42 research outputs found
CFD modeling of natural gas engine combustion with a flame area evolution model
No full textA detailed description of the combustion process is fundamental in modern spark-ignition (SI) engines to guarantee control of pollutants formation and to meet future emission standards. Within this context, computational fluid dynamics (CFD) simulations represent an efficient and powerful tool to understand the different involved phenomena as mixture ignition, combustion development and pollutant formation. Object of this work is to find a CFD methodology to model premixed natural gas light-duty SI engines. The ignition stage is modeled by means of a simplified Eulerian spherical kernel approach (deposition model). Then, turbulent flame propagation is reproduced by means of two variables (regress variable and flame wrinkling factor) as proposed by Weller. Laminar to turbulent flame transition is taken into account using Herweg and Maly formulation and a zero-dimensional flame kernel radius evolution. Tabulated kinetics is used to estimate chemical composition of burned gases and to speed up the simulation since no chemical equilibrium calculations are necessary. The proposed CFD methodology was validated with experimental data of in-cylinder pressure, heat release rate and gross indicated work at different loads and speeds
Development and Validation of a CFD Combustion Model for Natural Gas Engines Operating with Different Piston Bowls
No full textNowadays, an accurate and precise description of the combustion phase is essential in spark-ignition (SI) engines to drastically reduce pollutant and greenhouse gas (GHG) emissions and increase thermal efficiency. To this end, computational fluid dynamics (CFD) can be used to study the different phenomena involved, such as the ignition of the charge, combustion development, and pollutant formation. In this work, a validation of a CFD methodology based on the flame area model (FAM) was carried out to model the combustion process in light-duty SI engines fueled with natural gas. A simplified spherical kernel approach was used to model the ignition phase, whereas turbulent flame propagation was described through two variables. A zero-dimensional evolution of the flame kernel radius was used in combination with the Herweg and Maly formulation to take the laminar-to-turbulent flame transition into account. To estimate the chemical composition of burnt gas, two different approaches were considered—one was based on tabulated kinetics, and the other was based on chemical equilibrium. Assessment of the combustion model was first performed by using different operating points of a light-duty SI engine fueled with natural gas and by using the original piston. The results were validated by using experimental data on the in-cylinder pressure, apparent heat release rate, and pollutant emissions. Afterward, two other different piston bowl geometries were investigated to study the main differences between one solution and the others. The results showed that no important improvements in terms of combustion efficiency were obtained by using the new piston bowl shapes, which was mainly due to the very low ((Formula presented.)) or null increase in turbulent kinetic energy during the compression stroke and due to the higher heat losses ((Formula presented.)) associated with the increased surface area of the new piston geometries
CFD Modeling of a DME CI Engine in Late-PCCI Operating Conditions
No full textPredictive combustion models are useful tools towards the development of clean and efficient engines operating with alternative fuels. This work intends to validate two different combustion models on compression-ignition engines fueled with Dimethyl Ether. Both approaches give a detailed characterization of the combustion kinetics, but they substantially differ in how the interaction between fluid-dynamics and chemistry is treated. The first one is single-flamelet Representative Interactive Flamelet, which considers turbulence-kinetic interaction but cannot correctly describe the stabilization of the flame. The second, named Tabulated Well Mixed, correctly accounts for local flow and mixture conditions but does not consider interaction between turbulence and chemistry. An experimental campaign was carried out on a heavy-duty truck engine running on DME at a constant load considering trade-off of EGR and SOI. Simulations results of 10 operating conditions show that both models can be successfully employed to predict cylinder pressure, heat release rate and pollutant emissions
Combustion Modeling in a Heavy-Duty Engine Operating with DME Using Detailed Kinetics and Turbulence Chemistry Interaction
No full textDimethyl ether (DME) represents a promising fuel for heavy-duty engines thanks to its high cetane number, volatility, absence of aromatics, reduced tank-to-wheel CO2 emissions compared to Diesel fuel and the possibility to be produced from renewable energy sources. However, optimization of compression-ignition engines fueled with DME requires suitable computational tools to design dedicated injection and combustion systems: reduced injection pressures and increased nozzle diameters are expected compared to conventional Diesel engines, which influences both the air-fuel mixing and the combustion process. This work intends to evaluate the validity of two different combustion models for the prediction of performance and pollutant emissions in compression-ignition engines operating with DME. The first one is the Representative Interactive Flamelet while the second is the Approximated Diffusive Flamelet. Both incorporate detailed kinetics and turbulence chemistry interaction but they are different in the way they account for mixing and flow conditions. A base case was simulated, comparing Diesel and DME before moving to an extensive validation of several different operating points of interest with variations of injection pressure, start of injection, engine speed and load. Analysis of the flame structure and validation with the experimental data of in-cylinder pressure and pollutant emissions will allow identifying the most suitable model for combustion simulations in DME compression-ignition engines. Finally, a new geometry for the piston bowl was tested with the validated numerical setup, evaluating the pros and cons associated with it
CFD modeling of combustion of a natural gas Light-Duty Engine
No full textA CFD methodology to model natural gas Light-Duty SI (Spark-Ignition) engines is here proposed. The ignition stage is modeled by means of a simplified Eulerian spherical kernel approach (deposition model). Then, the fully turbulent flame propagation is reproduced by the Coherent Flamelet Model (CFM), where turbulence effects are taken into account by considering the flame surface density evolution. The laminar to turbulent flame transition is managed by the CFM model and it is assumed to occur when the flame radius reaches a fraction of the integral length scale. This methodology was validated with experimental data of in-cylinder pressure and heat release rate at different loads and speeds
A Novel 1D Co-Simulation Framework for the Prediction of Tailpipe Emissions under Different IC Engine Operating Conditions
No full textLate Medieval Greek πάλιν: A Discourse Marker Signalling Topic Switch
No full textLinguistic criteria (semantic, syntactic, and prosodic) applied to the late medieval romances show that πάλιν can function as a discourse marker, which is consistent with modern dialectic evidence.</p
The polytropic volume method to detect engine events based on the measured cylinder pressure
No full textFrom Enclisis to Proclisis in Medieval Greek: σὲ λέγω and its Uses in the <i>Chronicle of Morea</i>
No full textExpressions of saying, frequent in the Chronicle, supply a context for the late shift to proclisis, as they are found treated as a whole and rendered proclitic through a reanalysis that made the first word dependent on the second rather than being enclitic on what precedes.</p
Defining Road and Rail Vehicles with a Low Environmental Footprint
No full textAbstractDetermining the environmental footprint of heavy vehicles and limiting this footprint is a complex task that requires the involvement of all stakeholders. The ongoing Ecovehicle project that is summarized in this paper demonstrates that the footprint of heavy vehicles can be quantified. It was shown that in each vehicle category there are those with a high total footprint indicating a large difference between vehicles in every category and a high potential for improvement. A recent study in Switzerland has calculated the external costs of the four modes of transport, to be over CHF 9’400 million for 2010. It was shown that most of these costs are not recovered. Considering the external cost of freight transport, the report shows that the freight traffic cost 7.1 Rp/tkm of which 4.4 Rp/tkm was internalized through the heavy vehicle fee (LSVA), implying in turn that 2.7 Rp/tkm was not recovered by the fee. The external cost of rail on the other hand was 2.8 Rp/tkm, air freight 7.6 Rp/tkm whereas the cost of ship transport on the Rhein was 0.5 Rp/tkm. Promoting ecofriendly vehicles however requires the introduction of incentives, and bonus-malus systems Europe wide. Data quality is of particular importance when comparing the environmental effects in different European countries. The data reported here, the external costs as well as the incentives discussed are from Switzerland however, the general conclusions can be extended to all modes of transport and other countries as the results are universal
