6112 Control valves

A wide variety of gas flow control valves are possible in modern diesel engines, usually opened and closed using algorithms relating their area to other parameters in the engine. The most common examples are wastegates and exhaust gas recirculation valves. The turbine wastegate performs some of the functions of the alternative VG turbine, reducing turbine flow and hence power output at high engine speeds to give a better match to engine requirements; the wastegate by-passes flow around the turbine. It can be represented in a model by a variable area valve in a pipe in parallel with the turbine, the actual valve area being determined in general by an algorithm using other sensed parameters in the engine (typically boost and exhaust manifold pressures) and its controller characteristics. The latter can be modelled similarly to a VG turbine controller, or a simple mechanical wastegate can be modelled as the actual mechanical system. EGR can be represented simply by a fraction of the gas flow being recycled from exhaust to inlet manifolds or again by a more complex control system algorithm. Other flow control valves are becoming more common on engines in order to provide ever more close matching of flows to requirements, and these can usually be modelled in similar ways provided the basic model structure is flexible enough.

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