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Similar to the classical solution of hydraulic pump-turbine plant, new means for accumulation of eletrical energy are given for lower but respectable quantities by the so called BESS (Battery Energy Storage System) and SMES (Super conducting Magnet Energy Storage). Another energy accumulator is given by using mecanichal kinetic energy of fly-wheel. Each system has advantages and disadvantage from the point of wiew of the quantity of stored energy and magnitude of the instantaneous usable power. A realistic application of energy storage, using the advantages of their complementarity. The modern energy conversion techniques allow fast, and flexible power control, and also reactive power compensation.

This work highlights the modelling and simulation of a micro-grid connected renewable energy system. It comprises of wind turbine (WT) based on doubly fed induction generator (DFIG), photovoltaic generator (PV), fuel cell (FC) generator, a Hydrogen tank, a water electrolyser used for long-term storage, and a battery bank energy storage system (BBESS) utilized for short-term storage. In this paper, a global control strategy and an energy management strategy are proposed for the overall system. This strategy consists in charging the BBESS and producing hydrogen from the water electrolyser in case of power excess provided from WT-DFIG and photovoltaic generators. Therefore, the FC and the BBESS will be used as a backup generator to supply the demand required power, when the WT-DFIGs and the PV energy are deficient. The effectiveness of this contribution is verified through computer simulations under Matlab/Simulink, where very satisfactory results are obtained.

Abstract Research and design in the field of spark ignition engines seek to achieve high performance while conserving fuel economy and low pollutant emissions. For the evaluation of various engine configurations, numerical simulations are favored, since they are quick and less expensive than experiments. Various zero-dimensional combustion models are currently used. Both flame front reactions and post-flame processes contribute to the heat release rate. The first part of this study focuses on the role of the flame front on the heat release rate, by modeling the interaction of the flame front with the chamber wall. Post-flame reactions are dealt with in Part B of the study. The basic configurations of flame quenching in laminar flames are also applicable in turbulent flames, which is the case in spark ignition engines. A simplified geometric model of the combustion chamber was used to calculate the mean flame surface, the flame volume and the distribution of flame surface as a function of the distance from the wall. The flame–wall interaction took into account the geometry of the combustion chamber and of the flame, aerodynamic turbulence and the in-cylinder pressure and temperature conditions, through a phenomenological attenuation function of the wrinkling factor. A modified global wrinkling factor as a function of the mean surface distance distribution from the wall was calculated. The impact of flame–wall interaction was simulated for four configurations of the sparkplug position and length: centered and lateral position, and standard and projected tip sparkplug. Results show that the position of the sparkplug has a greater influence than its length. The heat release rate was significantly altered in the lateral sparkplug position, when running the model with flame wall interaction. With the projected tip sparkplug, the impact of the wall on the initial flame kernel was delayed, since the flame is not close to the cylinder head. The maximum pressure was reduced when using the flame–wall interaction model for all four configurations. The attenuation of the wrinkling factor and of the mean flame surface at the end of combustion was captured by taking into account the impact of the chamber geometry, while this is not the case in global models, which impose an exponential decay of the heat release rate. The measured values for the four sparkplug configurations gave consistent results in terms of cylinder pressure and heat release.

Abstract Reduced fuel consumption, low pollutant emissions and adequate output performance are key features in the contemporary design of spark ignition engines. Zero-dimensional numerical simulation is an attractive alternative to engine experiments for the evaluation of various engine configurations. Both flame front reaction and post-flame processes contribute to the heat release rate. The contribution of this work is to highlight and model the role of post-flame reactions (CO and hydrocarbons) in the heat release rate. The modeling approach to CO kinetics used two reactions considered to be dominant and thus more suitable for the description of CO chemical mechanism. Equilibrium concentrations of all the species involved were calculated by a two-zone thermodynamic model. The computed characteristic time of CO kinetics was found to be of a similar order to the results of complex chemistry simulations. The proposed model captured the ‘freezing’ effect (reaction rate is almost zero) for temperatures lower than 1800 K and followed the trends of the measured values at exhaust. However, a consistent underestimation of CO levels at the exhaust was observed. The impact of the remaining CO on the combustion efficiency is considerable especially for rich mixtures. For a remaining 0.4% CO mass fraction, the impact on combustion inefficiency is 0.1%. Unburnt hydrocarbon, which have not reacted within the flame front before quenching, diffuse in the burnt gas and react. In this work, a global reaction rate models the kinetic behavior of hydrocarbon. The diffusion process was modeled by a relaxation equation applied on the calculated kinetic concentration. The relaxation time was calculated by the reduction of a general hydrocarbon diffusion equation. This modeling approach enabled the final part of combustion to be simulated. The HC consumption predicted by the model is consistent with the HC measurements at the exhaust. The hydrocarbon consumption at the final combustion stage varied from 1% to 6% depending on the operating point.

The effect of finite Reynolds numbers and/or internal intermittency on the total kinetic energy and scalar energy transfers is examined in detail. For this purpose, two distinct models for velocity and scalar energy transfer are proposed in the specific context of freely decaying isotropic turbulence. The first one extends the already existing dynamical models (hereafter DYM, i.e. based on transport equations originated in Navier–Stokes and advection-diffusion transport equations). The second one relies on the characteristic time of the strain at a specific scale (hereafter SBM). Both models account for the Reynolds number dependence of the scaling exponent of the second-order structure functions, over a range of scales where such exponents may be defined, i.e. a restricted scaling range (RSR). Therefore, the models developed aim at reproducing the energy transfer over the RSR. The predicted energy transfer is very sensible to variations of the scaling exponent, especially at low Reynolds numbers. The app...

The potential of butanol as an additive in iso-octane used as gasoline fuel was characterized with respect to laminar combustion, and compared with ethanol. New sets of data of laminar burning velocity are provided by using the spherical expanding flame methodology, in a constant volume vessel. This paper presents the first results obtained for pure fuels (iso-octane, ethanol and butanol) at an initial pressure of 0.1 MPa and a temperature of 400 K, and for an equivalence range from 0.8 to 1.4. New data of laminar burning velocity for three fuel blends containing up to 75% alcohol by liquid volume are also provided. From these new experimental data, a correlation to estimate the laminar burning velocity of any butanol or ethanol blend iso-octane-air mixture is proposed.

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Abstract This paper presents an experimental investigation of the influence of fuel density and fuel viscosity on the flow characteristics generated from a high pressure Diesel injector, equipped with conical orifices. For this purpose, mass flow rate measurements were performed with nine different fuels over operating conditions from 30 to 180 MPa of injection pressure and from 1 to 9 MPa of back pressure. Fuel viscosity was varied from 0.6 to 7 mm2/s and fuel density from 683 to 876 kg/m3 at the operating temperature. Fuel viscosity induces a decrease of up to 10% in the discharge coefficient at low pressure difference but for higher pressure difference, fuel density remains the only fuel property driving the mass flow rate. The discharge coefficient is also a function of the pressure difference at any given Reynolds number under non-cavitating conditions. A correlation is suggested to estimate the discharge coefficient taking into account the fuel properties and the operating conditions.