The Experimental Comparison between Stratified Flame Ignition and Micro Flame Ignition in a Gasoline SI-CAI Hybrid Combustion Engine

Paper #:
  • 2017-01-0737

  • 2017-03-28
Controlled Auto-Ignition (CAI), also known as Homogeneous charge compression ignition (HCCI), has been the subject of extensive research because of their ability to providing simultaneous reductions in fuel consumption and NOx emissions from a gasoline engine. However, due to its limited operation range, switching between CAI and spark ignition (SI) combustion is needed to cover the complete operational range of a gasoline engine for passenger car applications. Previous research has shown that the SI-CAI Hybrid Combustion (SCHC) has the potential to control the ignition timing and heat release process during both steady state and transient operations. However, it was found that the SCHC process is often characterised with large cycle-to-cycle variations, due to the flame instability at high dilution conditions. In order to control the heat release process stably and expand the operating range of SCHC, the stratified flame ignition (SFI) and micro flame ignition strategy (MFI) involved in the SCHC operation were analysed respectively based on the engine experiments carried out on a single cylinder research engine equipped with both intake and exhaust mechanical VVA systems. The premixed homogenous dilution charge as main fuel was injected by intake port injector. Meanwhile, the stratified gasoline fuel (in SFI) or DME (in MFI) injected by direct injector in the cylinder was used as an enhanced flame kernel. The results showed that no matter SFI or MFI strategy was useful to improve the combustions stability and control the combustion phase of SCHC. SFI strategy focuses on injection pressure, correspondingly the key issue of MFI is injection times which determines in-cylinder fuel activity stratified degree. The difference between those two strategies were shown in the heat release process.
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