<div class="section abstract"><div class="htmlview paragraph">The discrete multi-component model for residual heavy fuel oil (HFO), developed in the mid-2000s, proved to be a simple but practical approximation in reproduction of the combustion process of HFO sprays on a couple of CFD simulation codes. The model succeeded in providing qualitative explanation about the spray and flame progression of HFO inside constant-volume chambers (CVC), but its practical use is still underway because of its higher calculation costs.</div><div class="htmlview paragraph">Two-component HFO model, which was introduced relatively recently, separates every spray droplet virtually into two smaller droplets of each component to calculate their evaporation process separately. The model showed good agreement with the observation results on the various HFO spray behaviors in some visualized CVCs (VCVCs).</div><div class="htmlview paragraph">However, all the above examinations were done only qualitatively not quantitatively since the heat releases measured in the visualizing-oriented chambers of large internal volume were difficult to detect accurately.</div><div class="htmlview paragraph">In the present study, a FIA vessel of much smaller volume was newly introduced in order to evaluate the heat release process of HFOs with good or poor fuel qualities. The results indicated strongly that the original two-component model should be modified in order to keep the compatibility with a conventional single component model and the modification was so effective in predicting the heat release rates from HFOs of different ignitability and combustibility.</div></div>