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A wider use of biofuels in internal combustion engines could reduce the emissions of pollutants and greenhouse gases from the transport sector. In particular, due to stringent emission regulatory programs, compression ignition engine requires interventions aimed at reducing their polluting emissions. Ethanol, a low carbon fuel generally produced from biomass, is a promising alternative fuel applicable in compression ignition engines to reduce CO2 and soot emissions. In this paper, the application of a dual fuel diesel-ethanol configuration in a light-duty compression ignition engine has been numerically investigated. Ethanol is injected into the intake port, while diesel fuel is directly injected into the combustion chamber of the analyzed engine. CFD simulations have been carried out by means of the AVL Fire 3-D code. The operation at given engine load and speed has been simulated considering different diesel injection timings.

In the field of gasoline turbocharged engines, the improvement of combustion efficiency represents a critical point when increased engine torque and reduced fuel consumption are simultaneously expected. Though gasoline port fuel injection is a well known and wide spread technology for fuel delivery in spark-ignition engines, detailed information on the features of the liquid fuel spray and the wall film formation could significantly contribute, in terms of emission control, to the engine development. In this paper, air-fuel mixture formation and smoke emissions of a turbocharged port-fuel-injected gasoline engine have been investigated by using experimental and numerical analysis techniques. The objective of this activity is to properly choose the injection system and strategy aimed to optimize both engine performance and emission levels. 3-D CFD calculations have been performed in order to deeply investigate the complex phenomena occurring before the combustion process starts.

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.

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.

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.

Recently, it has been worth pointing out the relevance of alternative fuels in the improvement of air quality conditions and in the mitigation of global warming. In order to deal with these demands, in recent studies, it has been considered a great variety of alternative fuels. It goes without saying that the alternative fuels industry needs the best of the efficiency with a moderate layout. From this perspective, Liquefied Petroleum Gas (LPG) could represent a valid option, although it is not a renewable fuel. In terms of polluting emissions, the LPG can reduce nitrous oxides and smoke concentrations in the air, a capability that has a relevant importance for the modern pollution legislation. LPG is well known as an alternative fuel for Spark Ignition (SI) engines and, more recently, LPG systems have also been introduced in the Compression Ignition (CI) engines in dual-fuel configuration.