Effect of valve offset on inner nozzle flow and spray shape of fuel injector for gasoline direct injection engine

Abstract

Reduction of particulate matter (PM) in exhaust gas from automobile engines is in high demand. Fuel stuck on the engine wall causes incomplete combustion, and generates a large amount of PM. To prevent this, shape of fuel injection spray must be controlled with precision. We focused on the valve offset of the injector as a factor influencing the spray shape. Computational analysis was conducted to investigate the effects of the valve offset on inner nozzle flow and spray shape (spray direction and liquid penetration). Simulated spray behavior image, footprint, and liquid penetration agreed well with experimental results. From the inner nozzle flow simulation results with the valve offset, it was found that fuel tends to flow in the direction of the valve offset near a sac in the nozzle to provide the fuel to the holes. This flow was caused by the smaller flow path fomed in the valve offset direction. From the spray simulation results, shifts in the spray direction of the plumes were caused by the flows near the sac. Some plumes were injected in the direction opposite to the valve offset. The holes with larger drill angle located in the valve offset direction, and larger valve offset caused larger changes of spray directions. Furthermore, liquid penetration was investigated. We showed that the flow separation in the holes caused by the valve offset affects the velocity distribution at the hole outlet and results in changes of the penetration length when the drill angle is small. It was found that the valve offset causes the change in the inner nozzle flow, and results in the change of the spray shape. We concluded that the correlation of nozzle geometry and valve offset is important for controlling the spray shape.