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The in-cylinder extent of liquid-phase fuel penetration (i.e., the liquid length) is an important parameter in combustion-chamber design because liquid lengths that are too long can lead to wall impingement and corresponding degradation of engine efficiency, emissions, and durability. Previous liquid-length measurements in constant-volume combustion chambers have shown that the liquid length is nominally independent of injection pressure, but these measurements have employed common-rail fuel systems where injection rate is approximately constant during the entire injection event, and they have been conducted under quasi-steady ambient thermodynamic conditions. The objective of the current work is to better understand the effects of injection-rate shape and injection pressure on the liquid length, including possible effects of unsteady ambient conditions in an engine.

Natural luminosity (NL) and chemiluminescence (CL) imaging diagnostics are employed to investigate fuel-property effects on mixing-controlled combustion, using select research fuels-a #2 ultra-low sulfur emissions-certification diesel fuel (CF) and four of the Fuels for Advanced Combustion Engines (FACE) diesel fuels (F1, F2, F6, and F8)-that varied in cetane number (CN), distillation characteristics, and aromatic content. The experiments were performed in a single-cylinder heavy-duty optical compression-ignition (CI) engine at two injection pressures, three dilution levels, and constant start-of-combustion timing. If the experimental results are analyzed only in the context of the FACE fuel design parameters, CN had the largest effect on emissions and efficiency.