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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]

• 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]

Recently, ammonia is considered to be an energy medium for hydrogen or energy storage and ammonia/hydrogen can be a potential fuel blend for the spark-ignition engine. Nevertheless, the combustion properties of ammonia/hydrogen mixtures could be distinctive under different initial conditions. In this study, several essential combustion properties, including laminar burning velocity, minimum ignition energy, NOx and ammonia emissions, combustion efficiency, and mixture heating values of ammonia/hydrogen/air premixed combustion were extensively studied under a wide range of equivalence ratios (ϕ), hydrogen fractions (α) and different compression ratio using one-dimensional laminar planar flame and compared with stoichiometric methane, methanol, and ethanol combustion. The behavior of NOx generation changing with ϕ and α was analyzed in detail. Results showed that most properties of ammonia/hydrogen combustion could be comparable to that of hydrocarbon fuels under engine-relevant conditions, except for the mixture heating value is slightly lower in all conditions. Besides, the NO mole fraction non-monotonically changes with ϕ and α due to the competition between the effects caused by the reduction of nitrogen-atom species and the enrichment of H/O radicals. The NO mole fraction of stoichiometric ammonia/hydrogen could be even lower than that of hydrocarbons. Considering the properties of hydrocarbon fuels as a reference, promising working conditions for ammonia/hydrogen mixtures are ϕ from 1.0 to 1.05 and α from 40% to 60%. Besides, a high compression ratio is more suitable for ammonia/hydrogen mixtures due to the excellent knock resistance ability of NH 3 /H 2 and better improvement than hydrocarbon fuels under high compression ratio. • Combustion properties of premixed NH 3 /H 2 /air were assessed under engine conditions. • One dimensional steady flame was simulated under different initial conditions. • NOx generation of NH 3 /H 2 /air combustion is analyzed in detail. • Most combustion properties, including NOx are comparable to light hydrocarbon fuels. • Potential working conditions are suggested based on the analysis. [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]

Highlights • A CFD model of gasoline/H 2 fueled Wankel engine was established and verified. • The ignition mode consisted of synchronous ignition and asynchronous ignition. • H 2 was direct injected in the combustion chamber under varying twin-spark timing. • The optimal combustion was achieved when the TSP ignited asynchronously. • There was no increase in NO x generation with the enhanced combustion rate. Abstract A Wankel engine with hydrogen direct-injection enrichment is recognized as an attractive method to enhance combustion efficiency. In this paper, on the basis of the chemical kinetic mechanisms, a three-dimensional simulation model was established and validated by the measured results. The ignition and combustion processes in a gasoline Wankel engine with hydrogen direct-injection enrichment were implemented for numerical simulation. The influence of twin-spark timing was firstly analyzed by synchronous ignition. Further investigation was then conducted to simulate how to effect the combustion by asynchronous ignition based on the favorable synchronous ignition timing. Results showed that, the average flow velocities were 18.8, 20.7, 23.6, and 25.4 m/s for the spark timings (ST) of 45, 35, 25, and 15°CA BTDC respectively. With retarded ST, the rich equivalence ratio approached to twin-spark plug continually. For synchronous ignition, at a larger advance of ST, the duration between the timing of the vortex dissipation and ST was longer, and the ignition delay was more prolonged. As the ST advanced, the combustion rate was enhanced with the increment in chamber temperature, the reactants (C 8 H 18 , C 7 H 16 , and H 2) consumption and intermediates (H 2 O 2 , OH, and CH 2 O) generation were accelerated, the maximum H 2 O 2 and CH 2 O decreased whereas the maximum OH increased, and nitrogen oxides (NO x) and carbon monoxide (CO) increased sequentially. For asynchronous ignition, the accelerated flame front was in accordance with the rotating direction of the rotor while the opposite direction was inhibited during the combustion process. An earlier ignition of leading-spark plug (L-plug) or trailing-spark plug (T-plug) provided the higher flame speed and faster H 2 consumption, which contributed to the higher in-cylinder pressure, combustion temperature, and NO x and CO production. The preferable ignition and combustion characteristics was realized when the L-plug angle was 25°CA BTDC, and the T-plug angle was 35°CA BTDC. Compared with the favorable synchronous ignition timing, the flame propagation and H 2 consumption were expedited, the peak pressure increased by 2.8%, the corresponding crank position advanced by 3°CA and there was no increase in NO x and CO generation. Therefore, it was recommended in engineering applications that the ST of T-plug advanced appropriately while the ST of L-plug remained constant. [ABSTRACT FROM AUTHOR]

• The effect of intake valve timing on hydrogen-rich ammonia engines was studied. • Delaying the valve timing to increase the power of hydrogen-rich ammonia engines. • Advanced valve timing to improve BTE of hydrogen-rich ammonia engine. • Increasing valve overlap increases the cycle variation of hydrogen-rich ammonia engines. To reduce carbon emissions and increase the efficiency of internal combustion engines (ICEs), it is necessary to use renewable alternative fuels and to use Miller cycle technology. Ammonia is an energy storage medium as well as a hydrogen storage medium. In this experiment, a Miller cycle ICE using ammonia-hydrogen fuel was investigated at 1500 rpm and 60% throttle opening. The excess air factor of 1 and the ammonia volume share of 70% were maintained during the experiment. The objective of the experiment was to vary the intake valve timing and investigate its effect on engine performance. The results show that when the intake valve timing is advanced and the valve overlap angle is kept larger, the combustion stability deteriorates, the flame development period (CA0-10) is prolonged, the cycle variation increases, COV pmax will exceed 25%, and the brake thermal efficiency (BTE) quickly dropped from 32.8% to 30%. When the intake valve timing is retarded by 25°CA, IMEP and BMEP can be increased by 8% and 16% compared with the minimum values. Generally speaking, the Miller cycle hydrogen-enriched ammonia engine is not suitable for the early opening strategy of the intake valve. [ABSTRACT FROM AUTHOR]

• A rotary engine simulation model with gasoline port and direct injection was established and validated. • The combined effects of ignition position and injection method were investigated. • Higher in-cylinder pressure can be obtained by direct injection under the same ignition strategy. • Using double spark plugs ignition and port injection can reduce carbon-based emissions. This research aims to numerically investigate the combined effect of ignition position and injection method on the gasoline rotary engine. The three-dimensional dynamic model was established by CONVERGE software and validated by the experimental data. The results indicate that compared with port injection, the direct injection leads to obvious fuel stratification in the combustion chamber, and the local equivalence ratios around the two spark plugs are different. The index of in-cylinder fuel inhomogeneity corresponding to direct injection decreases linearly with the progress of the mixing process. Adopting the double spark plug can obtain a higher release heat rate and combustion efficiency than adopting the single spark plug ignition. Higher in-cylinder peak pressure and indicated thermal efficiency also can be obtained by using double spark plugs ignition. Only using leading spark plug ignition would cause a large in-cylinder unburned area, resulting in poor power performance of the rotary engine. In particular, the direct injection can obtain higher mean in-cylinder pressure than the port injection, but the indicated thermal efficiency of port injection is higher than that of direct injection. In the aspect of emissions, double spark plugs ignition would lead to higher in-cylinder temperature and NOx content than other ignition modes, but double spark plugs ignition can alleviate incomplete combustion and reduce HC emission. Under the same ignition strategy, the port injection can effectively reduce CO emission than direct injection. [ABSTRACT FROM AUTHOR]

• Implementation of oxygen enriched air on rotary engine combustion was performed. • Thorough 3D CFD models of rotary engines was built and verified by experiment data. • Increasing oxygen content stimulated the growth of initial flame and burned volume. • Oxygen enrichment markedly reduced the formations of CO, HC, and soot emissions. • The optimum combustion behavior can be achieved by α O2 = 30% and λ = 1.1 operation. The attractiveness of oxygen-enriched combustion advantages are making a comeback in the implementation of the rotary engine concept. In this connection, a numerical investigation on influences of intake oxygen enrichment combined with excess air ratio on combustion behavior of the rotary engine needs to be clarified. A three-dimensional computational fluid dynamics simulations coupling with chemical kinetic mechanisms was performed in this study, and the numerical results had been validated with existing experimental data. The species evolution, combustion characteristics, and pollutant formation were monitored to assess the oxygen-enriched combustion of the rotary engine. Results showed that there was a significant influence of intake oxygen enrichment for improving flame development and burned volume due to the reasonable species concentration and intense turbulence intensity. Increasing oxygen enrichment led to the enhanced peak pressure and advanced corresponding position, resulted in a rapid combustion period for improving heat-release efficiency and combustion efficiency, meanwhile made a higher indicated mean effective pressure at the price of a smaller increment of nitrogen oxide formation. The substantial reductions of carbon monoxide, unburned hydrocarbon, and soot were recorded, which is attributed to the higher-oxygen mixture with suitable lean operations. Considering combustion characteristics and emissions performance, the operation of intake oxygen volume of 30% accompanying the excess air ratio of 1.1 is the best choice for the engine used in the current study. [ABSTRACT FROM AUTHOR]

• A simulation model of the hydrogen-enriched Wankel engine was built and validated. • Single-spark ignition strategies consist of split ignition, high-energy ignition. • Twin-spark ignition strategies cover asynchronous ignition and energy allocation. • The preferable arrangement of the twin spark plug was T/L = 1.5. • Optimal combustion was gained as the leading plug was ignited earlier and stronger. For the hydrogen-enriched spark-ignited Wankel engine, the optimization of ignition strategy is conducive to improve combustion performance and specifically effective to lessen the unburned region due to the elongated rotor chamber. In this paper, the role of the number of the ignition source, twin-spark plug location, asynchronous ignition, and energy allocation in improving lean combustion was investigated through the three-dimensional computational fluid dynamics model coupling with kinetic mechanisms. The model was validated by experiment, and good agreements between measured and predicted combustion pressure and the heat release rate was obtained. Results showed that the improvements of engine combustion were limited by single-spark ignition strategies, and the twin-spark ignition configuration was capable of enhancing combustion efficiency drastically. The arrangement of the twin-spark plug determined the space for flame development, and it was favorable for the trailing plug to stand a greater offset from the minor axis of the engine. An earlier leading-spark ignition enabled flame propagation faster and occurred quenching rapidly, which contributed to higher pressure-output and better heat-release. The higher energy of leading-spark ignition made the mixture consumption faster, combustion pressure higher, and combustion duration shorter. The optimum strategy on combustion was expressed as follows: the location of trailing-spark plug is offset from the minor axis by 20.7 mm; the spark timing and discharge energy of leading-spark plug is 325°EA and 0.03 J, respectively; and those of trailing-spark plug is 335°EA and 0.01 J. It was recommended that the leading-spark ignition was set earlier and stronger for practical operations. [ABSTRACT FROM AUTHOR]