Numerical Study on the Effects of Fuel Injection Characteristics on the Performance of a Lean Burn SG-GDI Engine towards High Efficiency and Emissions Reduction

The effects of spark and injection characteristics as well as split injection on the performance and emissions of a spray-guided gasoline direct injection (SG-GDI) engine operating close to stoichiometric conditions are assessed. To accomplish this, a 6-holes injector is simulated and the results are validated against available experimental data for spray penetration length. In addition, an open-cycle multi-dimensional model is developed for a port fuel injection (PFI) engine and the model outcomes are verified against in-cylinder pressure profile and normalized heat release rate. The GDI engine model is yielded under the light of embedment of the above-mentioned models. The model is then employed for investigation of the effects of injector angle, injection pressure, start of first and second injections and two-stage fuel injection with different fuel mass ratios at first and second injections, i.e., split injection, on mixture formation, combustion and engine emissions. The results show the pivotal role of the injector angle on formation of the mixture and output power. On the other hand, it is indicated that while practicing the split injection strategy, the flammability of the relatively stratified lean mixture with fuel to air equivalence ratio of 1.15 around the spark plug, surpasses that of stratified mixture

Mutual inductance instability of the tip vortices behind a wind turbine

Two modal decomposition techniques are employed to analyse the stability of wind turbine wakes. A numerical study on a single wind turbine wake is carried out focusing on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier-Stokes equations using the actuator line (ACL) method to simulate the wake behind the Tj ae reborg wind turbine. The wake is perturbed by low-amplitude excitation sources located in the neighbourhood of the tip spirals. The amplification of the waves travelling along the spiral triggers instabilities, leading to breakdown of the wake. Based on the grid configurations and the type of excitations, two basic flow cases, symmetric and asymmetric, are identified. In the symmetric setup, we impose a 120 degrees symmetry condition in the dynamics of the flow and in the asymmetric setup we calculate the full 360 degrees wake. Different cases are subsequently analysed using dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD). The results reveal that the main instability mechanism is dispersive and that the modal growth in the symmetric setup arises only for some specific frequencies and spatial structures, e.g. two dominant groups of modes with positive growth (spatial structures) are identified, while breaking the symmetry reveals that almost all the modes have positive growth rate. In both setups, the most unstable modes have a non-dimensional spatial growth rate close to pi/2 and they are characterized by an out-of-phase displacement of successive helix turns leading to local vortex pairing. The present results indicate that the asymmetric case is crucial to study, as the stability characteristics of the flow change significantly compared to the symmetric configurations. Based on the constant non-dimensional growth rate of disturbances, we derive a new analytical relationship between the length of the wake up to the turbulent breakdown and the operating conditions of a wind turbine

Model for End‐Stage Liver Disease‐Lactate and Prediction of Inpatient Mortality in Patients With Chronic Liver Disease

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163652/3/hep31199.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163652/2/hep31199_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163652/1/hep31199-sup-0001-Supinfo.pd