skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: An experimental investigation of flame and autoignition behavior of propane
Autoignition delay time data are one important means to develop, quantify, and validate fundamental understanding of combustion chemistry at low temperatures (T<1200 K). However, low-temperature chemistry often has higher uncertainties and scatter in the experimental data compared with high-temperature ignition data (T>1200 K). In this study, autoignition properties of propane and oxygen mixtures were investigated using the University of Michigan rapid compression facility in order to understand the effects of ignition regimes on low-temperature ignition data. For the first time for propane, autoignition delay times were determined from pressure histories, and autoignition characteristics were simultaneously recorded using high-speed imaging of the test section through a transparent end-wall. Propane mixtures with fuel-to-O2 equivalence ratios of ϕ = 0.25 and ϕ = 0.5 and O2-to-inert gas molar ratios of 1:3.76 were studied over the pressure range of 8.9 to 11.3 atm and the temperature range of 930 – 1070 K. The results showed homogeneous or strong autoignition occurred for all ϕ = 0.25 experiments, and inhomogeneous or mixed autoignition occurred for all ϕ = 0.5 experiments. While a limited temperature range is covered in the study, importantly the data span predicted transitions in autoignition behavior, allowing validation of autoignition regime hypotheses. Specifically, the results agree well with strong-autoignition limits proposed based on the Sankaran Criterion. The autoignition delay time data at the strong-ignition conditions are in excellent agreement with predictions using a well-validated detailed reaction mechanism from the literature and a zero-dimensional modeling assumption. However, the experimental data at the mixed autoignition conditions were systematically faster than the model predictions, particularly at lower temperatures (T< ~970 K). The results are an important addition to the growing body of data in the literature that show mixed autoignition phenomena are important sources of the higher scatter observed in the low-temperature autoignition data for propane and other fuels. The results are discussed in terms of different methods to capture the effects of pre-autoignition heat release associated with mixed autoignition conditions and thereby address some of the discrepancies between kinetic modeling and experimental measurements.  more » « less
Award ID(s):
1701343
PAR ID:
10286889
Author(s) / Creator(s):
Date Published:
Journal Name:
Combustion and flame
Volume:
224
ISSN:
0010-2180
Page Range / eLocation ID:
24-32
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, International Journal of Chemical Kinetics)
    Abstract The current work presents new experimental autoignition and speciation data on the twocis‐hexene isomers:cis‐2‐hexene andcis‐3‐hexene. The new data provide insights on the effects of carbon‐carbon double bond location and stereoisomeric structures on ignition delay times and reaction pathways for linear hexene isomers. Experiments were performed using the University of Michigan rapid compression facility to determine ignition delay times from pressure‐time histories. Stoichiometric (ϕ = 1.0) mixtures at dilution levels of inert gas to O2 = 7.5:1 (mole basis) were investigated at an average pressure of 11 atm and temperatures from 809 to 1052 K. Speciation experiments were conducted atT = 900 K for the twocis‐hexene isomers, where fast‐gas sampling and gas chromatography were used to identify and quantify the twocis‐hexene isomers and stable intermediate species. The ignition delay time data showed negligible sensitivity to the location of the carbon‐carbon double bond and the stereoisomeric structure (cis‐trans), and the species data showed no correlation with the stereoisomeric structure, but there was a strong correlation of some of the measured species with the location of the double bond in the hexene isomer. In particular, 2‐hexene showed strong selectivity to propene, acetaldehyde, and 1,3‐butadiene, and 3‐hexene showed selectivity to propanal. Model predictions of ignition delay times were in excellent agreement with the experimental data. There was generally good agreement for the model predictions of the species data for 2‐hexene; however, the mechanism overpredicted some of the small aldehyde (C2‐C4) species for 3‐hexene. Reaction pathway analysis indicates the hexenes are almost exclusively consumed by H‐atom abstraction reactions at the conditions studied (P = 11 atm,T > 900 K), and not by C3‐C4scission as observed in high‐temperature (>1300 K) hexene ignition studies. Improved estimates for 3‐hexene + OH reactions may improve model predictions for the species measured in this work. 
    more » « less
  2. ; ; ; ; (, Proceedings of the Combustion Institute)
    Poly- and Perfluorinated alkyl substances (PFAS) pose environmental and public health concerns. While incineration remains the most common PFAS remediation method, the complete combustion and pyrolysis mechanism of PFAS is unknown. This study aims to expand our understanding of the kinetics of gas-phase PFAS incineration by measuring the effect of difluoromethane (CHF) on propane ignition delay times (IDTs). The ignition delay times were measured by OH* emission and end-wall pressure time histories behind the reflected shock wave. Different concentrations of CH2F2 were mixed with fuel-lean propane-oxygen mixtures diluted in argon. Experiments were conducted at a nominal reflected shock pressure of P5 = 1 atm and reflected shock temperatures of 1200 < T5 < 1800 K. A new detailed chemical kinetic mechanism is presented. 135 new rate constants were computed using RRKM/ME theory, based upon stationary points computed using ANL0. The new mechanism is in excellent agreement with the measured ignition delay time. A novel sensitivity analysis helps to explain the elementary steps by which CH2F2 increases the ignition delay time. 
    more » « less
  3. ; (, Fuel)
    The ammonia (NH3) and dimethyl ether (DME) mixture is a promising alternative fuel that offers the potential for cleaner combustion. This study presents an investigation of the autoignition-assisted flame speeds of stochiometric NH3/DME mixtures under conditions relevant to practical combustion systems. Experiments were conducted at pressures of 5 and 10 bar, gas temperatures ranging from 625 to 708 K, and three DME concentrations (10, 20, and 30%, mole fraction basis) in NH3/DME fuel mixtures using a rapid compression machine-flame (RCM-Flame) apparatus. For the majority of the autoignition experiments, first-stage ignition delay time was observed. Thus, the flame experiments were performed by igniting the spark both before and after the first-stage ignition delay time. The results are presented in terms of the Beta-Damköhler Number, defined as the ratio of spark ignition time to the first-stage ignition delay. The flame speed changes depending on the Beta-Damköhler Number, pressure, gas temperature, and DME concentration. The flame speed increases by increasing the temperature, decreasing the pressure, and increasing DME concentrations. However, the effect of Beta-Damköhler Number on flame speed is complicated: with 10% DME in the mixture, the flame speed is independent to Beta-Damköhler Number, and slight observed slight decrease of flame speed is due to the temperature drop during the post-compression period; with 20% DME in the mixture, at both pressures, the flame speed jumps after the first ignition delay (or Beta-Damköhler Number of one) , and remains constant before and after; similar behavior was observed with 30% DME in the mixture at 5 bar, however, at some temperatures, the flame speed increases at Beta-Damköhler Number of greater than one, and at 10 bar, the first ignition delay was short and flame speed was not measured at Beta-Damköhler Number of less than one. For all studied conditions, a linear trend was observed between burning velocity and stretch rate. Positive Markstein lengths were observed at most conditions, except for two specific gas temperatures (664 K at 5 bar and 671 K at 10 bar) with 30% DME, where negative Markstein lengths are found. One-dimensional laminar flame speed simulations agreed with measured data for Beta-Damköhler Numbers. less than one, but underpredicted the measured data at other conditions. 
    more » « less
  4. ; (, Energy & Fuels)
    The autoignition characteristics of ammonia (NH3) and dimethyl ether (DME) blends were examined in this research project. The study investigates the autoignition characteristics by measuring ignition delay times across a range of gas temperatures from 621 to 725 K and at pressures of 5, 10, and 20 bar by using a rapid compression machine (RCM). Ignition delays of NH3/DME blends, with DME concentrations in the fuel mixture ranging from 0 to 50%, were measured, simulated, and compared with JP-8 and JP-5 fuel ignition delays. At a pressure of 20 bar, blends containing 30 and 50% DME concentrations exhibited ignition delay times similar to those of JP-8 and JP-5. Furthermore, the fuel blend with a 30% DME concentration showed similar ignition delays at the lower pressures of 5 and 10 bar. Several kinetic models were used to model the autoignition and compared with the measured data. Simulation results fairly matched the measured ignition delays. Through rigorous experimental verification, this comprehensive analysis evaluated the reliability of existing chemical models and paved the way for further studies on customized fuel blends, thereby contributing to the ongoing debate on sustainable energy alternatives. 
    more » « less
  5. ; ; ; ; (, Combustion Institute)
    This work investigates the ignition behavior of cellulose hydrochar fuels carbonized at two different temperatures. Particles are burned in a Hencken burner under various O2/N2 mixtures where the impacts of ambient temperature and oxygen mole fractions are assessed independently. CH* chemiluminescence imaging and particle image velocimetry are used to characterize the ignition delay time. Results reveal that for both hydrochars ignition delay time is inversely proportional to the surrounding gas temperature. Ignition delay time shows a non-monotonic dependency on O2 mole fraction. Increasing the O2 fraction decreases the ignition delay time until O2 concentration is at a critical value, after which it increases. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email