Fully Compressible Hydrodynamic Simulation of Non-Equidiffusive Premixed Flames Propagation in Channels

Premixed combustion remains of fundamental interest in energy generation and propulsion systems as well as in implementation of safety measures for residential and industrial accidental fire explosions. While the fast pace and complex nature of the combustion process has previously necessitated the analytical and computational studies to employ the simplifying assumption of equidiffusivity, when the Lewis number defined as the thermal-to-mass diffusivities ratio is unity , the ongoing advancements in technology and the requirements for efficiently operating combustors over a wide range of conditions make the combustion process more non-equdiffusive ( ) than ever. The impact of non-equidiffusivity on the dynamics and morphology of a flame, and thereby on the combustion efficiency, becomes aggravated by the interactions with combustor geometric parameters as well as thermochemical properties of the fuel mixture. Therefore, by representing combustors as channels with various extreme conditions (open channels, when both ends are open, or semi-open, when one end is closed, while the other one remains open), boundary conditions (non-slip or free slip, adiabatic or isothermal walls) and internal structures (obstructed or unobstructed), the current work addresses the effects of non-equidiffusivity and its interplays with other parameters on flame propagation in channels. Specifically, propagation of non-equidiffusive flames in channels is investigated by means of the computational simulations of the reacting flow equations with fully-compressible hydrodynamics and Arrhenius chemical kinetics. A detailed parametric study is performed for the Lewis numbers in the range ; the channel half-width , where is the thermal flame thickness; the blockage ratios, , being from to ; and the spacing between the obstacles being . The diffusional-thermal combustion instability, associated with , and the flame thickening at are found to play a major role in determining the flame dynamics in a channel. Regarding finger flame acceleration in semi-open channels with adiabatic slip walls, it is shown that the flames accelerate slower than equidiffusive ones. In contrast, the flames acquire stronger distortion, associated with the diffusional-thermal combustion instability, and thereby accelerate much faster than at . Increased surface area of the flame front and thus, a higher burning rate and stronger acceleration is also obtained in wider channels. Presence of equally spaced obstacles in such channel produced higher acceleration, with the increase being more significant at and high blockage ratio. When both ends of the channels are open, the flames show oscillations, acceleration or a sequence of both, depending on other parameters. For a channel with adiabatic non-slip walls, the oscillation amplitude and frequency decreases with , and the low- flames exhibiting different morphologies. A drastic change in flame dynamics is however seen for channel with isothermal wall. In narrow channels with small blockage ratios, the oscillations amplitude and frequency changes with , with the frequency decreasing and the amplitude increasing as grows from 0.3 to 2. In other conditions, a transition from flame oscillations to its sudden acceleration or propagation at constant velocity, is singularly influenced by the Lewis number, or by coupling to the geometric parameters. The delay time before the onset of flame acceleration, especially at , also varies as channel width and the blockage ratio changes. In all cases, the Lewis number shows both quantitative and qualitative effects on flame propagation in obstructed channel

Assessment of Decentralized Electricity Production from Hybrid Renewable Energy Sources for Sustainable Energy Development in Nigeria

This paper presents technical and economic assessment of a hybrid energy system for electricity generation in rural communities in the six geopolitical zones of Nigeria. The study was based on a 500 rural household model having an electric load of 493 kWh per day. To simulate long-term continuous implementation of the hybrid system, 21 years (1992 – 2012) hourly mean global solar radiation and wind speed data for the selected sites were used. The mean annual wind speed and solar radiation for the locations ranged from 2.31 m/s for Warri to 3.52 m/ s for Maiduguri and 4.53 kWh/m2 for Warri to 5.92 kWh/m2 for Maiduguri, respectively. These weather data were used for simulation with the Micro-power Optimization Model software HOMER. From the optimum results of the hybrid system,Warri has the highest NPC and COE of $2,441,222 and$0.721/kWh, respectively while Maiduguri has the least NPC and COE of $2,225,387 and$0.658/kWh, respectively for the 21 years project lifespan. The high value of COE for Warri is due to its low renewable energy resource while low COE for Maiduguri is due to its high renewable energy resource. The Northern part of the country has ample renewable energy resource availability and with a strong political will, optimal utilization of these renewable resources (solar and wind) can be actualized. Researchers, Industrialists, Policy Makers and the Nigerian government should therefore seize this opportunity in developing a sustainable energy through utilization of abundant renewable energy resources in the country