Experimental and simulation study of diesel/methane/hydrogen triple-fuel combustion progression
The global concern about climate change and environmental pollution is largely caused by the massive emissions of greenhouse gases such as carbon dioxide during the combustion of fossil fuels.Carbon peak and carbon neutrality has become important guidelines for China' s energy utilization.There is an urgent need for the development and utilization of new renewable energy sources.With the growing awareness of environmental protection among people,dual fuel engines are one of the effective ways to cut engine emission pollution and promote the development of more environmentally friendly combustion technologies.Dual fuel engine refers to the use of fuels with lower emissions to replace diesel in traditional diesel engines,which reduces pollutants and greenhouse gas emissions.Methane is a clean fuel that produces lower greenhouse gas emissions due to its low C/H ratio.Biomethane produced from renewable energy can replace fossil natural gas while maintaining zero net greenhouse gas emissions.Due to the high C-H bond energy in methane,the combustion rate and the flame propagation rate of natural gas are low.Incomplete combustion occurs during lean combustion,resulting in low thermal efficiency and large combustion cycle variability in actual use of natural gas.Hydrogen has active chemical properties,wide ignition limits,high self-ignition temperature,and is prone to backfire and early combustion.It is commonly used as a blended fuel for natural gas,biomass gas,gasoline,diesel,and other fuels,which greatly increases combustion speed and reduces combustion cycle variations.In this study,we conduct experiments in an optical engine,and the effects of hydrogen ratio on the combustion process of diesel/methane/hydrogen triple fuel combustion with 5％ diesel fuel ratio are studied.The natural photometric images of the combustion process are recorded by a high-speed camera.Combined with the optical experimental results,the combustion process of methane and hydrogen mixture ignited by trace diesel oil is simulated.The development process of cylinder temperature,OH group and combustion components during combustion with different hydrogen ratios is investigated.The main conclusions of our study are:1) The addition of hydrogen increases the reactivity of combustion and the speed of flame propagation,and the maximum combustion pressure increases with the increase of hydrogen proportion.The increase in the proportion of hydrogen causes the peak of the main heat release rate to rise and narrow,gradually transitioning from a bimodal to a unimodal heat release process;2) The increase in hydrogen proportion gradually increases the proportion of Q1 in the first stage and Q2 in the second stage,while the proportion of Q3 in the third stage gradually decreases.The main reason is that the increased activity of premixed gases leads to an earlier release of heat during combustion;3) Our simulation shows the cylinder edge first forms a combustion initial temperature of around 1200 K,and the temperature rises to over 2000 K in a short time.The consistency between high temperature areas and high brightness areas is high;4) The ignition point of the mixed combustion stage begins to form OH groups and gradually strengthens and expands.As the intake pressure increases,the ignition delay period decreases for the same hydrogen ratio.But it does not reduce CA90 and combustion duration.The main reason may be a rise in the total mass of gas in the cylinder,leading to an increase in the overall combustion duration.
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