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For many years, compression ignition combustion has been studied by a combination of generic studies on fuel spray formation and analysis of results from single and multicylinder engines. The results and insight have been applied to design and develop advanced fuel injection equipment for high-speed direct injection engines. Experimental fuel injection equipments, including early common rail designs, have been matched to combustion chambers in single cylinder research engines to tackle the conflicting requirements of efficiency and minimum nitric oxide formation, combustion noise and soot. A clear strategy evolved from the work with experimental equipment that is being applied to multicylinder engines. If sufficient oxygen is available in the gas charge trapped in each cylinder, the LDCR common rail injection system will provide the fuel required to develop high torque at low engine speeds.

Lucas Diesel Systems has designed a Common Rail fuel injection system for modern high speed direct injection diesel engines. The components of the system include a new high pressure pump, a rail, and injectors which accommodate a rapid control valve within the envelope of a 17 mm diameter. The injection pressure can be controlled at all engine operating conditions within the range of 150 to 1600 bar. This paper describes the major components of this system, which is designed to provide multiple injections into the combustion chamber during each engine cycle with a good control of small deliveries. In comparison with cam-driven diesel injection systems, the common rail approach needs some additional control and supervision strategies; for example, detection of small leakages due to high pressure at the needle seat throughout the engine cycle.

The non-reactive diesel spray is studied in a constant volume combustion chamber. Droplet sizes and velocities are measured using Particle Doppler Analyzer instrumentation. The effects of aerodynamic drag and vaporization on the droplets size are emphasized. An increase of the mean diameters is observed downstream of the break-up region. The well known KIVA-II code is used to achieve spray computations. The break-up model is disabled and the spray is assumed to be already atomized at the nozzle exit. Size distribution and velocities of the injected droplets are deduced from downstream experimental data. A good agreement is obtained between numerical and experimental results. Size distributions at various locations and temperature conditions are correctly predicted. A diesel spray can be thus modeled in a satisfactory way, when we alleviate the complex processes of break-up, but with appropriate initial droplets conditions.