Luca Montorsi

Modelling a Dual-fuelled Multi-cylinder HCCI Engine Using a PDF based Engine Cycle Simulator

Operating the HCCI engine with dual fuels with a large difference in auto-ignition characteristics (octane number) is one way to control the HCCI operation. The effect of octane number on combustion, emissions and engine performance in a 6 cylinder SCANIA truck engine, fuelled with n-heptane and isooctane, and running in HCCI mode, are investigated numerically and compared with measurements taken from Olsson et al. [SAE 2000-01-2867]. To correctly simulate the HCCI engine operation, we implement a probability density function (PDF) based stochastic reactor model (including detailed chemical kinetics and accounting for inhomogeneities in composition and temperature) coupled with GT-POWER, a 1-D fluid dynamics based engine cycle simulator. Such a coupling proves to be ideal for the understanding of the combustion phenomenon as well as the gas dynamics processes intrinsic to the engine cycle. The convective heat transfer in the engine cylinder is modeled as a stochastic jump process and accounts for the fluctuations and fluid-wall interaction effects. Curls coalescence-dispersion model is used to describe turbulent mixing. A good agreement is observed between the predicted values and measurements for in-cylinder pressure, auto-ignition timing and CO, HC as well as NOx emissions for the base case. The advanced PDF-based engine cycle simulator clearly outperforms the widely used homogeneous model based full cycle engine simulator. The trends in combustion characteristics such as ignition crank angle degree and combustion duration with respect to varying octane numbers are predicted well as compared to measurements. The integrated model provides reliable predictions for in-cylinder temperature, CO, HC as well as NOx emissions over a wide range of octane numbers studied.

CFD Modeling of Diesel Oil and DME Performance in a Two-Stroke Free Piston Engine

This paper presents the CFD KIVA3V, rel. 2 model and numerical results of combustion process simulations in a two-stroke, uniflow scavenging dual free piston engine, FPE, designed for electricity generation. Two fuels, diesel oil and dimethyl ether (DME), were studied in order to achieve HCCI-like combustion. Limited size reaction mechanisms were constructed and used in the modeling. The diesel oil surrogate mechanism consisting of a mixture of n-heptane and toluene includes 70 species participating in 305 reactions, whereas the mechanism for DME consists of 43 species participating in 211 reactions. The combustion development has been simulated in a FPE prototype geometry. It is illustrated that by varying the direct injection timings, a comparably efficient, low-emission operation has been achieved for both fuels. Specific difficulties when using slowly vaporizing diesel oil and rapidly vaporizing DME are outlined.

CFD Combustion and Emission Formation Modeling for a HSDI Diesel Engine Using Detailed Chemistry

In order to comply with current emissions regulations, a detailed analysis of the combustion and emission formation processes in the Diesel engines accounting for the effect of the main operating parameters is required. The present study is based both on 0D and 3D numerical simulations by compiling 0D chemical kinetics calculations for Diesel oil surrogate combustion and emission (soot, NOx) formation mechanisms to construct a φ-T (equivalence ratio - temperature) parametric map. In this map, the regions of emissions formation are depicted defining a possible optimal path between the regions by placing on the same map the engine operation conditions represented by the computational cells, whose parameters (equivalence ratio and temperature) are calculated by means of 3D engine modelling. Unlike previous approaches based on static parametric φ-T maps to analyze different combustion regimes and emission formations in Diesel engines, the present paper focuses on a construction of dynamic φ-T maps, in which the pressures and the elapsed times were taken in compliance with those calculated in the 3D engine simulations. The 0D chemical kinetics calculations have been performed by the SENKIN code of the Chemkin-2 library. In-cylinder conditions represented by computational cells with known φ and T are predicted using KIVA-3V code. When cells are plotted on the map, they identify the trajectories helping to navigate between the emissions regions by varying hardware and injection parameters. Sub-models of the KIVA-3V, rel. 2 code has been modified including spray atomization, droplet collision and evaporation, accounting for multi-component fuel vapor coupled with the improved versions of the chemistry/turbulence interaction model and new formulation of the combustion kinetics for the diesel oil surrogate (consisting in 70 species participating in 310 reactions). Simulations were performed for the HSDI 1.300 Fiat Diesel engine at optimized engine operating conditions and pilot injections. Finally, numerical results are compared with the experimental data on in-cylinder pressure, Rate of Heat Release, RoHR, and selected species distributions.Copyright

Numerical and Experimental Analysis of the Wall Film Thickness for Diesel Fuel Sprays Impinging on a Temperature-Controlled Wall

Analysis of spray-wall interaction is a major issue in the study of the combustion process in DI diesel engines. Along with spray characteristics, the investigation of impinging sprays and of liquid wall film development is fundamental for predicting the mixture formation. Simulations of these phenomena for diesel sprays need to be validated and improved; nevertheless they can extend and complement experimental measurements. In this paper the wall film thickness for impinging sprays was investigated by evaluating the heat transfer across a temperature-controlled wall. In fact, heat transfer is significantly affected by the wall film thickness, and both experiments and simulations were carried out to correlate the wall temperature variations and film height. The numerical simulations were carried out using the STAR-CD and the KIVA-3V, rel. 2, codes. Different wall impingement models and liquid film approaches were analyzed and numerical results were compared with measurements available in the literature and with experiments carried out at Chalmers. The conditions for which the simulations were performed correspond to those found during the compression stroke in a diesel engine. The fuel used was a 2-component model fuel (Idea, 70% n-decane and 30% α methylnaphthalene). The experiments were carried out in the Chalmers high-pressure/high-temperature spray rig for non-evaporating and evaporating conditions. The spray chamber was equipped with a temperature-controlled wall, including coaxial thermocouples for recording the surface temperature. The time histories of the surface temperatures were used to calculate the local heat fluxes applying a 1-dimensional transient heat conduction model.

Knock modeling: an integrated tool for detailed chemistry and engine cycle simulation

For the simultaneous evaluation of the influence on engine knock of both chemical conditions and global operating parameters, a combined tool was developed. Thus, a two-zone kinetic model for SI engine combustion calculation (Ignition) was implemented into an engine cycle simulation commercial code. The combined model predictions are compared with experimental data from a single-cylinder test engine. This shows that the model can accurately predict the knock onset and in-cylinder pressure and temperature for different lambda conditions, with and without EGR. The influence of nitric oxide amount from residual gas in relation with knock is further investigated. The created numerical tool represents a useful support for experimental measurements, reducing the number of tests required to assess the proper engine control strategies. (Less)

An integrated approach to energy recovery from biomass and waste: Anaerobic digestion-gasification-water treatment.

The article investigates the performance of an integrated system for the energy recovery from biomass and waste based on anaerobic digestion, gasification and water treatment. In the proposed system, the organic fraction of waste of the digestible biomass is fed into an anaerobic digester, while a part of the combustible fraction of the municipal solid waste is gasified. Thus, the obtained biogas and syngas are used as a fuel for running a cogeneration system based on an internal combustion engine to produce electric and thermal power. The waste water produced by the integrated plant is recovered by means of both forward and inverse osmosis. The different processes, as well as the main components of the system, are modelled by means of a lumped and distributed parameter approach and the main outputs of the integrated plant such as the electric and thermal power and the amount of purified water are calculated. Finally, the implementation of the proposed system is evaluated for urban areas with a different number of inhabitants and the relating performance is estimated in terms of the main outputs of the system.

A Numerical and Experimental Study of Diesel Fuel Sprays Impinging on a Temperature Controlled Wall

Spray-wall as well as spray-spray interactions in direct injection diesel engines have been found to influence both the rate the heat release and the formation of emissions. Simulations of these phenomena for diesel sprays need to be validated and an issue is investigating what kind of fuels can be used in both experiments and spray calculations. The objective of this work is to compare numerical simulations with experimental data of sprays impinging on a temperature controlled wall, regarding spray characteristics and heat transfer. The numerical simulations were carried out using the STAR-CD and KIVA 3V codes. The CFD simulations accounted for the actual spray chamber geometry and operating conditions used in the experiments. Particular attention has been devoted to the fuel used for the simulations. Firstly a single component model fuel (n heptane) has been adopted; subsequently a 2 component model fuel (Idea, 70% n-decane and 30 % α methylnaphthalene) has been implemented into the code fuel libraries in order to account for the fuel used in the experiments. Finally, different break-up and wall impingement models were analyzed. The experiments were performed in the high pressure, high temperature spray rig at Chalmers with conditions corresponding to those found during the compression stroke in a heavy duty diesel engine. The temperature controlled wall was equipped with three coaxial thermocouples for recording the surface temperature. The time histories of the surface temperatures were used to calculate the local heat fluxes applying a 1 dimensional transient heat conduction model. The spray characteristics were measured using two different optical methods; Phase Doppler Anemometry and high speed imaging. Image analysis gave the characteristics of the general behavior of the axial and radial penetration. PDA-data gave the characteristics of droplet penetration before and after impinging the wall.

Numerical analysis of an entire ceramic kiln under actual operating conditions for the energy efficiency improvement

The paper focuses on the analysis of an industrial ceramic kiln in order to improve the energy efficiency and thus the fuel consumption and the corresponding carbon dioxide emissions. A lumped and distributed parameter model of the entire system is constructed to simulate the performance of the kiln under actual operating conditions. The model is able to predict accurately the temperature distribution along the different modules of the kiln and the operation of the many natural gas burners employed to provide the required thermal power. Furthermore, the temperature of the tiles is also simulated so that the quality of the final product can be addressed by the modelling. Numerical results are validated against experimental measurements carried out on a real ceramic kiln during regular production operations. The developed numerical model demonstrates to be an efficient tool for the investigation of different design solutions for the kilns components. In addition, a number of control strategies for the system working conditions can be simulated and compared in order to define the best trade off in terms of fuel consumption and product quality. In particular, the paper analyzes the effect of a new burner type characterized by internal heat recovery capability aimed at improving the energy efficiency of the ceramic kiln. The fuel saving and the relating reduction of carbon dioxide emissions resulted in the order of 10% when compared to the standard burner.

Analysis of a 6 Cylinder Turbocharged HCCI Engine Using a Detailed Kinetic Mechanism

When analyzing HCCI combustion engine behavior, the integration of experimental tests and numerical simulations is crucial. Investigations of possible engine control strategies as a function of the different operating conditions have to take the behavior of the whole HCCI engine into account, including the effects both of the combustion process and of complex devices. Therefore the numerical simulation code must be able both to model accurately the gas-dynamic of the system and to evaluate the combustion chemical kinetics. This paper focuses on the coupling between the commercial one-dimensional fluid-dynamic GT-Power Code and our in-house detailed chemical kinetic Ignition Code. An interface has been developed in order to exchange information between the two codes: the Ignition Code considers as boundary conditions the GT-Power Code values provided for the gas composition at IVC and the pressure and temperature at every time step and passes back to GT-Power the burnt fuel fraction and stores in an external file the in cylinder gas composition. Thus the whole engine cycle can be accurately simulated, estimating the interactions between the gas-dynamics phenomena along the intake and exhaust pipes and through the valves, and the chemical processes occurring during the closed valves period. This tool makes it possible to analyze the engine behavior under duty cycle operating conditions, and therefore it represents a useful support to the experimental measurements, reducing the number of tests required to assess the proper engine control strategies.Copyright

Analysis of a HSDI Diesel Engine Intake System by Means of Multi-Dimensional Numerical Simulations: Influence of Non Uniform EGR Distribution

In order to comply with stringent pollutant emissions regulations a detailed analysis of the overall engine is required, assessing the mutual influence of its main operating parameters. The present study is focused on the investigation of the intake system under actual working conditions by means of 1D and 3D numerical simulations. Particularly, the effect of EGR distribution on engine performance and pollutants formation has been calculated for a production 6 cylinder HSDI Diesel engine in a EUDC operating point. Firstly a coupled 1D/3D simulation of the entire engine geometry has been carried out to estimate the EGR rate delivered to every cylinder; subsequently the in-cylinder flow field has been evaluated by simulating the intake and compression strokes. Finally the spray and combustion processes have been studied accounting for the real combustion chamber geometry and particularly the pollutants formation has been determined by using a detailed kinetic mechanism combustion model. The 1D/3D analysis highlighted a significant cylinder to cylinder EGR percentage variation affecting remarkably the pollutant emissions formation, as evaluated by the combustion process simulations. A combined use of commercial and in-house modified codes has been adopted.Copyright