An experimental and numerical characterization has been conducted for high-pressure hydraulically actuated fuel injection systems. One single and one doubleguided multi-hole Valve-Covered-Orifice (VCO) type injector was used with a Common Rail (CR) injection system, and two mini-sac injectors for Hydraulic electronic Unit Injection system (HEUI) were used with different orifice diameters. The purpose of the study was to explore the effects of the injection system and the operating conditions on

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... the engine emissions for a direct injection small bore diesel engine. The diesel spray was injected into a pressurized chamber with optical access at ambient temperature. The gas density inside the chamber was representative of the density in a High Speed Direct Injection (HSDI) diesel engine at the time of injection. The experimental spray parameters included: injection pressure, injection duration, nozzle type, and nozzle diameter. Images of the transient sprays were obtained with a high-speed digital camera. From these images, spray tip penetration and cone angles were obtained directly. Moreover, spray droplet sizes averaged over the entire spray (SMD) were derived from the images using the Light Extinction Method (LEM). Engine tests were conducted on an instrumented single cylinder small bore diesel engine. Data were taken at 1757 RPM, and 45 % load. Engine emissions results include nitrogen oxide (NO x ) emissions and particulate emissions. The KIVA code and engine emissions measurements were used to correlate the spray characteristics and the engine emissions, NO x and soot. The results emphasize the correlation between spray behavior and engine emissions. EXPERIMENTAL SETUP AND DIAGNOSTICS FUEL INJECTION SYSTEMS: To study the characteristics of transient diesel sprays injected from a multi-hole nozzle with high pressure, two different experimental fuel injection systems were designed and constructed. The first one is the Common Rail (CR)