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This paper reports a numerical and experimental analysis on a twin-cylinder turbocharged Spark Ignition engine carried out to investigate the cylinder-to-cylinder variability in terms of performance, combustion evolution and exhaust emissions. The engine was tested at 3000 rpm in 20 different steady-state operating conditions, selected with the purpose of observing the influence of cylinder-by-cylinder A/F ratio variations and the EGR effects on the combustion process and exhaust emissions for low to medium/high loads. The experimental outcomes showed relevant differences in the combustion evolution (characteristic combustion angles) between cylinders and not negligible variations in the emissions of the single cylinder exhaust and the overall engine one. This misalignment resulted to be due to differences in the injected fuel amount by the port injectors in the two cylinders, mainly deriving from the specific fuel rail geometry.

One-dimensional (1D) models are commonly employed to study the performances of turbocharged engine. Manufacturers' provided steady turbomachinery maps are usually utilized, although they operate in unsteady conditions as a consequence of pressure pulses propagating into the intake and exhaust systems. This may lead to some inaccuracies in the engine-turbocharger matching calculations, which may be solved through the introduction of proper time-delays (virtual pipe corrections). These drawbacks, however, became more relevant when engine operates under low speed and high load conditions, or during a transient maneuver, because of possibilities of compressor surging.

Knock occurrence is a widely recognized phenomenon to be controlled during the development and optimization of S.I. engines, since it bounds both compression ratio and spark advance, hence reducing the potential in gaining a lower fuel consumption. As a consequence, a clear understanding of the engine parameters affecting the onset of auto-ignition is mandatory for the engine setup. In view of the complexity of the phenomena, the use of combined experimental and numerical investigations is very promising. The paper reports such a combined activity, targeted at characterizing the combustion behavior of a small unit displacement two-stroke SI engine operated with either Gasoline or Natural Gas (CNG). In the paper, detailed multi-cycle 3D-CFD analyses, starting for preliminary 1D computed boundary conditions, are performed to accurately characterize the engine behavior in terms of scavenging efficiency and combustion.

The paper presents a 1D-3D numerical model to simulate the scavenging and combustion processes in a small-size spark-ignition two-stroke engine. The engine is crankcase scavenged and can be operated with both gasoline and Natural Gas (NG). The analysis is performed with a modified version of the KIVA3V code, coupled to an in-house developed 1D model. A time-step based, two-way coupled procedure is fully described and validated against a reference test. Then, a 1D-3D simulation of the whole two-stroke engine is carried out in different operating conditions, for both gasoline and NG fuelling. Results are compared with experimental data including instantaneous pressure signals in the crankcase, in the cylinder and in the exhaust pipe. The procedure allows to characterize the scavenging process and quantify the fresh mixture short-circuiting, as well as to analyze the development of the NG combustion process for a diluted mixture, typically occurring in a two-stroke engine.

The work relates to the use of multidimensional modelling as a tool for improving the robustness of combustion of a Gasoline Direct Injection (GDI) Spark Ignition (SI) engine. A procedure is assessed for the prediction of the thermo-fluid-dynamic processes occurring in a single-cylinder, four-stroke engine, characterised by a bore-to-stroke ratio close to the unity, and a pent-roof head with four valves. The engine is at a design stage, under development for application on two wheels vehicles. A new generation six-holes Bosch injector is considered as realising a jet guided combustion mode. This last is preferred for its potential in realising effective charge stratification and great combustion stability under various operating conditions. The three-dimensional (3D) numerical model is developed within the AVL FIRE™ software environment.

Automotive exhaust systems give a major contribution to the sound quality of a vehicle and must be properly designed in order to produce acceptable acoustic performances. Obviously, noise attenuation is strictly related to the used materials and to its internal geometry. This last influences the wave propagation and the gas-dynamic field. The purpose of this paper is to describe advantages and disadvantages of different numerical approaches in evaluating the acoustic performance in terms of attenuation versus frequency (Transmission Loss) of a commercial two perforated tube muffler under different conditions. At first, a one-dimensional analysis is performed through the 1D GTPower® code, solving the nonlinear flow equations which characterize the wave propagation phenomena. The muffler is characterized as a network of properly connected pipes and volumes starting from 3D CAD information. Then, two different 3D analyses are performed within the commercial STS VNOISE® code.

The paper describes preliminary results of a research activity finalized to the development of a new scavenging concept for the reduction of the HC emitted by a small-size two-stroke carbureted crankcase-scavenged SI engine. Further developments of a well-established model (1Dime code) are presented, with particular emphasis on combustion and scavenging processes simulation. The rate of heat release is computed through a two-zone model, based on a “fractal” representation of the turbulent flame front. A CAD procedure evaluating, at each crank-angle and flame radius, the intersections between the flame surface and the actual combustion chamber walls, has been developed. Scavenging is modeled through an original two-zone approach which accounts for mixing and short-circuiting processes. The latter are directly related to the in-cylinder turbulent flow regime, inlet and exhaust flow velocities, and engine speed.

A theoretical-experimental analysis of a VVT engine and a methodology for the definition of its optimal control is presented. The analyses are based on the employment of a very accurate 1D simulation model of the engine, developed by the authors. The code is validated by comparison with experimental data collected on a traditionally fixed- and a variable-valve timing engine as well. The model is then linked to an efficient optimization procedure, which is able to select - for each assigned operating condition - the most appropriate values of control parameters (spark advance, intake/exhaust valve opening/closing, and valve lift), with the objective of pursuing part-load BSFC improvements. Various VVT or VVA arrangements are analyzed and compared.

One dimensional (1D) and three dimensional (3D) simulations are widely used in technical acoustics to predict the behavior of duct system elements including fluid machines. In particular, referring to internal combustion engines, the numerical approaches can be used to estimate the Transmission Loss (TL) of mufflers, air boxes, catalytic converters, etc. TL is a parameter commonly used in almost any kind of acoustical filters, in order to assess the passive effects related to their sound attenuation. In this paper, a previous 1D-3D acoustical analysis of a commercial muffler, has been improved and experimentally validated. Features related to the manufacturing process, like the coupling of adjacent surfaces and the actual shape of components, have been noticed to heavily affect the muffler behavior.

Despite the recent efforts devoted to develop alternative technologies, it is likely that the internal combustion engine will remain the dominant propulsion system for the next 30 years and beyond. Also as a consequence of more and more stringent emissions regulations established in the main industrialized countries, strongly demanded are methods and technologies able to enhance the internal combustion engines performance in terms of both efficiency and environmental impact. Present work focuses on the development of a numerical method for the optimization of the control strategy of a diesel engine equipped with a high pressure injection system, a variable geometry turbocharger and an EGR circuit. A preliminary experimental analysis is presented to characterize the considered six-cylinder engine under various speeds, loads and EGR ratios.