A conceptual framework for evaluating cooking systems

PUBLISHED 7 March 2022Tami C Bond, Christian L, Orange, Paul R Medwell, George Sizoomu, Samer Abdelnour, Verena Brinkmann, Philip Lloyd and Crispin Pemberton-Pigot

A Theoretical Review of Rotating Detonation Engines

Rotating detonation engines are a novel device for generating thrust from combustion, in a highly efficient, yet mechanically simple form. This chapter presents a detailed literature review of rotating detonation engines. Particular focus is placed on the theoretical aspects and the fundamental operating principles of these engines. The review covers both experimental and computational studies, in order to identify gaps in current understanding. This will allow the identification of future work that is required to further develop rotating detonation engines

Analysis of the lawn bowl trajectory as a teaching tool for sports engineering: development of a graphical user-interface

Procedia Engineering ; 13Sports engineering graduates require a range of competencies. The ability to interactively process and analyse data is a useful skill that may not be fully covered in more traditional engineering subjects. One particular focus within this area that many graduates will find invaluable is the ability to write computer programmes incorporating a graphical user-interface (GUI). This paper outlines the development of a GUI in MATLAB® to interactively present the trajectory of a lawn bowl. Through the developed MATLAB® GUI, numerous parameters can be varied and the influence on the trajectory of a lawn bowl can be shown graphically. This practical example also provides an excellent opportunity to teach many other relevant aspects of MATLAB®. The skills that are introduced in this paper may readily be applied to a range of other sports engineering applications. © 2011 Published by Elsevier Ltd.Paul R. Medwell, Laura A. Brooks and Barry S. Medwel

Transient interaction between a reaction control jet and a hypersonic crossflow

This paper presents a numerical study that focuses on the transient interaction between a reaction control jet and a hypersonic crossflow with a laminar boundary layer. The aim is to better understand the underlying physical mechanisms affecting the resulting surface pressure and control force. Implicit large-eddy simulations were performed with a round, sonic, perfect air jet issuing normal to a Mach 5 crossflow over a flat plate with a laminar boundary layer, at a jet-to-crossflow momentum ratio of 5.3 and a pressure ratio of 251. The pressure distribution induced on the flat plate is unsteady and is influenced by vortex structures that form around the jet. A horseshoe vortex structure forms upstream and consists of six vortices: two quasi-steady vortices and two co-rotating vortex pairs that periodically coalesce. Shear-layer vortices shed periodically and cause localised high pressure regions that convect downstream with constant velocity. A longitudinal counter-rotating vortex pair is present downstream of the jet and is formed from a series of trailing vortices which rotate about a common axis. Shear-layer vortex shedding causes periodic deformation of barrel and bow shocks. This changes the location of boundary layer separation which also affects the normal force on the plate.</p

Numerical investigation of a pulsed reaction control jet in hypersonic crossflow

This paper presents a numerical study on the flow structures developed when a pulsed reaction control jet is operated in a hypersonic crossflow with a laminar boundary layer. Understanding these flow structures is important to the design of reaction control jets and scramjet fuel injectors. Implicit large-eddy simulations were performed with a round, sonic, perfect air jet issuing normal to a Mach 5 crossflow over a flat plate, at a jet-to-crossflow momentum ratio of 5.3 and a pressure ratio of 251, and with square-wave pulsing at Strouhal numbers of 1/6 to 1/3, based on jet diameter and free-stream velocity. Pulsing the jet allows the shock structure to partially collapse when the jet is off. This shock collapse affects the shedding frequency of shear-layer vortices, the formation of shear-layers downstream of the jet outlet, and the formation of longitudinal counter-rotating vortices. The lead shocks formed at jet start-up allow deeper penetration by increasing the effective jet-to-crossflow momentum ratio near the jet outlet and by preventing interaction between hairpin vortices. Normalised penetration was increased by a maximum of 68% compared with the steady jet. Pulsing also provides a higher jet interaction force per unit mass flow rate compared with a steady jet, with a 52% increase recorded at a 33% duty cycle. Temporal and spatial variations of surface pressure are important for reaction control applications and have been quantified. Pressure distribution depends strongly on duty cycle, and higher interaction force per unit mass flow rate was observed in cases with low duty cycle.</p

The reactor-based perspective on finite-rate chemistry in turbulent reacting flows: A review from traditional to low-emission combustion

In flames, turbulence can either limit or enhance combustion efficiency by means of strain and mixing. The interactions between turbulent motions and chemistry are crucial to the behaviour of combustion processes. In particular, it is essential to correctly capture non-equilibrium phenomena such as localised ignition and extinction to faithfully predict pollutant formation. Reactor-based combustion models — such as the Eddy Dissipation Concept (EDC) or Partially Stirred Reactor (PaSR) — may account for turbulence-chemistry interactions at an affordable computational cost by calculating combustion rates relying upon canonical reactors of small fluid size and timescale. The models may include multiscale mixing, detailed chemical kinetic schemes and high-fidelity multispecies diffusion treatments. Although originally derived for conventional, highly turbulent combustion, numerous recent efforts have sought to generalise beyond simple empirical correlations using more sophisticated relationships. More recent models incorporate the estimation of scales based on local variables such as turbulent Reynolds and Damköhler numbers, phenomenological descriptions of turbulence based on fractal theory or specific events such as extinction. These modifications significantly broaden the effective range of operating conditions and combustion regimes these models can be applied to, as in the particular case of Moderate or Intense Low-oxygen Dilution (MILD) combustion. MILD combustion is renown for its ability to deliver appealing features such as abated pollutant emissions, elevated thermal efficiency and fuel flexibility. This review describes the development and current state-of-the-art in finite-rate, reactor-based combustion approaches. Recently investigated model improvements and adaptations will be discussed, with specific focus on the MILD combustion regime. Finally, to bridge the gap between laboratory-scale canonical burners and industrial combustion systems, the current directions and the future outlook for development are discussed

Laminar flame calculations for analyzing trends in autoignitive jet flames in a hot and vitiated coflow

Experiments of autoignitive jet flames in a hot and vitiated coflow have previously shown various flame behaviors, spanning lifted flames to moderate or intense low oxygen dilution (MILD) combustion. For better understanding the behavior of flames in this configuration, regime diagrams and ignition delay results are presented from well-stirred reactor calculations across a wide range of operating conditions for methane and ethylene fuels. In conjunction with two-dimensional calculations, the importance of flame precursors and oxygen penetration across the reaction zone is revealed. It is found that widely accepted definitions and regime diagrams are inadequate to classify and reconcile the different flame behaviors that are observed experimentally. For accurate prediction of the ignition process, it is necessary to incorporate boundary conditions that capture minor species in the oxidizer. The role of fuel type also has a major impact on the ignition process and flame appearance.Paul R. Medwell, Michael J. Evans, Qing N. Chan and Viswanath R. Katt

An experimental study on MILD combustion of prevaporised liquid fuels

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