Investigation of Spray and Combustion of a Piezoelectric Fuel Injector for Gasoline Direct Injection Engines

摘要

In recent years, more stringent emission standard and high fuel economy demands have forced vehicle manufactures to seek alternative techniques to synchronize benefits of both gasoline and diesel fuels. In this work, experimental studies of spray characteristics and fuel auto-ignition properties from an outwardly opening piezoelectric gasoline direct injection fuel injector were conducted in an optically accessible constant volume combustion chamber (CVCC) experiment system.;Fuel sprays of light naphtha (LN), primary reference fuel (PRF), and E10 gasoline under different ambient pressures from 1 bar to 12.5 bar were investigated first. Spray was visualized by applying a Mie-scattering technique. A high-speed camera was employed to capture the spray images. Results show that a clear filamentary hollow-cone spray structure is formed for all three fuels at atmospheric conditions, and toroidal recirculation vortices are observed at the downstream spray edges. A higher ambient pressure leads to a stronger vortex located closer to the injector outlet. Larger spray angles are found under higher ambient pressure conditions for all three fuels.;Ambient pressure conditions were then extended to a lower range for iso-octane sprays. Five ambient pressure conditions were selected from 0.01 bar to 0.10 bar to evaluate the effect of superheated conditions on the spray structure from the piezoelectric fuel injector. Results indicate that spray under a superheated condition presents a distinct spray structure in the flash boiling regime. A lower ambient pressure within the superheated condition range results in a stronger deformation on spray structure, a faster spray front penetration velocity and a faster liquid vaporization rate. These phenomena are dominated by ambient pressures. Effects of fuel the injection pressure and the fuel injection duration are relatively negligible.;Next, the auto-ignition characteristics of LN, primary reference fuels (PRF65, PRF95), gasoline (Haltermann CARB LEV III) and a gasoline surrogate under conditions similar to the spray G condition (3.5 kg/m3 gas density, 21% ambient oxygen concentration) were studied. Five different ambient temperatures from 650 K to 950 K with a 75 K step were investigated. Fuel auto-ignition was observed with noticeable ignition delay for five investigated fuels under all selected experiment conditions. Results show that the locations of the occurrence of autoignitions are randomly distributed in combustion chamber. Ignition delay of each fuel is always longer than fuel injection duration under all selected experiment conditions. Differences in ignition delay among the five fuels are more significant when the ambient temperature is lower than 750K.;At last, two-color measurements were conducted for LN under diesel engine conditions. Five ambient oxygen concentrations varying from 10% to 21% and three ambient temperature conditions, 800K, 100K and 1200K, were selected to simulate both conventional diesel engine operation environment and low temperature and low oxygen concentration environment. Flame temperature distribution and KL factor distribution under different ambient conditions were calculated and discussed.