Search

Wankel rotary engine (WRE) is welcomed due to its high power density and compact layout and is criticized due to its low efficiency and poor emission. To develop low-carbon emission and high-efficiency WRE, the present work discusses the potential of hydrogen/methane dual-fueled WRE with varied fuel components. The test was conducted at 1500 r/min, 80 kPa manifold absolute pressure and stoichiometric ratio. The results indicate that compared with pure hydrogen or pure methane WRE, hydrogen/methane dual-fueled WRE can achieve higher thermal efficiency and output power, the maximum values of which are 30.7% and 12.4 kW under test conditions, respectively. Besides, it also has satisfactory NO, CO2 and HC emissions. In particular, there is a linear relationship between NO emission and methane volumetric percentage with a 0.9949 determination coefficient in logarithmic coordinates, which means that the NO emission can be easily predicted. In addition, the cyclic variation is acceptable at maximum-efficiency CH4% and the knock can be almost eliminated in hydrogen-methane dual-fueled WRE when the volume ratio of methane exceeds about 40%. In general, WRE is recommended to be fueled by a mixture of hydrogen and methane with a high methane volumetric percentage. • Discussion on the potential of hydrogen/methane dual-fueled Wankel rotary engines. • Dual fuel is better than single fuel in terms of power, efficiency, emission, etc. • There is a linear relationship between NO and CH4% in logarithmic coordinates. • Knock can be almost eliminated when the CH4% exceeds about 40%. [ABSTRACT FROM AUTHOR]

Abstract The influences of wall are important in practical combustion devices. In present study, the propagating processes of near wall ignited laminar methane/hydrogen/air flame were explored under different hydrogen fractions in a constant volume combustion vessel mimicking engine geometry. Results showed that both effects of heat losses and wall compression cause difference of local flame speed at different directions. The flow inside burned zone induced by compression accelerates local flame speed at direction opposing to the wall, makes the local flame speed higher than freely propagating laminar flame speed. Meanwhile, flame shape changing process was quantified by fitted ellipses. It was found that flame shapes are strongly affected by the wall compression but not obviously influenced by hydrogen addition. Hydrogen addition exacerbated flame instabilities, notably improved the local and global flame speeds due to both increase of laminar flame speed and flow velocity inside burned zone. The maximum local speed increase from 258 cm/s for 20% hydrogen fraction to 695 cm/s for 80% hydrogen fraction. Maximum combustion pressure and maximum pressure rise rate were slightly increased by hydrogen addition. On contrary, the combustion duration notably decreased nearly 3 times when hydrogen fraction increased from 20% to 80%. Highlights • Near wall ignited lean CH 4 /H 2 /air flame were studied in a constant volume chamber. • Compression induced flow inside burned zone played a role for near wall flame. • Hydrogen addition enhances the flame propagation and compression induced flow. • Effects of heat transfer are more obvious for later combustion stage. [ABSTRACT FROM AUTHOR]

To achieve more efficient and robust combustion, split direct-injected hydrogen as a new injection strategy for rotary engines was used to clarify the influences of various injection parameters, including hydrogen amount for each pulse, the dwell between pulses, and secondary injection pulse-width, on combustion performance and emissions formation by CFD modeling. The results of this investigation confirmed the benefit of split direct-injection as a useful means to govern mixture stratification which enabled the combustion more effective and rapid compared to single-injection mode. Enhanced combustion could be achieved by increasing the mass fraction of post-injection with an optimized dwell between injections. Further investigation on secondary injection pulse-width demonstrated that engine performance was substantially improved with a wider second injection pulse. From one side, as the secondary injection pulse-width was increased, the surrounding mixture distribution of the spark-plug location was richer, which was confirmed as a beneficial inhomogeneous circumstance of hydrogen to accelerate the burning rate. From another side, strong tumble level and turbulence intensity were of significant importance for facilitating the combustion process and getting optimal thermal efficiency. For emissions formation, split direct-injected hydrogen made a near-zero HC and CO emissions at the price of a comparable increase of NOx emissions. • Hydrogen split direct-injection is implemented on a gasoline SI Wankel engine. • Analyzing three factors for amelioration including first, post-injection, and dwell. • Split injection strategies can realize desirable stratified conditions of hydrogen. • Injecting proper hydrogen in each pulse with an adequate dwell is of importance. • Thermal efficiency can be notably improved benefits from the wide second injection. [ABSTRACT FROM AUTHOR]