Search Results

The paper reports the research activity related to the development of a twin-spark SI engine equipped with a variable valve timing (VVT) device. Improvements on the fuel consumption at part load are expected when an high internal exhaust gas recirculation (internal EGR) level is realized with a proper phasing of the VVT device. The twin-spark solution is implemented to improve the burning speed at low load, and to increase the EGR tolerance levels. Both experimental and theoretical analyses are carried out to investigate the real advantages of the proposed engine architecture. In particular an original quasi-dimensional model for the simulation of the burning process in a twin-spark engine is presented. The model is mainly utilized to find the proper combination of VVT device position (and hence EGR level) and spark advance for different engine operating conditions. A comparison with the single-spark solution is also provided.

The consequences of global warming have forced the governments of developed economies to impose strict regulations on the emission of so called ‘green house gases’. Carbon dioxide, a by-product of fossil fuel combustion, is a major contributor to global warming. The focus of government treaties, in the face of continued globalization and third world development, has been to stabilize contributions of carbon dioxide to the atmosphere. Vehicle manufacturers and suppliers have tackled legislation and consumer pressures in a variety of ways. One of the most effective ways to reduce fuel consumption of passenger vehicles, consequently reducing their CO2 emissions, is so-called “engine downsizing”. This involves the improvement of the torque of a smaller displacement engine with respect to (w.r.t.) a given engine installed in a vehicle, and the use of longer gear ratios in the transmission.

In this paper a new testing methodology has been developed to objectively measure the gear rattle noise. This kind of noise has become very important especially since car manufacturers have pointed their attention to the engine noise reduction. In fact, when efforts are focused to reduce engine noise, the gearbox noise becomes more audible. This article describes the experimental analysis that has been made to measure transmission gear rattle noise on an innovative NVH (Noise, Vibration & Harshness) transmission test rig. Also, emphasis on the capability of the test rig set-up to decouple the gear rattle noise from other vehicle noises is presented. Using such set-up, the gear rattle problem is pronounced and, consequently, noise investigation becomes easier and objective unlike what happens in a vehicle or in the power train test cell. In order to obtain reliable results from this test rig, its performance has been correlated to measurements performed on the car.

During recent years several VVT devices have been developed, in order to improve either peak power and low end torque, or part load fuel consumption of SI engines. This paper describes an experimental activity, concerning the integration of a continuously variable cam phaser (CVCP), together with an intake port deactivation device, on a small 4 cylinder 16V engine. The target was to achieve significantly lower fuel consumption under normal driving conditions, compared to a standard MPFI application. A single hydraulic cam phaser is used to shift both the intake and the exhaust cams to retarded positions, at constant overlap. Thus, high EGR rates in the combustion chamber and late intake valve closure (“reverse Miller cycle”) are combined, in order to reduce pumping losses at part load.

The low-pressure side of the fuel system of a car plays an important role to ensure the performances of the engine, both for pressure drops and thermal phenomena. This is particularly true for modern common-rail diesel engines. An one-dimensional model of the low pressure section of the system has been built up accounting for the feed and return lines (including pipes, bends and pipe-fitting), diesel filter and by-pass valve. The high-pressure side has been modeled in a very essential way considering only high-pressure pump volume and leakage, and engine fuel consumption, because its only purpose is to close the circuit and allow thermal evaluations. The model has been tested in both steady and unsteady conditions. In the first case the main results are the pressure drops of the main fuel segments; in the second case, also transient fuel temperature rise is simulated, due to the compression in the common-rail pump.

The objective of this paper is to present the development and the use of a numerical model to predict noise radiated from manual gearboxes due to gear rattle using Computer-Aided Engineering (CAE) technologies. This CAE process, as outlined in this paper, includes measured data, computational flexible multibody dynamics, and vibro-acoustic analysis. The measured data is used to identify and reproduce the input excitation which is primarily generated from engine combustion forces. The dynamic interaction of the gearbox components, including flywheel, input/output shafts, contacting gear-pairs, bearings, and flexible housing is modeled using flexible multibody techniques. The acoustic response to the vibration of the gearbox housing is then predicted using vibro-acoustic techniques. These different technologies are augmented together to produce a virtual gearbox that can be used in noise, vibration, and harshness (NVH) performance evaluations.

An experimental activity aimed to analyze the noise emission of a small gasoline engine equipped with two spark plugs per cylinder was performed. A custom electronic device permitted to set the delay time between the first and second spark ignition with three different modalities: single spark, synchronous double spark and sequential double spark. Engine noise emission was analyzed at full load and at part load engine condition. The measurements were carried out in a semi-anechoic engine test cell. An acoustic binaural head system also permitted a subjective evaluation of the noise emission. Indicated measurements were also performed and correlated to the noise emission levels. With appropriate sequential double spark advances chosen, the experimental results put on evidence the satisfying noise emission of the sequential double spark versus synchronous double spark.

The intention of the presented work was to develop a new simulation tool that fits into a CFD (computational fluid dynamics) workflow and provides information about the soot particle size distribution. Additionally it was necessary to improve and use state-of-the-art measurement techniques in order to be able to gain more knowledge about the behavior of the soot particles and to validate the achieved simulation results. The work has been done as a joint research financed by the European Community under FP5.