Analysis of first stage ignition delay times of dimethyl ether in a laminar flow reactor

Ignition delay times of a “real” synthetic jet fuel (S8) were measured using an atmospheric pressure flow reactor facility. Experiments were performed between 900 K and 1200 K at equivalence ratios from 0.5 to 1.5. Ignition delay time measurements were also performed with JP8 fuel for comparison. Liquid fuel was prevaporized to gaseous form in a preheated nitrogen environment before mixing with air in the premixing section, located at the entrance to the test section of the flow reactor. The experimental data show shorter ignition delay times for S8 fuel than for JP8 due to the absence of aromatic components in S8 fuel. However, the ignition delay time measurements indicate higher overall activation energy for S8 fuel than for JP8. A detailed surrogate kinetic model for S8 was developed by validating against the ignition delay times obtained in the present work. The chemical composition of S8 used in the experiments consisted of 99.7 vol% paraffins of which approximately 80 vol% was iso-paraffins and 20% n-paraffins. The detailed kinetic mechanism developed in the current work included n-decane and iso-octane as the surrogate components to model ignition characteristics of synthetic jet fuels. The detailed surrogate kinetic model has approximately 700 species and 2000 reactions. This kinetic mechanism represents a five-component surrogate mixture to model generic kerosene-type jets fuels, namely, n-decane (for n-paraffins), iso-octane (for iso-paraffins), n-propylcyclohexane (for naphthenes), n-propylbenzene (for aromatics) and decene (for olefins). The sensitivity of iso-paraffins on jet fuel ignition delay times was investigated using the detailed kinetic model. The amount of iso-paraffins present in the jet fuel has little effect on the ignition delay times in the high temperature oxidation regime. However, the presence of iso-paraffins in synthetic jet fuels can increase the ignition delay times by two orders of magnitude in the negative temperature (NTC) region between 700 K and 900 K, typical gas turbine conditions. This feature can have a favorable impact on preventing flashback caused by the premature autoignition of liquid fuels in lean premixed prevaporized (LPP) combustion systems.

Download Full-text

Tailoring the Temperature Sensitivity of Ignition Delay Times in Hot Spots Using Fuel Blends of Dimethyl Ether, Methane, and Hydrogen

Energy & Fuels ◽

10.1021/acs.energyfuels.9b02619 ◽

2019 ◽

Vol 34 (2) ◽

pp. 2246-2259

Author(s):

J. Vinkeloe ◽

L. Zander ◽

M. Szeponik ◽

N. Djordjevic

Keyword(s):

Dimethyl Ether ◽

Temperature Sensitivity ◽

Ignition Delay ◽

Hot Spots ◽

Fuel Blends ◽

Ignition Delay Times ◽

Delay Times

Download Full-text

Interpretation of Flow Reactor Based Ignition Delay Measurements

Volume 2: Combustion, Fuels and Emissions ◽

10.1115/gt2009-60268 ◽

2009 ◽

Cited By ~ 3

Author(s):

David Beerer ◽

Vincent McDonell ◽

Scott Samuelsen ◽

Leonard Angello

Keyword(s):

High Pressure ◽

Gas Turbine ◽

Residence Time ◽

Ignition Delay ◽

Delay Time ◽

Ignition Delay Time ◽

Flow Reactor ◽

Ignition Delay Times ◽

Delay Times ◽

Recirculation Zones

Compositional variation of global gas supplies is becoming a growing concern. Both the range and rate-of-change of this variation is expected to increase as global markets for Liquefied Natural Gas (LNG) continue to expand. Greater fuel composition variation poses increased operational risk to gas turbine engines employing lean premixed combustion systems. Information on ignition delay at high pressure and intermediate temperatures is valuable for lean premixed gas turbine design. In order to avoid autoignition of the fuel/air mixture within the premixer, the ignition delay time must be greater than the residence time. Evaluating the residence time is not a straight forward task because of the complex aerodynamics due to recirculation zones, separation regions, and boundary layers effects which may create regions where the local residence times may be longer than the bulk or average residence time. Additionally, reliable experiments on ignition delay at gas turbine conditions are difficult to conduct. Devices for testing include shock tubes, rapid compression machine and flow reactors. In a flow reactor ignition delay data are commonly determined by measuring the distance from the fuel injector to the reaction front (L) and dividing it by the bulk or average flow velocity (U) under steady flow conditions to obtain a bulk residence time which is assumed to be equal to the ignition delay time. However this method is susceptible to the same boundary layer effects or recirculation zones found in premixers. An alternative method for obtaining ignition delay data in a flow reactor is presented herein, where ignition delay times are obtained by measuring the time difference between fuel injection and ignition using high speed instrumentation. Ignition delay times for methane, ethane and propane at gas turbine conditions were in the range of 40–500 ms. The results obtained show excellent agreement with recently proposed chemical mechanisms for hydrocarbons at low temperature/high pressure conditions.

Download Full-text

Experimental and Modeling Study on Ignition Delay Times of Dimethyl Ether/Propane/Oxygen/Argon Mixtures at 20 bar

Energy & Fuels ◽

10.1021/ef4009967 ◽

2013 ◽

Vol 27 (7) ◽

pp. 4007-4013 ◽

Cited By ~ 25

Author(s):

Erjiang Hu ◽

Zihang Zhang ◽

Lun Pan ◽

Jiaxiang Zhang ◽

Zuohua Huang

Keyword(s):

Dimethyl Ether ◽

Ignition Delay ◽

Ignition Delay Times ◽

Delay Times ◽

Modeling Study

Download Full-text

Shock Tube Measurements and Modeling Study on the Ignition Delay Times ofn-Butanol/Dimethyl Ether Mixtures

Energy & Fuels ◽

10.1021/ef5009727 ◽

2014 ◽

Vol 28 (6) ◽

pp. 4206-4215 ◽

Cited By ~ 10

Author(s):

Zhuang Geng ◽

Lili Xu ◽

Hua Li ◽

Jiaxing Wang ◽

Zhen Huang ◽

...

Keyword(s):

Shock Tube ◽

Dimethyl Ether ◽

Ignition Delay ◽

Ignition Delay Times ◽

Delay Times ◽

Modeling Study

Download Full-text

Experimental and Kinetic Studies on Ignition Delay Times of Dimethyl Ether/n-Butane/O2/Ar Mixtures

Energy & Fuels ◽

10.1021/ef301617j ◽

2012 ◽

Vol 27 (1) ◽

pp. 530-536 ◽

Cited By ~ 32

Author(s):

Erjiang Hu ◽

Xue Jiang ◽

Zuohua Huang ◽

Jiaxiang Zhang ◽

Zihang Zhang ◽

...

Keyword(s):

Dimethyl Ether ◽

Ignition Delay ◽

Kinetic Studies ◽

Ignition Delay Times ◽

Delay Times

Download Full-text

Autoignition of Hydrogen and Air Inside a Continuous Flow Reactor With Application to Lean Premixed Combustion

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2939007 ◽

2008 ◽

Vol 130 (5) ◽

Cited By ~ 22

Author(s):

D. J. Beerer ◽

V. G. McDonell

Keyword(s):

Gas Turbine ◽

Ignition Delay ◽

Flow Reactor ◽

Initial Conditions ◽

Premixed Combustion ◽

Nox Formation ◽

Lean Premixed Combustion ◽

Ignition Delay Times ◽

Delay Times ◽

Lean Premixed

With the need to reduce carbon emissions such as CO2, hydrogen is being examined as potential “clean” fuel for the future. One potential strategy is lean premixed combustion, where the fuel and air are allowed to mix upstream before entering the combustor, which has been proven to curb NOx formation in natural gas fired engines. However, premixing hydrogen and air may increase the risk of autoignition before the combustor, resulting in serious engine damage. A flow reactor was set up to test the ignition delay time of hydrogen and air at temperatures relevant to gas turbine engine operations to determine maximum possible mixing times. The results were then compared to past experimental work and current computer simulations. The current study observed that ignition is very sensitive to the initial conditions. The ignition delay times follow the same general trend as seen in previous flow reactor studies: ignition within hundreds of milliseconds and relatively low activation energy. An experimentally derived correlation by Peschke and Spadaccini (1985, “Determination of Autoignition and Flame Speed Characteristics of Coal Gases Having Medium Heating Values,” Research Project No. 2357-1, Report No. AP-4291) appears to best predict the observed ignition delay times. Homogenous gas phase kinetics simulations do not appear to describe ignition well in these intermediate temperatures. Therefore, at the moment, only the current empirical correlations should be used in predicting ignition delay at engine conditions for use in the design of gas turbine premixers. Additionally, fairly large safety factors should still be considered for any design to reduce any chance of autoignition within the premixer.

Download Full-text