Two-phase fuel distribution measurements in a gasoline direct injection engine with an air-assisted injector using advanced optical diagnostics

Abstract

The fuel distribution and mixture formation processes within an internal combustion (IC) engine can greatly affect its ignition, combustion, pollutant formation, and fuel consumption. For more than two decades the laser-induced fluorescence (LIF) technique has been successfully applied to the study of mixture formation and distribution. However, in a gasoline direct injection (GDI) engine the fuel may exist in either the liquid or vapour phase, and it is therefore advantageous to be able to observe both phases simultaneously. One means of achieving this is the laser-induced exciplex fluorescence (LIEF) technique. This paper details its application to a single-cylinder GDI engine equipped with an air-assisted fuel injection system and full optical access. Naphthalene and N, N-dimethlylaniline (DMA) tracers were used to track the fuel and were excited using the expanded beam from an XeCl excimer laser at 308 nm. An image doubler and optical filtering system was used to collect the images that were recorded from the front of the cylinder. Early and late injection timings were investigated, and the spray characteristics and mixture formation from the two strategies were found to differ considerably. In order to investigate the effect of absorption on the fluorescence signal, the beam was introduced into the cylinder from three directions. Crank angle resolved results, from the start of injection to the end of the compression stroke, are presented, with an image for each illumination direction and injection timing.

Tomographic imaging of the liquid and vapour fuel distributions in a single-cylinder direct-injection gasoline engine

“…However, a delay of approximately 1.3 ms occurred between the start of the electrical pulse to the injector and the observation of the start of liquid injection into the chamber, as reported in Leach et al [17]. The engine was motored on a dynamometer at an engine speed of 1200 rpm.…”

“…(i) high-speed video of Mie-scattered light from sprays, illuminated by sources such as copper-vapour lasers or high-intensity discharge lamps [13,14] (ii) Laser-Induced Exciplex Fluorescence (LIEF) [15][16][17], the principle of which has been summarised in [7].…”

“…[16,17], exactly because of its ability to image both liquid-and gas-phase constituents. Therefore, LIEF does indeed offer the prospect of imaging the spray-dominated stage as well as the gas-dominated stage of the GDI mixture preparation process, within a given engine cycle.…”

“…The fuel used was a mixture of iso-octane (90% by volume) and 3-pentanone (10%). Further details of the engine specification are given in [17]. …”

Operational assessment of selected gasoline and LPG vapour injector dosage regularity

“…GDI engines, owing to their design, require placing analyzers inside the cylinder in order to explore the injection processes. The crank angle from the beginning of the injection to the end of the compression stroke is presented with an image for each direction of the illumination and injection time using the light fluorescence absorption [29].…”