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The paper analyses a procedure, based on thermodynamics concepts, to calculate the isentropic outlet temperature taking into account the changes in specific heat during the thermodynamic process; the results obtained were compared whit those given by the traditional methods. Besides, using data from tests, performed in a specific turbochargers test bench, the differences in isentropic efficiency have been evaluated and compared too. Moreover, another factor related with the influence of the gas specific heat on turbocharger performance is the effect that the humidity contents on gas has on the efficiency calculations. Normally, ambient conditions are taken into account just to obtain the corrected values of the main variables in compressor calculations, however the humidity ratio is not included and its effect is neglected. This study presents also a theoretical- experimental analysis about the effect of taking into account this factor.

Modern DI Diesel engines are widely used in automotive applications. Improvements in performance and emissions have been produced in the last ten years on these engines, so that they are now very competitive in comparison with petrol engines. However, cold startability is one of the main challenges of Diesel engines, since great differences with petrol engines still can be noticed. Today, in small engines glow plugs are universally used as an aid system for cold start. In large engines, where the cold start is less critical, intake air heating technology is employed. In this paper the application of this technology to small engines is evaluated in terms of its viability for cold starting and HC/CO emissions and combustion noise reduction during the warm-up phase of the engine.

An extensive experimental study is described whose main objective is to characterize the acoustic and flow dynamic response of turbocompressors to flow pulsation from a four cylinder high speed direct injection (HSDI) diesel engine. Four different turbochargers with centrifugal compressors of different size were considered, each one with a different turbine. Compressors were excited with pulsating flow in real engine conditions. Wave decomposition was used to obtain incident and reflected pressure perturbations upstream and downstream of the turbochargers, which allowed determining the zones of the compressor charts where they are more permeable to pressure oscillations, and to study the correlation of these magnitudes with turbocharger operating conditions.

In this paper is described a heat transfer sub-model whose main objective is to help a global 1-D gas dynamic code to calculate reciprocal internal combustion engine performance in steady and transient operation. From the point of view of heat transfer the engine is divided into four different zones that will show different calculation peculiarities: the intake line, the engine cylinders, the exhaust ports and the exhaust line. The heat transfer sub-model has been programmed to deal with three different possibilities with respect the engine walls temperature: constant with time, variable but without thermal inertia considerations and variable taking into account walls thermal inertia. In the paper, the main emphasis will be devoted to explain the temperature calculation of the engine walls, which are mainly ducts in the 1-D calculation codes. In these walls, only radial heat transfer is considered.

The objective of this paper is to describe a turbochargers test bench capable of elaborating turbochargers maps, under pulsating or continuous flow conditions. With this experimental tool it is possible to obtain information about turbocharger performance at realistic engine operative points. Consequently, the experimental tool is able to complete and validate manufacturers turbochargers maps. In order to deeply achieve these objectives, the turbocharger test bench is used in combination with a gas-dynamic code, which provides an accuracy simulation of the experimental installation. In addition, the obtained information will increase the power of modelling codes used for turbocharged engines design.

The scavenging and injection processes on a 50 cc. crankcase-scavenged compressed air-assisted direct fuel injection 2-stroke engine are analyzed by means of multidimensional CFD modeling. A moving mesh including the intake ports, cylinder and exhaust port has been built, solving the interface at ports. The information at boundaries is obtained from a one-dimensional wave action model. A detailed analysis of the scavenging process is presented. A motored engine with suitable optical access has been used to measure in-cylinder velocities by Laser Doppler Velocimetry LDV. Due to the small engine size some technical problems had to be solved to carry out the measurements. The comparison between the modeled and measured velocities shows good agreement. Finally, the validated multidimensional modeling has been used for the optimization of the injection process in terms of fuel short-circuit to the exhaust and also of mixture quality.

In the paper is described how to characterise the combustion process of a high speed turbocharged direct injection diesel engine (HSDI) during a transient process, which consists on a full load acceleration at constant engine speed, known as load transient. The combustion characterisation is based on the cycle to cycle combustion analysis and the Rate of Heat Release calculation (RoHR). The information presented in the paper includes, the transient recorded data at three different engine speeds joint with information about transducers characteristics and measurement frequencies. The post-processing of the obtained information and its synchronization is described in detail; a protocol of the process is finally obtained. The RoHR of every transient cycle is calculated and shown as final objective of the work.

A theoretical-experimental study is presented in the paper, whose objective is to propose a method that allows determining the average efficiency of the radial turbines, usually employed in the internal combustion engines, under real operating conditions. Due to the unsteady behaviour of the exhaust gasses flow, the efficiency information obtained from steady flow tests cannot be considered when the turbine is connected to an internal combustion engine. The efficiency differences between steady and unsteady flow patterns, can be obtained by testing the turbine, connected to the engine, under real pulsating flow conditions. For the correct turbine workflow characterisation, a wave action model has been used, together with information obtained from engine tests. The engine test cell includes a specific measuring device for this purpose. The results obtained have been compared with those provided by the turbine manufacturer.

The results of a predictive modelling study on the transient load response of a heavy-duty turbocharged diesel engine are presented in this paper. The model is based on a wave-action calculation code, whose input parameters are managed by an external module, which updates their value according to the changing engine running conditions. The transient operation aimed at is a load increase from idle to full load, at constant engine speed. Several modifications to the engine design have been simulated: valve size and timing, inlet manifold dimensions, insulation of the exhaust manifold, and turbine design. The response of the engine operation to these modifications has been evaluated by means of the transient duration and of the evolution of relevant engine parameters.

A modelling study is presented in this paper, whose objective is to obtain design criteria for optimum layouts and dimensions of exhaust manifolds in automotive engines. The first step has been the characterisation of the pulsating flow phenomena in the exhaust manifold, focusing on the pressure wave propagation process and on the interaction between cylinders across the manifold. Two relevant phenomena have been studied: the reflection of under-pressure pulses at pipe junctions and open ends, and the interference between exhaust processes of different cylinders. These phenomena have been characterised respectively by non-dimensional parameters, related to the layout and dimensions of the manifold. A parametric modelling study has been performed in order to evaluate the effects of the manifold dimensions on the engine performance. The work has been focused on a four-cylinder engine with a four-branch manifold.