The present study intends to explore the in-cylinder combustion and evolution of soot emission during the transition from conventional compression ignition (CI) combustion to partially premixed combustion (PPC) under low load conditions. In-cylinder combustion images and engine-out emissions were measured in an optical engine fueled with low octane heavy naphtha fuel (RON = 50). Full cycle engine simulations were performed using a three-dimensional computational fluid dynamics code CONVERGE, coupled with gas-phase chemical kinetics, turbulence, and a particulate size mimic soot model. The simulations were performed under low load conditions (indicated mean effective pressure (IMEP) of ∼2-3 bar) at an engine speed of 1200 rpm. The start of injection (SOI) was advanced from late (-10 CAD aTDC) to early fuel injection timings (-40 CAD aTDC) to realize the combustion transition from CI combustion to PPC. The simulation results of combustion and emission are compared with the experimental results in both CI and PPC combustion modes. The results of the study show a typical low-temperature stratified lean combustion in PPC mode, while high-temperature spray-driven combustion is evident in CI mode. The in-cylinder small intermediates species such as acetylene (C2H2), propargyl (C3H3), cyclopentadienyl (C5H5), and polycyclic aromatic hydrocarbons (PAHs) were significantly suppressed at PPC mode. Nucleation reaction of PAHs collision contributed to main soot mass production. The distribution of soot mass and particle number density was consistent with the distribution of high-temperature zones in CI and PPC combustion modes.
Bibliographical noteFunding Information:
This work was funded by competitive research funding from King Abdullah University of Science and Technology (KAUST), and by Saudi Aramco under the FUELCOM-II program. The authors would like to thank Adrian I. Ichim and Riyad Jambi for their technical support in conducting the engine experiments, and Convergent Science for providing licenses for the CONVERGE software. In addition, Yanzhao An would like to thank my wife, Jing Huang, and daughter, Huangjiaxi An for their sweet love and great support over the past years.
© 2018 American Chemical Society.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology