  Computational fluid dynamics (CFD) simulations of a single-cylinder gasoline
compression ignition engine are performed to investigate the impact of
gasoline-ethanol blending on autoignition, nitrogen oxide (NOx), and soot
emissions under low-load conditions. A four-component toluene primary reference
fuel (TPRF) + ethanol (ETPRF) surrogate (with 10% ethanol by volume; E10) is
employed to represent the test gasoline (RD5-87). A 3D engine CFD model
employing finite-rate chemistry with a skeletal kinetic mechanism, adaptive
mesh refinement (AMR), and hybrid method of moments (HMOM) is adopted to
capture in-cylinder combustion and soot/NOx emissions. The engine CFD model is
validated against experimental data for three gasoline-ethanol blends: E10, E30
and E100, with varying ethanol content by volume. Model validation is carried
out for multiple start-of-injection (SOI) timings (-21, -27, -36, and -45 crank
angle degrees after top-dead-center (aTDC)) with respect to in-cylinder
pressure, heat release rate, combustion phasing, NOx and soot emissions. For
late injection timings (-21 and -27oaTDC), E30 yields higher soot than E10;
while the trend reverses for early injection cases (-36 and -45oaTDC). E100
yields the lowest amount of soot among all fuels irrespective of SOI timing.
Further, E10 shows a non-monotonic trend in soot emissions with SOI timing:
SOI-36>SOI-45>SOI-21>SOI-27, while soot emissions from E30 exhibit monotonic
decrease with advancing SOI timing. NOx emissions from various fuels follow a
trend of E10>E30>E100. NOx emissions increase as SOI timing is advanced for all
fuels, with an anomaly for E10 and E100 where NOx decreases when SOI is
advanced beyond -36oaTDC. Detailed analysis of the numerical results is
performed to investigate the emission trends and elucidate the impact of
chemical composition and physical properties on autoignition and emissions
characteristics.
