Diesel autogignition at elevated in-cylinder pressueres

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Abstract
The autoignition of diesel sprays at in-cylinder pressures from 5 to 9 MPa and injection pressures from 100 to 160 MPa was investigated. A pseudo three-dimensional view was obtained by using two high-speed video cameras recording the autoignition process simultaneously from two different viewpoints, so that the positional ambiguity of the ignition sites may be removed. The autoignition recordings were related to spray liquid core and vapour phase video recordings reported previously, in order to obtain a detailed understanding of the structure of the sprays. The autoignition delay was found to decrease with an increase of in-cylinder pressure up to 7 MPa. However, contrary to common belief, a reverse in this trend was observed at higher pressures, with a rapid increase in the delay at in-cylinder pressures above 7 MPa. This effect was related to a decrease in spray penetration, a decrease of diffusion coefficient and an increase in chemical delay.