHOR]

As a zero-carbon fuel and hydrogen carrier, ammonia has received much attention for its excellent carbon reduction potential. To explore the feasibility of zero-carbon ammonia as fuel for in small-scaled Wankel rotary engines, a computational fluid dynamics model coupled with a kinetic mechanism was established and validated. It is found that the fuel mixture cannot be ignited when the hydrogen substitution ratio (HSR) is less than 5%. Increasing HSR shortens flame development period and intensifies combustion. When HSR is greater than 12.5%, the fuel can be burned up, and the position of peak heat release rate remains close to 20°EA aTDC. Elevated HSR leads to higher NO emissions but lower NO 2 and N 2 O emissions. As expected, advancing ignition timing (IT) significantly enhances combustion efficiency and reduces emissions. Advancing the IT results in a slight increase in the unburned area at the rear of combustion chamber, coupled with a rapid decrease in the unburned area at the front, collectively reducing unburned fuel. When IT is advanced from −5 to −35°EA aTDC, emissions and performance increase rapidly, whereas when advanced to −45°EA aTDC, both are nearly unchanged and combustion efficiency decreases. • Using ammonia and hydrogen in small-scaled Wankel rotary engines • Flame propagation is highly dependent on ammonia mass fraction. • Optimizing ignition timing can reduce emissions while increasing efficiency. • Increasing the hydrogen mass fraction reduces NO 2 and N 2 O but increases NO. [ABSTRACT FROM AUTHOR]

In this study, a double spark plugs direct injection rotary engine is used to investigate the effects of synchronous and asynchronous changes of ignition timing on combustion and emission performance. The three-dimensional dynamic model was established by CONVERGE software and validated by the experimental data. The results indicate that setting the fuel injector toward the spark plug can reduce the fuel distribution at the tail of the combustion chamber, and the in-cylinder mixture inhomogeneity index gradually increases with the advance of the ignition timing. Compared with the synchronous change of ignition timing, advancing the ignition timing of the tailing spark plug can promote the combustion process. When the ignition timing of the leading spark plug is too early, the flame front will be irregular. With the advance of ignition timing, CA 0–10 corresponding to synchronous and asynchronous change all gradually increase, and the change of CA 10–90 is more stable than that of CA 0–10. Whether the ignition timing is changed synchronously or asynchronously, with the advance of the ignition time, the in-cylinder pressure shows an upward trend. The mean in-cylinder pressure corresponding to the synchronous change with the same change amplitude is slightly higher than that of asynchronous change. The peak pressure of 16.4% higher than that of the original engine can be obtained by adopting the ignition strategy of the synchronous advance of 30° CA. Under this ignition strategy, the temperature and NOx mole fraction in the combustion chamber are all the lowest. • A direct injection rotary engine CFD model was established and validated. • The combined effects of direct injection and ignition strategy were investigated. • The mixture formation, combustion, and emissions process were analyzed. • The in-cylinder inhomogeneity index increases with the advance of ignition timing. • The synchronous advance of ignition time by 30° CA can increase the pressure by 16.40%. [ABSTRACT FROM AUTHOR]

• The centurial development and progress of WRE were fully reviewed. • Fuel, sealing, ignition, cooling, combustion chamber design, etc. are discussed. • The future commercialization and development direction of WRE is summarized. Wankel rotary engine (WRE) featured high power density, compact structure and smooth operation takes advantage of the powertrain assembly and has been highly valued by many countries and regions. However, under the restriction of increasingly strict emission regulations, the development of WRE is gradually depressed, and WRE begins to fade out of the sight of the public and is only active in a few fields. Fortunately, many scholars and institutions are still contributing to the development of WRE. In nearly-one century since the WRE was proposed, a large number of studies on WRE have emerged that need to be organized and comprehensively to provide guidance for the subsequent development of WRE. This work is designed to present a comprehensive review of WRE's centurial progress and development from aspects of fuel selection and supply, sealing and friction, cooling, combustion chamber design, etc. First of all, the characteristics of WRE are introduced and a nearly centurial history of WRE is provided to better understand WRE. Secondly, the progress, development and application of WRE are reviewed. Finally, the key issues of the further commercialization and development of WRE are discussed. [ABSTRACT FROM AUTHOR]

This study aims to explore the combined effect of injection angle and injection pressure in a gasoline direct injection rotary engine through numerical simulation. Simulation results show that with the increase of injection angle, the fuel impinging position changes from the rotor recess to the middle cylinder block. At the same injection angle, the fuel enrichment area turns to the front of the combustion chamber with the increase of injection pressure. The lower injection angle is helpful to obtain a more uniform fuel distribution. Especially, with increase of injection pressure, the in-cylinder inhomogeneity index presents a downward trend. Under different injection pressures, the flame propagation period of the 0° injection angle is the most stable. The stable flame development and propagation processes make it easy to obtain higher indicated thermal efficiency. The highest indicated thermal efficiency is obtained at 0° injection angle and 15 MPa injection pressure, which is up to 24.99%. Moreover, compared with the fuel intake port injection, part of direct injection strategies help to get higher in-cylinder peak pressure. The higher in-cylinder temperature promotes the formation of NOx, but the organization of the in-cylinder fuel distribution can effectively reduce CO and Soot emissions. • A rotary engine simulation model with gasoline direct injection was established and validated. • The combined effects of injection angle and injection pressure were investigated. • The lower injection angle can obtain higher in-cylinder pressure and indicated thermal efficiency. • Lower in-cylinder inhomogeneity index is helpful to reduce Soot and CO emissions. [ABSTRACT FROM AUTHOR]

Hydrogen-fueled Wankel rotary engine (HWRE) as a promising power device overcomes some of the drawbacks of the hydrogen-fueled reciprocating engine. However, its elongated combustion chamber makes it prone to knock, and little research has been done in this area. Hence, to understand the knock characteristics of HWRE, the present work focus on parameters of HWRE knock at 2000r/min, an excess air ratio of 1.2 and an ignition timing of −7°CA ATDC. The main results are as follows: As with knock intensity, knock duration and maximum pressure rising rate also can characterize the knock of HWRE because of the logarithmic or linear relationship among three parameters. For the knock intensity, two parameters are needed to precisely characterize the HWRE knock, while only one parameter is needed for the knock duration and the maximum pressure rising rate. Considering the computing cost, the maximum pressure rising rate is better than others. The knock intensity has a significant influence on the timed sequence of peak knock pressure and peak in-cylinder pressure. Besides, the mechanism of backfire caused by the knock of HWRE is different from that of the hydrogen-fueled reciprocating piston engine, which results from the inter-cylinder flame leakage. • The knock characteristic of hydrogen-fueled Wankel rotary engine is analyzed. • There are mathematical relationships among parameters characterizing knock. • Maximum pressure rise rate is a better metric to characterize WRE knock. • Misfire caused by knock in WRE is different from reciprocating piston engines. [ABSTRACT FROM AUTHOR]

• A thorough 3D CFD model of the H 2 -gasoline Wankel engine is built up and validated. • Burning-source connection of the twin-plug has a negative influence on flame spread. • Combustion is enhanced in the L-side of the rotor chamber by increased spark-energy. • The improvement of ignitability was gained in the H 2 -enriched ignition environment. • Maximum mass fraction of the temperature region is closely related to NO x formation. Due to the elongated shape of the combustion chamber and strong one-way flow characteristic, changing the location of enhanced combustion is an effective means to ameliorate the indicated efficiency of the Wankel engine. For this purpose, strengthening combustion can happen by allocating spark-energy in the desired location along with a favorable ignition environment. In this study, three-dimensional CFD simulations were implemented and the numerical results were compared with existing measured data, in which ignition environment variations were achieved by hydrogen enrichment within the intake manifold of a spark-ignition Wankel engine. Based on CONVERGE code with the SAGE detailed chemistry solver, the twin-plug engine model was then used to assess the location of strengthened combustion employing a spark-energy allocation from the perspective of species evolution, combustion characteristics, and emissions formation. The results indicate that enhancing spark-energy at the leading side of the rotor chamber has an overall higher burned volume rate and faster species evolution due to the later connection of two burning sources prior to quenching. Increasing the hydrogen content in the ignition environment causes richer active radicals and higher turbulence, ultimately promoting flame propagation and combustion intensity. A larger T-plug spark-energy decreases the indicated mean effective pressure, heat release rate, and thermal efficiency because of the intensified wall heat flux and the lower mass burning rate at the leading side. There is no doubt that the introduction of hydrogen enrichment presents a positive effect on both thermal efficiency and specific fuel consumption at the price of a slighter increase of nitrogen oxide formation due to higher mass fraction of high-temperature regions. It is recommended that enhancing local mass burning rate in the leading part of the rotor chamber under the hydrogen-enriched ignition environment can provide a great potential in the quest towards high-efficiency Wankel rotary engine. [ABSTRACT FROM AUTHOR]

• A compound intake rotary engine model was established and validated. • The effects of intake modes on mixture formation and combustion was studied. • H2/gasoline/air in peripheral port and air in side port has best performance. • The mean in-cylinder pressure and temperature of S-HGP was increased. • The CO emission of S-HGP was reduced, but NOx emissions were increased. This work aimed to realize stratified mixtures distribution in a hydrogen-enriched compound-intake gasoline Wankel engine by utilizing the difference of gas velocity from different intake ports. A three-dimension computational fluid dynamics (CFD) WRE model was established to investigate the mixture formation and combustion process under five different intake modes, i.e. the way of the binary fuel enters the combustion chamber through different intake ports (side intake port, peripheral intake port or both port). The intake mode S-HGP (the mixtures of H 2 , gasoline and air are in the peripheral intake port and pure air is in the side intake port) realized an optimal equivalence ratio distribution, in which condition, the most fuels gather near the spark plug and the minority fuel in the rear region of the combustion chamber. Since the unburned mixtures always exist in the rear region of the chamber due to the mainstream in the WRE, the stratified distribution of S-HGP could consume most of the fuel. Because the faster flame propagation release a large amount of heats near top dead center (TDC), S-HGP possesses the highest average in-cylinder pressure under five intake modes, is about 1.264 times than the worst intake mode. Moreover, S-HGP has the maximum average in-cylinder temperature, the ideal thermal condition and moderate lean combustion get the lowest CO emission, comparing with the intake mode performing the highest CO emissions, the CO emission of S-HGP is decreased by 745% near the exhaust valve opening timing (210 °CA ATDC). However, owing to the higher temperature inside cylinder, S-HGP has slightly high NO emission. In conclusion, the results mean that compound intake combined with intake modes control is an effective method for fuel distribution optimization besides the fuel direct injection. [ABSTRACT FROM AUTHOR]