Low-temperature ignition delay times measured in shock tubes (below 1000 K) and in RCMs (below 960 K) could not be well-predicted.
This study presents the first experimental low-temperature ignition delay data of cyclopentane, a potential fuel-blending component of particular interest due to its desirable antiknock characteristics.
A rapid compression machine has been used to determine the low-temperature ignition delay times for stoichiometric mixtures at pressures close to 20 bar over the temperature range from 646 K up to 861 K.
The results show that adding (1000 ppm) NO enhances both low and intermediate temperature ignition delay times by the rapid OH radical pool formation (one to two orders of magnitude higher OH radicals concentrations are observed).
For low-temperature coflow, the ignition delay and the liftoff height are sufficiently large to allow premixing between fuel and oxidizer before the onset of high-temperature combustion; in this case, a lean-to-stoichiometric premixed burn combustion is established downstream of the liftoff height, and no obvious triple-flame structure is formed at this condition.
Particularly, PC-thermites, due to their flocculent structures, exhibit the shortest ignition delay time, lowest reaction onset temperature, and highest amount of heat release.
In this study, we employ this improved description in a detailed numerical and analytical exploration of the first-stage ignition delay for low-temperature auto-ignition of propane, which may be considered as a prototype for larger alkane fuels.
A 4-step reduced mechanism using steady-state approximations for HO2 and H2O2 yields good results for laminar flame speed and extinction limits, but fails to predict ignition delay at low temperatures.
Several comparisons with experimental measurements, carried out under various operating conditions, confirm that the proposed model is a useful tool for characterizing low-temperature and high-temperature ignition delay times.
For the low-temperature case, the minimum ignition delay time was determined by the competition between the quicker ignition of the cool flame and the longer second induction time resulting from the decrease in the droplet size; for the high-temperature case, it was the results of phenomena occurring early during the droplet lifetime.
