Exhaust Smoke Research Articles

Numerical investigation on the effect of ambient pressure on mechanical smoke extraction efficiency in tunnel fires

This paper has analyzed the ambient pressure on the effect of the efficiency of the mechanical smoke extraction system in tunnel fires. These were simulated by Large Eddy Simulation (LES) with Fire Dynamics Simulator (FDS). The simulation results indicate that it is not the instance that the higher the exhaust rate, the better the smoke exhaust efficiency of the exhaust vent. There is a critical exhaust rate at which excessive fresh air entrainment, such as plug-holing of the smoke layer, can be avoided. The mechanical smoke exhausting process is affected by two competitive forces: horizontal inertial force and vertical suction force. The thickness and horizontal velocity of the thermal smoke layer in the tunnel increase as the ambient pressure decreases. At this time, the vertical suction force required for the occurrence of the plug-holing phenomenon increases, and thus the critical exhaust rate increases. A linear relationship between the dimensionless critical exhaust rate Vcri∗ and the modified heat release rate Q˙∗ was proposed to characterize the influence of ambient pressure on the mechanical smoke exhaust efficiency. When the exhaust rate is 0.5 times the critical exhaust rate, the smoke mass fraction exhausted from the exhaust vent (E) reaches the maximum value.

Study on the Smoke Spread Law of a Subway Tunnel Fire under the Synergistic Action of Shaft Smoke Exhaust and Longitudinal Ventilation

Urban rail transit improves the urban spatial structure, solves the problem of urban traffic congestion, so its safety problem can not be ignored. Fire is one of the major factors threatening the safety of urban rail transit. Taking the tunnel between wengjiao road and Maqing road of Xiamen Rail Transit Line 2 as an example, the paper uses FDS software to simulate the mechanical smoke exhaust of the shaft under different wind speed conditions of the main tunnel, and deeply analyzes the smoke and temperature distribution under the fire conditions of the tunnel with the shaft. The results show that when the longitudinal wind speed v=1.7m/s and the shaft uses mechanical exhaust, there is no smoke upstream of the fire source, all the smoke is discharged through the shaft, and the height of the flue gas layer is significantly smaller than the thickness of the flue gas layer without longitudinal ventilation. The combination of longitudinal wind and mechanical smoke exhaust is more conducive to the safe evacuation of people.

A numerical study on the effect of the shaft group arrangement on the natural ventilation performance in tunnel fires

A series of numerical simulations about tunnel fires are carried out to study the performance of different arrangements of natural ventilation shafts in a 500 m tunnel. Two to four identical shafts are arranged in a group at the centerline and the sideline of the tunnel ceiling. The characteristics of the temperature distribution, velocity field and the total amount of smoke exhausted from each shaft group are investigated for each arrangement. The results have shown that when the fire heat release rate is 20 MW, boundary layer separation occurs in all the shafts in the series of simulations. At the same fire heat release rate, when the number of shafts, n, is ≤ 2, the smoke exhaust performance of the shaft groups arranged on the centerline of the tunnel ceiling is better than that on the sideline of the tunnel ceiling while n is >2, the shaft groups arranged on the sideline have a better overall smoke exhaust performance. The Richardson number of 1.4 proposed by Ji et al. is still applicable to determine the flow phenomena between boundary layer separation and plug-holing.

Smoke evacuation, is it important for prevention of COVID-19?

Smoke evacuation, is it important for prevention of COVID-19?

Influence of multisource fire on temperature distribution and natural smoke exhaust effect in urban tunnels with a shaft

SummaryThe combustion characteristics of multisource fire and single‐source fire are quite different, and there is little research on the influence of multisource fire on the natural smoke extraction effect of shaft in urban tunnels. Therefore, in this article, the method of numerical simulation was used to study the influence of fire power and distance between two fire sources on the natural smoke extraction effect of shaft and the temperature distribution in tunnel in the case of multisource fire. Typical characteristics of smoke are analyzed, such as mass flow rate, temperature distribution, velocity vector, and CO concentration. The simulation results show that when there is a certain distance between the fire sources, the two flames are inclined and close to each other. The smoke temperature under the ceiling is higher under multiple fire sources than that under single fire source. In addition, when one of the fire sources is located at the downstream of the shaft, the smoke emission in the shaft is relatively high. As the distance between fire sources continues to increase, the smoke exhaust rate basically remains stable, and an empirical relationship between smoke exhaust rate and fire source location is established.

Effects of ambient pressure on smoke movement patterns in vertical shafts in tunnel fires with natural ventilation systems

Smoke exhaust is of vital importance for life safety and structural safety in a tunnel fire. The smoke movement pattern could affect smoke exhaust efficiency, so it is necessary to determine the patterns in shafts in tunnel fires with natural ventilation systems. However, previous studies have focused on this problem at standard atmospheric conditions, but the ambient pressure, which could have an effect on smoke movement characteristics and temperature distribution, decreases in high-altitude areas. First, theoretical analysis is carried out to find that the smoke velocity is higher under reduced pressure due to lower heat loss. In addition, a set of numerical simulations based on Fire Dynamics Simulator (FDS) is conducted to investigate the effects of ambient pressures on smoke movement patterns in vertical shafts in tunnel fires with natural ventilation systems. The results show that the critical Richard number deceases under reduced ambient pressure, and the higher smoke temperature and velocity caused by lower ambient pressure are the reasons for the decrease in critical Ri. We hope that our work can provide a design reference for tunnel natural ventilation system design in high-altitude areas.

Optimization of diesel engine operating parameters fueled with palm oil-diesel blend: Comparative evaluation between response surface methodology (RSM) and artificial neural network (ANN)

Engine performance and emission characteristics of palm oil-diesel blends tested on single-cylinder diesel engine by several engine loads and injection advances. Exhaust emissions and smoke were recorded using MRU Delta 1600L and MRU Optrans 1600 model gas analyzer, respectively. Brake thermal efficiency (BTE), exhaust gas temperature (EGT), carbon monoxide (CO), hydrocarbon (HC), smoke and nitrogen oxides (NOx) were optimized as output factors considering engine load, injection advance and palm oil percentage as input variables using response surface methodology (RSM) and artificial neural network (ANN). The developed ANN and RSM models showed superior predictive certainty with big R2 (correlation coefficient) values. The RSM models showed better performance and have higher R2 values than ANN models. The developed RSM model has R2 values over 0.90 while the R2 values of ANN model are between 0.88 and 0.95. The values of mean relative error (MRE) and root mean square error (RMSE) for all the responses were low. Optimum responses were found by 69.11%, 196.25 ppm, 0.126%, 189.764 ppm, 155.49 ℃ and 30.75%, respectively for smoke, NOx, CO, HC, EGT and BTE with optimum operating factors as 17.88% palm oil percentage, 35 °CA injection advance and 780-watt engine load. The applied models gave good results that are beneficial for estimating and optimizing the engine performance and emission characteristics.

Effect of operating parameters on performance and emissions of a diesel engine fueled with ternary blends of palm oil biodiesel/diethyl ether/diesel by Taguchi method

Since operating factors play an important role on engine emissions and performance, it is important to explore the common influence of several operating factors on diesel engine performance and emission parameters. In this paper, it was aimed to investigate the effects of diethyl ether (DEE) ratio, palm oil ratio, injection advance and engine load on diesel engine performance and emission parameters. Test were planned based on Taguchi L27 orthogonal array (OA) that considered DEE ratio, palm oil ratio, injection advance and engine load as factors and brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), exhaust gas temperature (EGT), carbon monoxide (CO), hydrocarbon (HC), nitrogen oxides (NOx) and smoke emissions as responses. The effects of engine operating parameters on responses were determined by variance analysis (ANOVA). Considering the outcomes of the study, optimal levels of each factor were assigned from the point of engine performance and emission attributes. The highest signal-to-noise (S/N) ratios of BTE, BSFC and EGT were observed with the low DEE ratios, low injection advance values and average engine load. Overall, the highest S/N ratios achieved for emission responses were obtained with high DEE percentages and 35 CAs. While the highest S/N ratios for CO and smoke were seen with 20% palm oil, the highest S/N ratios were obtained with 0% palm oil for all other responses. These results showed that ANOVA-supported Taguchi design method is an effective tool with the aim of define the effect rates of engine operating parameters.

Diesel Engine Exhaust Exposure, Smoking, and Lung Cancer Subtype Risks. A Pooled Exposure-Response Analysis of 14 Case-Control Studies.

Rationale: Although the carcinogenicity of diesel engine exhaust has been demonstrated in multiple studies, little is known regarding exposure-response relationships associated with different exposure subgroups and different lung cancer subtypes.Objectives: We expanded on a previous pooled case-control analysis on diesel engine exhaust and lung cancer by including three additional studies and quantitative exposure assessment to evaluate lung cancer and subtype risks associated with occupational exposure to diesel exhaust characterized by elemental carbon (EC) concentrations.Methods: We used a quantitative EC job-exposure matrix for exposure assessment. Unconditional logistic regression models were used to calculate lung cancer odds ratios and 95% confidence intervals (CIs) associated with various metrics of EC exposure. Lung cancer excess lifetime risks (ELR) were calculated using life tables accounting for all-cause mortality. Additional stratified analyses by smoking history and lung cancer subtypes were performed in men.Measurements and Main Results: Our study included 16,901 lung cancer cases and 20,965 control subjects. In men, exposure response between EC and lung cancer was observed: odds ratios ranged from 1.09 (95% CI, 1.00-1.18) to 1.41 (95% CI, 1.30-1.52) for the lowest and highest cumulative exposure groups, respectively. EC-exposed men had elevated risks in all lung cancer subtypes investigated; associations were strongest for squamous and small cell carcinomas and weaker for adenocarcinoma. EC lung cancer exposure response was observed in men regardless of smoking history, including in never-smokers. ELR associated with 45 years of EC exposure at 50, 20, and 1 μg/m3 were 3.0%, 0.99%, and 0.04%, respectively, for both sexes combined.Conclusions: We observed a consistent exposure-response relationship between EC exposure and lung cancer in men. Reduction of workplace EC levels to background environmental levels will further reduce lung cancer ELR in exposed workers.

The Cfd Analysis of Ventilation and Smoke Control System with Jet Fan in a Parking Garage

Basements of buildings are generally used as parking garages and vehicles located in there release harmful gases. It is generally not possible to ventilate parking garages with natural ventilation methods. For this reason, ventilation systems should be used to keep the concentration of harmful gases below certain limits. One of these ventilation systems is jet fan system. It can also be used for smoke control and exhaust of harmful gases in case of fire. In this study, the jet fan system was designed for a parking garage and its performance has been observed by Computational Fluid Dynamics (CFD). Carbon monoxide concentration and air velocity parameters were investigated according to the different car occupancy rates with the CFD analyses for daily ventilation. In the results, when the number of cars increased, the air velocities decreased in the areas where the cars located and exhaust of the CO gas took longer time. In fire analyses, the same parameters were analyzed according to the different jet fan hanging heights. In the fire ventilation results, when the jet fan hanging height was increased, distribution of the air velocity profiles changed and it took longer time to exhaust the CO gas from the car park.

Emulsion templated amino functionalised polymeric monolith filter for innovative air purification technology

Due to deteriorating air quality, air pollution has become one of the most serious environmental issue especially in urban localities. Therefore, in the current study we have focused on a new route for the efficient capture of CO2 and PM2.5 from the automobile exhaust smoke of light motor vehicle with the aid of amino functionalised high internal phase emulsion (HIPE) polymeric monolith. The Poly (Styrene-co-methyl methacrylate) monolith (PSM) was synthesised by copolymerising styrene with methyl methacrylate and cross linked with divinylbenzene. The –NH2 functionalization of the synthesised PSM monolith was carried out with ethylenediamine. The amino functionalised porous hydrophobic monolith (APSM) comprising of voids (cavity spaces) and pores (tiny openings) in the range of 3.0–7.4 µm and 1.1–2.4 µm respectively exhibited excellent thermal stability up to 323 °C. Capturing efficiency of the porous monolith filter for CO2 and PM2.5 was found to be 73% and 77.2% respectively. The filter also demonstrated outstanding dust loading capacity with a reduced pressure drop. Good resistance and quality factor value proved the viability of the membrane to act as an air filter. Regeneration capacity of the filter was also studied to demonstrate the effective filtration on continuous usage.

Performance and emission prediction of a compression ignition engine fueled with biodiesel-diesel blends: A combined application of ANN and RSM based optimization

In the present study, the performance and emission parameters of a single cylinder diesel engine powered by biodiesel-diesel fuel blends were predicted by Artificial Neural Network (ANN) and optimized by Response Surface Methodology (RSM). The data to be used for ANN and RSM applications were obtained by using biodiesel/diesel fuel blends at different engine loads and various injection pressures. ANN model has been developed to predict the outputs such as brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), exhaust gas temperature (EGT), nitrogen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO) and smoke regarding engine load, biodiesel ratio and injection pressure. A feed-forward multi-layer perceptron network is used to show the correlation among the input factors and the output factors. The RSM is applied to find the optimum engine operating parameters with the purpose of simultaneous reduction of emissions, EGT, BSFC and increase BTE. The obtained results reveal that the ANN can correctly model the exhaust emission and performance parameters with the regression coefficients (R2) between 0.8663 and 0.9858. It is seen that the maximum mean relative error (MRE) is less than 10%, compared with the experimental results. The RSM study demonstrated that, biodiesel ratio of 32% with 816-W engine load and 470 bar injection pressure are the optimum engine operating parameters. It is found that the ANN with RSM support is a good tool for predict and optimize of diesel engine parameters powered with diesel/biodiesel mixtures.

Experimental Investigation on the Discharge of Pollutants from Tunnel Fires

Many pollutants are generated during tunnel fires, such as smoke and toxic gases. How to control the smoke generated by tunnel fires was focused on in this paper. A series of experiments were carried out in a 1:10 model tunnel with dimensions of 6.0 m × 1.0 m × 0.7 m. The purpose was to investigate the smoke layer thickness and the heat exhaust coefficient of the tunnel mechanical smoke exhaust mode under longitudinal wind. Ethanol was employed as fuel, and the heat release rates were set to be 10.6 kW, 18.6 kW, and 31.9 kW. The exhaust velocity was 0.32–3.16 m/s, and the longitudinal velocity was 0–0.47 m/s. The temperature profile in the tunnel was measured, and the buoyant flow stratification regime was visualized by a laser sheet. The results showed that the longitudinal ventilation leads to a secondary stratification of the smoke flow. In the ceiling extract tunnel under longitudinal ventilation, considering the research results of the smoke layer height and the heat exhaust coefficient, a better scheme for fire-producing pollutants was that an exhaust velocity of 1.26–2.21 m/s (corresponding to the actual velocity of 4.0–7.0 m/s) should be used. The longitudinal velocity should be 0.16–0.32 m/s (corresponding to the actual velocity of 0.5–1.0 m/s).

Environmental and social impacts identification for small-scale alluvial mining projects

PurposeThe purpose of the work is to use a systematic process to identify the environmental and social impacts of small-scale alluvial gold mining projects using data from Ghana.Design/methodology/approachIn this work, we used survey data collected from experts in the mining sector. This was followed by the use of a risk analysis approach to identify the significant and non-significant environmental and social impacts.FindingsSeven key impacts associated with typical alluvial mining operations were identified. The first two are the loss of vegetation and the issue of airborne diseases from dust as a result of vegetation losses during the clearing of vegetation in the block out area. The third and fourth issues were loss of vegetation and airborne diseases as a result of vegetation losses during the removal of overburden. The fifth, sixth and seventh, most significant issues identified were the pollution from smoke fumes from the processing machines; and wastewater from the washing process. The last issue of significance was the dust pollution from the transportation of the washed gravel back to the mined pit.Research limitations/implicationsOne main limitation is that the data for this study were collected from Ghana.Practical implicationsThe results indicate the need for proper and systematic measures to identify the environmental and social impacts of mining activities.Originality/valueThe work provides some insights into the strategies of identifying environmental and social impacts of mining activities. It is also one of the key works that systematically identify environmental and social impacts of small-scale alluvial gold projects.

Global and regional burden of cancer in 2016 arising from occupational exposure to selected carcinogens: a systematic analysis for the Global Burden of Disease Study 2016

ObjectivesThis study provides a detailed analysis of the global and regional burden of cancer due to occupational carcinogens from the Global Burden of Disease 2016 study.MethodsThe burden of cancer due...

Experimental Study on Smoke Exhaust of Circular Fire Lane in Underground Vehicle Base of Urban Railway

To discuss the natural ventilation design parameters of fire lane for underground car parking, a full scale experiment is adopted in this study to analyse the heat release rate and minimum clear height of underground fire lane. As a supplement, FDS numerical simulations are carried out to further study the smoke exhaust effect of natural ventilation under different external wind speed. Analytical results of full scale experiment and FDS numerical simulations show that the natural ventilation of underground circular fire lane of this case can effectively discharge the flue gas due to combustion. Through the results of this study, the natural ventilation design parameters of fire lane for underground car parking are determined primarily, which will provide reference for the fire protection design and approval of the underground car parking in the future.

3D simulations of smoke exhaust system in two types of subway station platforms

In this study, smoke evacuation in two kinds of subway station platform models, namely: an island platform station and a two side platforms station is simulated in a three-dimensional configuration. FDS 6.1.1 (Fire Dynamic Simulator) software has been employed to perform numerical simulations. The results showed noticeable effects of platform architecture on the process of smoke evacuation and emission spreading. The location of the connecting stairs (station accesses) between floors in both types of subway stations, installing the walls around these stairs in island platform type, the presence or absence of fireproof and antismoke curtains in suitable areas in two side platforms type have significant impacts on the smoke spreading. At the end, after the comparison between smoke dispersion in these two types of subway's platform, different architecture corrections were suggested and evaluated. Overall, it is concluded that an island platform station is more challenging in smoke control point of view, because the openings at the ceiling of the platform (stairway path) provide a convenient space for smoke to escape to the upper floors. In summary station architecture and even the smallest architectural changes at a subway station can change the smoke dispersion in space.

A simplified mathematical model for estimating gas temperature and velocity under natural smoke exhaust in sloping city tunnel fires

In the previous study, the prediction of gas temperature and velocity in the naturally-ventilated inclined tunnels under traffic blockage has been well concerned (Y. Zhou et al., Sustain. Cities Soc. 45, 2019, 258–270). In this paper, we continue to pay attention to the estimation of internal gas temperature and velocity under natural smoke extraction in both single-slope and gable-slope tunnel fires, a more hazardous scenario. A series of simplified mathematical models based on the equations of continuity, energy and pressure balance was proposed to estimate the gas temperature and velocity in sloping tunnel fires, in which the influences of fire source location, tunnel slope and tunnel geometry were taken into account. In addition, corresponding numerical simulations based on full-size tilted urban tunnel fires were performed using Computational Fluid Dynamics (CFD) method. The results show that the variation trends between CFD and analytical results are basically the same, and the iterative values of gas temperature and velocity coincide well with the simulations. A fast and convenient method for the estimation of gas temperature and velocity in sloping tunnel fires has been proposed, and the results of this work can provide a reference for the optimal design and management of natural smoke extraction systems, and help to ensure the fire safety of single-slope and gable-slope city tunnels.

Fire characteristics of rescue station inside railway tunnel with semi-transverse ventilation

Rescue stations are essential in long railway tunnels to provide a safe, smoke-free refuge for evacuated passengers in the event of a fire. The fire characteristics of rescue stations with semi-transverse ventilation are significantly different from those with longitudinal ventilation. In this work, the fire characteristics of a rescue station with semi-transverse ventilation are studied using numerical simulations. The numerical method is verified using 1:20 scale model experiment. The dependencies of the temperature and visibility on the smoke exhaust velocity, fire source position, and piston wind are discussed in detail. The results demonstrate that the smoke temperature distribution at the top of rescue station is related to the fire source location. When the fire source is under the shaft, the maximum smoke temperature at the top of the rescue station decreases with an increase in the smoke exhaust velocity; when the fire source is in the middle of two shafts, the maximum smoke temperature is independent of the smoke exhaust velocity. When the smoke exhaust velocity is 3 m/s, all of the smoke is controlled between vertical shafts no. 2 and no. 4. This conclusion is significantly different from that of longitudinal ventilation. On the evacuation platform of the rescue station, the smoke exhaust velocity has little influence on the smoke temperature distribution, and the temperature at a height of 2 m can meet the specification requirements of lower than 60 °C for a 20 MW fire source. Moreover, the piston wind has an influence on the visibility of the evacuation platform, which is another obvious fire characteristic for semi-transverse ventilation.

Exhaust Smoke of Non-Road Vehicles in Typical Cities of Eastern China

In typical cities of East China, more than 900 non-road vehicles were tested for exhaust smoke. Based on the investigation of the properties of these non-road vehicles, exhaust smoke intensities for different kinds of non-road vehicles are recommended. We also quantitatively study the differences in smoke intensity among vehicle age, vehicle power, test conditions, and fuels. The results showed that smoke intensity of non-road vehicles was (1.02±0.57) m-1 and that Ringelmann smoke was 2.10±0.19. In comparison to Chinese national standard (GB 36886), approximately 12%-25% of tested non-road vehicles' smoke intensity exceeded the standard limit. The smoke intensity of 80% of tested non-road vehicles was higher during start-up than under free acceleration. In comparison to ordinary diesel, the smoke intensities of tested non-road vehicles that used automotive diesel were lower. The instantaneous increase in fuel injection during start-up, as well as poor fuel quality, can directly affect the exhaust smoke of non-road vehicles.