Development of a High Performance NG Engine Embedding Direct Gas Injection and Variable Valve Actuation

Paper #:
  • 2017-24-0152

  • 2017-09-04
The present paper is the outcome of the research activity carried out by Centro Ricerche Fiat, Politecnico di Torino, Delphi and AVL within the Gason research project of the EC (H2020 program). The overall goal of the research project is to develop CNG-only SI engines which are able to comply with post-EuroVI emission regulations and 2020+ CO2 emission targets, with reference to the new homologation cycle and real driving conditions. The work presented in this paper aimed at developing a small displacement turbocharged engine, which combines the advanced VVA MultiAir system for the air metering with the direct injection of natural gas. The activity focused on the development and fluid-dynamic characterization of the gaseous-fuel injector. Moreover, the combined use of CFD analysis and optical-access PLIF experimental techniques allowed the design of the combustion chamber to be optimized from the mixture formation point of view. The optimization process also focused on the tumble formation and evolution, so as to guarantee an efficient and stable combustion process. The results showed that the designed injector is able to provide the required amount of fuel per cycle and moreover guarantees a jet exit angle suitable for a side mounting. The experimental PLIF investigations performed at partial load highlighted the high impact of the Coanda effect on the jet evolution for late injection timings, as the jet is deviated to the cylinder head roof due to its interaction with the chamber walls. Such an effect is inhibited at early injection timings due to the presence of a strong inlet flow from the intake valves. The CFD analyses confirmed this behavior and pointed out the formation of a swirl-like tangential motion of the injected fuel, which resulted to be highly beneficial for the homogenization process. Concerning the turbulent flow evolution and its interaction with the gaseous jet, provided a sufficient homogenization is guaranteed a late injection timing supports the tumble development, thus leading to a more stable and efficient combustion process. The engine design was successfully completed, and the engine is ready for an extensive and thorough experimental performance and emission analysis at the dynamic test bench.
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