Analysis of Transition from HCCI to CI via PPC with Low Octane Gasoline Fuels using Optical Diagnostics and Soot Particle Analysis

Paper #:
  • 2017-01-2403

  • 2017-10-08
Low temperature combustion concepts are studied recently to simultaneously reduce NOX and soot emissions. Optical studies are performed to study gasoline PPC in compression ignition (CI) engines to investigate in-cylinder combustion and stratification. It is imperative to perform emission measurements and couple soot and NOX emissions with combustion images. In this research work, we attempt to investigate the soot particulates during the transition from CI to HCCI for gasoline like fuels. The experiments are performed in a single cylinder optical diesel engine that runs at a speed of 1200 rpm. Considering the safety of engine, testing was done at lower IMEP (2 to 3 bar) and combustion is visualized using a high speed camera. From the engine experiments, it is clear that combustion phasing decreases as SOI is swept from late fuel injection timings, before it detaches completely at early injection. Stratification analysis of combustion images provided useful information on in-cylinder happenings and its impact on emissions. The degree of stratification is higher at late fuel injection timings and decreases as SOI is swept to early fuel injection timings, indicating homogenous combustion. The natural luminosity of images decreases as SOI is swept from late to early fuel injection timings, which is inline with the observed trend in NOX and soot emissions. Higher the luminosity, higher is the NOX emission and lower is the soot emission and vice versa. The soot particle number and size are lower for gasoline like fuel than diesel, due to better premixing and combustion. Soot characteristics at CI, PPC and HCCI mode are analyzed and reported.
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