Pulse combustion: The quantification of characteristic times

doi:10.1016/0010-2180(90)90040-X

Combustion and Flame

Volume 79, Issue 2, February 1990, Pages 151-161

https://doi.org/10.1016/0010-2180(90)90040-X Get rights and content

Abstract

Measurements of the total ignition delay time in a pulse combustor have been made for several chemical kinetic ignition delay times and several fluid dynamic mixing times. These measured total ignition delay times are compared with calculated values of the characteristic time for mixing and with calculated values for the homogeneous ignition delay time. A chemical kinetic model was used to calculate the homogeneous chemical kinetic ignition delay time for conditions typical of an operating pulse combustor. Similarly, a fluid dynamic mixing model was used to estimate characteristic times for a transient jet of cold reactants to mix with an ambient environment of hot products to an ignition temperature. These calculated time scales compared well with measured values in both trend and magnitude. It has also been shown that a simple sum of the characteristic mixing times and chemical kinetics times provides a good first-order approximation to the total ignition delay time.

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Citation Excerpt :
When the ambient temperature was less than −10 °C in winter, the gas turbine for syngas in Huaneng Tianjin IGCC power station experienced an obvious combustion oscillation phenomenon, which seriously affected the production safety and efficiency. This study uses the characteristic time-scale theory [28,29] to guide the operation and reduce the combustion oscillation of the gas turbine for syngas. The remainder of this paper is organized as follows.
When the ambient temperature is less than −10 °C in winter, the gas turbine for syngas in Huaneng Tianjin integrated gasification combined cycle (IGCC) power station has an evident combustion oscillation phenomenon, which seriously affects the production safety and efficiency. This study used the characteristic time-scale theory to guide the operation, thereby reducing the combustion oscillation of the gas turbine for syngas. The work progressed as follows. First, the boundaries of the combustion oscillation and maximum temperature safe limitations were defined based on the operational data from the extreme ambient temperature in summer and winter in the Huaneng Tianjin IGCC power station. Then, the mathematical model of combustion with critical parameters, such as ignition delay time, the adiabatic temperature of the flame, and flame speed, was constructed using the binary quadratic regression method under various combinations of dry syngas, natural gas, and steam flow rates. Finally, an operation scheme for reducing the combustion oscillation of the gas turbine for syngas in winter was designed, as well as the limitation boundary and computation model. This operation scheme can effectively reduce the combustion oscillation in winter; this was confirmed in actual operation. The results of this study should assist gas turbine designers in improving the safety, reliability, and stability of syngas turbines.
Effect of fuel injection parameters on performance characteristics and emissions of a thermoacoustic system
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Citation Excerpt :
These characteristics make pulse combustor be used in many domestic and propulsion systems [16] in addition to being used as typical experimental device. Considerable research has been performed in the field, both theoretically [17–19] and experimentally [20–22], to reveal the mechanism of pulse combustion. For theoretical study, a one-dimensional analytical model was found to be most favorable due to its easy adaptability and relative flexibility.
The present study experimentally investigates the effects of different fuel injection parameters on performance characteristics and emissions of a thermoacoustic pulse combustor. Several fuel nozzles were designed to enable various injection schemes. Pressure, photoelectric and radical spectra signals were measured for different fuel nozzles under the same fuel supply pressure; evaluation indexes, to describe the running performance of the pulse combustor, were introduced based on the pressure signal. Preliminary analysis of the pressure signals and evaluation indexes showed that the fuel nozzle with a small top angle was beneficial to the operation performance of the pulse combustor, and there exist an optimal spacing of nozzle holes to enhance the combustor performance most effectively. To further study the influence mechanism, a detailed analysis of the cyclic behaviors of pressure and photoelectric signals was then conducted. Several crests were observed in the cyclic photoelectric signal, all showed different characteristics for different fuel nozzle parameters. It was found that these crests influenced heat release distribution, and therefore, the thermoacoustic behavior and operation performance of the pulse combustor. Rayleigh's efficiency was calculated to quantitatively analyze the effect of various crests on the thermoacoustic coupling in the combustor. In addition to operation performance, radical emissions for different fuel nozzle parameters were also investigated. The obtained radical signals have five spectra peaks (309.35 nm, 430.48 nm, 516.19 nm, 766.19 nm and 927.12 nm) for liquefied petroleum gas. The larger spectra peaks of the free radicals generally indicated higher combustion chemical reaction intensity. Results showed that the fuel nozzle with the small top angle has large spectra peak values and an optimal spacing of nozzle holes that maximized the combustion intensity. This study benefits the optimal design of the nozzle and the improvement of performance as well as efficiency of the combustor.
Impact of alternative fuel properties on combustion instabilities, noise, and vibrations
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Combustion instability is an event where small disturbances in a flame caused by fuel flow rate fluctuations, heat release rate fluctuations combustor design where poor mixing occurs and other factors grow in an uncontrolled manner to then affect the flame in detrimental manner such as excessive noise, vibration increased flame turbulence and in dire situations flame outs. This chapter aims to describe how the fuel used in a gas turbine can impact the stability of a flame in the combustion chamber with a special focus trained upon the use of alternative fuels in gas turbines, a pressing concern given the climate imperative.
This chapter discusses the impact of different fuels and their properties on combustion instabilities, noise, and vibrations. This area of research is fairly new in aviation, and very little literature is available about this topic. Overall, this chapter has shown that different fuels and their properties can impact noise, vibrations, and combustion instability at combustor and engine levels.
Pulse combustion reactor as a fast and scalable synthetic method for preparation of Li-ion cathode materials
2017, Journal of Power Sources
Citation Excerpt :
First it is necessary to combust a fuel rich mixture, then a suitable frequency of combustion has to be reached for a complete combustion and the spray gas must be inert (nitrogen). The frequency of combustion was altered using the characteristic mixing time and characteristic kinetic time [28–30], for the reductive atmosphere we operated at around 240 Hz. Finally, also the stoichiometry of the precursor has to be fuel rich [18].
In this work a novel pulse combustion reactor method for preparation of Li-ion cathode materials is introduced. Its advantages and potential challenges are demonstrated on two widely studied cathode materials, LiFePO₄/C and Li-rich NMC. By exploiting the nature of efficiency of pulse combustion we have successfully established a slightly reductive or oxidative environment necessary for synthesis. As a whole, the proposed method is fast, environmentally friendly and easy to scale. An important advantage of the proposed method is that it preferentially yields small-sized powders (in the nanometric range) at a fast production rate of 2 s. A potential disadvantage is the relatively high degree of disorder of synthesized active material which however can be removed using a post-annealing step. This additional step allows a further tuning of materials morphology as shown and commented in some detail.
A state-of-the-art review of pulse combustion: Principles, modeling, applications and R&D issues
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Citation Excerpt :
However, so far the authors had not addressed the relative and absolute magnitudes of the characteristic time scales. Later on, Keller and co-workers [124] studied the quantification of characteristic times, which made it possible to predict and control τtotal for the P-C devices. Two numerical models were established to calculate τmixing and τkinetic, and these were validated by experimental measurements.
Combustion of fuels provides more than 90% of the worlds׳ primary energy demand at the costs of negative environmental impacts. In the recent years, substantial research has been carried out to explore clean and efficient combustion technologies to meet the ever-increasing demand for sustainable energy production using both fossil and renewable fuels at stringent environmental standards. In relation to advanced combustion technologies such as moderate or intense low-oxygen dilution (MILD), pulse combustion is one of the most promising techniques to burn diversified fuels ranging from high-grade natural gas and propane to low-grade fuels such as biogas, syngas or biodiesel high combustion efficiencies and minimal pollutant emissions (e.g., SO_x, NO_x). In spite of growing interest in pulse combustion technology, its state-of-the art is largely missing in the literature. The aim of this paper is to provide a comprehensive yet concise review of pulse combustion regarding the phenomenon and background of such combustion, modeling, experimental findings and industrial applications. First, the basics of pulse combustion are presented which include pulse combustor classification and types, operation principles, and advantages and disadvantages. In view of sustainability, pulse combustion characteristics with different fuel (e.g., biogas) are fully elaborated. Then, pulse combustion models described in topical literature are classified into different types and thoroughly examined. Next, experimental and numerical studies performed by numerous researchers are summarized, and the applications of pulse combustion in different fields, particularly in drying are presented, and its great potential to promote the utilization of renewable fuels is analyzed. Finally, the barriers, challenges, and R&D for pulse combustion are identified and a constructive discussion on these issues is provided. Key publications for the readers seeking broader and in-depth information are also given.
Pressure-heat release measurements during start-up conditions in a pulse combustor
2005, Proceedings of the Combustion Institute
Citation Excerpt :
They are often cited in the literature as having high thermal efficiencies, low pollutant emissions, and high rates of heat and mass transfer resulting from their oscillating pressure, temperature, and velocity fields [1–4]. Active research in the field of pulse combustion has led to significant improvements in our understanding of the mechanisms behind their emission’s performance [3–5], the importance and interdependence of characteristic chemical, flow and resonance times [6,7], tailpipe velocity and temperature characteristics [8,9], and the role of fluid dynamic strain on the periodic combustion processes [10,11]. Perhaps, most importantly, many of the mechanisms elucidated by pulse combustion studies have penetrated into the broader field of thermo-acoustic combustion instability.
An experimental study focusing on the temporal evolution of the global OH heat release (q′) and dynamic pressure (p′) from ignition to limit cycle conditions in an aerovalved pulse combustor has been carried out. The motivation of the work was to investigate how the thermo-acoustic relationships evolve, as very little is understood regarding how pressure and heat release couplings develop prior to establishing limit cycle conditions. The start-up experiments demonstrated that the total start-up sequences occurred within 100 ms and can be subdivided into three regimes: (i) ignition and decay; (ii) instability growth; and (iii) onset of limit cycle operation. The main results showed that upon ignition the high amplitude impulse pressure wave corresponded to the natural frequency of the pulse combustor at ambient gas temperature and was verified by an acoustic model. The pressure field over the growth period exhibited two main trends, either steady amplitude growth or a short delay interval followed by steady amplitude growth to limit cycle conditions. Overall, no reproducibility in frequency or phase during the growth period was observed pointing to the influence of strong non-linear interactions. When operating under limit cycle conditions, the heat release and pressure oscillations were in phase, possessed high levels of coherence, and exhibited narrow band frequency response at the operating frequency and several harmonics.

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^☆: This work was supported by the U.S. Department of Energy, Office of Energy Utilization Research, Division of Energy Conversion and Utilization Technologies and the Gas Research Institute.

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Pulse combustion: The quantification of characteristic times☆

Abstract

Prog. Energy Combust. Sci.

Pulse Combustion: The Importance of Characteristic Times

Combust. Flame

Photographic and Analytical Study of Diesel Combustion Machine

SAE Trans.

The Role of Fluid Dynamic Mixing in Pulse Combustors

Sandia National Laboratories Report SAND87-8622

The Theory of Turbulent Jets

The Turbulent Exponential Jet

Phys. Fluids