Experiments and Computational Fluid Dynamics Modeling Analysis of Large n-Alkane Ignition Kinetics in the Ignition Quality Tester

This paper presents experimental measurements of ignition delays from low- to high-volatility n-alkanes representative of diesel and jet fuel compounds that are supplemented with a computational fluid dynamics (CFD) analysis. The ignition quality tester (IQT) is shown to be effective for studying ignition of low-volatility fuels, such as n-hexadecane, which are typically difficult to measure. Ignition delays, both experimental and modeled, are presented using an eight-point experimental design matrix (1.5 and 3.0 MPa, 823 and 723 K, and 15 and 21% O₂). A detailed n-alkane mechanism (C₈-C ₁₆ with a total of 2115 species) was reduced to a skeletal 237 species n-hexadecane mechanism using a targeted search algorithm. A CFD model of the IQT (developed using KIVA-3V) coupled with skeletal mechanisms predicted ignition delays of n-heptane and n-hexadecane with reasonable accuracy over the eight-point matrix, with the exception of the highest temperature, lowest pressure, and oxygen concentration conditions. Temperature sweeps across a range of pressures (0.1-1.0 MPa) and temperatures (673-973 K) were performed for n-heptane, n-decane, n-dodecane, and n-hexadecane. The negative temperature coefficient (NTC) region was observed experimentally for the first time for n-hexadecane. The NTC region for n-dodecane and n-decane has previously been observed in shock tubes and rapid compression machines and is reported here for the first time in the IQT. The IQT is thus capable of capturing NTC behavior for large alkanes and can serve as an additional experimental validation tool for chemical kinetic mechanisms of low-volatility surrogates for diesel and jet fuels.