| Duo to the rapid increase in energy consumption and increasingly stringent emission regulation,it has become imperative to develop clean energy.Because of its advantages of high energy density,wide range of sources and non-pollution,hydrogen energy has been widely concerned in the clean energy field.However,compared with other convertional fuels,hydrogen also has many disadvantages that are not conducive to storage and transportation,such as the high liquefaction cost,low ignition energy,and high diffusitivity.Moreover,the spontaneous ignition that may be caused by the pressurized hydrogen release poses a great threat to the hydrogen storage safety and severely restricts the hydrogen economy development.Therefore,understanding the characteristics of spontaneous combustion and seeking low-cost technical means to reduce the risk of spontaneous combustion are urgent needs of the hydrogen energy industry.At the same time,hydrogen blending is regarded as an important approach to adjust the combustion porperties of convertional fuels,but the spontaneous ignition risk of the pressurized hydrogen-rich gases is still unrevealed.Based on the above considerations,numerical and experimental methods are used to study the reaction flow characteristics and suppression methods of the spontaneous combustion of pressurized hydrogen and hydrogen-rich gas.First,in the spontaneous ignition process of the pressurized fuels releases,the complicated coupling among high-intensity shock waves,multi-component chemical reactions,and delicate heat and mass transport results in the great challenges to the numerical modelling.To ensure the accurate capture of the strong shock waves and the transport-reaction interactions,a 2D transient compressible reacting flow solve,SURMS,is developed with the WENO（weighted essentially non-oscillatory）algorithm,ERENA（extended robustness-enhanced numerical algorithm）chemical reaction acceleration method,the SSPRK3（third order strong stability preserving Runge-Kutta method）Runge-Kutta method,adaptive mesh refinement technology and immersed boundary method.The numerical results of the detonation wave formation,laminar flame propagation and Schardin problem prove the SURMS solver’s ability to chapture the reacting-flow characteristics involved with shock waves.Then,based on SURMS,the spontaneous ignition processes of the pressurized hydrogen releases in the restricted and open spaces are simulated.Combined with the experimental data,the shock waves evolution,mixing layer propogation,flames structures,heat release distribution and key reaction pathways are analyzed.The research on the spontaneous ignition in the restricted spaces shows:the intensity of shock wave produced by high-pressure hydrogen release plays a decisive role in the occurrence of spontaneous ignition,but the shocks reflection and wall boundary layer effects are not a necessary condition;at the same time,the release spontaneous ignition onset is always located in the high-temperature and high-pressure,fuel-lean region which near the air side,and different types of falmes are formed in the mxing layer;the competition between H+O2<=>O+OH chain branching reaction and H+O2（+M）<=>HO2（+M）chain termination reaction is the key to determining the flame structures and ignition delay times.The studied results of the spontaneous ignition in the open spaces shows:duo to the release of pressurized hydrogen,the normal and diffraction shock waves are formed;the large-scale vortex generated by the jet shear layer instability significantly increases the local hydrogen/air mixing rate,but the mixture temperature behind the diffraction shock wave is too low to cause the spontaneous ignition near the vortex;the spontaneous ignition begins at the center of the supersonic hydrogen jet and develops along the contact toward the two sides of the jet;H+O2+M<=>HO2+M,H2+OH<=>H+H2O,H2+O<=>H+OH,H+O2<=>O+OH and H2+O2<=>H+HO2 are the key elementary reactions that affect the ignition delay time.Moreover,aimed to reveal the characteristics of high-pressure hydrogen-rich gases release spontaneous ignition,the equivalent experiment approach is proposed utilizing the theoretical solution of the Riemann problem.A large number of experiments and simulations about pressurized hydrogen and hydrogen-rich gases show:fuel composition and shock wave Mach number are the determinants of spontaneous ignition;other low-activity gas changes H radicals reation pathways significantly.Finally,in order to develop effective means to suppress the spontaneous combustion of pressurized fuel,the release of pressurized CH4/H2 mixture and acritical fuels are simulated with SURMS.From the perspectives of shocked air temperature,blended fuel chemical activity and transport-reaction interactions,the inhibition mechanism of low-activity gases addition on the spontaneous ignition are demonstrated.The numerical results show:ever the low dilution of CH4（3%vol.）can significantly increase the spontaneous ignition delay time（6 to 7 times）;the low-activity gas addition greatly reduces the intensity of the shock wave after the release and decreases the accumulation rate of radicals at the flame front;the key of addition to inhibit the spontaneous ignition is that it improves the molar mass of the fuel and increases the loss of free radicals.From the above research,it can be seen that the high-resolution CFD simulation program SURMS developed in this thesis provides a powerful numerical analysis tool for studying the characteristics of pressurized fuel release spontaneous ignition and exploring the means for reducing the spontaneous ignition risk;the anlysis of the key reaction pathways,shock-diffusion-reaction interaction and other characteristics can effectively promote the understanding of the spontaneous ignition of pressurized gaseous fuel releases;the equivalent spontaneous ignition experiment method provides a new and effective idea for the acquisition of ultra-high pressure gas release spontaneous ignition experiment data;the pressurized blended hydrogen release spontaneous ignition characteristics study provides a theoretical basis for the development of high-pressure fuel safe storage technology. |
PDF Full Text Request