Analysis of chemical effects on reflected-shock flow fields in combustible gas

1985 ◽  
Vol 160 ◽  
pp. 29-45 ◽  
Author(s):  
Yasunari Takano ◽  
Teruaki Akamatsu
Keyword(s):  
Heat Release ◽  
Chemical Reactions ◽  
Induction Time ◽  
Combustion Process ◽  
Chemical Species ◽  
Flow Fields ◽  
Rate Equations ◽  
Reflected Shock ◽  
Combustible Gas ◽  
Analytical Results

This paper analyses effects of chemical reactions on reflected-shock flow fields in shock tubes. The method of linearized characteristics is applied to analyse gasdynamic disturbances due to chemical reactions. The analysis treats cases where combustible gas is highly diluted in inert gas, and assumes that flows are one-dimensional and that upstream flows in front of the reflected-shock waves are in the frozen state. The perturbed gasdynamic properties in the reflected-shock flow fields are shown to be expressible mainly in terms of a heat-release function for combustion process. In particular, simple relations are obtained between the heat-release function and the physical properties at the end wall of a shock tube. As numerical examples of the analysis, the present formulation is applied to calculate gasdynamic properties in the reflected-shock region in a H2–O2–Ar mixture. Procedures are demonstrated for calculation of the heat-release function by numerically integrating rate equations for chemical species. The analytical results are compared with rigorous solutions obtained numerically by use of a finite-difference method. It is shown that the formulation can afford exact solutions in cases where chemical behaviours are not essentially affected by gasdynamic behaviours. When the induction time of the combustion process is reduced to some extent owing to gasdynamic disturbances, some discrepancies appear between analytical results and rigorous solutions. An estimate is made of the induction-time reduction, and a condition is written down for applicability of the analysis.

scholarly journals Some Effects of Hydrogen Self-Ignition and Combustion in Supersonic Flow

2014 ◽  
Vol 16 (2-3) ◽  
pp. 245
Author(s):  
U. Zhapbasbayev ◽  
V. Zabaykin ◽  
Y. Makashev ◽  
A. Tursynbay ◽  
B. Urmashev
Keyword(s):  
Supersonic Flow ◽  
Heat Release ◽  
Chemical Reactions ◽  
Laboratory Data ◽  
Combustion Process ◽  
Supersonic Combustion ◽  
Low Flow ◽  
Diffusion Combustion ◽  
Maximum Pressure ◽  
Combustion Mode

<p>Results are presented of computational and experimental investigations of the influence of temperature and flow composition on the hydrogen combustion kinetics for a coaxial fuel supersonic flow. Depending on the flow parameters, combustion is shown to occur with an intense heat release governed by the speed of chemical reactions, or a diffusion combustion with heat release governed by mixing. The computational results are in good agreements of with laboratory data and portrays many important features of supersonic combustion. The influence of the gas temperature and composition on the diffusion combustion of a circular hydrogen jet in supersonic coaxial flow at the over expanded exhaust regimes is investigated. It is found that at low flow temperatures (Т<sub>2 </sub>~ 900 K) and in the absence of water vapors in the oxidizer gas composition, the speed of chemical reactions is the determining factor for combustion. An increase in the flow temperature (Т<sub>2</sub> &gt; 1200 K) causes a reduction of the induction time of the reactive mixture, because the mixing of fuel with oxidizer decreases, and a “sluggish” diffusion combustion of non-mixed gases is observed. The presence of water vapor and active radicals in the gas ensures the self-ignition from the start of the mixing, and the diffusion combustion mode is limited by mixing of the hydrogen jet with the coaxial flow (similar to the case with high initial temperatures of the air stream). In the case of the delay combustion process the maximum pressure level on the wall is 10% more than that in the combustion mode with ignition at the start of mixing. A sluggish combustion regime may lead to an incomplete hydrogen burnout.</p>

Shock-Induced Mixing With Chemical Reactions Using the FLASH Code

2014 ◽  
Author(s):  
H. Varshochi ◽  
N. Attal ◽  
P. Ramaprabhu
Keyword(s):  
Heat Release ◽  
Chemical Reactions ◽  
Heat Release Rate ◽  
Release Rate ◽  
Methane Combustion ◽  
Single Mode ◽  
Driving Mechanism ◽  
Detailed Chemical Kinetics ◽  
Reflected Shock ◽  
Mixing Behavior

FLASH is a massively parallel, multi-physics, open source code developed by the University of Chicago [1] for investigating astrophysical phenomena. FLASH was modified [2] to handle detailed chemical kinetics for hydrogen and methane combustion and heat release, in order to enable the code to be used for combustion applications. These capabilities have been tested and validated [2, 3] through an extensive suite of simulations. These modifications include the addition of detailed H2-air and CH4-air chemistry along with temperature dependent thermodynamic and transport properties. The aim of this work is to apply the modified version of FLASH to three cases of highly compressible supersonic flows, involving chemical reactions. The first problem is a reacting shock-bubble interaction, in which the shock triggers combustion in a fuel bubble. In the second problem, a two-dimensional, Richtmyer-Meshkov Instability leading to combustion of the fuel at a non-premixed, single mode perturbed interface has been studied numerically. In these cases, the relationship between the integral heat release rate, the integral H2O production rate and total circulation is investigated. In the third example, a multimode perturbed interface has been implemented into a 3D simulation. Time evolution of the interface undergoing reacting RMI is studied. By defining a reflecting endwall for RMI simulations, the effect of a second reflected shock on the mixing behavior and combustion on an already shocked interface has been studied. Numerical simulations of the interaction of a shock (Mach number 2) in air with H2 bubble was performed [2]. The misalignment between the pressure gradient across the shock front and the density gradient at the site of H2-Air interface generates baroclinc vorticity. This phenomenon generates counter-rotating vortices that breakdown the H2 bubble (fuel). The rapid breakdown of the H2 bubble transitions to turbulent mixing, intensifying the heat release rate. In two more general configurations, chemically reacting, single-mode and multimode Richtmyer-Meshkov Instability has been studied. RMI is the driving mechanism for growth of small interfacial perturbations. Initially single-mode perturbations of small amplitude grow linearly due to impulsive acceleration by shock. This is followed by non-linear growth at late times due to the formation of secondary Kelvin-Helmholtz instability. Heat release and product formation in the vicinity of interface will affect perturbation growth rates which will affect the mixing behavior and therefore the combustion efficiency [4].

scholarly journals The Effect of RME-1-Butanol Blends on Combustion, Performance and Emission of a Direct Injection Diesel Engine

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2941
Author(s):  
Wojciech Tutak ◽  
Arkadiusz Jamrozik ◽  
Karol Grab-Rogaliński
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Direct Injection ◽  
Specific Energy Consumption ◽  
Combustion Process ◽  
Constant Load ◽  
Combustion Stability ◽  
Performance And Emission ◽  
Energy Share ◽  
The Stability

The main objective of this study was assessment of the performance, emissions and combustion characteristics of a diesel engine using RME–1-butanol blends. In assessing the combustion process, great importance was placed on evaluating the stability of this process. Not only were the typical COVIMEP indicators assessed, but also the non-burnability of the characteristic combustion stages: ignition delay, time of 50% heat release and the end of combustion. The evaluation of the combustion process based on the analysis of heat release. The tests carried out on a 1-cylinder diesel engine operating at a constant load. Research and evaluation of the combustion process of a mixture of RME and 1-butanol carried out for the entire range of shares of both fuels up to 90% of 1-butanol energetic fraction. The participation of butanol in combustion process with RME increased the in-cylinder peak pressure and the heat release rate. With the increase in the share of butanol there was noted a decrease in specific energy consumption and an increase in engine efficiency. The share of butanol improved the combustion stability. There was also an increase in NOx emissions and decrease in CO and soot emissions. The engine can be power by blend up to 80% energy share of butanol.

scholarly journals Combustion Thermodynamics of Ethanol, n-Heptane, and n-Butanol in a Rapid Compression Machine with a Dual Direct Injection (DDI) Supply System

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2729
Author(s):  
Ireneusz Pielecha ◽  
Sławomir Wierzbicki ◽  
Maciej Sidorowicz ◽  
Dariusz Pietras
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
Internal Combustion Engines ◽  
Direct Injection ◽  
Combustion Process ◽  
Combustion Efficiency ◽  
Injection System ◽  
Rapid Compression Machine ◽  
Process Indicators ◽  
Rapid Compression

The development of internal combustion engines involves various new solutions, one of which is the use of dual-fuel systems. The diversity of technological solutions being developed determines the efficiency of such systems, as well as the possibility of reducing the emission of carbon dioxide and exhaust components into the atmosphere. An innovative double direct injection system was used as a method for forming a mixture in the combustion chamber. The tests were carried out with the use of gasoline, ethanol, n-heptane, and n-butanol during combustion in a model test engine—the rapid compression machine (RCM). The analyzed combustion process indicators included the cylinder pressure, pressure increase rate, heat release rate, and heat release value. Optical tests of the combustion process made it possible to analyze the flame development in the observed area of the combustion chamber. The conducted research and analyses resulted in the observation that it is possible to control the excess air ratio in the direct vicinity of the spark plug just before ignition. Such possibilities occur as a result of the properties of the injected fuels, which include different amounts of air required for their stoichiometric combustion. The studies of the combustion process have shown that the combustible mixtures consisting of gasoline with another fuel are characterized by greater combustion efficiency than the mixtures composed of only a single fuel type, and that the influence of the type of fuel used is significant for the combustion process and its indicator values.

scholarly journals The Synergy of Two Biofuel Additives on Combustion Process to Simultaneously Reduce NOx and PM Emissions

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2784
Author(s):  
Jerzy Cisek ◽  
Szymon Lesniak ◽  
Winicjusz Stanik ◽  
Włodzimierz Przybylski
Keyword(s):  
Heat Release ◽  
Combustion Rate ◽  
Combustion Process ◽  
The Other ◽  
Fuel Additive ◽  
Exhaust Gas ◽  
Synergy Effect ◽  
Engine Exhaust ◽  
Other Hand ◽  
Heat Released

The article presents the results of research on the influence of two fuel additives that selectively affect the combustion process in a diesel engine cylinder. The addition of NitrON® reduces the concentration of nitrogen oxides (NOx), due to a reduction in the kinetic combustion rate, at the cost of a slight increase in the concentration of particulate matter (PM) in the engine exhaust gas. The Reduxco® additive reduces PM emissions by increasing the diffusion combustion rate, while slightly increasing the NOx concentration in the engine exhaust gas. Research conducted by the authors confirmed that the simultaneous use of both of these additives in the fuel not only reduced both NOx and PM emissions in the exhaust gas but additionally the reduction of NOx and PM emissions was greater than the sum of the effects of these additives—the synergy effect. Findings indicated that the waveforms of the heat release rate (dQ/dα) responsible for the emission of NOx and PM in the exhaust gas differed for the four tested fuels in relation to the maximum value (selectively and independently in the kinetic and diffusion stage), and they were also phase shifted. Due to this, the heat release process Q(α) was characterized by a lower amount of heat released in the kinetic phase compared to fuel with NitrON® only and a greater amount of heat released in the diffusion phase compared to fuel with Reduxco® alone, which explained the lowest NOx and PM emissions in the exhaust gas at that time. For example for the NOx concentration in the engine exhaust: the Nitrocet® fuel additive (in the used amount of 1500 ppm) reduces the NOx concentration in the exhaust gas by 18% compared to the base fuel. The addition of a Reduxco® catalyst to the fuel (1500 ppm) unfortunately increases the NOx concentration by up to 20%. On the other hand, the combustion of the complete tested fuel, containing both additives simultaneously, is characterized, thanks to the synergy effect, by the lowest NOx concentration (reduction by 22% in relation to the base). For example for PM emissions: the Nitrocet® fuel additive does not significantly affect the PM emissions in the engine exhaust (up to a few per cent compared to the base fuel). The addition of a Reduxco® catalyst to the fuel greatly reduces PM emissions in the engine exhaust, up to 35% compared to the base fuel. On the other hand, the combustion of the complete tested fuel containing both additives simultaneously is characterized by the synergy effect with the lowest PM emission (reduction of 39% compared to the base fuel).

scholarly journals A Review on Recent Progress of Glycan-Based Surfactant Micelles as Nanoreactor Systems for Chemical Synthesis Applications

2021 ◽  
Vol 2 (1) ◽  
pp. 168-186
Author(s):  
Bahareh Vafakish ◽  
Lee D. Wilson
Keyword(s):  
Chemical Synthesis ◽  
Chemical Reactions ◽  
Recent Progress ◽  
Chemical Species ◽  
Reaction Rates ◽  
Bulk Solution ◽  
Surfactant Micelles ◽  
Conventional Surfactant ◽  
Recent Developments ◽  
To Receive

The nanoreactor concept and its application as a modality to carry out chemical reactions in confined and compartmentalized structures continues to receive increasing attention. Micelle-based nanoreactors derived from various classes of surfactant demonstrate outstanding potential for chemical synthesis. Polysaccharide (glycan-based) surfactants are an emerging class of biodegradable, non-toxic, and sustainable alternatives over conventional surfactant systems. The unique structure of glycan-based surfactants and their micellar structures provide a nanoenvironment that differs from that of the bulk solution, and supported by chemical reactions with uniquely different reaction rates and mechanisms. In this review, the aggregation of glycan-based surfactants to afford micelles and their utility for the synthesis of selected classes of reactions by the nanoreactor technique is discussed. Glycan-based surfactants are ecofriendly and promising surfactants over conventional synthetic analogues. This contribution aims to highlight recent developments in the field of glycan-based surfactants that are relevant to nanoreactors, along with future opportunities for research. In turn, coverage of research for glycan-based surfactants in nanoreactor assemblies with tailored volume and functionality is anticipated to motivate advanced research for the synthesis of diverse chemical species.

scholarly journals Detailed Derivations of Formulas for Heat Release Rate Calculations Revisited: A Pedagogical and Systematic Approach

2019 ◽  
Vol 124 ◽  
Author(s):  
Jiann C. Yang
Keyword(s):  
Oxygen Consumption ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Chemical Engineering ◽  
Chemical Species ◽  
Flow Process ◽  
Generalized Framework ◽  
Oxygen Consumption Calorimetry ◽  
Engineering Practices

The derivations of the formulas for heat release rate calculations are revisited based on the oxygen consumption principle. A systematic, structured, and pedagogical approach to formulate the problem and derive the generalized formulas with fewer assumptions is used. The operation of oxygen consumption calorimetry is treated as a chemical flow process, the problem is formulated in matrix notation, and the associated material balances using the tie component concept commonly used in chemical engineering practices are solved. The derivation procedure described is intuitive and easy to follow. Inclusion of other chemical species in the measurements and calculations can be easily implemented using the generalized framework developed here.

Novel rate equations describing isochronous chemical reactions

2010 ◽  
Vol 49 (4) ◽  
pp. 870-879
Author(s):  
F. Calogero ◽  
F. Leyvraz ◽  
M. Sommacal
Keyword(s):  
Chemical Reactions ◽  
Rate Equations

Analysis of Incylinder Pressure and Temperature Variation in a Four-Stroke S. I. Engine Using Wiebe’s Combustion Model

2014 ◽  
Vol 984-985 ◽  
pp. 957-961
Author(s):  
Vijayashree ◽  
P. Tamil Porai ◽  
N.V. Mahalakshmi ◽  
V. Ganesan
Keyword(s):  
Heat Release ◽  
Combustion Process ◽  
Pressure Variation ◽  
Spark Ignition Engine ◽  
Working Fluid ◽  
Combustion Model ◽  
Cylinder Pressure ◽  
Crank Angle ◽  
Experimental Values ◽  
Release Model

This paper presents the modeling of in-cylinder pressure variation of a four-stroke single cylinder spark ignition engine. It uses instantaneous properties of working fluid, viz., gasoline to calculate heat release rates, needed to quantify combustion development. Cylinder pressure variation with respect to either volume or crank angle gives valuable information about the combustion process. The analysis of the pressure – volume or pressure-theta data of a engine cycle is a classical tool for engine studies. This paper aims at demonstrating the modeling of pressure variation as a function of crank angle as well as volume with the help of MATLAB program developed for this purpose. Towards this end, Woschni heat release model is used for the combustion process. The important parameter, viz., peak pressure for different compression ratios are used in the analysis. Predicted results are compared with experimental values obtained for a typical compression ratio of 8.3.

Real-time capable simulation of diesel combustion processes for HiL applications

2017 ◽  
Vol 19 (2) ◽  
pp. 214-229 ◽  
Author(s):  
Daniel Neumann ◽  
Christian Jörg ◽  
Nils Peschke ◽  
Joschka Schaub ◽  
Thorsten Schnorbus
Keyword(s):  
Heat Release ◽  
Real Time ◽  
Fuel Injection ◽  
Combustion Process ◽  
Boost Pressure ◽  
Diesel Combustion ◽  
Main Challenge ◽  
Combustion Properties ◽  
Input Variables ◽  
Improved Model

The complexity of the development processes for advanced diesel engines has significantly increased during the last decades. A further increase is to be expected, due to more restrictive emission legislations and new certification cycles. This trend leads to a higher time exposure at engine test benches, thus resulting in higher costs. To counter this problem, virtual engine development strategies are being increasingly used. To calibrate the complete powertrain and various driving situations, model in the loop and hardware in the loop concepts have become more important. The main effort in this context is the development of very accurate but also real-time capable engine models. Besides the correct modeling of ambient condition and driver behavior, the simulation of the combustion process is a major objective. The main challenge of modeling a diesel combustion process is the description of mixture formation, self-ignition and combustion as precisely as possible. For this purpose, this article introduces a novel combustion simulation approach that is capable of predicting various combustion properties of a diesel process. This includes the calculation of crank angle resolved combustion traces, such as heat release and other thermodynamic in-cylinder states. Furthermore, various combustion characteristics, such as combustion phasing, maximum gradients and engine-out temperature, are available as simulation output. All calculations are based on a physical zero-dimensional heat release model. The resulting reduction of the calibration effort and the improved model robustness are the major benefits in comparison to conventional data-driven combustion models. The calibration parameters directly refer to geometric and thermodynamic properties of a given engine configuration. Main input variables to the model are the fuel injection profile and air path–related states such as exhaust gas recirculation rate and boost pressure. Thus, multiple injection event strategies or novel air path control structures for future engine control concepts can be analyzed.

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