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

Journal Article · Fri Nov 13 00:00:00 EST 2020 · Proceedings of the Combustion Institute

DOI:https://doi.org/10.1016/j.proci.2020.11.005· OSTI ID:1783249

Rajasegar, Rajavasanth  ^[1]; Niki, Yoichi ^[2]; Li, Zheming ^[1]; García-Oliver, Jose Maria ^[3]; Musculus, Mark P.B. ^[1]

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1. Sandia National Lab. (SNL-CA), Livermore, CA (United States). Combustion Research Facility
2. National Institute of Maritime, Port and Aviation Technology, Tokyo (Japan)
3. Universitat Politècnica de València, Valencia (Spain)

The spatial and temporal locations of autoignition for direct-injection compression-ignition engines depend on fuel chemistry, temperature, pressure, and mixing trajectories in the fuel jets. Dual-fuel systems can provide insight into both fuel-chemistry and physical effects by varying fuel reactivities and engine operating conditions. In this context, 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 is imaged in an optically accessible heavy-duty diesel engine. The lean-premixed charge of NG is prepared by fumigation upstream of the engine intake manifold. Optical diagnostics include high-speed (15kfps) cool-flame chemiluminescence-imaging as an indicator of low-temperature heat-release (LTHR) and OH* chemiluminescence-imaging as an indicator high-temperature heat-release (HTHR). NG prolongs the ignition delay of the pilot fuel and increases the combustion duration. Zero-dimensional chemical-kinetics simulations provide further understanding by replicating a Lagrangian perspective for mixtures evolving along streamlines originating either at the fuel nozzle or in the ambient gas, for which the pilot-fuel concentration is either decreasing or increasing, respectively. The zero-dimensional simulations predict that LTHR initiates 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) is important for quickly creating auto-ignitable mixtures. To achieve 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), adjusting injection parameters could tailor mixing trajectories to offset changes in fuel ignition chemistry.

• Research Organization: Sandia National Lab. (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• Grant/Contract Number: AC04-94AL85000; NA0003525
• OSTI ID: 1783249
• Alternate ID(s): OSTI ID: 1809773
• Report Number(s): SAND-2020-12856J; 692586
• Journal Information: Proceedings of the Combustion Institute, Vol. 38, Issue 4; ISSN 1540-7489
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Lean-premixed natural-gas combustion
diesel
two-stage autoignition chemical kinetics
cool-flame imaging
OH*chemiluminescence imaging