Instead, the leakage is caused by the deformation due to thermal fatigue. The gasket leakage problem is usually not caused by the manifold pressure. The gasket can tolerate a much higher pressure than the normal operating pressure level of the exhaust manifold. A gasket is used between the exhaust manifold and the cylinder head to prevent high temperature exhaust leaks or air seepages from the outside. A very high exhaust manifold pressure itself does not cause structural failure of the manifold because the manifold wall is usually sufficiently thick. If the spring preload is too high, valvetrain friction and cam stress may be too high.Įxhaust manifold pressure usually has large pulsating amplitude due to gas wave dynamic effects. If the spring preload is too low, excessive exhaust valve bouncing may occur after the valve floating. A sufficiently high exhaust valve spring preload needs to be used in order to prevent the exhaust valve from floating off the valve seat. During the fast transient acceleration, operation in cold climate or exhaust braking, the EGR valve may stay closed so that a large amount of exhaust gas flows through the turbine to create a very high engine delta P. It also affects exhaust valve floating off the valve seat during the intake stroke. The engine delta P is an indicator of pumping loss. There are two different limits that should not be exceeded in engine design and performance/emissions calibration due to durability concerns: the engine delta P and the exhaust manifold pressure. (Note that the compressor out temperature affects the LCF life of the compressor wheel and housing, the rubber seals, and the charge air cooler.) This results in the challenging demand on the engine structural strength to sustain the higher peak cylinder pressure, higher compressor outlet pressure and temperature, and higher exhaust manifold pressure. As the engine power density increases and the allowable engine-out soot level decreases, higher intake manifold pressure is required at the rated power condition.
It also largely affects the engine delta P (i.e., exhaust manifold pressure minus intake manifold pressure). It affects turbine pressure ratio and hence intake manifold boost pressure. Exhaust manifold pressure is governed mainly by engine exhaust flow rate, turbine area, and exhaust manifold volume. A thorough understanding of the impact of this parameter on durability is required in order to specify an appropriate design limit for the exhaust manifold pressure. Qianfan Xin, in Diesel Engine System Design, 2013 Impact of exhaust manifold pressure on durabilityĮxhaust manifold pressure is one of the most important engine system design parameters.
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