Effect of SOI, Excess Air Ratio and Spark Timing on Direct Injection Spark Ignition Engine Particulate Emissions with EGR

Paper #:
  • 2017-01-2399

Published:
  • 2017-10-08
Affiliated:
Abstract:
Particulate matter emissions have become a concern for the development of direct injection spark ignition (DISI) engine. Besides, exhaust gas recirculation (EGR) has been demonstrated as a beneficial technology contributing to the improvement of fuel economy and nitrous oxide emissions, which is also attracting more attention to particulate emissions. The primary focus of this work is investigation of the effect of operating parameter variations on DISI engine particulate emissions with EGR. A 1.8 liter, turbocharged engine with cooled EGR was used for this experiment. The engine was operated at a steady cruise condition with various operating parameters including start of injection (SOI), excess air ratio and spark timing under EGR conditions to characterize the particle number (PN) emissions. This work indicates there is a high sensitivity of PN emissions to variations of these parameters with EGR. SOI timings vary from 320°CA BTDC to 200°CA BTDC, for early injection timings, PN emissions increases significantly, especially for the accumulation mode particles because of pool fires, and geometric mean diameter becomes larger. Meanwhile, as EGR rate is increased, PN emissions increase; For middle SOI timings,PN emissions decrease clearly due to improvement of fuel impingement. Late injections cause PN emissions increase slightly because of poor mixture homogeneity. Under these conditions, the increase in EGR leads to the decreased PN emissions. Excess air ratio λ is sensitive to particle emissions, as λ is increased, PN emissions decrease non-linearly. A high sensitivity is also observed to excess air ratio at different EGR rates. Retarding spark timing from maximum brake torque (MBT) spark timing causes the improvement of PN emissions but a negative impact on fuel economy. In general, the results reveal the sensitivity of PN emissions to a range of operating parameters with EGR.
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