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Does overlap reduce HC emissions?
In this study, the strategy of varying the valve overlap was employed to reduce methane emissions. Although a torque valve cannot meet engine emission specifications, the hydrocarbon and methane emissions were reduced by approximately 41% by decreasing the valve overlap duration while using HCNG fuel.
How does variable valve timing reduce emissions?
VVT controls the flow of air and exhaust Engine valves control the intake of fresh air and fuel, and the exhaust of combustion gases. VVT and lift systems adjust the timing of the valves to match the operating conditions of the engine. This improves efficiency over a wide range of engine operating speeds.
What is the significance of valve overlap?
Valve overlap is designed into the engine and is most useful at higher speeds. At higher speeds, the extra amount of intake charge brought into the combustion chamber provides a substantial increase in available power. The amount of time that both valves are open in directly related to engine rpm.
Why do exhaust valves open before TDC?
The inlet valve usually opens few degrees before the piston reaches TDC in its exhaust stroke. This is because the downward movement of the piston creates the vacuum (or negative pressure) in the cylinder and the air-fuel mixture gets filled in the empty space.
Does valve timing affect emissions?
The timing of EVC has a very significant affect on how much of the Exhaust gas is left in the cylinder at the start of the engine’s intake stroke. Moving EVC Timing further after TDC increases the level of internal EGR (Exhaust Gas Recirculation) with a corresponding reduction in exhaust emissions.
What happens if there is too much valve overlap?
A reasonable positive vale overlap helps to clean combustion residuals in engine cylinder, too much valve overlap would help to expel the fresh charges into exhaust pipe thus increase HC and CO emission and hence results in bad fuel economy.
How does overlap affect the performance of an engine?
Generally, the torque at higher engine speeds and loads can benefit from increased overlap due to pressure waves in the exhaust manifold aiding the intake of fresh charge. Large amounts of overlap tend to result in poor emissions at lower speeds as fuel from the intake charge can flow directly into the exhaust.
Why is too much overlap bad for fuel economy?
Join ResearchGate to ask questions, get input, and advance your work. A reasonable positive vale overlap helps to clean combustion residuals in engine cylinder, too much valve overlap would help to expel the fresh charges into exhaust pipe thus increase HC and CO emission and hence results in bad fuel economy.
Why are the inlet and exhaust valves open?
During the overlap period where both inlet and exhaust valve are open is useful in clearing the combustion chamber from combustion products of the previous cycle. This period is variable in length. Does it have a negative or positive effect on the produced power?