Understanding the Reactivity of N-Heptane Blended with Ethanol or Ethyl Acetate

Fuel properties (viscosity, density, surface tension, ignition delay times) of binary mixtures containing a highly reactive fuel (n-heptane) and a low-reactive fuel (ethanol or ethyl acetate) are investigated in this study. For certain mixing ratios, the ethanol blend is found to exhibit longer ignition delay times after injection than the ethyl acetate blend, particularly noting that pure ethanol shows shorter ignition delay times than pure ethyl acetate. To explore the underlying causes, a comprehensive analysis is conducted, focusing on injection dynamics, mixture formation, and the chemical mechanisms leading up to ignition. Experiments on physical fluid properties, including viscosity, density, and surface tension, are performed to assess potential fluid mechanical effects on ignition delay times, with these properties fitted to existing mixing rules. Theoretical ignition delay times for different mixing ratios are calculated using a kinetic model, while experiments using a rapid compression machine provide insights into the purely chemical ignition delay for specific mixture ratios across various temperatures. Additionally, a rate-of-production analysis is conducted to offer a deeper understanding of the changes in reactivity observed in these fuel blends. Through this analysis, it becomes apparent that the change in reactivity is due to a change in the reaction pathways for ethyl acetate.