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With ever-demanding emission legislations in Compression Ignition (CI) engines, new premixed combustion strategies have been developed in recent years seeking both, emissions and performance improvements. Since it has been shown that in-cylinder air flow affects the combustion process, and hence the overall engine performance, the study of swirling structures and its interaction with fuel injection are of great interest. In this regard, possible Turbulent Kinetic Energy (TKE) distribution changes after fuel injection may be a key parameter for achieving performance improvements by reducing in-cylinder heat transfer. Consequently, this paper aims to gain an insight into spray-swirl interaction through the analysis of in-cylinder velocity fields measured by Particle Image Velocimetry (PIV) when PCCI conditions are proposed. Experiments are carried out in a single cylinder optical Diesel engine with bowl-in-piston geometry.

The reduction of carbon footprint of compression ignition engines for road transport makes it necessary to search for clean fuels alternative to diesel and to evaluate them under engine conditions. For this reason, in this paper, the combustion behaviour of different blends of synthetic fuels has been analyzed in an optical single cylinder engine of Medium Duty size (0,8 liters per cylinder) by means of optical techniques. The aim is to evaluate the effect of synthetic fuels, both partly or completely fossil diesel, in terms of combustion behaviours and soot formation. Therefore, different blends of oxymethylene dimethyl ether (OMEX) with diesel and neat hydrotreated vegetable oil (HVO) were studied. A conventional common rail injection system and a single injection strategy was used. In addition, special care was taken to ensure that conditions inside the engine cylinder at the injection start were as close as possible to the conditions used in previous studies.

The upcoming emission regulations for Diesel engines will become more restrictive. This has made it necessary to develop new diagnostic tools and methods that allow to obtain a more accurate knowledge about the chemical and physical phenomena that occur during the atomization, evaporation and ignition of the fuel spray. This paper describes an experimental setup for injection and combustion research. The system is based on a two-stroke direct injection Diesel engine whose cylinder head is equipped with four optical accesses. Inlet flow can be switched either to nitrogen or to ambient air. In both cases, thermodynamic properties are controlled to reproduce the actual conditions of density, temperature and pressure at the end of the compression stroke in a real engine. A high-pressure common-rail system with an electronic control unit makes it possible to modify injection parameters: pressure, timing, duration and frequency.