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Due to experimental challenges, combustion of diesel-like jets has rarely been characterized by laser-based quantitative multiscalar measurements. In this work, recently developed laser diagnostics for combustion temperature and the concentrations of CO, O2, and NO are applied to a diesel-like jet, using a highly oxygenated fuel. The diagnostic is based on spontaneous Raman scattering (SRS) and laser-induced fluorescence (LIF) methods. Line imaging yields multiscalar profiles across the jet cross section. Measurements turn out to be particularly accurate, because near-stoichiometric combustion occurs in the central region of the jet. Thereby, experimental cross-influences by light attenuation and interfering emissions are greatly reduced compared to the combustion of conventional, sooting diesel fuel jets. This is achieved by fuel oxygenation and enhanced premixing.

The occurrence of severe events of ‘super-knock’ originating from random pre-ignition kernels which sometimes is observed in turbo-charged spark-ignition engines was recently attributed by Kalghatgi and Bradley [4] to developing detonations which originate from a resonance between acoustic waves emitted by an auto-igniting ‘hot spot’ and a reaction wave which propagates along negative temperature gradients in the fuel-air mixture. Their occurrence depends on the steepness of the local instantaneous temperature gradient and on the length of the region of negative gradient. The theory requires that the temperature gradient extends smoothly over a sufficient length in the turbulent flow field. Then localized detonations may develop which are able to autoignite the entire charge within less than a millisecond and thus cause pre-ignition and ‘super-knock’.