The effects of injector geometry and operating conditions on spray mass, momentum and development using high-pressure gasoline

Abstract

High fuel injection pressure (>500 bar) in direct injection gasoline engines is an important means to reduce particulate emissions. While decades of fuel spray research has dramatically advanced the understanding high-pressure diesel fuel sprays, few studies focus on high-pressure gasoline sprays. The objective of this work was to quantify the effects of different injector nozzle geometries on important high-pressure gasoline spray characteristics including injection mass flow rate, momentum flux, and spray imaging at evaporative and non-evaporative conditions. Three categories of nozzle internal geometry were evaluated: inlet rounding; converging-, diverging-, and straight-cylindrical internal flow passages; and different nozzle outlet diameters. Reference grade gasoline was used at injection pressures of 600, 900, 1200, and 1500 bar at chamber pressures from 1 to 30 bar and chamber temperatures from 293 to 800 K. Two fuel injector temperatures of 293 K and 363 K were studied. The mass and momentum measurements were used to quantify differences in injector geometry as well as to evaluate for effects of cavitation. The visualization data were analyzed to determine spray penetration and spray angle development for a broad range of operating and state conditions. The results showed internal flow significantly impacts injector performance, where nozzles with inlet rounding resulted in 20% higher mass flow rate compared with straight cylindrical nozzles. Higher fuel injector temperatures also increased mass flow rate by up to 5%. Spray momentum coefficients showed a linear relationship with cavitation number indicating all nozzles were cavitating at all conditions tested. Trends in fuel spray penetration and spray angle development were similar to those observed previously for diesel sprays, which was unexpected given the significant differences in thermal-physical properties of the fuels. Chamber pressure had the strongest influence on penetration distance, and the momentum measurements were good indicators of the injector geometry with the highest penetration distance.