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Rapid compression machine (RCM) and shock-tube facilities have been employed to study the oxidation of natural gas blends at high pressure and intermediate to high temperatures. The use of both types of facilities allows a broad temperature envelope to be investigated and therefore encompasses the complete range applicable to gas turbines. A detailed chemical kinetic mechanism has been developed to simulate these results and will be used to approximate similar fuels. Mixtures of CH 4 /C 2 H 6 /C 3 H 8 /n-C 4 H 10 /n-C 5 H 12 have been studied in the temperature range 630-1550 K, in the pressure range 8-30 bar, and at equivalence ratios of 0.5, 1.0, and 2.0 in "air". For shock-tube experiments, the diluent gas was nitrogen, whereas in the RCM experiments the diluent gas composition ranged from pure nitrogen (at lower temperatures) to pure argon (at the highest temperatures). In addition, the combustion chamber in the RCM was fitted with a thermostat and heating tape to control and vary the initial temperature thereby varying the compressed gas temperature. Because the time-scale of a rapid compression machine experiment is so long, heat losses are significant. Thus, a series of nonreactive experiments were performed in order to account for the heat loss associated with each mixture composition and pressure.

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The oxidation of methane/ethane/propane mixtures, for blends containing 90/6.6/3.3, 70/15/15 and 70/20/10 percent by volume of each fuel respectively in 'air,' has been studied over the temperature range 770-1580 K, at compressed gas pressures of approximately 1, 10, 20, 30, 40 and 50 atm, and at equivalence ratios of 0.5, 1.0 and 2.0 using both a high-pressure shock tube and a rapid compression machine. The present work represents the most comprehensive set of methane/ethane/propane ignition delay time measurements available in a single study which extends the composition envelope over an industrially relevant pressure range. It is also the first such study to present ignition delay times at significantly overlapping conditions from both a rapid compression machine and a shock tube. The data were simulated using a detailed chemical kinetic model comprised of 289 species and 1580 reactions. It was found that qualitatively, the model reproduces correctly the effect of change in equivalence ratio and pressure, predicting that fuel-rich, high-pressure mixtures ignite fastest while fuel-lean, low-pressure mixtures ignite slowest. Moreover, the reactivity as a function of temperature is well captured with the model predicting negative temperature coefficient behavior similar to the experiments. Quantitatively the model is in general excellent agreement with the experimental results but is faster than experiment for the fuel-rich (φ = 2.0) mixture containing the highest quantity of propane (70/15/15 mixture) at the lowest temperatures (770-900 K).

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