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

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 phi and initial pressure apparently reduced the IDT as well. The rates of contribution of temperature, phi, 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 phi also had a obvious impact in most regions other than a pure hydrogen mixture or under low-temperature/high-phi 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.