Review of the Influence of Oxygenated Additives on the Combustion Chemistry of Hydrocarbons

This review summarizes the chemical impact of oxygenated additives on the combustion chemistry of hydrocarbons. Experimental studies in shock tubes, rapid compression machines, jet-stirred reactors, flow reactors, and premixed flames are summarized for additions of ethers, alcohols, esters, and other oxygenates to hydrocarbon fuels. Special emphasis is on the ignition behavior at low and high temperatures and on how molecule-specific intermediate chemistry impacts pollutant emissions by the addition of oxygenated components to hydrocarbon fuels. The literature work indicates that at high temperatures, i.e., in flames, the combustion chemistry of the oxygenate/hydrocarbon can be accurately modeled by merging the individual's submechanisms, excluding cross reactions. The observed trend in the intermediate species pool is largely due to a replacement effect, which describes a linear dependence of the intermediate concentration on the mixture composition. At low-temperatures, the chemistry is slightly more complex because of the fuel-specific reactivity in this temperature range. It was shown that unreactive fuels can undergo low-temperature oxidation processes when a highly reactive fuel component is present. As such, the sensitivities of specific reactions on ignition delay times varies.