The growing severity of global environmental issues in recent years, including air pollution and the depletion of fossil fuels, has made it necessary for internal combustion engines to achieve higher efficiency and lower exhaust emission levels. Calls for reducing atmospheric emissions of carbon dioxide (CO₂) necessitate thoroughgoing measures to lower the levels of CO₂ originating in the combustion process of internal combustion engines and to facilitate operation on diverse energy sources. Homogeneous Charge Compression Ignition (HCCI) combustion has attracted widespread interest because it achieves high efficiency and can reduce particulate matter (PM) and nitrogen oxide (NOx) emissions simultaneously. These characteristics are obtainable because HCCI combustion can take place at ultra-lean conditions exceeding the limits of flame propagation. However, controlling the ignition timing of HCCI combustion is difficult because much of the process leading to ignition depends on chemical reactions. Additionally, because ignition of the mixture occurs simultaneously at multiple points in the HCCI combustion process, the resultant rapid rise of the cylinder pressure makes stable engine operation difficult at high loads. Therefore, the rapid nature of HCCI combustion must be moderated in order to expand the operating range on the high load side. The present study focused on two different combinations of blended fuels obtained by mixing DME or the standard reference fuel n-heptane (C7H16) with methane or toluene. The effects of different mixing ratios and supercharging on HCCI combustion characteristics were investigated and compared using spectroscopic measurement techniques. The results indicated that two-stage heat release of the hot flame was only observed in the experimental results for the former fuel blend.