Effect of Fuel Reactivity on Ignitability and Combustion Phasing in a Heavy-Duty Engine Simulation for Mixing-Controlled and Partially-Premixed Combustion

Abstract

Light-end fuels have recently garnered interest as potential fuel for advanced compression ignition engines. This next generation of engines, which aim to combine the high efficiency of diesel engines with the relative simplicity of gasoline engines, may allow engine manufacturers to continue improving efficiency and reducing emissions without a large increase in engine and aftertreatment system complexity. In this work, a 1-D heavy-duty engine model was validated with measured data and then used to generate boundary conditions for the detailed chemical kinetic simulation corresponding to various combustion modes and operating points. Using these boundary conditions, homogeneous simulations were conducted for 242 fuels with research octane number (RON) from 40 to 100 and sensitivity (S) from 0 to 12. Combustion phasing (CA50) was most dependent on RON and less dependent on S under all conditions. Both RON and S had a greater effect on combustion phasing under partially-premixed compression ignition (PPCI) conditions (19.3°) than under mixing-controlled combustion (MCC) conditions (5.8°). The effect of RON and S were also greatest for the lowest reactivity (RON>90) fuels and under low-load conditions. The results for CA50 reflect the relative ignition delay for the various fuels at the start-of-injection (SOI) temperature. At higher SOI temperatures (>950K), CA50 was found to be less dependent on fuel sensitivity due to the convergence of ignition delay behavior of different fuels in the high-temperature region. Combustion of light-end fuels in CI engines can be an important opportunity for regulators, consumers and engine-makers alike. However, selection of the right fuel specifications will be critical in development of the combustion strategy. This work therefore provides a first look at quantifying the effect of light-end fuel chemistry on advanced CI engine combustion across the entire light-end fuel reactivity space, and provides a comparison of the trends for different combustion modes.