Effects of EGR and combustion phasing on the combustion and emission characteristic of direct-injection CI engine fueled with n-butanol/diesel blends

Shortage of fossil fuel and stringent emission regulations require less pollutant emissions and better fuel conversion efficiency from modern internal combustion (IC) engines. Butanol is of particular interest as a renewable biofuel for advanced compression ignition (CI) engines, which has been receiving widely researches consequently. In order to more comprehensively evaluate the application of butanol on modern CI engine, exploration strategy was focused on the combining of EGR and combustion phasing control to achieve ultra-low NOx and smoke emission without penalty on fuel economy. Experiment was conducted under constant engine speed and both the high and low engine load conditions with three volume fractions of butanol up to 30%. Results indicate that butanol blending causes extended ignition delay, increased premixed combustion ratio (PCR) and retarded combustion phasing, which is more significant at low load condition. Butanol/diesel blends can dramatically reduce exhaust smoke and particle emissions without increasing NOx emissions at, however, the expense of lower thermal efficiency than that of pure diesel. Reduced thermal efficiency can be recovered by properly matching EGR and combustion phasing under a low level of overall emission.