Shockless Explosion Combustion: Experimental Investigation of a New Approximate Constant Volume Combustion Process

2016 ◽  
Author(s):  
Thoralf G. Reichel ◽  
Bernhard C. Bobusch ◽  
Christian Oliver Paschereit ◽  
Jan-Simon Schäpel ◽  
Rudibert King ◽  
...  
Keyword(s):  
Shock Waves ◽  
Ignition Delay ◽  
Gas Turbines ◽  
Control Algorithm ◽  
Ambient Pressure ◽  
Pressure Sensors ◽  
Constant Volume ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Constant Volume Combustion

Approximate constant volume combustion (aCVC) is a promising way to achieve a step change in the efficiency of gas turbines. This work investigates a recently proposed approach to implement aCVC in a gas turbine combustion system: shockless explosion combustion (SEC). The new concept overcomes several disadvantages such as sharp pressure transitions, entropy generation due to shock waves, and exergy losses due to kinetic energy which are associated with other aCVC approaches like, e.g., pulsed detonation combustion. The combustion is controlled via the the fuel/air mixture distribution which is adjusted such that the entire fuel/air volume undergoes a spatially quasi-homogeneous autoignition. Accordingly, no shock waves occur and the losses associated with a detonation wave are not present in the proposed system. Instead, a smooth pressure rise is created due to the heat release of the homogeneous combustion. An atmospheric combustion test rig is designed to investigate the autoignition behavior of relevant fuels under intermittent operation, currently up to a frequency of 2Hz. Application of OH*- and dynamic pressure sensors allows for a spatially- and time-resolved detection of ignition delay times and locations. Dimethyl ether (DME) is used as fuel since it exhibits reliable autoignition already at 920K mixture temperature and ambient pressure. First, a model-based control algorithm is used to demonstrate that the fuel valve can produce arbitrary fuel profiles in the combustion tube. Next, the control algorithm is used to achieve the desired fuel stratification, resulting in a significant reduction in spatial variance of the auto-ignition delay times. This proves that the control approach is a useful tool for increasing the homogeneity of the autoignition.

Shockless Explosion Combustion: Experimental Investigation of a New Approximate Constant Volume Combustion Process

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Thoralf G. Reichel ◽  
Jan-Simon Schäpel ◽  
Bernhard C. Bobusch ◽  
Rupert Klein ◽  
Rudibert King ◽  
...  
Keyword(s):  
Shock Waves ◽  
Ignition Delay ◽  
Gas Turbines ◽  
Control Algorithm ◽  
Pressure Sensors ◽  
Constant Volume ◽  
Ignition Delay Times ◽  
Auto Ignition ◽  
Delay Times ◽  
Constant Volume Combustion

Approximate constant volume combustion (aCVC) is a promising way to achieve a step change in the efficiency of gas turbines. This work investigates a recently proposed approach to implement aCVC in a gas turbine combustion system: shockless explosion combustion (SEC). The new concept overcomes several disadvantages such as sharp pressure transitions, entropy generation due to shock waves, and exergy losses due to kinetic energy which are associated with other aCVC approaches such as pulsed detonation combustion. The combustion is controlled via the fuel/air mixture distribution which is adjusted such that the entire fuel/air volume undergoes a spatially quasi-homogeneous auto-ignition. Accordingly, no shock waves occur and the losses associated with a detonation wave are not present in the proposed system. Instead, a smooth pressure rise is created due to the heat release of the homogeneous combustion. An atmospheric combustion test rig is designed to investigate the auto-ignition behavior of relevant fuels under intermittent operation, currently up to a frequency of 2 Hz. Application of OH*– and dynamic pressure sensors allows for a spatially and time-resolved detection of ignition delay times and locations. Dimethyl ether (DME) is used as fuel since it exhibits reliable auto-ignition already at 920 K mixture temperature and ambient pressure. First, a model-based control algorithm is used to demonstrate that the fuel valve can produce arbitrary fuel profiles in the combustion tube. Next, the control algorithm is used to achieve the desired fuel stratification, resulting in a significant reduction in spatial variance of the auto-ignition delay times. This proves that the control approach is a useful tool for increasing the homogeneity of the auto-ignition.

scholarly journals Aerosol Shock Tube Designed for Ignition Delay Time Measurements of Low-Vapor-Pressure Fuels and Auto-Ignition Flow-Field Visualization

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 683
Author(s):  
Erwei Liu ◽  
Qin Liao ◽  
Shengli Xu
Keyword(s):  
Flow Field ◽  
Vapor Pressure ◽  
Shock Tube ◽  
Ignition Delay ◽  
Pressure Sensors ◽  
Local Pressure ◽  
Ignition Delay Times ◽  
Auto Ignition ◽  
Delay Times ◽  
Sequential Images

An aerosol shock tube has been developed for measuring the ignition delay times (tig) of aerosol mixtures of low-vapor-pressure fuels and for visualization of the auto-ignition flow-field. The aerosol mixture was formed in a premixing tank through an atomizing nozzle. Condensation and adsorption of suspended droplets were not observed significantly in the premixing tank and test section. A particle size analyzer was used to measure the Sauter mean diameter (SMD) of the aerosol droplets. Three pressure sensors and a photomultiplier were used to detect local pressure and OH emission respectively. Intensified charge-coupled device cameras were used to capture sequential images of the auto-ignition flow-field. The results indicated that stable and uniform aerosol could be obtained by this kind of atomizing method and gas distribution system. The averaged SMD for droplets of toluene ranged from 2 to 5 μ m at pressures of 0.14–0.19 MPa of dilute gases. In the case of a stoichiometric mixture of toluene/O2/N2, ignition delay times ranged from 77 to 1330 μs at pressures of 0.1–0.3 MPa, temperatures of 1432–1716 K and equivalence ratios of 0.5–1.5. The logarithm of ignition delay times was approximately linearly correlated to 1000/T. In contrast to the reference data, ignition delay times of aerosol toluene/O2/N2 were generally larger. Sequential images of auto-ignition flow-field showed the features of flame from generation to propagation.

Low hydrocarbon mixtures ignition delay times investigation behind reflected shock waves

Shock Waves ◽  
2002 ◽  
Vol 11 (4) ◽  
pp. 309-322 ◽  
Author(s):  
N. Lamoureux ◽  
C.-E. Paillard ◽  
V. Vaslier
Keyword(s):  
Shock Waves ◽  
Ignition Delay ◽  
Hydrocarbon Mixtures ◽  
Reflected Shock ◽  
Ignition Delay Times ◽  
Delay Times

DME as a Potential Alternative Fuel for Gas Turbines: A Numerical Approach to Combustion and Oxidation Kinetics

2011 ◽  
Author(s):  
Pierre A. Glaude ◽  
Rene´ Fournet ◽  
Roda Bounaceur ◽  
Michel Molie`re
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Heat Input ◽  
Ignition Delay ◽  
Gas Turbines ◽  
Ignition Temperature ◽  
Alternative Fuels ◽  
Ignition Delay Times ◽  
Auto Ignition ◽  
Delay Times

Many investigations are currently carried out in order to reduce CO2 emissions in power generation. Among alternative fuels to natural gas and gasoil in gas turbine applications, dimethyl ether (DME; formula: CH3-O-CH3) represents a possible candidate in the next years. This chemical compound can be produced from natural gas or coal/biomass gasification. DME is a good substitute for gasoil in diesel engine. Its Lower Heating Value is close to that of ethanol but it offers some advantages compared to alcohols in terms of stability and miscibility with hydrocarbons. While numerous studies have been devoted to the combustion of DME in diesel engines, results are scarce as far as boilers and gas turbines are concerned. Some safety aspects must be addressed before feeding a combustion device with DME because of its low flash point (as low as −83°C), its low auto-ignition temperature and large domain of explosivity in air. As far as emissions are concerned, the existing literature shows that in non premixed flames, DME produces less NOx than ethane taken as parent molecular structure, based on an equivalent heat input to the burner. During a field test performed in a gas turbine, a change-over from methane to DME led to a higher fuel nozzle temperature but to a lower exhaust gas temperature. NOx emissions decreased over the whole range of heat input studied but a dramatic increase of CO emissions was observed. This work aims to study the combustion behavior of DME in gas turbine conditions with the help of a detailed kinetic modeling. Several important combustion parameters, such as the auto-ignition temperature (AIT), ignition delay times, laminar burning velocities of premixed flames, adiabatic flame temperatures, and the formation of pollutants like CO and NOx have been investigated. These data have been compared with those calculated in the case of methane combustion. The model was built starting from a well validated mechanism taken from the literature and already used to predict the behavior of other alternative fuels. In flame conditions, DME forms formaldehyde as the major intermediate, the consumption of which leads in few steps to CO then CO2. The lower amount of CH2 radicals in comparison with methane flames seems to decrease the possibility of prompt-NO formation. This paper covers the low temperature oxidation chemistry of DME which is necessary to properly predict ignition temperatures and auto-ignition delay times that are important parameters for safety.

Reaction Mechanisms for Methane Ignition

2000 ◽  
Author(s):  
S. C. Li ◽  
F. A. Williams
Keyword(s):  
Temperature Sensitivity ◽  
Reaction Mechanisms ◽  
Ignition Delay ◽  
Low Temperatures ◽  
Gas Turbines ◽  
Elementary Reactions ◽  
Detailed Mechanism ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Flame Chemistry

To help understand how methane ignition occurs in gas turbines, dual-fuel diesel engines and other combustion devices, the present study addresses reaction mechanisms with the objective of predicting autoignition times for temperatures between 1000 K and 2000 K, pressures between 1 bar and 150 bar and equivalence ratio between 0.4 and 3. It extends our previous methane flame chemistry and refines earlier methane ignition work. In addition to a detailed mechanism, short mechanisms are presented that retain essential features of the detailed mechanism. The detailed mechanism consists of 127 elementary reactions among 31 species and results in 9 intermediate species being most important in autoignition, namely, CH3, OH, HO2, H2O2, CH2O, CHO, CH3O, H, O. Below 1300 K the last 3 of these are unimportant, but above 1400 K all are significant. To further simplify the computation, systematically reduced chemistry is developed, and an analytical solution for ignition delay times is obtained in the low-temperature range. For most fuels, a single Arrhenius fit for the ignition delay is adequate, but for hydrogen the temperature sensitivity becomes stronger at low temperatures. The present study predicts that, contrary to hydrogen, for methane the temperature sensitivity of the autoignition delay becomes stronger at high temperatures, above 1400 K, and weaker at low temperatures, below 1300 K. Predictions are in good agreement with shock-tube experiments. The results may be employed to estimate ignition delay times in practical combustors.

scholarly journals The Influence of Mixedness on Ignition for Hydrogen Direct Injection in a Constant Volume Combustion Chamber

2018 ◽  
Author(s):  
Martia Shahsavan ◽  
Mohammadrasool Morovatiyan ◽  
John Hunter Mack
Keyword(s):  
Combustion Chamber ◽  
Ignition Delay ◽  
Gas Turbines ◽  
Flame Temperature ◽  
Constant Volume ◽  
Working Fluid ◽  
Scalar Dissipation ◽  
Mixing Rate ◽  
Constant Volume Combustion ◽  
Constant Volume Combustion Chamber

The ignition behavior of the fuel in non-premixed turbulent combustion applications such as diesel engines and gas turbines is dependent on the mixing rate of the injected fuel and the working fluid. In this study, three-dimensional modeling of hydrogen injection into a constant volume combustion chamber (CVCC) is used to investigate the correlation between the mixing rate and important parameters of non-premixed combustion, such as ignition delay. Mixedness is quantified using mean spatial variation, which reflects the homogeneity of the mixture, and mean scalar dissipation, which represents the local gradients of the scalar. The case studies include nitrogen and argon as working fluids; injection velocities and nozzle diameters are varied for comparison. For consistency, the injected mass is kept constant and the injection duration is adjusted accordingly. The results indicate that a strong correlation exists between ignition delay and the defined mixedness parameters. The cases with higher mixedness values lead to a shorter ignition delay and a higher maximum flame temperature. Changing the working fluid and injection parameters can effectively modify the mixedness, and consequently affect the ignition onset and flame properties.

Shock-Induced the Ignition Mechanism of Micrometer Aluminum/Propylene Oxide

2010 ◽  
Vol 129-131 ◽  
pp. 1088-1092
Author(s):  
Chang Ying Yuan ◽  
Zheng Xin Yan
Keyword(s):  
Shock Wave ◽  
Propylene Oxide ◽  
Ignition Delay ◽  
Ignition Time ◽  
Pressure Sensors ◽  
Incident Shock ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Ignition Mechanism ◽  
Spectral Intensities

An incident shock tube technique has been used to measure the ignition delay time for propylene oxide-oxygen-nitrogen mixtures in the temperature range of 900 to 1250K. Ignition delay times of CO*(460.3nm) and AlO (470.5nm) were measured using pressure sensors under series of shock strength. The ignition time of AlO was linearly decreased as the induced shock wave strength was increased. The spectral intensities of AlO under corresponding to shock wave strength were evaluated by intensity CCD(ICCD) spectral system triggered by optic signal.

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