Auto-ignition and reaction kinetic characteristics of hydrogen-enriched n-dodecane mixtures under engine-like thermodynamic conditions

Abstract

The hydrogen/diesel dual-fuel engine has attracted extensive attention in recent years. To acquire ignition control methods for a dual-fuel engine, the mutual effects and separate influencing scales of multiple factors on the auto-ignition and reaction kinetic characteristics of a hydrogen/n-dodecane mixture under engine-like thermodynamic conditions were revealed by detailed chemical kinetic mechanism and experimental data based on the colormap and Taguchi methods. The results showed that blending a small amount of n-dodecane induced the initial production of OH and the early oxidation of fuels, which dramatically reduced the IDT of the hydrogen mixture. With a continuous increase in n-dodecane content, the improved reaction rates of the fuels outweighed the reduced reaction rates of active radicals, which resulted in a further reduction in the IDT and an enhancement in NTC behavior. Elevating ϕ and initial pressure apparently reduced the IDT as well. The rates of contribution of temperature, ϕ, pressure, and n-dodecane content on IDT are 62.9%, 27.0%, 5.1%, 5.0%, respectively. The temperature exerted a great influence under all conditions. The ϕ also had a obvious impact in most regions other than a pure hydrogen mixture or under low-temperature/high-ϕ conditions. The effect of pressure was ignorable under low-temperature or pure hydrogen mixture conditions due to the dramatically weakened mixture reactivity. While the influence of n-dodecane fraction was also negligible when it was more than 10% at mid-temperature or 20% at low temperature. Further, the sensitivity analysis showed the sensitivity coefficients of decomposition reactions and H/HO₂ related reactions reduced and increased, respectively, with increasing temperature. The sensitivity coefficients of OH/H₂O₂ related reactions reached their peak values in the NTC region, which represents the region where H₂O₂/OH radicals were the significant intermediate products in the hydrogen/n-dodecane reaction system. This investigation not only revealed the coupled influence law of multiple factors and the internal interaction mechanism between fuels and active radicals in the hydrogen/n-dodecane reaction system, but also provided fundamental insights into precise ignition control methods for a diesel/hydrogen dual-fuel engine.