Abstract
Some authors had proposed an idea of HCCI timing control with CH2O addition to an air/hydrocarbon fuel mixture. When reactions start with LTO (low-temperature oxidation or cool-flame reaction), the addition retards the ignition timing. When reactions start without LTO, the addition advances the timing. These opposed impacts on the ignition timing were explained by a kind of reaction path analysis, based on a universal rule of hydrocarbon fuel oxidation proposed by other authors. With LTO, the CH2O retards LTO by scavenging OH, resulting in the negative impact. Without LTO, that is at high temperatures in the process, H2O2 generated from fuel and the CH2O enhances the heat release rate of a loop of reactions, H2O2→2OH+M, CH2O+OH→HCO+HO2, HCO+O2→HO2+CO, 2HO2→H2O2+O2, leading to the positive impact. H2O2 addition to a mixture advances LTO by supplying initial OH, and also enhances the heat release rate of the loop. What is to be noted is that those impacts of CH2O and H2O2 addition on reactions can be on an additivity rule.
