Fuel Volatility Effects on Mixture Preparation and Performance in a GDI Engine During Cold Start

摘要

The objective of this research was to characterize the effects of fuel component volatility on gasoline direct injection (GDI) engine cold start. Three different fuel components, representing gasoline light end, mid-point and heavy end components, were used to form three fuel blends of different volatility. Performance tests and in-cylinder fuel distribution imaging tests using these fuel blends were carried out in a firing single-cylinder optically-accessible engine following a simulated cold-start test schedule. Performance results, based on in-cylinder pressure and engine-out hydrocarbon measurements, during the initial transient phase of GDI cold-start showed significantly degraded performance with the low volatility fuel blend, while the high volatility blend showed slightly improved performance. Neither the low nor high volatility fuel, however, showed a discernable effect on the quasi-steady-state, cold-start performance. Simultaneous planar laser-induced fluorescence and Mie scattering images showed that fuel volatility affects spray development and fuel-air mixing and as a result the in-cylinder fuel distribution. In particular, high-volatility components, because they vaporize more quickly, result in smaller drops, which have less penetration; whereas, low volatility components, because they vaporize more slowly, result in larger drops, which have greater penetration and as a result are more likely to impinge on the cylinder walls. The increased wall wetting that occurs with low-volatility fuels effectively reduces the equivalence ratio, causing the poor cold-start performance observed with the low-volatility fuel blend.