D-Dalus VTOL – efficiency increase in forward flight

The computational fluid dynamical software AVL-FIRE code was used for investigating the impact of multiply injection strategies and spray included angles on combustion and emissions in a marine diesel engine. The fuel injection parameters of spray included angle and pilot injection timing with pilot-main injection, as well as post injection ratio and post injection duration angle with pilot-main-post injection, were all investigated and optimized. The results indicate that retarding pilot injection timing with pilot-main injection declines high temperature region, resulting in a notable reduction in NOx emissions. Since fuel evaporation and burn are hampered by long spray penetration due to low temperature and pressure with pilot injection, a suitable spray included angle are used to offer more efficient air-fuel mixing process. A wider spray included angle simultaneously reduces soot emission and indicated specific fuel consumption (ISFC). Post injection fuel exerts impact on combustion process by causing a great disturbance to flow field during post combustion. Increasing post injection ratio from 4% to 10% at a small post injection duration angle great emission performance is achieved by simultaneous reduction in NOx and soot emissions while only using a slight consumption of ISFC. To summarize, the defeat of traditional NOx-soot trade-off occurs as both NOx and soot emissions are decreased with optimized multiple injection strategy and spray included angle. Particularly, there are respectively four cases with pilot-main injection and two cases with pilot-main-post injection, that achieve simultaneous reduction in NOx emissions, soot emission, and ISFC, compared to the prototype.

In this paper, detailed development of a nonlinear aeroelastic coupled trim model of a twin-cyclocopter in forward flight is presented. Twin-cyclocopter consists of two cycloidal rotors as main thrusters and a conventional nose rotor for pitch-torque balance. It is shown that five control inputs (mean and differential rpm, mean and differential phase offset of cyclorotors, rpm of nose rotor) are needed to balance three moments and two forces on cyclocopter in forward flight while forces along lateral direction remain balanced at all stages. In this coupled trim procedure, blade aeroelastic response equations and vehicle trim equations are solved together by simultaneously updating control inputs and blade response. To obtain the blade response and forces for a given set of control inputs, an aeroelastic model of cyclorotor and an aerodynamic model of the conventional nose rotor in forward flight is developed. The nonlinear aeroelastic model of the cyclorotor is developed by coupling unsteady aerodynamic model of cyclorotor in forward flight with a geometrically exact beam based structural framework capable of predicting large bending and torsional deflections of rotor blade. Towards this, complex aerodynamics of the cyclorotor is thoroughly investigated and various underlying phenomena, such as dynamic virtual camber, effects of near and shed wake and leading-edge vortices are rigorously modeled. A modified Double Multiple Streamtube (D-MS) model is implemented to capture the complex dynamic inflow characteristics of cyclorotor in forward flight. The present model is validated with previously published in-house experimental data on the performance of a trimmed cyclorotor at different forward speeds.

Simultaneous reduction of NOx emission and SOx emission aided by improved efficiency of a Once-Through Benson Type Coal Boiler

Fluxes of nitrogen oxides (NOx = NO + NO2) and carbon dioxide (CO2) were measured using eddy covariance at the BT Tower in central London during the coronavirus pandemic. Comparing fluxes to those measured in 2017 prior to the pandemic restrictions and the introduction of the Ultra-Low Emissions Zone (ULEZ) highlighted a 75 % reduction in NOx emissions between the two periods but only a 20 % reduction in CO2 emissions and a 32 % reduction in traffic load. Use of a footprint model and the London Atmospheric Emissions Inventory (LAEI) identified transport and heat and power generation to be the two dominant sources of NOx and CO2 but with significantly different relative contributions for each species. Application of external constraints on NOx and CO2 emissions allowed the reductions in the different sources to be untangled identifying that transport NOx emissions had reduced by > 75 % since 2017. This was attributed in part to the success of air quality policy in central London, but crucially due to the substantial reduction in congestion that resulted from pandemic reduced mobility. Spatial mapping of the fluxes suggests that central London was dominated by point source heat and power generation emissions during the period of reduced mobility. This will have important implications on future air quality policy for NO2 which until now, has been primarily focused on the emissions from diesel exhausts.

Aerodynamic interference between the main and tail rotor can have a strong negative influence on the flight mechanics of a conventional helicopter. Significant unsteadiness in the tail rotor loading is encountered under certain flight conditions, but the character of the unsteadiness can depend on the direction of rotation of the tail rotor. Numerical simulations, using Brown's vorticity transport model, of the aerodynamic interaction between the main and tail rotors of a helicopter are presented for a range of forward and lateral flight trajectories. Distinct differences are predicted in the behavior of the system in left and right sideward flight that are consistent with flight experience that the greatest fluctuations in loading or control input are required in left sideways flight (for a counterclockwise rotating main rotor). These fluctuations are generally more extreme for a system with tail rotor rotating top-forward than top-aft. Differences are also exposed in the character of the lateral excitation of the system as forward flight speed is varied. The observed behavior appears to originate in the disruption of the tail rotor wake that is induced by its entrainment into the wake of the main rotor. The extent of the disruption is dependent on flight condition, and the unsteadiness of the process depends on the direction of rotation of the tail rotor. In intermediate-speed forward flight and right sideward flight, the free stream delays the entrainment of the tail rotor wake far enough downstream for the perturbations to the rotor loading to be slight. Conversely, in left sideward and quartering flight, the free stream confines the entrainment process close to the rotors, where it causes significant unsteadiness in the loads produced by the system.

Impact of H2 addition on flame stability and pollutant emissions for an atmospheric kerosene/air swirled flame of laboratory scaled gas turbine

Atmospheric distribution of photochemical oxidants has been a subject of interest and concern not only because of their deleterious effects on human health and vegetation but also because of their crucial role in determining the chemical composition of the atmosphere. Several important issues related to the distribution and production of photochemical species are examined through an analysis of results obtained from applications of a comprehensive three‐dimensional regional scale photochemical model over the Northeast United States. The Regional Oxidant Model (ROM) is used to simulate the response of various photochemical species to specific anthropogenic emission strategies involving NOx, and hydrocarbon reductions for an episodic period during July 1988. Domain and temporal averages of predicted concentrations are examined for various species. Their relative influence on oxidant chemistry over the modeled domain is investigated. Further, spatial distributions of O3 with respect to those of NOx, NOy, and hydrocarbons over the modeled domain are examined and the variations in O3 levels for different chemical regimes classified by characteristic NOx/reactive organic gases and NOx/NOy ratios are investigated. Temporal trends in domain‐averaged concentrations indicate that the model replicates the expected diurnal trends in species concentrations. The relative benefits of reductions in NOx and hydrocarbon emissions on predicted O3 levels are also examined. In general, for this modeled domain, reductions in NOx emissions with or without reductions in hydrocarbon emissions have more impact on reducing predicted O3 levels compared to reductions only in hydrocarbon emissions.

New-particle nucleation within coal-fired power-plant plumes can have large effects on particle number concentrations, particularly near source regions, with implications for human health and climate. In order to resolve the formation and growth of particles in these plumes, we have integrated TwO-Moment Aerosol Sectional (TOMAS) microphysics in the System for Atmospheric Modelling (SAM), a large-eddy simulation/cloud-resolving model (LES/CRM). We have evaluated this model against aircraft observations for three case studies, and the model reproduces well the major features of each case. Using this model, we have shown that meteorology and background aerosol concentrations can have strong effects on new-particle formation and growth in coal-fired power-plant plumes, even if emissions are held constant. We subsequently used the model to evaluate the effects of SO2 and NOx pollution controls on newparticle formation in coal-fired power-plant plumes. We found that strong reductions in NOx emissions without concurrent reductions in SO2 emissions may increase new-particle formation, due to increases in OH formation within the plume. We predicted the change in new-particle formation due to changes in emissions between 1997 and 2010 for 330 coal-fired power plants in the US, and we found a median decrease of 19% in new-particle formation. However, the magnitude and sign of the aerosol changes depend greatly on the relative reductions in NOx and SO2 emissions in each plant. More extensive plume measurements for a range of emissions of SO2 and NOx and in varying background aerosol conditions are needed, however, to better quantify these effects.

According to the World Health Organization, social prescribing is a holistic approach to health and wellbeing that promotes integrated care. There is growing interest in social prescribing around the world, with over 20 countries involved in the social prescribing movement. However, an agreed definition of social prescribing has yet to emerge. This is problematic for social prescribing research, policy, and practice. Since there are two types of definitions – conceptual and operational, agreement on both types of definitions is needed. The aim of this study was to establish internationally accepted conceptual and operational definitions of social prescribing. This study was conducted for the social prescribing community to support the advancement of the social prescribing movement. The research team – one doctoral student and four committee members, collectively designed, implemented, and monitored this research. This study involved an international, multidisciplinary panel of experts. The expert panel (n=48) represented 26 different countries across five continents and numerous expert groups, including service providers, service users, researchers, students, and representatives of the Global Social Prescribing Alliance, the Social Prescribing Network, the Social Prescribing Youth Network, the National Academy for Social Prescribing, and the Canadian Institute for Social Prescribing. A three-round Delphi study was conducted. Consensus was defined a priori as ≥80% agreement. In Round 1, participants were asked to list key elements that are essential to the conceptual definition of social prescribing and to provide corresponding statements that operationalize each of the key elements. In Round 2, participants were asked to rate their agreement with items from the first round for inclusion in the conceptual and/or operational definitions of social prescribing. Based on the findings from this round, the conceptual and operational definitions of social prescribing were developed, including long and short versions of the conceptual definition. In Round 3, participants were asked to rate their agreement with the conceptual and operational definitions of social prescribing. Consensus was reached on the definitions in this round, which signified the successful development of internationally accepted conceptual and operational definitions of social prescribing. The definitions were transformed into the Common Understanding of Social Prescribing (CUSP) conceptual framework. For the first time in the history of the social prescribing movement, we now have internationally accepted conceptual and operational definitions of social prescribing. Additionally, the conceptual definitions are distinct from pre-existing definitions, and to our knowledge, the operational definition is the first in the world. Together, the CUSP conceptual framework and the definitions offer a common thread – a shared sense of what social prescribing is. Social prescribing researchers, policymakers, and practitioners are encouraged to use the outputs of this work in social prescribing research, policy, and practice to foster common understanding of this concept.

Experimental and numerical studies were performed to investigate the simultaneous reduction of NOx and CO for stoichiometric diesel combustion with a 3-way catalyst. A single-cylinder engine was used for the experiments and KIVA simulations were used in order to characterize the combustion efficiency and emissions of throttled stoichiometric diesel combustion at 0.7 bar boost pressure and 90MPa injection pressure. In addition, the efficiency of emission conversion with the 3-way catalysts in stoichiometric diesel combustion was investigated experimentally. The results showed CO and NOx emissions can be controlled with the 3-way catalyst in spite of the fact that CO increases more at high equivalence ratios compared to conventional diesel combustion (i.e., lean combustion). At stoichiometric operation, the 3-way catalyst reduced CO and NOx emissions by up to 95%, which achieves lower emissions compared to conventional diesel combustion or low temperature diesel combustion, while keeping better fuel consumption than a comparable gasoline engine.

Experimental and numerical studies were performed to investigate the simultaneous reduction in NOx and CO for stoichiometric diesel combustion with a three-way catalyst. A single-cylinder engine was used for the experiments and KIVA simulations were used in order to characterize the combustion efficiency and emissions of throttled stoichiometric diesel combustion at 0.7 bar boost pressure and 90 MPa injection pressure. In addition, the efficiency of emission conversion with three-way catalysts in stoichiometric diesel combustion was investigated experimentally. The results showed CO and NOx emissions can be controlled with the three-way catalyst in spite of the fact that CO increases more at high equivalence ratios compared with conventional diesel combustion (i.e., lean combustion). At a stoichiometric operation, the three-way catalyst reduced CO and NOx emissions by up to 95%, which achieves lower emissions compared with conventional diesel combustion or low temperature diesel combustion, while keeping better fuel consumption than a comparable gasoline engine.

Hydrogen serves as an optimal fuel for engines. Pure hydrogen engines do not generate carbon monoxide and hydrocarbon emissions; instead, they encounter significant nitrogen oxide emissions. Inner-engine control and outer-engine control are two methods to reduce NOx emissions. Outer-engine control primarily mitigates NOx emissions by selective catalytic reduction (SCR), a process that has been extensively researched. Nevertheless, there is a paucity of research about NOx emission regulation in pure hydrogen engines via internal engine management. This work utilised the closed homogeneous reactor (CHR) in Chemkin Pro to model the primary NOx emission control within pure hydrogen engines. The findings indicate that single exhaust gas recirculation (EGR) reduces NOx emissions by 45.3% at an EGR ratio of 20%, suggesting that the reduction in NOx emissions is not substantial. Nonetheless, EGR combined with lean burn reduces NOx emissions by 96.31% at a λ of 1.4 and an EGR ratio of 20%, resulting in ultra-low NOx emissions from pure hydrogen engines. In comparison to single EGR and EGR combined with lean-burn, SNCR is more effective for NOx emission control. An NH3 ratio of merely 10% can reduce NOx emissions by 96.32% in pure hydrogen engines, whilst a 15% NH3 ratio can attain zero NOx emissions in pure hydrogen engines without necessitating a high λ value or EGR ratio. It is essential to precisely regulate the NH3 ratio in the cylinder; otherwise, residual NH3 may be generated, leading to environmental pollution.

This study evaluates the effects of Al2O3 and CeO2 nanoparticles as additives to standard diesel and biodiesel fuels on the combustion and emissions characteristics of a CR diesel engine with split injection (pilot and main injections). Three nanoparticle dosing levels (50 ppm, 100 ppm, and 150 ppm) were compared with undoped standard diesel and biodiesel fuels. The results showed that the presence of both Al2O3 and CeO2 in biodiesel increased the ignition delay of the pilot fuel by about 8.0% at low load and about 3.5% at high load. The addition of both nanoparticles to diesel and biodiesel fuels had an insignificant effect on the main injection fuel’s ignition delay, MBF50 position and combustion duration. The thermal efficiency was up to 1.0% lower. Al2O3 additive in diesel had no significant effect on NOx emissions. CO emissions were higher by 4.4–7.5% in most cases. The Al2O3 additive in biodiesel reduced NOx emissions by an average of 38%, 17.1%, and 9.4% at low, medium, and high engine loads, respectively. The reduction in CO emissions averaged 15%. The addition of CeO2 nanoparticles to diesel fuel reduced NOx emissions by 22.5%, 8.5%, and 3.1% on average across the corresponding load ranges. When the engine was operated on CeO2-doped biodiesel, NOx emissions were lower by an average of 25.7%, 9.6%, and 2.5% at low, medium, and high loads, respectively. Adding CeO2 nanoparticles to diesel fuel increased CO emissions, whereas adding them to biodiesel significantly reduced CO emissions.

Meteorological variations impeded the benefits of recent NOx mitigation in reducing atmospheric nitrate deposition in the Pearl River Delta region, Southeast China

Effect of hydrogen on ethanol–biodiesel blend on performance and emission characteristics of a direct injection diesel engine