Roman Grzeszik

Development of laser-induced fluorescence to quantify in-cylinder fuel wall films

Laser-induced fluorescence of a fuel tracer is a very sensitive technique to image in-cylinder liquid fuel films, but quantification of the measured film thickness has proven difficult so far. This article describes improvements in the quantification procedure and presents an example application in a motored, optically accessible spark-ignition engine with direct injection. We designed a calibration tool that could be pressurized and heated, allowing investigation of the laser-induced fluorescence intensities at temperatures exceeding the liquid’s standard-pressure boiling point. The fluorescence intensity of liquid toluene and 3-Pentanone dissolved in isooctane upon excitation with a pulsed laser at 266 nm was investigated as a function of temperature and pressure. Consistent with the literature results on gas-phase laser-induced fluorescence, the signal from toluene was much stronger than from 3-Pentanone, about two orders of magnitude for films thinner than 50 μm. Laser-induced fluorescence from both tracers decreased with increasing temperature but that of toluene significantly more. The response to pressure was less pronounced. For imaging across a large field of view, the spatial non-uniformity of laser excitation and detection efficiency was taken into account using a solid fluorescing substrate, an inexpensive Schott-glass WG280 filter. Isooctane with 0.5 vol.% toluene was used for application in the motored engine, imaging the liquid film on the piston-top window after direct injection from a central multi-hole injector. Air as a bulk gas was found to be advantageous over nitrogen in that gas-phase fluorescence was quenched by oxygen. The imaged film distributions and thicknesses and the derived total fuel film mass were physically plausible. Consistent with the recent literature results from a constant pressure vessel, increasing injection pressure from 50 to 100 bar did not decrease wall wetting but further increase to 200 bar did.

Spatially Resolved Determination of Fuel/Air Ratio Inside a Direct Injection SI-Engine Under Real Fuel Conditions

The present work describes a new method which allows the spatially resolved quantitative determination of gaseous hydrocarbon densities in droplet laden flows. The technique is especially dedicated to a quantitative and linearly spatially resolved measurement of air/fuel ratio (λ-value) in direct injection Otto engines under stratified operation and by use of regular gasoline (Euro Super). The new method is based on spontaneous Raman scattering. It is applied to the investigation of the air/fuel ratio distribution inside an in the close surroundings of the spray cone of different Dl-fuel injectors under stratified and homogeneous engine operation conditions. Both crank angle resolved snap shot and cyclical averaged measurements are presented. Simultaneously the planar gasoline distribution is detected by LIF of aromatic hydrocarbons which are native constituents of regular gasoline. It is shown, that the linear spatially resolved air/fuel distributions measured by means of LIF correlates well with the Raman data.

Optische Messtechniken zur Bewertung innermotorischer Wandfilme

Downsizing verbunden mit Turboaufladung hat bei der Benzindirekteinspritzung zur Entwicklung von sparsameren Verbrennungsmotoren gefuhrt. Ein wesentlicher Vorteil gegenuber der Saugrohreinspritzung ist bei der Direkteinspritzung die Ladungskuhlung, die durch die Verdampfung des Kraftstoffs im Brennraum der Ladung die notwendige Verdampfungsenthalpie entzieht. Nachteilig ist, dass bei gleichgehaltener Motorleistung durch das Downsizing das Hubvolumen und damit der fur das Kraftstoffspray zur Verfugung stehende Raum deutlich reduziert ist. Als Folge kann eine Benetzung der Brennraumoberflachen nicht mehr vermieden werden. Gerade im Kaltstart des Motors konnen die Wandfilme bis Zundeinleitung nicht ausreichend verdampfen und fuhren wahrend und nach der Verbrennung durch Bildung fetter Gemische zu einer rusenden Verbrennung. Die dabei entstandene Rusmasse ist von untergeordneter Bedeutung. Kritisch ist die hohe Anzahl gebildeter Ruspartikel mit Grosen zwischen 23 und 500nm, die aufgrund ihrer geringen Grose lungengangig und damit als gesundheitsgefahrdend einzustufen sind. Durch Beschrankung der Partikelanzahl im Neuen Europaischen Fahrzyklus (NEFZ) tragt der Gesetzgeber seit Einfuhrung von EURO6 diesem Sachverhalt Rechnung. Der derzeitige Grenzwert von 6x1012 Partikel/km muss seit 2014 von neuzugelassenen Fahrzeugen erfullt werden. Offen ist, ob der ab 2017 reduzierte Grenzwert von 6x1011Partikel/km auch ohne einen zusatzlichen kostentreibenden Partikelfilter erreicht werden kann.