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Abstract The comparative study on performance of the hydrogen/gasoline and hydrogen/n-butanol rotary engines was conducted in the present paper. Considering the stable operation of the engine, for both hydrogen/gasoline case and hydrogen/n-butanol case, the operating conditions were set at: 4000 rpm (engine speed), 35 kPa (intake pressure) and 30 °CA BTDC (spark timing). The total excess air ratio of mixture was maintained at 1.0 through all the tests. The testing results displayed that hydrogen enrichment improved performance of both gasoline and n-butanol rotary engines. To be more specific, brake thermal efficiency was increased, flame development and propagation periods were shortened, the coefficient of variation in flame propagation period was decreased, and the emissions of HC and CO were decreased. NOx emissions were mildly increased after hydrogen addition. Besides, hydrogen/n-butanol rotary engine possessed the similar performance to hydrogen/gasoline rotary engine. Highlights • Performance of HGRE and HBRE was studied. • BTE and Tmax was increased after H 2 blending. • CA0-10, CA10-90 and engine instability were shortened by H 2 addition. • H 2 addition resulted in the reduced HC and CO emissions. • HBRE shares highly similar performance with HGRE. [ABSTRACT FROM AUTHOR]

Highlights • A CFD model of H 2 -gasoline fueled rotary engine was established and validated. • H 2 was direct injected in the combustion chamber under different strategies. • In-cylinder pressure increased with retarded HIT and extended HID. • The lowest CO emission was achieved in HIT of 110 °CA BTDC, HID of 40 °CA. • Higher NO x emissions were acquired in retarded HIT and extended HID. Abstract In Wankel rotary engine (WRE), high mainstream velocity in combustion chamber blocks flame propagating to the end of combustion chamber, which causes high emissions and low combustion efficiency due to unburned mixtures. To solve this problem, a three-dimensional dynamic simulation model of a hydrogen-gasoline blends fueled WRE is built and validated. The in-cylinder mixture formation and combustion process are investigated under different hydrogen injection timing (HIT) and duration (HID) conditions. The study results show that the concentration of hydrogen distributed between the spark plug region and rear combustion chamber increases with retarded HIT and extended HID. Faster flame speeds are obtained for HIT of 110 °CA BTDC and HID of 40 °CA. At a fixed HID of 20 °CA, compared with HITs of 210 and 160 °CA BTDC, the peak in-cylinder pressures for HIT of 110 °CA BTDC are increased by 14.3% and 6.8%, respectively. At a fixed HIT of 110 °CA BTDC, the peak in-cylinder pressure in HID of 40 °CA is 52.3% and 9.21% higher than HIDs of 20 and 30 °CA. The highest in-cylinder pressure is achieved with the hydrogen injection strategy that HIT of 110 °CA BTDC, HID of 40 °CA. However, as the temperature increases with pressure, nitrogen oxide emissions are also increased with retarded HIT and extended HID obviously. Considering the lowest carbon monoxide is achieved and the unburned zone in the rear region of combustion chamber is eliminated in HIT of 110 °CA BTDC, HID of 40 °CA. The hydrogen direct injection strategy that HIT of 110 °CA BTDC, HID of 40 °CA acquires the best engine performance in this research. [ABSTRACT FROM AUTHOR]

A CFD model of hydrogen-enriched gasoline Wankel rotary engine is established and validated. The mixture formation and combustion processes are investigated under both hydrogen port and direct injection enrichment conditions with different hydrogen addition levels. It was found that, under hydrogen port injection enrichment conditions, the peak in-cylinder pressure of 6% is 8.4% higher that of 3%. Meanwhile, under hydrogen direct injection enrichment conditions, the peak in-cylinder pressure of 3% hydrogen direct injection enrichment is 15.3% higher than that of 3% hydrogen port injection enrichment. It was also found that the mainstream field with same direction of rotor rotation is formed during the compression stroke and a vortex with high vorticity existed in the combustion chamber. With the effects of mainstream field and vortex, the hydrogen fills more than half volume of the entire combustion chamber under 4%, 5% and 6% HDIE conditions. At the same time, a local low velocity zone is formed around the vortex because the hydrogen direct injection flow slows down the dissipation of vortex. According to the analysis by PREMIX, the fastest flame speed is achieved at equivalence ratios around 1.4. The proper rich hydrogen region distribution is obtained under 4%, 5% and 6% hydrogen direct injection enrichment conditions. Both the enhanced flame propagation by proper equivalence ratio distribution and the reduced local mainstream flow velocity by vortex existence contribute to solving the unburned zone problem. Compared with 6% hydrogen port injection enrichment, the maximum value of in-cylinder pressure of 4%, 5% and 6% hydrogen direct injection enrichment is improved by 59.6%, 88.4% and 91.6%, respectively. However, carbon monoxide and nitrogen oxide emissions are increased obviously. As a relatively low carbon monoxide emission is obtained with 4% case under hydrogen direct injection enrichment conditions and the problem of unburned zone in the rear region of combustion chamber is solved. The hydrogen volume fraction of 4% with direct injection enrichment achieves the best engine performance in this study. [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]

• 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]