Shock Tube Ignition Delay Data Affected by Localized Ignition Phenomena
Figueroa Labastida, Miguel
Chung, Suk Ho
Im, Hong G.
KAUST DepartmentChemical Kinetics & Laser Sensors Laboratory
Clean Combustion Research Center
Combustion and Laser Diagnostics Laboratory
Computational Reacting Flow Laboratory (CRFL)
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division
Online Publication Date2016-12-29
Print Publication Date2017-07-03
Permanent link to this recordhttp://hdl.handle.net/10754/623236
MetadataShow full item record
AbstractShock tubes have conventionally been used for measuring high-temperature ignition delay times ~ O(1 ms). In the last decade or so, the operating regime of shock tubes has been extended to lower temperatures by accessing longer observation times. Such measurements may potentially be affected by some non-ideal phenomena. The purpose of this work is to measure long ignition delay times for fuels exhibiting negative temperature coefficient (NTC) and to assess the impact of shock tube non-idealities on ignition delay data. Ignition delay times of n-heptane and n-hexane were measured over the temperature range of 650 – 1250 K and pressures near 1.5 atm. Driver gas tailoring and long length of shock tube driver section were utilized to measure ignition delay times as long as 32 ms. Measured ignition delay times agree with chemical kinetic models at high (> 1100 K) and low (< 700 K) temperatures. In the intermediate temperature range (700 – 1100 K), however, significant discrepancies are observed between the measurements and homogeneous ignition delay simulations. It is postulated, based on experimental observations, that localized ignition kernels could affect the ignition delay times at the intermediate temperatures, which lead to compression (and heating) of the bulk gas and result in expediting the overall ignition event. The postulate is validated through simple representative computational fluid dynamic simulations of post-shock gas mixtures which exhibit ignition advancement via a hot spot. The results of the current work show that ignition delay times measured by shock tubes may be affected by non-ideal phenomena for certain conditions of temperature, pressure and fuel reactivity. Care must, therefore, be exercised in using such data for chemical kinetic model development and validation.
CitationJaved T, Badra J, Jaasim M, Es-Sebbar E, Labastida MF, et al. (2016) Shock Tube Ignition Delay Data Affected by Localized Ignition Phenomena. Combustion Science and Technology 189: 1138–1161. Available: http://dx.doi.org/10.1080/00102202.2016.1272599.
SponsorsWe would like to acknowledge the funding provided Saudi Aramco under the FUELCOM program and by King Abdullah University of Science and Technology (KAUST). We would like to thank Prof. Mani Sarathy (KAUST) for useful discussions on chemical kinetic mechanisms of n-alkanes.
PublisherInforma UK Limited
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Two-stage Lagrangian modeling of ignition processes in ignition quality tester and constant volume combustion chambersAlfazazi, Adamu; Kuti, Olawole Abiola; Naser, Nimal; Chung, Suk Ho; Sarathy, Mani (Fuel, Elsevier BV, 2016-08-10) [Article]The ignition characteristics of isooctane and n-heptane in an ignition quality tester (IQT) were simulated using a two-stage Lagrangian (TSL) model, which is a zero-dimensional (0-D) reactor network method. The TSL model was also used to simulate the ignition delay of n-dodecane and n-heptane in a constant volume combustion chamber (CVCC), which is archived in the engine combustion network (ECN) library (http://www.ca.sandia.gov/ecn). A detailed chemical kinetic model for gasoline surrogates from the Lawrence Livermore National Laboratory (LLNL) was utilized for the simulation of n-heptane and isooctane. Additional simulations were performed using an optimized gasoline surrogate mechanism from RWTH Aachen University. Validations of the simulated data were also performed with experimental results from an IQT at KAUST. For simulation of n-dodecane in the CVCC, two n-dodecane kinetic models from the literature were utilized. The primary aim of this study is to test the ability of TSL to replicate ignition timings in the IQT and the CVCC. The agreement between the model and the experiment is acceptable except for isooctane in the IQT and n-heptane and n-dodecane in the CVCC. The ability of the simulations to replicate observable trends in ignition delay times with regard to changes in ambient temperature and pressure allows the model to provide insights into the reactions contributing towards ignition. Thus, the TSL model was further employed to investigate the physical and chemical processes responsible for controlling the overall ignition under various conditions. The effects of exothermicity, ambient pressure, and ambient oxygen concentration on first stage ignition were also studied. Increasing ambient pressure and oxygen concentration was found to shorten the overall ignition delay time, but does not affect the timing of the first stage ignition. Additionally, the temperature at the end of the first stage ignition was found to increase at higher ambient pressure and oxygen concentration. Sensitivity analysis was performed using the TSL model to elucidate the reactions that control the overall ignition process. The present TSL modeling approach demonstrates the suitability of using detailed chemical kinetic models to provide insights into spray combustion processes. © 2016 Elsevier Ltd
Relating the octane numbers of fuels to ignition delay times measured in an ignition quality tester (IQT)Naser, Nimal; Yang, Seung Yeon; Kalghatgi, Gautam; Chung, Suk Ho (Fuel, Elsevier BV, 2016-09-21) [Article]A methodology for estimating the octane index (OI), the research octane number (RON) and the motor octane number (MON) using ignition delay times from a constant volume combustion chamber with liquid fuel injection is proposed by adopting an ignition quality tester. A baseline data of ignition delay times were determined using an ignition quality tester at a charge pressure of 21.3 bar between 770 and 850 K and an equivalence ratio of 0.7 for various primary reference fuels (PRFs, mixtures of isooctane and n-heptane). Our methodology was developed using ignition delay times for toluene reference fuels (mixtures of toluene and n-heptane). A correlation between the OI and the ignition delay time at the initial charge temperature enabled the OI of non-PRFs to be predicted at specified temperatures. The methodology was validated using ignition delay times for toluene primary reference fuels (ternary mixtures of toluene, iso-octane, and n-heptane), fuels for advanced combustion engines (FACE) gasolines, and certification gasolines. Using this methodology, the RON, the MON, and the octane sensitivity were estimated in agreement with values obtained from standard test methods. A correlation between derived cetane number and RON is also provided. (C) 2016 Elsevier Ltd. All rights reserved.