Experimental Investigation On The Combustion And Emissions Characteristics Of A Rotary Engine With Hydrogen Addition

As a special type of internal combustion engine,rotary engine is applied in many special fields because of its advantages of small volume,small weight,high power to weight ratio and good operating stability.As the combustion chamber is narrow and long,the rotary engine generally suffers the difficulties in evaporation,flame propagation and quenching effect when fueled with liquid fuels,such as gasoline and n-butanol.These lead to low thermal efficiency,high fuel consumption and high pollutant emissions.Improving combustion by changing fuel property to reduce the fuel consumption and toxic emissions is a feasible method to extend the practical application of rotary engine.Comparatively,because hydrogen possesses characteristics of low ignition energy,small quenching distance,high flame propagation speed,wide flammability limit and high adiabatic flame temperature,adding small amount of hydrogen into the intake can improve the combustion and emissions of the original rotary engine.This paper investigated the effect of hydrogen addition on combustion and emissions characteristics of gasoline and n-butanol rotary engines,and pure hydrogen rotary engine.Because many basic parameters of the rotary engine are different from those of the traditional internal combustion engine,this study firstly introduced the generating methods of the cylinder block and rotor profile of the rotary engine.Besides,the calculations of some basic parameters of the rotary engine were presented.Then,with the help of thermodynamics,heat transfer and internal combustion engine fundamentals,the special thermodynamics and heat transfer process of the rotary engine were theoretically investigated.In addition,the calculation procedures suitable for analyzing the combustion and heat release of the rotary engine were proposed.Then the combustion and emission characteristics of hydrogen-blended rotary engine were studied on the experimental bench.The effects of hydrogen volume fractions,excess air ratio and spark timing on the combustion and emission characteristics of hydrogen blended gasoline and n-butanol rotary engines were studied under idle and partial load conditions.Besides,idle performance of the pure hydrogen rotary engine at various excess ratios was studied.The idle test results of the hydrogen-blended gasoline rotary engine displayed that the combustion and emission were improved under idle and various excess air ratios,and at reduced idle speed and stoichiometric excess air ratio.Adding hydrogen reduced the cyclic variation coefficient and fuel energy flow rate of hydrogen-blended gasoline rotary,shortened flame development period and flame propagation period.Meanwhile,the relatively high HC and CO emissions at idle were significantly reduced by hydrogen addition,especially at lean combustion and reduced idle speed conditions.The results of partial load test of the hydrogen-blended gasoline rotary engine indicated that hydrogen enrichment improved brake thermal efficiency and cylinder pressure,reduced flame development period and flame propagation period,lowered cyclic variation coefficient,dropped heat losses and exhaust loss,as well as HC and CO emissions.NOx emissions of partial load conditions were decreased by lean combustion strategy.N-butanol has the similar combustion and physicochemical characteristics to gasoline.Therefore,the combustion and emission characteristics of the hydrogen-enriched n-butanol rotary engine at idle and under partial load conditions were studied in this paper.Similar to the gasoline rotary engine,the n-butanol rotary engine also discharged high HC and CO emissions at idle and partial load conditions.It was found that adding hydrogen into the intake effectively reduced HC and CO emissions of the n-butanol rotary engine at idle and partial load operations.At partial load conditions,with hydrogen volume fraction increasing from 0 to 6.3%,brake thermal efficiency increased from 15.7%to 19.7%,flame development shortened from 51.1^oCA to30.8^oCA,reducing by 39.7%,flame propagation period decreased from 73.4 ^oCA to61.7 ^oCA,dropping by 15.9%,peak chamber temperature increased from 1064K to1102K,increasing by 38K,the cyclic variation coefficient of flame propagation period decreased from 6.03%to 0.81%,and HC emissions reduced from 6675ppm to 3034ppm,reducing by 54.5%,CO emission dropped from 3914ppm to 1910ppm,reducing by51.2%.In addition,the effects of excess air ratio and spark timing on combustion and emission characteristics of the hydrogen-enriched n-butanol rotary engine were conducted.It was found that adding hydrogen improved brake thermal efficiency and work capacity of the n-butanol rotary engine under different excess air ratios and spark timings,especially under lean condition.Beyond that,hydrogen addition also effectively reduced the cyclic variation coefficient,HC and CO emissions of the n-butanol rotary engine at different excess air ratios and spark timings.NOx emissions of the hydrogen-blended n-butanol rotary engine was effectively reduced by using lean combustion and spark delay strategy.Hydrogen is very suitable to combust in the rotary engine.Lean combustion performance of the pure hydrogen rotary engine at idle was experimentally carried out in this study.It was found that,different from the gasoline and n-butanol rotary engines,when the increase of excess air ratio,the cyclic variation coefficient of idle speed,cylinder pressure,peak cylinder temperature,flame development period and flame propagation period changed slightly,indicating that the lean combustion limit of the pure hydrogen rotary engine was relatively wide.Due to the evaporation of lubricating oil,the pure hydrogen rotary engine also produced HC and CO₂ emissions,and NOx emissions were reduced at lean combustion condition.In this study,it was found that hydrogen addition improved the combustion of the gasoline rotary and n-butanol rotary engines.Besides,emissions of the gasoline rotary and n-butanol rotary engines were reduced.Combustion of the pure hydrogen rotary the changed slightly,indicating that the pure hydrogen rotary can operate at high excess air ratio.