Experimental and numerical evaluation of diesel-hydrogen dual-fuel combustion in a HD single cylinder engine

Climate changes emerging in the last few decades have resulted in accelerated efforts to guarantee a viable global ecosystem. Despite the aim of low-carbon economies to integrate all aspects for the minimal GHG outputs, the transport sector is under severe obligation to abide due to the related substantial contribution of CO2 emissions. Although, in the last few years the electrification of powertrain systems has gained significant attention in the media, it is widely acknowledged by the industry that the internal combustion engine will remain a dominant source of propulsion for decades to come. In recent years, conventional fossil fuels (gasoline and diesel) have been partially replaced with the alternative fuels such as biodiesel, natural gas, ethanol, hydrogen, etc. These substitutions were beneficial in diverse perspectives making significant reductions in exhaust pollutants with maintained performance. The currently reported work was concerned with experimental and numerical evaluation of the potential to partially replace diesel with hydrogen fuel, which continues to attract attention as a potential longer term alternative fuel solution, whether produced on-board or remotely via sustainable methods. The test engine adopted was of a single cylinder HD diesel with typical common rail diesel fuel injection and EGR of a production HGV’s engine. The experimental work was involved with the fumigation of hydrogen and intake air enrichment with oxygen at two particular engine loads (6 and 12 bar net indicated mean effective pressure -IMEPn-) typically visited under real world HGV driving conditions. Highest practical hydrogen substitution ratios could increase indicated efficiency by up to 4.6% and 2.4% while reducing CO2 emissions by 58% and 32% at 6 and 12 bar IMEPn respectively. Soot and CO emissions were reduced as more hydrogen was supplied, particularly at 6bar IMEP. Furthermore, intake air enrichment with oxygen resulted in a faster combustion process. This could restraint soot and minimised CO emissions at the expense of considerably higher NOx emissions. The numerical study was made using the commercial engine simulation package, GT-Power. Initially a reverse-run calculation known as Three Pressure Analysis (TPA) was applied for determining the cylinder trapped conditions in addition to the measured burn rate. Two distinct phenomenological models were used in parallel with aim of modelling the dual-fuel combustion. By comparing the optimised calibration factors in different operating points, in-depth evaluation of the unique dual-fuel combustion phenomenon was possible, including evaluation of burning velocities and the knock-on effects on performance under varied mixture compositions. It was concluded that hydrogen substitution provides a viable method of displacing diesel and the associated carbon emissions with favourable accompanying reductions in soot. The phenomenological “DualFuel” model performed well under ‘conventional’ dual-fuel conditions but was less reliable when a proportion of the diesel was premixed. The arising error was largely associated with lack of dual-fuel burning velocity data, which will remain a key barrier to dual-fuel simulation as the premixing is largely acknowledged to improve the combustion efficiency

On the Measurement of Energy Dissipation of Adhered Cells with the Quartz Microbalance with Dissipation Monitoring

We previously reported the finding of a linear correlation between the change of energy dissipation (ΔD) of adhered cells measured with the quartz crystal microbalance with dissipation monitoring (QCM-D) and the level of focal adhesions of the cells. To account for this correlation, we have developed a theoretical framework for assessing the ΔD-response of adhered cells. We rationalized that the mechanical energy of an oscillating QCM-D sensor coupled with a cell monolayer is dissipated through three main processes: the interfacial friction through the dynamic restructuring (formation and rupture) of cell-extracellular matrix (ECM) bonds, the interfacial viscous damping by the liquid trapped between the QCM-D sensor and the basal membrane of the cell layer, and the intracellular viscous damping through the viscous slip between the cytoplasm and stress fibers as well as among stress fibers themselves. Our modeling study shows that the interfacial viscous damping by the trapped liquid is the primary process for energy dissipation during the early stage of the cell adhesion, whereas the dynamic restructuring of cell-ECM bonds becomes more prevalent during the later stage of the cell adhesion. Our modeling study also establishes a positive linear correlation between the ΔD-response and the level of cell adhesion quantified with the number of cell-ECM bonds, which corroborates our previous experimental finding. This correlation with a wide well-defined linear dynamic range provides a much needed theoretical validation of the dissipation monitoring function of the QCM-D as a powerful quantitative analytical tool for cell study

The LINC complex, mechanotransduction, and mesenchymal stem cell function and fate

Mesenchymal stem cells (MSCs) show tremendous promise as a cell source for tissue engineering and regenerative medicine, and are understood to be mechanosensitive to external mechanical environments. In recent years, increasing evidence points to nuclear envelope proteins as a key player in sensing and relaying mechanical signals in MSCs to modulate cellular form, function, and differentiation. Of particular interest is the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex that includes nesprin and SUN. In this review, the way in which cells can sense external mechanical environments through an intact nuclear envelope and LINC complex proteins will be briefly described. Then, we will highlight the current body of literature on the role of the LINC complex in regulating MSC function and fate decision, without and with external mechanical loading conditions. Our review and suggested future perspective may provide a new insight into the understanding of MSC mechanobiology and related functional tissue engineering applications

Experimental and numerical evaluation of diesel-hydrogen dual-fuel combustion in a HD single cylinder engine

Climate changes emerging in the last few decades have resulted in accelerated efforts to guarantee a viable global ecosystem. Despite the aim of low-carbon economies to integrate all aspects for the minimal GHG outputs, the transport sector is under severe obligation to abide due to the related substantial contribution of CO2 emissions. Although, in the last few years the electrification of powertrain systems has gained significant attention in the media, it is widely acknowledged by the industry that the internal combustion engine will remain a dominant source of propulsion for decades to come. In recent years, conventional fossil fuels (gasoline and diesel) have been partially replaced with the alternative fuels such as biodiesel, natural gas, ethanol, hydrogen, etc. These substitutions were beneficial in diverse perspectives making significant reductions in exhaust pollutants with maintained performance. The currently reported work was concerned with experimental and numerical evaluation of the potential to partially replace diesel with hydrogen fuel, which continues to attract attention as a potential longer term alternative fuel solution, whether produced on-board or remotely via sustainable methods. The test engine adopted was of a single cylinder HD diesel with typical common rail diesel fuel injection and EGR of a production HGV’s engine. The experimental work was involved with the fumigation of hydrogen and intake air enrichment with oxygen at two particular engine loads (6 and 12 bar net indicated mean effective pressure -IMEPn-) typically visited under real world HGV driving conditions. Highest practical hydrogen substitution ratios could increase indicated efficiency by up to 4.6% and 2.4% while reducing CO2 emissions by 58% and 32% at 6 and 12 bar IMEPn respectively. Soot and CO emissions were reduced as more hydrogen was supplied, particularly at 6bar IMEP. Furthermore, intake air enrichment with oxygen resulted in a faster combustion process. This could restraint soot and minimised CO emissions at the expense of considerably higher NOx emissions. The numerical study was made using the commercial engine simulation package, GT-Power. Initially a reverse-run calculation known as Three Pressure Analysis (TPA) was applied for determining the cylinder trapped conditions in addition to the measured burn rate. Two distinct phenomenological models were used in parallel with aim of modelling the dual-fuel combustion. By comparing the optimised calibration factors in different operating points, in-depth evaluation of the unique dual-fuel combustion phenomenon was possible, including evaluation of burning velocities and the knock-on effects on performance under varied mixture compositions. It was concluded that hydrogen substitution provides a viable method of displacing diesel and the associated carbon emissions with favourable accompanying reductions in soot. The phenomenological “DualFuel” model performed well under ‘conventional’ dual-fuel conditions but was less reliable when a proportion of the diesel was premixed. The arising error was largely associated with lack of dual-fuel burning velocity data, which will remain a key barrier to dual-fuel simulation as the premixing is largely acknowledged to improve the combustion efficiency

Robust Impedance Control of a Teleoperation System With Friction Compensation Under Time Delay

ABSTRACT Friction forces in the robot joints insert nonlinearity in the dynamic and make errors in tracking. In this paper a new impedance control for the master is proposed to achieve force tracking. In addition, an impedance control for slave combined with sliding mode, which is based on perturbation estimation, is anticipated to reach position tracking. Friction compensators typically include a friction observer that provides a cancellation term in order to be added to the control input. Estimating and compensating the friction and other uncertainties will change the nonlinear equation to a linear one. The stability of entire system under time delay is guaranteed by Llewellyn's absolute stability criterion. Performance of the proposed controllers is investigated through experiments

On the Measurement of Energy Dissipation of Adhered Cells with the Quartz Microbalance with Dissipation Monitoring

We previously reported the finding of a linear correlation between the change of energy dissipation (ΔD) of adhered cells measured with the quartz crystal microbalance with dissipation monitoring (QCM-D) and the level of focal adhesions of the cells. To account for this correlation, we have developed a theoretical framework for assessing the ΔD-response of adhered cells. We rationalized that the mechanical energy of an oscillating QCM-D sensor coupled with a cell monolayer is dissipated through three main processes: the interfacial friction through the dynamic restructuring (formation and rupture) of cell-extracellular matrix (ECM) bonds, the interfacial viscous damping by the liquid trapped between the QCM-D sensor and the basal membrane of the cell layer, and the intracellular viscous damping through the viscous slip between the cytoplasm and stress fibers as well as among stress fibers themselves. Our modeling study shows that the interfacial viscous damping by the trapped liquid is the primary process for energy dissipation during the early stage of the cell adhesion, whereas the dynamic restructuring of cell-ECM bonds becomes more prevalent during the later stage of the cell adhesion. Our modeling study also establishes a positive linear correlation between the ΔD-response and the level of cell adhesion quantified with the number of cell-ECM bonds, which corroborates our previous experimental finding. This correlation with a wide well-defined linear dynamic range provides a much needed theoretical validation of the dissipation monitoring function of the QCM-D as a powerful quantitative analytical tool for cell study

Adaptive control of a macro/micro bilateral teleoperation system under variable time delay

In this paper a new stable adaptive control for a Macro-Micro bilateral teleoperation system is proposed. Our platform to implement the controllers consists of a servo DC motor (macro) as the master robot and a piezo-actuator (micro) as the slave robot. Piezo-actuator has some characteristics which disturb the transparency and stability of the teleoperation system. We add a nonlinear disturbance observer to the slave robot controller in order to observe and compensate the disturbances. It is recognized that the presence of time delay is one of the largest barriers in teleoperation systems. This problem is mainly due to the distance separating the master from the slave and also is due to lag effect of filters and motor drivers. Because the time delay is unknown and variable, it can make the system unstable. In this paper, all of the above controllers are discussed using variable time delay. The stability of the system under variable time delay is guaranteed by Lyapunov stability criterion and passivity based methods. Tracking of force/position is achieved by selecting the best design parameters. Performance of the proposed control is validated by experimental results.</jats:p

Microfluidic Systems with Embedded Cell Culture Chambers for High Throughput Biological Assays

The ability to generate chemical and mechanical gradients on chips is important both for creating biomimetic designs or enabling high-throughput assays. However, there is still a significant knowledge gap in the generation of mechanical and chemical gradients in a single device. In this study, we developed gradient-generating microfluidic circuits with integrated microchambers to allow cell culture and to introduce chemical and mechanical gradients to cultured cells. A chemical gradient is generated across the microchambers, exposing cells to a uniform concentration of drugs. The embedded microchamber also produces a mechanical gradient in the form of varied shear stresses induced upon cells among different chambers as well as within the same chamber. Cells seeded within the chambers remain viable and show normal morphology throughout the culture time. To validate the effect of different drug concentrations and shear stresses, doxorubicin is flowed into chambers seeded with skin cancer cells at different flow rates (from 0 to 0.2 μl/min). The experimental results show that increasing doxorubicin concentration (from 0 to 30 μg/ml) within chambers not only prohibits cell growth, but also induces cell death. In addition, the increased shear stress (0.005 Pa) at high flow rates poses a synergistic effect on cell viability by inducing cell damage and detachment. Moreover, the ability of the device to seed cells in a 3D microenvironment was also examined and confirmed. Collectively, the study demonstrate