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Starting and operating of diesel engines in cold conditions is a common and important problem. Many factors such as ambient conditions, fuel properties, fuel injection, cranking speed, etc, affect cold engine functionality. In order to improve diesel engine cold start, it is essential to understand better these problems. In this paper the injection development at cold temperatures is studied, since it is an important parameter that affects the fuel interaction with the air, so the future combustion process would also be influenced. In particular, a hydraulic characterization of diesel injection is made, using specialized test rigs that simulate real engine in-cylinder air pressure and density; the fuel is injected from three axi-symmetric convergent nozzles at several injection pressures (30, 50, 80, 120 and 180 MPa), two chamber densities and two temperatures of 255 K (winter) and 298 K (reference).

In order to study differences between Diesel nozzle holes, four methodologies have been tested. The techniques compared in this paper are: the internal geometry determination, hole to hole mass flow measurement, spray momentum flux and macroscopic spray visualization. The first one is capable of obtaining the internal geometry of each of the orifice of the nozzle; the second one is capable of measuring the mass flow of each nozzle hole in both, continuous and real injections. The third one gives the momentum flux of each orifice, and finally, with the macroscopic spray visualization, the spray penetration and spray cone angle of each hole, are obtained. Generally, all these techniques can be used in order to determine the hole to hole dispersion due to different angle inclination of the holes, different internal geometry of orifices, deposits, nozzle needle off-center, needle deflection, etc.

This paper deals with the problem of quantifying and predicting the macroscopic spray behaviour as a function of the parameters governing the injection process. The parameters studied were ambient gas density as a representative parameter external to the system, and nozzle hole diameter and injection pressure as influential system parameters. The main purpose of this research is to validate and extend the different correlations available in the literature to the actual Diesel engine conditions, i.e. high injection pressure, small nozzle holes, severe cavitating conditions, etc. The sprays from five axi-symmetrical nozzles with different diameters are characterized in two different test rigs that can reproduce the real engine in-cylinder air density and pressure. The wide parametric study that was performed has permitted to quantify the effects of the injection pressure, nozzle hole diameter and environment gas density on the spray tip penetration.

A study of the internal flow in the most used nozzle types in Diesel engines (microSAC and valve covered orifice VCO) was carried out in order to compare injection characteristics and understand the differences between them. To determine these differences, several experimental installations will be used, such as the injection rate test rig, steady flow test rig and spray momentum test rig, to obtain a full hydrodynamic characterization. With the help of the silicone methodology and a microscope, it is possible to determine the needle tip geometry (seat). As the geometrical characterization of the components in both nozzles was known, it was possible to carry out a CFD analysis at several needle lifts and thus observe the behavior of the internal flow in the nozzle seats and be able to compare both nozzles

The purpose of this paper is to describe a methodology based on experimental and theoretical studies for the modeling of typical exhaust systems used in two-stroke small engines. The steady and dynamic behaviors of these systems have been measured in a flow test rig and in an impulse test rig, respectively. Information obtained from these experiments is used in two ways: to find a suitable geometric model to be used in a finite-difference scheme code, and to provide a mean pressure and a frequency domain reflecting boundary, in the frame of a hybrid method. A complete 50cc engine was modeled and comparisons between predicted and measured instantaneous pressure at the exhaust port show a fair agreement, the results of the hybrid approach being more accurate.