Dzieminska Edyta

JP-10/air two-phase detonation and rotating detonation engine (RDE) are numerically studied to find out their limits of physical values as a function of equivalence ratio, prevaporization, fuel concentration, droplet diameter, and initial pressure and temperature. To find such limits, the JP-10/air two-step chemical reaction mechanism is used and the Eulerian–Eulerian two-phase governing system is developed to simulate those limits. Especially the JP-10/air two-phase detonation velocity and cell size are investigated in detail and the generation of nonreacted region and quenching mechanism of JP-10/air two-phase RDE are simulated. The findings from those studies are that 1) the JP-10/air two-phase detonation and RDE codes are developed and validated to calculate detonation and RDE 2) the JP-10/air detonation cell size is calculated by the developed code to show a good agreement with the experimental data and 3) the JP-10/air RDE simulation shows a detonation quenching at the condition when the droplet diameter is larger than 4 μm and the prevaporization factor is smaller than 20%.

© 2019 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. The present study will show a new development of a gasturbine engine with rotating detonation engine. Five universities and a venture company will study characteristics of rotating detonation engines to develop a gasturbine engine with RDE system in order to improve its performance of gas turbine engine, especially its efficiency. We have three teams; the experimental team, numerical team, and gasturbine team. The experimental team will perform several categories; concentric as well as disk type RDE development and measurement of its stable conditions and controlabilities as well as its efficiency; the cooling system of RDE; injection and ignition system; and DDT performance. The numerical group will simulate above experimental categories by real size calculations with both DNS and AMR base. And a micro-gasturbine engine will be run together with RDE system in a near future. We prefer to choose a disc type RDE instead of concentric cylinder type one. Hence the midterm report like presentation will be given at the SciTech meeting, Jan 2019 and 2020.

Overall efficiency of internal combustion engines are heavily depended on intake air temperature which is directly related to the heat transfer inside an intake system. Previously, authors developed an equation by using port model setup to calculate Nusselt number with introduction of Graetz and Strouhal numbers. This study modified the port model equation to improve its accuracy in a real engine experimental setup. Predicted intake air temperature was compared to the measured data with a maximum error of 5.6%. Additionally, 100 K of temperature difference was found between the boost pressure values of 944hPa and 678hPa from 1-D engine simulation results.

To investigate the safety properties of high-pressure hydrogen discharge or leakage, an under-expanded hydrogen jet flow with a storage pressure of 82 MPa from a small jet orifice with a diameter of 0.2 mm is studied by three-dimensional (3D) numerical calculations. The full 3D compressible Navier-Stokes equations are utilized in a domain with a size of about 3 × 3 × 6 m which is discretized by employing an adaptive mesh refinement (AMR) technology to reduce the number of grid cells. By AMR, the local mesh resolutions can narrowly cover the Taylor microscale lT and direct numerical simulations (DNS) are performed. Both the instantaneous and mean hydrogen concentration distributions in the present jet are discussed. The instantaneous concentrations of hydrogen CH2 on the axis presents significant turbulent pulsating oscillations. The centerline value of the intensity of concentration fluctuation σˆH2 asymptotically comes to 0.23, which is in a good agreement with the existing experimental results. It substantiates the conclusion that the asymptotic centerline value of σˆH2 is independent of jet density ratio. The probability distributions function (PDF) of instantaneous axial CH2 agree approximately with the Gaussian distribution while skewing a little to the higher range. The time averaged hydrogen concentration C¯H2 along the radial directions can also be described as a Gaussian distribution. The axial C¯H2 of 82 MPa hydrogen jet tends to obey the distribution discipline approximated with C¯H2 =4200/(z/θ) where z is the axial distance from the nozzle and θ is the effective ejection diameter, which is consistent with the experimental results. In addition, the hydrogen tip penetration Ztip is found to be in a linear relationship with the square root of jet flow time t. Meanwhile, the jet's velocity half-width LVh approximately gains an linear relation with z which can be expressed as LVh=0.09z.

Detonation in ducts is usually studied assuming adiabatic walls because of the high kinetic energy due to the incoming flow being supersonic. In the present work, numerical simulations of deflagration-to-detonation transition (DDT) using a detailed chemical reaction model are performed under adiabatic and isothermal boundary conditions in a tube with no-slip walls. The results show a local explosion driving DDT, which occurs near the tube wall in the case of an adiabatic wall, but close to the flame front in the case of an isothermal wall. Furthermore, to examine the effects of a turbulent boundary layer, a simulation using the Baldwin-Lomax turbulence model is carried out. In the case of the isothermal wall, there is again a local explosion near the tube wall, which leads to detonation. In summary, the present study confirms that the boundary conditions affect the transition to detonation and that the boundary layer is a key component of DDT.

Detonation research started just at the beginning of 1880s, but its generation mechanism is still a mystery and has not been explained in details yet. Many experimental research in the early 1900s reported that detonation is generated by a transition from deflagration, later known as deflagration-to-detonation transition (DDT). A high performance laser allowing to see a detailed phenomenon was developed later. However, even with nowadays experimental techniques a detailed view on detonation initiation cannot be provided. The present work shows for the first time in details that shock wave - boundary layer interactions are the key for an auto-ignition in the boundary layer in a smooth tube. From that process of the auto-ignition a new flame is developed and propagate along the wall with a sound speed, turns into a fast flame, and trigger DDT finally. The most important factors for the process of the auto-ignition in the boundary layer are thermodynamic interactions in the boundary layer and the induction time. Copyright (c) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Experiments concerning a fast flame have been performed by many researchers, but it is impossible to observe some phenomena in the experimental frames only. The aim of this study is to show the numerical analysis of the fast flame that leads to deflagration-to-detonation transition (DDT). It was found that flame propagates with a supersonic velocity for some time before it transits to detonation. Additionally a new flame is developed in the vicinity of the wall due to compression shocks heating up the mixture along with adiabatic wall conditions. Moreover, on the tip of each flame one can observe a dense high-pressure and high-temperature region that forms a small but strong bow shock. This shock may be partly a clue in flame acceleration and DDT.

In this study Lewis number (Le) for laminar premixed flame in oxy-hydrogen stoichiometric mixture was investigated numerically. This is the first time to analyze values of Le for the whole flow field. It is known from definition that low Le is beneficial in flame propagation and our numerical simulations are a proof for that. On the edge of the flame Le is extremely low, which indicates that the flame accelerates. Flame can propagate with more than a speed of sound in the reactive mixture, which results in deflagration-to-detonation transition (DDT) and detonation. The present paper shows such propagating process with low Le as well as the profiles of Le in the DDT domain.