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CFD techniques are more and more utilized in the development of new solutions for performance improvement of internal combustion engines. Three dimensional models, in general, are able to provide detailed and sound information on engine phenomena, but often they are time consuming and hard to be implemented. On the other hand, one-dimensional models can reproduce the entire engine cycle with acceptable computational times; however they need semi-empirical correlations in order to model the flow field details and the burning speed within each cylinder. In this paper, an example of hierarchical structure of 3-D and 1-D models has been proposed. The main performances of a small turbocharged spark-ignition engine have been calculated. Variable-speed and full load operating points have been analyzed. The 3-D model provided the details of the in-cylinder flow field and turbulent indices.

In a previous paper, the authors assessed the potential of CFD modeling in developing a new intake system for a small spark-ignition engine. The effect of the intake port and valve design on the charge motion within the cylinder was illustrated [1]. In this paper, a detailed analysis of the influence of the intake port geometry on the combustion process, therefore on the performance, of a MPI spark-ignition engine has been carried out. The purpose of such a theoretical analysis is to provide some guidelines, in developing new intake solutions, aimed to improve the combustion quality of a production engine on the market since the early 80's. A 3-D computer code has been used to model the intake, compression and combustion processes of the engine. The model has been validated comparing the computational results to the data, relative to the normal production engine, provided by the manufacturer.

A small spark-ignition engine, in wide spread commercial usage since numerous years, is at present under study with the aim of improving its performance, in terms of a reduction of both fuel consumption and pollutant emissions. In previous papers, the influence of piston geometry [1] and intake system [2] on the combustion process has been evaluated by means of a 3-D computational model. In this paper, a more extensive analysis of the parameters affecting the combustion rate, hence thermal efficiency, pollutant formation and engine stability, has been carried out. In particular, at ELASIS Research Center, three prototypes featuring different combustion chambers have been realized and analyzed to the aim of assessing the influence of the squish area percentage on the flame front propagating in a quiescent charge. Furthermore, the AVL FIRE computer code has been utilized in order to simulate the engine behavior at full load operation.

In previous papers [1, 2], the authors proposed a hybrid combustion model able to predict the behavior of a small spark-ignition, multivalve, multipoint injection engine, at different operating points. The combustion model proposed was implemented in the KIVA-3V [3] code for a closed valve simulation of engine operation. The results obtained for pressure cycles showed good agreement to the measured data and the characteristic constant of the model resulted less sensitive to the engine operating conditions such as rotational speed. Since the present research activity is aimed to investigate the potential for the adoption of alternate fuels, the latter point was considered of interest in modeling such off-design operation as a change in engine fueling. In this paper, the simulation results obtained by using the KIVA-3V code are compared to those provided by a different multidimensional code: AVL FIRE 72b [4].

Hydrogen and gasoline can be burned together in internal combustion engines in a wide range of mixtures. In fact, the addition of small hydrogen quantities increases the flame speed at all gasoline equivalence ratios, so the engine operation at very lean air-gasoline mixtures is possible. In this paper, the performance of a spark-ignition engine, fuelled by hydrogen enriched gasoline, has been evaluated by using a numerical model. A hybrid combustion model for a dual fuel, according to two one-step overall reactions, has been implemented in the KIVA-3V code. The indicated mean pressure and the fuel consumption have been evaluated at part load operating points of a S.I. engine designed for gasoline fuelling. In particular, the possibility of operating at wide-open throttle, varying the equivalence ratio of air-gasoline mixture at fixed quantities of the supplemented hydrogen, has been studied.

The intake system of a wide commercial spread spark-ignition engine has been modeled by using a 3-D code. The present configuration of the inlet manifold and inlet port does not generate any organized charge rotation, especially at low rotational speed. Objective of this paper is the research of new solutions, able to produce higher turbulence levels of the in-cylinder flow, without lowering the engine volumetric efficiency, in order to shorten the combustion duration and improve the energy conversion quality. A three-dimensional model for the calculation of the inlet port and valve performance under steady conditions has been developed. First, the normal production intake system has been modeled to the aim of validating the model set-up. The inlet valve discharge coefficient in a steady flow has been calculated. The results obtained showed a good agreement to the measured data and encouraged the authors to use the model for the development of new intake solutions.

Variable Valve Timing (VVT) technology is more and more adopted in modern spark-ignition engines for the optimization of torque delivery. Furthermore, a proper choice of valve timing could reduce the typical pumping losses of these engines thus improving fuel economy at part load. VVT mainly influences gas exchange processes, then the engine volumetric efficiency; in some circumstances, variations of valve timing could modify the charge composition and therefore the flame development and propagation. In this paper, the combustion process of a small displacement, 2 valve, spark-ignition engine, with variable valve timing, has been numerically and experimentally analyzed. The use of VVT allows obtaining combined internal EGR and Reverse Miller Cycle effects so to achieve a significant dethrottling at part load operation. A 3-D computer code has been utilized in order to calculate the details of the flow field within the cylinder and the combustion rate at different valve points.

Optimized valve timing, according to engine load, may lead to significant improvements in pumping losses and internal EGR generation. Thus, VVT technology constitutes an effective way to reduce both fuel consumption and pollutant emissions. In this paper, the behavior of a small displacement, 2 valve, Spark-ignition engine, with variable valve timing, has been numerically and experimentally analyzed. The use of VVT allows obtaining combined internal EGR and Reverse Miller Cycle effects so to achieve a significant dethrottling at part load operation. High EGR rates require high turbulence intensity in order to accelerate the combustion rate. The engine performs an accurate combustion chamber design and a tangential intake port able to generate optimized swirl motion, according to the engine speed and load, during both the exhaust gas re-aspiration and the intake stroke. Engine performances at different cam phaser positions have been calculated by means of a 3-D computer code.