On the Feasibility of Quantitative, Single-Shot, Spontaneous Raman Imaging in an Optically Accessible Engine Cylinder

Two-Dimensional, single-shot spontaneous Raman measurements of methane concentration were performed in an optically accessible engine after direct injection with the use of modified air-assisted injector. The spatial resolution of the measurements was determined by the thickness of the laser sheet which was 0.8 mm. The error in the methane number density measurement was determined by the noise in the intensified camera output and was 16% of pure methane number density at the experimental conditions. Effective suppression of the stray light background was the main experimental difficulty. Satisfactory results were acquired only when the spark plug was substituted by a plug covered with a velvet-like, black piece of cloth. These preliminary results show that, for the specific engine configuration, fast mixing of the charge yields a very mild stratification after the end of injection. However, uniformity of the equivalence ratio can not be established because of the significant error in the concentration measurement. To improve this aspect, some preliminary tests were carried out with the insertion of the engine head in the laser cavity.