The effects of hydrogen addition on the auto-ignition delay of homogeneous primary reference fuel/air mixtures in a rapid compression machine

The ignition delay time with mixtures of primary reference fuels (PRFs) and hydrogen were measured using a rapid compression machine (RCM), where the concentration of hydrogen was systematically varied. The experiments were performed for compressed temperatures in the range 735-847 K. The fuel/air equivalence ratio was varied to investigate its effects on the ignition delay of n-heptane and iso-octane. Hydrogen was added with hydrogen-energy-share ratios in the range of 0-10%, meaning that the energy of the hydrogen replaced 0-10% of that of either n-heptane or iso-octane. When hydrogen was added to n-heptane, there was a significant increase in the ignition delay, especially during the first-stage reaction region. This was explained using the chemical kinetic analysis software package CHEMKIN PRO; hydrogen consumed radical species related to the ignition of hydrocarbon fuels. With iso-octane, there was a significant increase in the ignition delay not only in the fist-stage reaction region, but also in second-stage reaction region. The effects of the hydrogen concentration were found to depend on the equivalence ratio and temperature for both fuels.