Effects of In-Cylinder Fuel Spray Formation on Emissions and Cyclic Variability in a Lean-Burn Engine. Part 2: Results

Paper #:
  • 982620

Published:
  • 1998-10-19
Citation:
Skippon, S. and Takagi, Y., "Effects of In-Cylinder Fuel Spray Formation on Emissions and Cyclic Variability in a Lean-Burn Engine. Part 2: Results," SAE Technical Paper 982620, 1998, https://doi.org/10.4271/982620.
Pages:
19
Abstract:
The effects of injection system design, air/fuel ratio, coolant temperature and fuel volatility on engine-out hydrocarbon emissions, NOx emissions and cyclic variability have been studied in a prototype 1.8l lean-burn SI engine. The results have been compared with ILIDS measurements of in-cylinder spray characteristics made under similar conditions, to establish the degree to which variations in fuel spray formation affect engine performance. The engine was found to exhibit a different behaviour when running lean compared to stoichiometric. In lean-burn operation, there was a clear tendency for the best performance to occur under operating conditions which produced charge stratification in the cylinder, whereas when the engine was run with a stoichiometric air/fuel ratio, the best performance was achieved under engine operating conditions which gave the most homogeneous charge in-cylinder. The main effects of increasing mid-range or back-end fuel volatility were to increase evaporation from the inlet port wall film, thereby reducing the contribution made by strip atomisation to the overall in-cylinder droplet population early in the intake stroke. The optimum fuel system for lean-burn operation was the combination of an air-assisted injector used with back-flow injection timing.
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