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In the present work the integral laser induced exciplex fluorescence (LIEF) measurement technique is used in a transparent engine to define the location of the spray where a maximum vapor occurrence probability is combined with the minimum of liquid fuel occurrence probability. This location, determined with additional boundary conditions, e.g. the temporal occurrence of the defined ignition condition relative to the end of injection, is presented for three different injector types, a swirl, a multi-hole and an outward opening injector. Finally, all spark locations are tested with all injectors throughout 250 combustion cycles in the transparent engine in order to prove if the initial criteria is suitable.

In a study using a single-cylinder engine a significant potential in fuel efficiency and emission reduction was found for stratified operation of a high pressure natural gas direct injection (DI) spark ignition (SI) engine. The control of the mixture formation process appeared to be critical to ensure stable inflammation of the mixture. Therefore, optical investigations of the mixture formation were performed on a geometric equivalent, optically accessible single-cylinder engine to investigate the correlation of mixture formation and inflammability. The two optical measurement techniques infrared (IR) absorption and laser-induced fluorescence (LIF) were employed. Mid-wavelength IR absorption appeared to be qualified for a global visualization of natural gas injection; LIF allows to quantify the equivalence ratio inside a detection level. While LIF measurements require complex equipment, the IR setup consists merely of a black body heater and a mid-wavelength sensitive IR camera.