Effects of hydraulic flow and spray characteristics on diesel combustion in CR direct-injection engine with indirect acting Piezo injector

Abstract

Recently, the automobile industry has focused on the FIE system of diesel engine with common-rail, EGR, and turbo charger in order to meet a more stringent emission and fuel economy regulations. High-pressure fuel direct injection by using common-rail system is widely accepted because diesel combustion and emission characteristics highly depend on the formation of air-fuel mixture quality. By this fact, an electro-hydraulic injector for common-rail fuel injection system should be designed to have precise and fast response of injector needle's opening and closing behavior to enhance air-fuel mixing rate. As know, most electro-hydraulic injectors provide its nozzle movement by solenoid coil energy or piezo-actuation. Relatively, servo-hydraulic type piezo injector with bypass-circuit mechanism, which it serve to amplify extension of the piezo stack, is also known for their good efficiency. So the piezo actuator triggers pilot valve for controlling pressure balance, which is accurately regulated by bypass-circuit system. Therefore, main actuation force of piezo injector to move injector needle is hydraulic, which is the key object as it is aimed towards all this research ranges: numerical and experimental approaches. In this study, firstly a full-circuit numerical model of an indirect acting piezo injector with bypass-circuit by using AMESim code has been developed to predict dynamic characteristics of hydraulic components and verified by comparison with experimental data. Also, two experiment schemes were carried out using a constant volume chamber with LED back-illumination system for Mie scattering and a single-cylinder CR direct-injection engine, equipped with a bypass-circuit type piezo and solenoid injector to compare high-speed spray and combustion characteristics in this study because spray penetration and duration are key factor in diesel diffusion combustion. As main results obtained by this study, the injection flow rate and injector internal pressure dynamics calculated by AMESim environment of a bypass type piezo-driven injector reasonably agreed with the experimental result. Also it has better capability in controlling injector needle closing delay and a beneficial effect on diesel diffusion combustion.