A Cooperative Perception Environment for Traffic Operations and Control

Existing data collection methods for traffic operations and control usually rely on infrastructure-based loop detectors or probe vehicle trajectories. Connected and automated vehicles (CAVs) not only can report data about themselves but also can provide the status of all detected surrounding vehicles. Integration of perception data from multiple CAVs as well as infrastructure sensors (e.g., LiDAR) can provide richer information even under a very low penetration rate. This paper aims to develop a cooperative data collection system, which integrates Lidar point cloud data from both infrastructure and CAVs to create a cooperative perception environment for various transportation applications. The state-of-the-art 3D detection models are applied to detect vehicles in the merged point cloud. We test the proposed cooperative perception environment with the max pressure adaptive signal control model in a co-simulation platform with CARLA and SUMO. Results show that very low penetration rates of CAV plus an infrastructure sensor are sufficient to achieve comparable performance with 30% or higher penetration rates of connected vehicles (CV). We also show the equivalent CV penetration rate (E-CVPR) under different CAV penetration rates to demonstrate the data collection efficiency of the cooperative perception environment

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Influence of combustor geometry on swirl stabilized premixed methane-air flame

Flame structures, blowout limits and emissions of swirlstabilized premixed methane-air flames were studied experimentally in a small atmospheric combustor rig. Combustion sections with rectangular cross section (30mm by 40mm) and circular cross section (inner diameter = 39mm) were used to investigate effects of combustor geometry on the flame's performance. Flame structures and instabilities were obtained from CH∗ chemiluminescence captured by a high speed intensified CMOS camera. Maps of flame blowout limits (ΦBO) versus total mass flow rates (m = 70∼130 standard liter per minute, SLPM) were obtained with the combustor inlet flow temperature (Tin) kept at Tin = 397 ± 5K and a flow swirl number of S = 0.6. Emission data of mole fraction of CO in the exhaust gas versus equivalence ratio was obtained under the conditions of Tin= 293 ± 5K and S = 0.66. It is found that the flame became longer and more unstable with decreasing equivalence ratio or increasing total mass flow rates. A strong high-amplitude and low-frequency oscillation was found to be the reason for the flame blowout. A possible reason for flame instability and blowout is presented in the paper. Within the parameters investigated in this study, the equivalence ratio had the strongest impact on flame stabilities and CO emission. Both in the rectangular and circular combustors, when the flame length increased to a critical value (LIBO, which was approximately the same for these two combustors), flame could not be stabilized anymore and blowout occurred. Compared with the rectangular combustor, the circular one had lower blowout limits and was better in stabilizing the flame. Combustor geometry did not significantly affect CO emission in the current study

Investigation of methane oxy-fuel combustion in a swirl-stabilised gas turbine model combustor

CO2 has a strong impact on both operability and emission behaviours in gas turbine combustors. In the present study, an atmospheric, preheated, swirl-stabilised optical gas turbine model combustor rig was employed. The primary objectives were to analyse the influence of CO2 on the fundamental characteristics of combustion, lean blowout (LBO) limits, CO emission and flame structures. CO2 dilution effects were examined with three preheating temperatures (396.15, 431.15, and 466.15 K). The fundamental combustion characteristics were studied utilising chemical kinetic simulations. To study the influence of CO2 on the operational range of the combustor, equivalence ratio (Φ) was varied from stoichiometric conditions to the LBO limits. CO emissions were measured at the exit of the combustor using a water-cooled probe over the entire operational range. The flame structures and locations were characterised by performing CH chemiluminescence imaging. The inverse Abel transformation was used to analyse the CH distribution on the axisymmetric plane of the combustor. Chemical kinetic modelling indicated that the CO2 resulted in a lower reaction rate compared with the CH4/air flame. Fundamental combustion properties such as laminar flame speed, ignition delay time and blowout residence time were found to be affected by CO2. The experimental results revealed that CO2 dilution resulted in a narrower operational range for the equivalence ratio. It was also found that CO2 had a strong inhibiting effect on CO burnout, which led to a higher concentration of CO in the combustion exhaust. CH chemiluminescence showed that the CO2 dilution did not have a significant impact on the flame structure

Influence of the steam addition on premixed methane air combustion at atmospheric pressure

Steam-diluted combustion in gas turbine systems is an effective approach to control pollutant emissions and improve the gas turbine efficiency. The primary purpose of the present research is to analyze the influence of steam dilution on the combustion stability, flame structures, and CO emissions of a swirl-stabilized gas turbine model combustor under atmospheric pressure conditions. The premixed methane/air/steam flame was investigated with three preheating temperatures (384 K/434 K/484 K) and the equivalence ratio was varied from stoichiometric conditions to the flammability limits where the flame was physically blown out from the combustor. In order to represent the steam dilution intensity, the steam fraction Ω defined as the steam to air mass flow rate ratio was used in this work. Exhaust gases were sampled with a water-cooled emission probe which was mounted at the combustor exit. A 120 mm length quartz liner was used which enabled the flame visualization and optical measurement. Time-averaged CH chemiluminescence imaging was conducted to characterize the flame location and it was further analyzed with the inverse Abel transform method. Chemical kinetics calculation was conducted to support and analyze the experimental results. It was found that the LBO (lean blowout) limits were increased with steam fraction. CH chemiluminescence imaging showed that with a high steam fraction, the flame length was elongated, but the flame structure was not altered. CO emissions were mapped as a function of the steam fraction, inlet air temperature, and equivalence ratios. Stable combustion with low CO emission can be achieved with an appropriate steam fraction operation range

Impact of vitiation on a swirl-stabilized and premixed methane flame

Vitiation refers to the condition where the oxygen concentration in the air is reduced due to the mix of dilution gas. The vitiation effects on a premixed methane flame were investigated on a swirl-stabilized gas turbine model combustor under atmospheric pressure. The main purpose is to analyze the combustion stability and CO emission performance in vitiated air and compare the results with the flame without vitiation. The N2, CO2, and H2O (steam) were used as the dilution gas. Measurements were conducted in a combustor inlet temperature of 384 K and 484 K. The equivalence ratio was varied from stoichiometric conditions to the LBO (Lean Blowout) limits where the flame was physically blown out from the combustor. The chemical kinetics calculation was performed with Chemkin software to analyze the vitiation effects on the flame reaction zone. Based on the calculation results, the changes in the temperature gradient, CO concentration, and active radicals across the flame reaction zone were identified. The time-Averaged CH chemiluminescence images were recorded and the results indicated the features of the flame shape and location. The CH signal intensity provided the information about the heat-release zone in the combustor. The combustion LBO limits were measured and the vitiation of CO2 and H2O were found to have a stronger impact to elevate the LBO limits than N2. Near the LBO limits, the instability of the flame reaction was revealed by the high-speed chemiluminescence imaging and the results were analyzed by FFT (Fast Fourier Transfer). CO emission was measured with a water-cooled probe which is located at the exit of the combustor. The combustion vitiation has been found to have the compression effect on the operation range for low CO emission. However, this compression effect could be compensated by improving the combustor inlet temperature

Experimental study of hydrogen addition effects on a swirl-stabilized methane-air flame

The effects of H2 addition on a premixed methane-air flame was studied experimentally with a swirl-stabilized gas turbine model combustor. Experiments with 0%, 25%, and 50% H2 molar fraction in the fuel mixture were conducted under atmospheric pressure. The primary objectives are to study the impacts of H2 addition on flame lean blowout (LBO) limits, flame shapes and anchored locations, flow field characteristics, precessing vortex core (PVC) instability, as well as the CO emission performance. The flame LBO limits were identified by gradually reducing the equivalence ratio until the condition where the flame physically disappeared. The time-averaged CH chemiluminescence was used to reveal the characteristics of flame stabilization, e.g., flame structure and stabilized locations. In addition, the inverse Abel transform was applied to the time-averaged CH results so that the distribution of CH signal on the symmetric plane of the flame was obtained. The particle image velocimetry (PIV) was used to detect the characteristics of the flow field with a frequency of 2 kHz. The snapshot method of POD (proper orthogonal decomposition) and fast Fourier transform (FFT) were adopted to capture the most prominent coherent structures in the turbulent flow field. CO emission was monitored with an exhaust probe that was installed close to the combustor exit. The experimental results indicated that the H2 addition extended the flame LBO limits and the operation range of low CO emission. The influence of H2 addition on the flame shape, location, and flow field was observed. With the assistance of POD and FFT, the combustion suppression impacts on PVC was found

An experimental study of effects of confinement ratio on swirl stabilized flame macrostructures

Swirl stabilized premixed flames are common in industrial gas turbines. The flame shape in the combustor is highly related to the combustion stability and the performance of the gas turbine. In the current paper, the effects of confinement on the time averaged flame structures or flame macrostructures are studied experimentally. Experiments are carried out with swirl number S = 0.66 in two cylindrical confinements with diameters of d1 = 39 mm and d2 = 64 mm and confinement ratio c1 = 0.148 and c2 = 0.0567. All the experiments were carried out in atmospheric. CH∗ chemiluminescence from the flame was recorded to visualize the flame behavior. An inverse Abel image reconstruction method was employed to better distinguish the flame macrostructures. Different mechanisms forming the time averaged M shape flames are proposed and analyzed. It is found that the confinement wall plays an important role in determining the flame macrostructures. The flow structures including the inner and outer recirculation zones formed in the confinement are revealed to be the main reasons that affects different flame macrostructures. Meanwhile, the alternation of flame shapes determines the flame stability characteristics. A smaller confinement diameter forced the flame front to bend upstream into the outer recirculation zone hence forming a M shape flame. A strong noise caused by the interaction of the flame front in the outer recirculation zone with the combustor wall was observed. Another unsteady behavior of the flame in the bigger combustor, which was caused by the alternation of the flame root position inside and outside the premixing tube, is also presented. The V shape flame in the two combustors radiated weaker chemiluminescence but the main heat release zone was elongated than the M shape flame. Other operating conditions, i.e. total mass flow rate of the air flow and the equivalence ratio also affect the flame macrostructures. The flame blowout limits were also altered under different test conditions. The bigger confinement has better performance in stabilizing the flame by having lower lean blowout limits