Browsing by Subject "Combustion"

Now showing 1 - 7 of 7
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    Assessment of Combustion Modes for Internal Combustion Wave Rotors
    (1999-04) Nalim, M. Razi
    Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Three modes of combustion are assessed: premixed autoignition (detonation), premixed deflagration, and non-premixed autoignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor. The autoignition modes will require inlet temperatures in excess of 800 K for reliable ignition with most hydrocarbon fuels. Examples of combustion mode selection are presented for two engine applications.
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    Experimental Investigation into Combustion Torch Jet Ignition of Methane-Air, Ethylene-Air, and Propane-Air Mixtures
    (2010-12) Perera, Ukwatte Lokuliyanage Indika Upendra; Nalim, M. Razi; Xie, Jian; Zhu, Likun
    Ignitability and the ignition delay time of a combustible mixture in a long combustion chamber, ignited by a hot combustion torch jet generated in a pre-chamber was investigated experimentally in relation to application as a viable igniter method for wave rotor combustors. Methane-air, ethylene-air, and propane-air in varying equivalence ratios were investigated as the combustible mixture in the combustion chamber. The effects of variation in the torch jet fuel, initial equivalence ratio in the pre-chamber, and nozzle geometry on the ignitability and the ignition delay time of combustible mixtures were observed and analyzed. The single-channel wave-rotor combustion rig at Combustion and Propulsion Research Laboratory at the Purdue School of Engineering and Technology at Indiana University-Purdue University, Indianapolis was used for this study. High-speed video imaging techniques to observe the ignition and flame propagation in the combustion chamber and fast-response pressure transducers to measure the dynamic pressure fluctuations in the combustion chambers were used in the current study. The present work explains how the experimental procedure and preliminary testing was carried out in order to conduct the necessary testing to find the ignitability and ignition delay time of a combustible mixture. Ignitability of methane, ethylene, and propane were much broader in range compared to conventional spark ignitable lean and rich limit equivalence ratios. The methane and propane ignition lean limits were similar to radical activated ignition lean limits found in previous studies of the same fuels. Ethylene exhibited the widest range in equivalence ratios from 0.4 to 2.4, while methane had the narrowest ranging from equivalence ratio 0.4 to 1.4. The ignition delay studies indicated both chemical kinetics and mixing between the combustion torch jet and the combustible mixture were critical. The mixing phenomena dominated chemical kinetics; unlike in ignition delay studies conducted using shock heated ignition techniques. Ethylene-air mixtures had the shortest ignition delay times ~1 ms for lean but near-stoichiometric mixtures. Methane and propane indicated similar ignition delay time characteristics with lean near-stoichiometric mixtures. The fuel-air equivalence ratio which was used to generate the combustion torch jet and the torch jet nozzle geometry had a direct influence over the ignition delay time in the main chamber combustible mixture. The slightly rich fuel-air ratios used to generate the combustion torch jet had the lowest delay times in igniting the main chamber fuel-air mixtures.
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    Experimental investigation on traversing hot jet ignition of lean hydrocarbon-air mixtures in a constant volume combustor
    (2013-12) Chinnathambi, Prasanna; Nalim, M. Razi; Yu, Huidan (Whitney); Zhu, Likun; Anwar, Sohel
    A constant-volume combustor is used to investigate the ignition initiated by a traversing jet of reactive hot gas, in support of combustion engine applications that include novel wave-rotor constant-volume combustion gas turbines and pre-chamber IC engines. The hot-jet ignition constant-volume combustor rig at the Combustion and Propulsion Research Laboratory at the Purdue School of Engineering and Technology at Indiana University-Purdue University Indianapolis (IUPUI) was used for this study. Lean premixed combustible mixture in a rectangular cuboid constant-volume combustor is ignited by a hot-jet traversing at different fixed speeds. The hot jet is issued via a converging nozzle from a cylindrical pre-chamber where partially combusted products of combustion are produced by spark- igniting a rich ethylene-air mixture. The main constant-volume combustor (CVC) chamber uses methane-air, hydrogen-methane-air and ethylene-air mixtures in the lean equivalence ratio range of 0.8 to 0.4. Ignition delay times and ignitability of these combustible mixtures as affected by jet traverse speed, equivalence ratio, and fuel type are investigated in this study.
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    Hot jet ignition delay characterization of methane and hydrogen at elevated temperatures
    (Pro Quest, 2017-08) Kojok, Ali Tarraf; Nalim, M. Razi; Larriba-Andaluz, Carlos; Zhu, Likhun
    This study contributes to a better understanding of ignition by hot combustion gases which finds application in internal combustion chambers with pre-chamber ignition as well as in wave rotor engine applications. The experimental apparatus consists of two combustion chambers: a pre chamber that generates the transient hot jet of gas and a main chamber which contains the main fuel air blend under study. Variables considered are three fuel mixtures (Hydrogen, Methane, 50\% Hydrogen-Methane), initial pressure in the pre-chamber ranging from 1 to 2 atm, equivalence ratio of the fuel air mixture in the main combustion chamber ranging from 0.4 to 1.5, and initial temperature of the main combustion chamber mixture ranging from 297 K to 500 K. Experimental data makes use of 4 pressure sensors with a recorded sampling rate up to 300 kHz, as well as high speed Schlieren imaging with a recorded frame rate up to 20,833 frame per seconds. Results shows an overall increase in ignition delay with increasing equivalence ratio. High temperature of the main chamber blend was found not to affect hot jet ignition delay considerably. Physical mixing effects, and density of the main chamber mixture have a greater effect on hot jet ignition delay.
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    Recurrence Plots for Diesel Engine Variability Tests
    (De Gruyter, 2009-02-20) Longwic, Rafał; Litak, Grzegorz; Sen, Asok K.; Mathematical Sciences, School of Science
    Cycle-to-cycle variations of maximum pressure in a diesel engine are studied by using the methods of recurrence plots and recurrence quantification analysis. The pressure variations are found to exhibit strong periodicities in low frequency bands and intermittent oscillations at higher frequencies. The results are confirmed by wavelet analysis.
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    Reduction of Mixture Stratification in a Constant-Volume Combustor
    (2021-12) Rowe, Richard Zachary; Nalim, M. Razi; Larriba-Andaluz, Carlos; Yu, Huidan(Whitney)
    This study contributes to a better working knowledge of the equipment being used in a well-established combustion lab. In particular, several constant-volume combustion properties (e.g., time ignition delay, flame propagation, and more) are examined to deduce any buoyancy effects between fuel and air mixtures and to develop a method aimed at minimizing such effects. This study was conducted on an apparatus designed to model the phenomena occurring within a single channel of a wave rotor combustor, which consists of a rotating cylindrical pre-chamber and a fixed rectangular main combustion chamber. Pressure sensors monitor the internal pressures within the both chambers at all times, and two slow-motion videography techniques visually capture combustion phenomena occurring within the main chamber. A new recirculation pump system has been implemented to mitigate stratification within the chamber and produce more precise, reliable results. The apparatus was used in several types of experiments that involved the combustion of various hydrocarbon fuels in the main chamber, including methane, 50%-50% methane-hydrogen, hydrogen, propane, and 46.4%-56.3% methane-argon. Additionally, combustion products created in the pre-chamber from a 1.1 equivalence ratio reaction between 50%-50% methane-hydrogen and air were utilized in the issuing pre-chamber jet for all hot jet ignition tests. In the first set of experiments, a spark plug ignition source was used to study how combustion events travel through the main chamber after different mixing methods were utilized – specifically no mixing, diffusive mixing, and pump circulation mixing. The study reaffirmed that stratification between fuel-air mixtures occurs in the main chamber through the presence of asymmetrical flame front propagation. Allowing time for mixing, however, resulted in more symmetric flame fronts, broader pressure peaks, and reduced combustion time in the channel. While 30 seconds of diffusion helped, it was found that 30 seconds of pumping (at a rate of 30 pumps per 10 seconds) was the most effective method at reducing stratification effects in the system. Next, stationary hot jet ignition experiments were conducted to compare the time between jet injection and main chamber combustion and the speed of the resulting shockwaves between cases with no mixing and 30 seconds of pump mixing. Results continued to show an improvement with the pump cases; ignition delay times were typically shorter, and shock speeds stayed around the same, if not increased slightly. These properties are vital when studying and developing wave rotor combustors, and therefore, reducing stratification (specifically by means of a recirculation system) should be considered a crucial step in laboratory models such as this one. Lastly, experiments between a fueled main chamber and rotating pre-chamber helped evaluate the leakage rate of the traversing hot jet ignition experimental setup paired with the new pump system. In its current form, major leaks are inevitable when attempting traversing jet experiments, especially with the pump’s suction action drawing sudden large plumes of outside air into the main chamber. To minimize leaks, gaps between the pre-chamber and main chamber should be reduced, and the contact surface between the two chambers should be more evenly distributed. Also, the pump system should only be operated as long as needed to evenly distribute the fuel-air mixture, which approximately happens when the main chamber’s total volume has been circulated through the system one time. Therefore, a new pump system with half of the original system’s volume was developed in order to decrease the pumping time and lower the risk of leaks.
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    Two-Dimensional Flow and NOx Emissions in Deflagrative Internal Combustion Wave Rotor Configurations
    (2003-07) Pekkan, K; Nalim, M. Razi
    A wave rotor is proposed for use as a constant volume combustor. A novel design feature is investigated as a remedy for hot gas leakage, premature ignition, and pollutant emissions that are possible in this class of unsteady machines. The base geometry involves fuel injection partitions that allow stratification of fuel/oxidizer mixtures in the wave rotor channel radially, enabling pilot ignition of overall lean mixture for low NOx combustion. In this study, available turbulent combustion models are applied to simulate approximately constant volume combustion of propane and resulting transient compressible flow. Thermal NO production histories are predicted by simulations of the STAR-CD code. Passage inlet/outlet/wall boundary conditions are time-dependent, enabling the representation of a typical deflagrative internal combustor wave rotor cycle. Some practical design improvements are anticipated from the computational results. For a large number of derivative design configurations, fuel burn rate, two-dimensional flow and emission levels are evaluated. The sensitivity of channel combustion to initial turbulence levels is evaluated.