| As a special type of internal combustion engine,Wankel rotary engine possesses many advantages,such as:small size,light weight,high speed and high power to weight ratio.Therefore,Wankel rotary engine has a good prospect in some specific fields.However,due to the flattened combustion chamber structure and the high surface to volume ratio,Wankel rotary engine always suffers poor fuel economy and high emissions.In comparison,hydrogen possessed many desirable physicochemical properties,hydrogen enrichment improves the combustion and emissions performace of gasoline Wankel rotary engine,effectively.Therefore,based on CFD model,the in-cylinder flow field characteristics of Wankel rotary engine were revealed,as well as,the effects of hydrogen port and direct injection enrichment on the in-cylinder mixture formation,flame propagaton and emissions formation and distribution.Meanwhile,the hydrogen nozzle position and direct injection strategies in gasoline Wankel rotary engine with hydrogen direct injection enrichment were optimized.Further more,the performance of gasoline Wankel rotary engine with compound-ported intake was numerical investigated.Using the computational fluid dynamics code CONVERGE,a CFD model of gasoline Wankel rotary engine with hydrogen port injection enrichment was established based on the RNG k-?turbulence model and the SAGE combustion model coupling PRF chemical kinetic mechanism.The experimental bench of hydroge-enriched gasoline Wankel rotary engine was built,the accuracy of CFD model was validated by comparing the results between calculation and experiments.The experiment results indicated that the flame development and propagation periods were shortened after hydrogen enrichment.Meanwhile,the increased flame speed promoted the constant volume heat release process,which decreased the coefficient of variation in flame propagation period and improved the brake thermal efficiency of hydrogen blended gasoline.Moreover,hydrogen enrichment effectively reduced HC,CO and CO2emissions of Wankel rotary engine.Based on CFD numerical simulation,the in-cylinder flow field properties,flame propagation process and emissions production of the hydrogen-enriched gasoline Wankel rotary engine were investigated.The numerical research results illustrated that a mainstream flow field along with the rotor movement was formed at the end of compression stroke.The mean in-cylinder mainstream flow velocity increases with hydrogen enrichment volume fraction.A tumble was also existed in the mainstream flow field.Due to the effect of the mainstream flow,the flame propagation in contrary direction of the mainstream flow was retarded.Consequently,the unburned mixtures exited in the narrow rear region,which were not burnt completely before the exhaust valve opening timing.After the hydrogen addition,the increased concentrations of H O,and OH radicals accelerated the combustion process,and the combustion and emissions performance of the rotary engine were improved.By hydrogen direct injection,fuel stratified strategy was utilized to solve the problem of unburned zone in the rear region of combustion chamber in gasoline Wankel rotary engine with hydrogen port injection enrichment.The mixtures formation and combustion processes were investigated under hydrogen direct injection enrichment conditions with different hydrogen addition levels.It was found that,much more hydrogen distributed in both spark plug and rear regions of combustion chamber.When the hydrogen volume fraction was higher than 3%,the flame propagated to the rear region of chamber and burned the entire fuels out.Therefore,a better combustion performance was obtained in hydrogen direct injection enrichment conditions.Compared with 6%hydrogen port injection enrichment,the peak pressure for 4%,5%and 6%hydrogen direct injection enrichment increased by 59.6%,88.4%and 90.6%,respectively.However,when the hydrogen volume fraction is higher than 4%,the excessive increase of in-cylinder pressure increased the negative work.Meanwhile,since the very rich fuel-air mixtures cannot be burned completely in these conditions,incomplete combustion products existing in the burned zone increased the emissions.Therefore,considering the tradeoff between engine output and emission performance of Wankel rotary engine,an optimal?H2 existed in hydrogen direct injection enrichment conditions.To control the distribution and concentration of direct injected hydrogen,the effects of hydrogen nozzle positions and direct injection strategies on Wankel rotary engine performance are numerical investigated.It was found that,the position of the hydrogen nozzle was offset from the major axis by 50 mm and the injection angle was in the normal direction of the cylinder wall.Hydrogen can be injected directly into the tumble and diffused rapidly to around,which increased the homogeneity of hydrogen distribution and eliminated the region of excessive concentration.At the same time,hydrogen injection timing of 110°CA BTDC,hydrogen injection duration of 40°CA can acquire the best combustion and emissions performances under current condition.Finally,in order to further improve the performance of gasoline Wankel rotary with hydrogen direct injection enrichment,this study numerical investigated the effect of compound intake,which combines the peripheral-ported intake and side-ported intake,on the mixture formation and combustion process under the optimized hydrogen nozzle position and direct injection strategy condition.The results showed that the peripheral-ported intake flow played a leading role in the compound-ported intake process,which shortened the formation time of mainstream flow field,increased the mean flow speed and accelerated the flame propagation to the front region of the combustion chamber.Meanwhile,the compound intake possesses large port area.Applying it in Wankel rotary engine increased volumetric efficiency from 0.886 in side-ported condition to0.955 in compound-ported condition.The in-cylinder pressure and temperature increased significantly.Furthermore,the improved in-cylinder thermal atmosphere promoted complete combustion of the fuel-air mixtures.Therefore,a higher indicated thermal efficiency and better emissions performance were obtained in compound-ported Wankel rotary engine.Hydrogen enrichment improves the combustion and emissions performances of gasoline Wankel rotary engine,effectively.However,the problem of unburned mixtures exited in the narrow rear region is not solved with hydrogen port injection enrichment.Due to the proper rich hydrogen distributes in both spark plug and rear regions of combustion chamber in hydrogen direct injection enrichment condition,the unburned zone in the rear region of combustion chamber is elimated.Meanwhile,applying the optimized hydrogen nozzle positions and direct injection strategies also eliminates the incomplete combustion products in the burned zone,which improves the combustion and emissions performance of gasoline Wankel rotary with hydrogen direct injection enrichment.In addition,compound intake could further improve the engine performance. |
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