Tailoring Ethanol High Temperature Ignition by Means of Chemical Additives and Water Content

The quest for sustainable alternatives to fossil fuels leads to a growing diversification of the molecular structures of fuel sources. Since ignition is a vital property in the choice of an engine combustion concept, the ability to tailor the ignition behavior of various fuel sources by means of fuel additives is expected to aid the development of fuel-flexible engines. Ethanol is one of the biofuels with a potential to play an important role in the transportation fuel mix of the future. One of the final processes during ethanol production involves distillation in order to minimize the water content. Using wet ethanol in combustion engines could lead to a reduction in the energy consumption during fuel processing. An understanding of fundamental combustion properties of ethanol in the presence of water vapor such as ignition behavior is expected to aid in the design of efficient engine combustion processes. In this work, the effect of two esters, isopropyl nitrate (IPN) and isopropyl formate (IPF), on the high temperature shock ignition of ethanol is investigated. Furthermore, the ignition of wet ethanol is investigated in order to shed light on the effect of water vapor content on the ignition chemistry of ethanol. New ethanol ignition data at 10 atm are also reported. Experiments are carried out in a shock tube at average pressures of 2, 10 and 12 atm over a temperature range of 949-1650 K. The ethanol and ethanol/additives are mixed with oxygen and argon. Ignition delay times are obtained behind reflected shock waves by means of pressure and light emission profiles. It is observed that while IPN addition to ethanol results in shorter ignition delay times, IPF addition leads to longer delay times. In case of water addition, it is found that for the same post-reflected temperatures and pressure, shorter ignition delay times are observed. However, this effect must be considered together with other physical processes of wet ethanol combustion such as heating and vaporization.