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Gaseous fuel originated from natural gas (NG) has been affected by industrial fields thanks to its low emission feature. The excellent knock resistance of methane, a major component of NG, is another advantage in engine applications, but the composition of NG varies depending on the production region. Methane number (MN) has been widely used to evaluate the knock resistance of certain NG. However, the selection of a reliable knock-resisting index has not been settled because of several definitions of MN, and a new index called the propane knock index was recently proposed. Moreover, the proper index could change with types of gas engines. In this study, a rapid compression-and-expansion machine (RCEM) was prepared to reproduce in-cylinder conditions and combustion processes of a pre-chamber type medium-speed gas engine, and the knocking-like combustion was intentionally generated by setting compression pressure, ignition timing, and fuel density in the mixture to the proper level.

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. 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).

With progression of so-called shale gas revolution, gas engines are expected as a strong substitute for diesel engines in marine fields, where strict emission regulations have been recently introduced. Thanks to the sulphur-free and low-carbon features of natural gas, gas engines emit much less CO2 and particulate matter than marine diesels burning heavy fuel oil. The premixed lean-burn gas engines, however, suffer two massive flaws. One is abnormal combustion called knocking and the other is a methane slip, which substantially means the unburned methane emitted into exhaust ports. One of the methane slip sources is thought to be flame quenching inside dead volumes around a combustion chamber or inside a boundary layer near a cylinder wall. Only supportive measures like cutdown of crevice volume have been conducted against the unburned methane.

The present study introduces a multi-component model for heavy fuel oil combustion based on two component approximation, implemented into KIVA-3V using modified evaporation, ignition and combustion models. The fuel is treated as a blend of residual portion and cutter stocks. Different fuel properties are assigned to each component affecting evaporation behavior in the liquid phase as well as ignition and combustion characteristics in the vapor phase. The model was validated regarding spray and flame appearance using photographs of spray combustion in a visual constant volume combustion chamber. Further the effects of fuel component properties on the ignition and combustion properties of the fuel blend have been investigated based on rate of heat release analysis.