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International Heat Transfer Conference 13

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

EXPERIMENTAL ANALYSIS OF HIGH PRESSURE DIESEL SPRAY IMPINGEMENT ON A FLAT WALL

L. Allocca
Istituto Motori−CNR, Via G. Marconi 4, 80125, Napoli, Italy

Luca Andreassi
Università di Roma “Tor Vergata”, Roma, Italy

A. De Vita
Università di L'Aquila Dipartimento di Energetica, L'Aquila, Italy

Vittorio Rocco
Department of Industrial Engineering, University of Rome Tor Vergata, Via Del Politecnico 1, Roma, 00133, Italy

Stefano Ubertini
University of Tuscia

DOI: 10.1615/IHTC13.p26.60
14 pages

Abstract

In modern direct injection diesel engines large quantities of fuel impact on the combustion chamber wall because of its short distance with the nozzle tip and the high values of the injection pressure. The fluidynamic interaction of impacting droplets and the air motion plays a fundamental role on the combustion process affecting performances and pollutant emissions. The characterization of the behaviour of a single droplet impacting on a heated plate is a well studied phenomenon and it is strongly related to fuel characteristic temperatures producing wetting, transition and non-wetting regimes.
In diesel engines, the impact of the fuel on a heated wall is very difficult to analyze because of the high velocities and densities of the droplets produced by the common rail (CR) injection apparatus. The measured data are very limited, time-consuming and difficult to interpret.
In this paper an experimental characterization and the effectiveness of numerical models of a diesel spray produced by high pressure injection systems and impinging on a heated flat wall is reported for different injection pressures, backpressures and plate temperatures.
The sprays have been generated by a Programmable Electronic Control Unit (PECU) Common Rail (CR) injection apparatus at two injection pressures: 80 and 120 MPa. The sprays emerge from an axial disposed single-hole nozzle and evolve in an optically accessible vessel, controlled in gas pressure up to 5.0 MPa at ambient temperature. The jets impact on a flat stainless steel wall, 100 mm in diameter and 1.077 μm mean roughness, heated up to 500°C by a 200 W electrical resistance and controlled in temperature. Impinging sprays have been lightened by a pulsed laser sheet generated on the second harmonic of a Nd- YAG laser at different instant from the start of injection, and the images acquired by a synchronized CCD camera. Digital image processing software has enabled extracting the radial penetration and thickness growth of the impacted fuel versus injection pressures, vessel backpressures and wall temperatures and following the fuel iso-density zone at different instant from the start of injection.

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Measurement of fluid temperature with an arrangement of three thermocouples