Publications Details

Influence of pilot-fuel mixing on the spatio-temporal progression of two-stage autoignition of diesel-sprays in low-reactivity ambient fuel-air mixture

Rajasegar, Rajavasanth R.; Niki, Yoichi; Li, Zheming L.; Garcia-Oliver, Jose M.; Musculus, Mark P.

The spatial and temporal progression of two-stage autoignition of a diesel-fuel surrogate, n-heptane, in a lean-premixed charge of synthetic natural-gas (NG) and air were studied in an optically accessible heavy-duty diesel engine. The lean-premixed charge of NG was prepared by fumigation upstream of the engine intake manifold. Optical diagnostics used high-speed (15 kfps) cool-flame chemiluminescence imaging as an indicator of low-temperature heat-release (LTHR) and OH* chemiluminescence imaging as an indicator of high-temperature heat-release (HTHR). NG prolonged the ignition delay of the pilot fuel and increased the combustion duration. Zero-dimensional chemical-kinetics simulations predicted that LTHR initiated most likely on the air streamlines before transitioning to HTHR, either on fuel-streamlines or on air-streamlines in regions of near-constant Φ Due to the relatively short pilot-fuel injection-durations, the transient increase in entrainment near the end of injection (entrainment wave) was important for quickly creating auto-ignitable mixtures. The desired combustion characteristics, e.g., multiple ignition-kernels and favorable combustion phasing and location (e.g., for reducing wall heat-transfer or optimizing charge stratification) and adjusting injection parameters can be achieved by tailor mixing trajectories to offset changes in fuel ignition chemistry.