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Water injection represents a promising tool to improve performance of spark-ignition engines. It allows reducing in-cylinder temperature, preventing knock risks. Optimizing the spark advance, water injection allows obtaining an increase of both efficiency and power output, particularly at medium and high loads. Water can be injected into the intake port or directly into the combustion chamber. In this paper, the authors investigated the effects of both direct and port water injection in a downsized PFI spark-ignition engine at high load operation. Different water-to-fuel ratios have been analyzed for both configurations. For the experimental analysis, low-pressure water injectors have been installed in the intake ports of the engine under study, upstream of the fuel injectors. Experimental tests have been carried out at various operating points. Furthermore, engine operation with port water injection has been simulated by means of the AVL Fire 3-D code.

In this paper, an experimental and numerical analysis of combustion process and knock occurrence in a small displacement spark-ignition engine is presented. A wide experimental campaign is preliminarily carried out in order to fully characterize the engine behavior in different operating conditions. In particular, the acquisition of a large number of consecutive pressure cycle is realized to analyze the Cyclic Variability (CV) effects in terms of Indicated Mean Effective Pressure (IMEP) Coefficient of Variation (CoV). The spark advance is also changed up to incipient knocking conditions, basing on a proper definition of a knock index. The latter is estimated through the decomposition and the FFT analysis of the instantaneous pressure cycles. Contemporary, a quasi-dimensional combustion and knock model, included within a whole engine one-dimensional (1D) modeling framework, are developed. Combustion and knock models are extended to include the CV effects, too.

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.

In this paper, the behavior of a downsized spark-ignition engine firing with alcohol/gasoline blends has been analyzed. In particular, different butanol-gasoline and ethanol-gasoline blends have been examined. All the alcohol fuels here considered are derived from biomasses. In the paper, a numerical approach has been followed. A one dimensional model has been tuned in order to simulate the engine operation when it is fueled by alcohol/gasoline mixtures. Numerous operating points, characterized by two different engine speeds and several low-medium load values, have been analyzed. The objective of the numerical analysis is determining the optimum spark advance for different alcohol percentages in the mixtures at the different engine operating points. Once the best spark timing has been selected, the differences, in terms of both indicated torque and efficiency, arising in the different kinds of fueling have been evaluated.

Spark-ignition engines are characterized by poor levels of thermal efficiency, it is known, especially when running at partial load. Since part-load operating points are the most commonly used in engine average life, achieving a given torque value with small displacement, high mean effective pressure engines, the so-called “downsizing”, permits, in general, to limit some typical engine losses (for instance: pumping and friction losses), improving the fuel consumption in a wide range of engine operating points. Small displacement engines, usually, achieve high toque values thanks to supercharging techniques. In this paper, knock risks for a small displacement turbo-charged spark-ignition engine have been analyzed. A parametric analysis of numerous variable influencing engine performance and knock resistance has been carried out by means of 1-D numerical simulations.

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.

Nowadays, the interest in carbon free fuels for internal combustion engines has increased due to the high levels of CO2 in the atmosphere. In particular, ammonia can be used either as a neat fuel, either as an energy carrier for hydrogen production. Adding hydrogen to ammonia is important in order to improve the combustion characteristics of this fuel, like the laminar flame speed. In this paper, the authors investigated the operation limits of a light duty spark ignition engine fueled by neat ammonia and by an ammonia-hydrogen blend (85% of ammonia by volume). The whole maps of the engine powered by the considered fuel mixtures have been obtained by means of 1-D simulations taking into account several operating constraints. The addition of hydrogen to ammonia extends the exploitable region of the engine. In particular, if the engine is powered by neat ammonia, the maximum reachable engine speed is 3000 rpm, while considering the blend, it can be extended up to 5000 rpm.