Effects of n-octanol energy-based substitution on combustion and emissions in an n-octanol/diesel dual direct injection compression ignition engine

Three-dimensional CFD simulations are used to investigate the effects of the n-octanol substitution percentage (OSP, 0–40%) on combustion and emission tendencies in an n-octanol/diesel dual-injection (DI2) compression ignition engine. Simulations are performed at a fixed EGR rate of 40% with constant total injected fuel energy and fixed injection sequence and timings. With increasing OSP, the main heat-release event shifts toward TDC with a reduced HRR peak and a smoother heat-release. The peak in-cylinder pressure generally increases, indicating a more constant-volume-like heat-release distribution and enhanced pressure rise during early expansion. Combustion phasing and duration exhibit a non-linear response, CA50 moves toward TDC and the late-combustion tail shortens at higher OSP, while the overall burn duration slightly increases at low-to-medium OSP but decreases at higher OSP. Emission trends are pollutant-specific: soot generally decreases, NOₓ shows limited sensitivity but a mild upward tendency at high OSP, and incomplete-combustion products diverge with monotonically increasing HC and CO reversal at high OSP correlating with the shortened late-combustion tail. These results clarify OSP-dependent trade-offs under high-EGR constraints and support further optimization of injection splitting and combustion organization under the present operating constraints.