The Orbital Combustion Process

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    The breakthrough in engine design achieved by Orbital is a stratified combustion process, which involves an air-assisted injection of fuel directly into the combustion chamber and uses electronic control of the fuel delivery, injection timing, ignition and other variables.

    The OCP and control is suitable for both 2-stroke and 4-stroke engines and has been applied successfully across a range of cylinder displacements from 50 cc to greater than 500 cc, including high speed engine operation.

    In a conventional engine, the fresh fuel/air mixture is prepared upstream of the cylinder (whether by carburettor or conventional EFI) and enters the cylinder during the intake stroke, with the intent of forming a homogenous
    mixture of air and fuel within the cylinder. The application of OCP technology enables systems allow a highly stratified combustion process to occur, containing the combustible fuel cloud to a small area within the
    cylinder, with the remainder of the air in the cylinder being not fuelled.

    This process at light loads allows engines with OCP to run very lean (in some cases, total engine operation is carried out without the use of an air intake throttle). Under high load conditions, the OCP system runs similar to a homogeneously-charged engine, with good mixing of the fuel/air mixtures within the cylinder.

    In the case of a 2-stroke engine, direct fuel injection is possible after the exhaust port closes at light loads, minimising the short-circuiting of fresh fuel/air mixture out of the exhaust port as occurs in conventional 2-stroke engines. In the case of a 4-stroke engine, direct fuel injection allows lean engine operation, significantly reducing the engine pumping work.

    The combustion process, due to control of the air to fuel ratio gradient within the spray plume, allows clean and controlled combustion, resulting in further improvements in fuel economy and emission control.

    Apart from the basic combustion process and the associated fuel and control system, Orbital has developed related technologies including catalyst systems, control systems, control hardware and control software for vehicle
    applications of engines using OCP technology.

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