Effect of Diluents on the Autoignition of Propane Mixtures Using a Rapid Compression Machine

Abstract

The autoignition process of different propane mixtures was studied to determine how the diluent choice (helium and argon/nitrogen) affects the ignition delay, the production of excited radicals, and the overall combustion process. An optically accessible rapid compression machine, high-speed camera, flame spectrometer, and numerical model were used to investigate the combustion process. The ignition delay times were measured at a wide range of compressed gas temperatures from 860 to 950 K, a compressed gas pressure of approximately 34 bar, and two equivalence ratios of 1.0 and 1.5. Chemiluminescence at wavelengths of 309, 555, 590, and 623 nm from the decay of excited radicals was detected during the autoignition process, and their respective intensities were measured and compared at various test conditions. A new kinetic model was built by combining reaction rates of excited radicals and species from the literature. The new model was validated against the measured ignition delay data of this work. The ignition delay and some of the excited radicals show a strong dependency on the diluent choice. A new numerical model was used to include the effect of heat transfer and the diluent choice in the temperature calculation and ignition delay modeling and measurements. Using the new numerical model, we found that the measured ignition delays are not dependent on the diluent choice.

Rapid Compression Machine Ignition Delay Time Measurements under Near-Constant Pressure Conditions

“…Mixtures 2 and 3 had a greater helium content than mixture 1, which resulted in accelerated heat loss from the system. The heat-transfer properties of helium have been thoroughly investigated in other works, 24,38 and the authors encourage the curious readers to refer to those papers for a better understanding. The helium content in the mixtures prevented ignition from occurring at gas temperatures below 890 K, whereas the mixture with exclusive use of argon as the diluent showed ignition at temperatures as low as 840 K. At temperatures where all mixtures would ignite, mixtures with the helium content displayed extended ignition delays.…”

“…The uncertainty of this system is approximately 0.56%, which includes the uncertainty in measurements (0.42%), linearity (0.3%), and thermal shock error (0.2%). Further details of the RCM can be found in previous work performed by the same research group. ,,− …”

“…Heat transfer during the autoignition, especially in the low to intermediate temperature range, reduces the gas temperature and pressure which affects the ignition delay. Samimi-Abianeh et al studied the effects of diluents on the ignition delay times of propane. In their literature review, the authors noted works which showed that diluents have different effects on the duration of the ignition delay depending on the experimental device employed.…”

Measurement and Simulation of n-Heptane Mixture Autoignition

“…The gas pressure during the compression and post-compression periods is measured using a Kistler piezoelectric pressure transducer (6045B) paired with a Kistler charge amplifier (5018). The measured pressures with this setup have an uncertainty of 0.56%, which include uncertainty in measurements (0.42%), linearity (0.3%), and thermal shock error (0.2%), as discussed in previous works. ,− An uncertainty of approximately ±0.1 ms is associated with the timing of the end of compression (EOC).…”

High-Temperature Ignition of Propane–Oxygen–Argon Mixtures in a Shock Tube at A Pressure of 30 Atm

“…Propane is the lightest hydrocarbon, which is characterized by the general laws of low-temperature and high-temperature ignition inherent in heavier hydrocarbons [1]. Due to the presence of propane in natural gas mixtures, and also because of its importance in its use as a model fuel and an intermediate product in combustion chemistry, there is a large amount of experimental data in the literature on the ignition of propane in various experimental installations, such as shock tubes [2][3][4][5], fast compressor machines [6][7][8], jet mixing reactors [9], and flow reactors [10,11].…”