Simulation Of Combustion And Emission Performance Of Natural Gas/Hydrogen Dual Fuel Engine

Due to the increasingly prominent problems of oil shortage and environmental pollution,it is necessary to develop new alternative energy sources to meet the increasingly stringent ship emission regulations and achieve the"dual carbon"strategic goal.Natural gas has attracted extensive attention due to its abundant reserves,cleanliness and environmental protection.However,when it is used as an engine fuel,it has problems of poor fuel economy and high emissions.Combined with the properties of hydrogen,mixing hydrogen into natural gas can effectively improve engine performance.At present,there are few studies on the performance optimization of marine natural gas/hydrogen dual-fuel engines,and commercial one-dimensional simulation software does not have a combustion model suitable for natural gas/hydrogen dual-fuel engines.Based on this,a natural gas/hydrogen dual-fuel combustion prediction model is developed based on Fortran code in this paper,and it is fitted with GT-Power software,and then a dual-fuel engine model is established to explore the optimal hydrogen mixing ratio of marine engines under different propulsion characteristics.and operating parameters to provide guidance for the overall performance optimization of marine natural gas/hydrogen dual-fuel engines.Firstly,the effects of ignition timing,excess air coefficient and hydrogen admixture ratio on ship engine performance were studied under the ship of E3 cycle propulsion condition.The development period and the rapid combustion period decreased,the optimum ignition advance angle decreased,the combustion thermal efficiency increased,the lean burn boundary expanded significantly,and the improvement effect weakened with the increase of the hydrogen doping ratio.The addition of hydrogen has an obvious improvement effect on low load conditions,but the effect gradually decreases with the increase of load.The emission of NO_X increases linearly with the increase of the hydrogen mixing ratio,but by retarding the ignition timing and adopting the lean burn technology,the NO_X emission of the marine engine can be significantly reduced.Then,the coupling effect of compression ratio and controllable parameters on the performance of natural gas-hydrogen engine was explored.The study found that with the increase of the compression ratio,the pressure,temperature and heat release rate in the engine cylinder will increase,the optimal ignition timing will be reduced,and the lean burn limit will be expanded.Increasing the compression ratio can effectively improve the thermal efficiency of the lean-burn engine under different hydrogen admixture ratios,but with the increase of the compression ratio,the improvement effect will be weakened.At the same time,increasing the compression ratio too high will increase the NO_X emission,but choosing the appropriate ignition timing and excess air ratio can significantly reduce its effect.Considering the improvement effect and safety,when the compression ratio is 12,it is more reasonable for the ship’s natural gas hydrogen blending engine.To sum up:select 30%-50%hydrogen mixing ratio under low load,choose 20%-30%hydrogen mixing ratio under medium and high load,use larger air-fuel ratio than natural gas engine,delay ignition timing,and choose reasonable It can effectively improve the problems of poor fuel economy and high emissions of marine natural gas engines.The results of this paper are of great significance for further improving the efficiency of marine natural gas engines,reducing emissions and realizing green shipping.