Water fugacity and oxygen fugacity can be controlled concomitantly in solid‐media high‐pressure apparatus by using CO2‐H2O vapors and the double‐capsule technique with oxygen buffers. Calculations based on an ideal‐solution model yield values of the fugacities of O2, H2, and H2O in the samples.

The purpose of this study was to characterize experimental n-heptane combustion behavior in a direct-injection constant-volume combustion chamber (DI-CVCC), using chamber pressure to infer ignition delay and heat-release rate. Measurements generally displayed expected trends and indicated entirely premixed combustion with no mixingcontrolled phase. A significant finding was the observation of negative temperature coefficient (NTC) behavior. Comparing results with CHEMKIN-PRO simulations, it was found that a homogeneous combustion model was reasonably accurate for ignition delays longer than 5 ms. The combination of NTC behavior and homogeneous fuel-air mixtures suggests that this DI-CVCC can be useful for validation of chemical-kinetic mechanisms.

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Lean premixed (LPM) combustion is a common strategy in the turbine industry for power generation to reduce emissions of nitric oxides and other pollutants. LPM combustion tends to produce thermoacoustic instabilities under specific conditions. Previously we have shown that an appropriately designed ring-shaped porous insert located on the dump plane can mitigate thermoacoustic instabilities in LPM swirl-stabilized combustion for a range of operating conditions, and explained results based on time-resolved flowfield measurements. In this study, experiments are conducted at higher inlet air temperatures than used before, and the flame structure in the combustor without and with porous insert is investigated for the first time using time-resolved OH planar laser-induced fluorescence technique operated at 10 kHz. Large pressure oscillations in the fuel-air mixing tube demonstrate the existence of thermoacoustic instabilities without the porous insert. The pressure oscillations diminish with the porous insert, which is attributed to the changes in the flow field and flame structure.

Limiting and extinction oxygen index techniques have been used to study the effects that fabric variables and blend composition have on the burning be haviour of 20/80, 50/50 and 65/35 polyester-cotton blended fabrics. Whilst LOI values were not dependent on ignition time, they were for a given blend com position dependent on fabric area density. Lo values determined at zero area density were little dependent on blend composition for the blends studied. EOI values, as shown previously for single fibre component fabrics, were de pendent on igniter application times. Derived [EOI]o values at zero ignition times, like LOI, increased with area density. Zero area density or "free-fibre" ex tinction oxygen index Eo values, like LOI and Lo, varied only slightly with blend composition. However, when compared with respective values for pure polyester and cotton fabrics, the respective magnitudes of blend Eo values pro vide a better indication than do Lo values of the difference of blend from indi vidual component fibre burning behaviour. Thus it is considered that the ex tinction concept provides a better indication of the variations of flammable character of polyester-cotton blends compared to the individual fibre-con taining fabrics.

The purpose of this study was to characterize combustion behavior for n-heptane using experimental measurements in a direct-injection constant-volume combustion chamber (CVCC) to validate chemical-kinetic mechanisms. This work is focused on compression-ignition (i.e., diesel) combustion, primarily because mechanisms for larger-chain diesel-relevant species are not well developed and require significant attention. The CVCC used in this work can be pressurized and heated to create engine-relevant conditions that enable study of autoignition behavior. In addition, the chamber is equipped with a high-pressure, common-rail diesel injector, making the study of autoignition and combustion in this system highly relevant to modern diesel engines. By varying injection pressure and duration, it is possible to control global equivalence ratio as well. Chamber pressure during injection and combustion is measured using a piezoelectric transducer, and can be subsequently used to infer heat-release rates. Experimental measurements for n-heptane mostly displayed expected trends. As initial chamber pressure increased, ignition delay decreased and peak pressure increased. As injection duration increased, ignition delay decreased due to faster ignition of richer mixtures, and peak pressure increased due to higher total heat release. The effect of temperature on ignition delay, however, was more complex and suggested some amount of NTC (negative temperature coefficient) behavior. For all conditions, heat-release rates indicated entirely premixed combustion with no hint of mixing-controlled combustion. Experimental data were compared with results from CHEMKIN-PRO simulations. The model simulated zero-dimensional combustion using a detailed n-heptane mechanism developed at Lawrence Livermore National Laboratory. These computations were used to infer local equivalence ratio information, based on equivalence ratio required in the model to match experimental ignition delay. For most test cases, the model required an equivalence ratio that was at least ∼2× richer than the global value. In addition, equivalence ratios in the model ranged a full order of magnitude, from ∼0.6 to 6, suggesting that local mixture equivalence ratios varied considerably as experimental conditions were varied. Results suggest that improved models that include details of spray physics are required in order to properly predict local equivalence ratios and resulting autoignition characteristics.

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