scholarly journals Experimental and computational investigation of temperature effects on soot mechanisms

2014 ◽  
Vol 79 (7) ◽  
pp. 881-895 ◽  
Author(s):  
Xiaojie Bi ◽  
Maoyu Xiao ◽  
Xinqi Qiao ◽  
Chia-Fon Lee ◽  
Liu Yu
Keyword(s):  
Ambient Temperature ◽  
Soot Formation ◽  
Oxidation Mechanism ◽  
Soot Oxidation ◽  
Ambient Temperatures ◽  
Operation Conditions ◽  
Constant Volume Chamber ◽  
Soot Mass ◽  
Soot Measurement ◽  
Soot Model

Effects of initial ambient temperatures on combustion and soot emission characteristics of diesel fuel were investigated through experiment conducted in optical constant volume chamber and simulation using phenomenological soot model. There are four difference initial ambient temperatures adopted in our research: 1000 K, 900 K, 800 K and 700 K. In order to obtain a better prediction of soot behavior, phenomenological soot model was revised to take into account the soot oxidation feedback on soot number density and good agreement was observed in the comparison of soot measurement and prediction. Results indicated that ignition delay prolonged with the decrease of initial ambient temperature. The heat release rate demonstrated the transition from mixing controlled combustion at high ambient temperature to premixed combustion mode at low ambient temperature. At lower ambient temperature, soot formation and oxidation mechanism were both suppressed. But finally soot mass concentration reduced with decreasing initial ambient temperature. Although the drop in ambient temperature did not cool the mean in-cylinder temperature during the combustion, it did shrink the total area of local high equivalence ratio, in which soot usually generated fast. At 700 K initial ambient temperature, soot emissions were almost negligible, which indicates that sootless combustion might be achieved at super low initial temperature operation conditions.

Computational Investigation of Diesel Combustion and Soot Formation With a Phenomenological Soot Model Under Different Temperatures in a Constant Volume Chamber

2014 ◽  
Author(s):  
Zhichao Zhao ◽  
Chia-Fon Lee ◽  
Yawei Chi ◽  
Jingping Liu
Keyword(s):  
Ambient Temperature ◽  
Soot Formation ◽  
Constant Volume ◽  
Diffusion Combustion ◽  
Soot Emission ◽  
Ambient Temperatures ◽  
Constant Volume Chamber ◽  
Constant Volume Combustion Chamber ◽  
Different Temperatures ◽  
Soot Model

The previous nine-step phenomenological soot model was revised by including the oxidation effect on soot number density. Using KIVA-3V Release 2 code coupled with this revised phenomenological soot model, multi-dimensional computational fluid dynamics (CFD) simulations of diesel spray combustion in a constant volume chamber was conducted to investigate the combustion physics and soot emission characteristics. Meanwhile, experiments were conducted in an optical constant volume combustion chamber under different ambient temperatures (800, 900, 1000 K), from which the combustion characteristics and soot distributions were obtained for validation. The results indicate that ignition retards with the decrease of ambient temperature, which results in more air-fuel mixing controlled diffusion combustion at high ambient temperature, and more premixed combustion at low ambient temperature. The corresponding soot formation and distribution shows that the soot emission is strongly related to the local equivalence ratio, which leads to lower soot emission in the lower initial temperature case with more homogeneous mixture. Compared to previous nine-step model, the revised model predicted lower soot number and bigger soot particles size.

A multistage combustion model and soot formation model for direct-injection diesel engines

2002 ◽  
Vol 216 (6) ◽  
pp. 495-504 ◽  
Author(s):  
G J Micklow ◽  
W Gong
Keyword(s):  
Diesel Engines ◽  
Soot Formation ◽  
Direct Injection ◽  
Combustion Process ◽  
Oxidation Mechanism ◽  
Soot Oxidation ◽  
Premixed Combustion ◽  
Combustion Model ◽  
Diffusion Combustion ◽  
Soot Model

A multistage combustion model for diesel engines is presented in this paper. Three combustion stages, ignition of diesel, premixed combustion and diffusion combustion, are considered in the combustion process in a typical medium speed direct injection diesel engine. The transition from the ignition delay to the premixed combustion stage occurs when the highest temperature in the cylinder is beyond a critical value, and the transition from the premixed combustion model to the diffusion combustion model occurs when a calculated fraction of the premixed fuel is burned, which is determined from an empirical correlation based on the engine design and running conditions. Significant improvements in the predictions for in-cylinder pressure and heat release rate were achieved compared with previous models. A soot model based on the Hiroyasu soot formation mechanism and the Nagle and Strickland-Constable soot oxidation mechanism was implemented in a standard KIVA3V code. The effect of the OH radical in soot oxidation was also incorporated into the soot model. Computations show that OH plays an important role during the late combustion stage. Predicted soot and NOx were compared with measured values and a good agreement was achieved.

Effects of Ambient Temperature and Oxygen Concentration on Soot Evolution in Diesel Spray Combustion

Volume 4 ◽  
2004 ◽  
Author(s):  
Yi Xu ◽  
Chia-Fon F. Lee
Keyword(s):  
Ambient Temperature ◽  
Heat Release ◽  
Oxygen Concentration ◽  
Heat Release Rate ◽  
Release Rate ◽  
Soot Formation ◽  
Premixed Combustion ◽  
Ambient Oxygen ◽  
Lower Heat ◽  
Soot Measurement

A newly developed Forward Illumination Light Extinction (FILE) soot measurement technique was applied in a constant volume spray chamber to study the effects of ambient temperature and oxygen concentration on soot evolution in diesel combustion. The FILE technique with the capability of two-dimensional time-resolved quantitative soot measurement provides the much-needed information to investigate the soot formation mechanism. The ambient temperatures of 1200K, 1000K and 800K were tested to study the temperature effects on soot formation. A decrease of ambient temperature results in a longer ignition delay, which promotes a larger premixed combustion zone combining with higher heat release rates. The change of ambient temperature from 1200K to 800K increases the fuel portion burnt in the premixed combustion period. At 800K, combustion is dominated by the premixed combustion and much less soot is formed. Diesel combustion with 21% and 15% ambient oxygen concentration was also studied. With lower ambient oxygen concentration, the combustion process is basically not changed, but expands into a longer time span with a lower heat release rate. The lower heat release rate results in a lower flame temperature, which benefits the NOx emission control. However, with about the same amount of soot within the flame, and much longer soot life, soot has more chance to escape to the exhaust.

Modeling Soot Formation Using Reduced PAH Chemistry in n-Heptane Lifted Flames With Application to Low Temperature Combustion

2008 ◽  
Author(s):  
Gokul Vishwanathan ◽  
Rolf D. Reitz
Keyword(s):  
Low Temperature ◽  
Soot Formation ◽  
Numerical Study ◽  
Low Temperature Combustion ◽  
Constant Volume Chamber ◽  
Soot Mass ◽  
Temperature Combustion ◽  
Lifted Flames ◽  
Polycyclic Aromatic ◽  
Species Comparisons

A numerical study of in-cylinder soot formation and oxidation processes in n-heptane lifted flames using various soot inception species has been conducted. In a recent study by the authors, it was found that the soot formation and growth regions in lifted flames were not adequately represented by using acetylene alone as the soot inception species. Comparisons with a conceptual model and available experimental data suggested that the location of soot formation regions could be better represented if polycyclic aromatic hydrocarbon (PAH) species were considered as alternatives to acetylene for soot formation processes. Since the local temperatures are much lower under low temperature combustion (LTC) conditions, it is believed that significant soot mass contribution can be attributed to PAH rather than to acetylene. To quantify and validate the above observations, a reduced n-heptane chemistry mechanism has been extended to include PAH species up to four fused aromatic rings (pyrene). The resulting chemistry mechanism was integrated into the multidimensional CFD code KIVA-CHEMKIN for modeling soot formation in lifted flames in a constant volume chamber. The investigation revealed that a simpler model that only considers up to phenanthrene (three fused rings) as the soot inception species has good possibilities for better soot location predictions. The present work highlights and illustrates the various research challenges toward accurate qualitative and quantitative predictions of soot for new low emission combustion strategies for I.C. engines.

Application of a Phenomenological Soot Model for Diesel Engine Combustion

2008 ◽  
Author(s):  
Xiaobei Cheng ◽  
Hongling Jv ◽  
Yifeng Wu
Keyword(s):  
Diesel Engine ◽  
Chemical Reactions ◽  
Oxidation Rate ◽  
Soot Formation ◽  
Soot Oxidation ◽  
Soot Concentration ◽  
Engine Operation ◽  
Soot Particles ◽  
Turbulent Eddies ◽  
Soot Model

The application of the improved CFD code for the simulation of combustion and emission formation in a high-speed diesel engine has been presented and discussed. The soot concentration transport equation is found and solved together with all other flow equations. A slip correction factor is introduced into this equation. In turbulent combustion, the soot particles are contained within the turbulent eddies, and burnt up swiftly with the dissipation of these eddies in the soot oxidation zone. However, the chemical reactions always process except the dissipation of turbulent eddies and the intermixing of soot particles and turbulent eddies. The soot oxidation rate should be controlled simultaneity by the chemical reactions rate and the dissipation rate of turbulent eddies. A hybrid particle turbulent transport controlled rate and soot oxidation rate model is present in this paper and Soot formation and oxidation processes have been modeled according to this model. A reasonable agreement of the measured and computed data of in-cylinder pressure, soot, and NO emissions for different engine operation conditions has been made. The precision of simulated soot concentration is improved compare with the commonly Hiroyasu—Nagel—Strickland (HNS) soot model.

Engine Performance and Emissions Formation for RME and Conventional Diesel Oil: A Comparative Study

2009 ◽  
Author(s):  
Junfeng Yang ◽  
Monica Johansson ◽  
Valeri Golovitchev
Keyword(s):  
Diesel Engine ◽  
Comparative Study ◽  
Soot Formation ◽  
Engine Performance ◽  
Oxidation Mechanism ◽  
Diesel Oil ◽  
Engine Operation ◽  
Operation Conditions ◽  
Performance And Emissions ◽  
Engine Performance And Emissions

A comparative study on engine performance and emissions (NOx, soot) formation has been carried out for the Volvo D12C diesel engine fueled by Rapeseed Methyl Ester, RME and conventional diesel oil. The combustion models, used in this paper, are the modifications of those described in [1–2]. After the compilation of liquid properties of RME specified as methyl oleate, C19H36O2, making up 60% of RME. The oxidation mechanism has been compiled based on methyl butanoate ester, mb, C5H10O2 oxidation model [3] supplemented by the sub-mechanisms for two proposed fuel constituent components, methyl decanoate, md, C11H22O2, n-heptane, C7H16, and soot and NOx formations reduced and “tuned” by using the sensitivity analysis. A special global reaction was introduced to “crack” the main fuel into constituent components, md, mb and propyne, C3H4, to reproduce accurately the proposed RME chemical formula. The sub-mechanisms were collected in the general one consisting of 99 species participating in 411 reactions. The combustion mechanism was validated using shock-tube ignition-delay data at diesel engine conditions and flame propagation speeds at atmospheric conditions. The engine simulations were carried out for Volvo D12C engine fueled both RME and conventional diesel oil. The numerical results illustrate that in the case of RME, nearly 100% combustion efficiency was predicted when the cumulative heat release, was compared with the RME LHV, 37.2 kJ/g.. To minimize NOx emissions, the effects of 20–30% EGR levels depending on the engine loads and different injection strategies were analyses. To confirm the optimal engine operation conditions, a special technique based on the time-transient parametric φ-T maps [4] has been used.

An Experimental Investigation of Flame Lift-Off Length and Soot Luminosity of the Emulsified Diesel Under Various Ambient Temperatures

2013 ◽  
Author(s):  
Ming Huo ◽  
Karthik Nithyanandan ◽  
Chia-fon F. Lee ◽  
Nan Zhou ◽  
Han Wu
Keyword(s):  
Ambient Temperature ◽  
Fuel Injection ◽  
Soot Formation ◽  
Cone Angle ◽  
High Ambient Temperature ◽  
Copper Vapor Laser ◽  
Engine Operation ◽  
Ambient Temperatures ◽  
Emulsified Fuel ◽  
Lift Off

The emulsified fuel remains attractive due to its potential capability of reducing the NOx and particular matter (PM) at the same time. In this work, the emulsified diesel, with the amount of water quantities ranged between 10% and 20% by volume, was injected and combusted in an optical constant volume chamber. With controlled combustion of acetylene mixture prior to the fuel injection, the chamber is able to provide high ambient temperature and pressure to mimic the real engine operation. In this study, ambient temperatures ranging from 800K to 1200K were investigated. Mie scattering images, at 15000 fps, were first taken to record the evolution of the spray using a Phantom 7.1 high speed camera coupled with a copper vapor laser as the light source. The spray images revealed longer liquid penetration and wider cone angle at the beginning stage of the injection event for emulsified fuel, supporting the occurrence of micro-explosion. Ambient temperature played an important role in the dynamic behavior of soot lift-off length as low ambient temperature features a long initial soot lift-off length and sharp decrease afterwards for both fuels while high ambient temperature enables the soot lift-off to achieve quasi-steady state immediately after the onset of the fuel injection. The broadband luminosity results indicate the advantage of using emulsified fuel to suppress soot formation, and this benefit can be maximized if coupled with a low temperature combustion strategy.

scholarly journals Influence of Ambient Temperature on Radiative and Convective Heat Dissipation Ratio in Polymer Heat Sinks

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2286
Author(s):  
Jan Kominek ◽  
Martin Zachar ◽  
Michal Guzej ◽  
Erik Bartuli ◽  
Petr Kotrbacek
Keyword(s):  
Heat Transfer ◽  
Ambient Temperature ◽  
Convective Heat ◽  
Heat Dissipation ◽  
High Surface ◽  
Heat Sinks ◽  
Fourth Power ◽  
Molding Process ◽  
Ambient Temperatures ◽  
University Of Technology

Miniaturization of electronic devices leads to new heat dissipation challenges and traditional cooling methods need to be replaced by new better ones. Polymer heat sinks may, thanks to their unique properties, replace standardly used heat sink materials in certain applications, especially in applications with high ambient temperature. Polymers natively dispose of high surface emissivity in comparison with glossy metals. This high emissivity allows a larger amount of heat to be dissipated to the ambient with the fourth power of its absolute surface temperature. This paper shows the change in radiative and convective heat transfer from polymer heat sinks used in different ambient temperatures. Furthermore, the observed polymer heat sinks have differently oriented graphite filler caused by their molding process differences, therefore their thermal conductivity anisotropies and overall cooling efficiencies also differ. Furthermore, it is also shown that a high radiative heat transfer leads to minimizing these cooling efficiency differences between these polymer heat sinks of the same geometry. The measurements were conducted at HEATLAB, Brno University of Technology.

scholarly journals Insufficient Stability of Clavulanic Acid in Widely Used Child-Appropriate Formulations

Antibiotics ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 225
Author(s):  
Ines Mack ◽  
Mike Sharland ◽  
Janneke M. Brussee ◽  
Sophia Rehm ◽  
Katharina Rentsch ◽  
...  
Keyword(s):  
Ambient Temperature ◽  
Clavulanic Acid ◽  
Storage Conditions ◽  
Essential Medicines ◽  
Active Components ◽  
Middle Income ◽  
Ambient Temperatures ◽  
Essential Medicines List ◽  
Dispersible Tablets ◽  
The Stability

Amoxicillin-clavulanic acid (AMC) belongs to the WHO Essential Medicines List for children, but for optimal antimicrobial effectiveness, reconstituted dry powder suspensions need to be stored in a refrigerated environment. Many patients in low- and middle-income countries who are sold AMC suspensions would be expected not to keep to the specified storage conditions. We aimed to assess the stability of both ingredients in liquid formulations and dispersible tablets, combined with nationally representative data on access to appropriate storage. Degradation of amoxicillin (AMX) and clavulanic-acid (CLA) was measured in suspensions and dispersible tablets commercially available in Switzerland at different ambient temperatures (8 °C vs. 28 °C over 7 days, and 23 °C vs. 28 °C over 24 h, respectively). Data on access to refrigeration and electricity were assessed from the USAID-funded Demographic and Health Survey program. In suspensions, CLA degraded to a maximum of 12.9% (95% CI −55.7%, +29.9%) at 8°C and 72.3% (95% CI −82.8%, −61.8%) at a 28 °C ambient temperature during an observation period of 7 days. Dispersible tablets were observed during 24 h and CLA degraded to 15.4% (95% CI −51.9%, +21.2%) at 23 °C and 21.7% (−28.2%, −15.1%) at a 28 °C ambient temperature. There is relevant degradation of CLA in suspensions during a 7-day course. To overcome the stability challenges for all active components, durable child-appropriate formulations are needed. Until then, prescribers of AMC suspensions or pharmacists who sell the drug need to create awareness for the importance of proper storage conditions regarding effectiveness of both antibiotics and this recommendation should be reflected in the WHO Essential Medicines List for children.

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