The effects of late intake valve closing and different cam profiles on the in-cylinder flow field and the combustion characteristics of a compression ignition engine

Abstract

The effects of the late-intake-valve-closing strategy and the different types of cam profile were observed in a singlecylinder compression ignition research engine. Experiments were carried out with two engine loads in naturally aspirated conditions. The late-intake-valve-closing strategy exhibited an improvement in the conventional trade-off between the nitrogen oxide emissions and the smoke emissions, as stated in other relevant work. However, it was found to be effective only for the premise that a sufficiently high mass of oxygen is trapped inside the cylinder, which ensured that the smoke emissions did not deteriorate with exhaust gas recirculation. This improvement in the trade-off decreased when the global air excess ratio inside the cylinder reached close to unity. The major disadvantages of the late-intake-valveclosing strategy included deterioration in the indicated mean effective pressure and the reduced mass of oxygen trapped inside the cylinder. The decrease in the indicated mean effective pressure was attributed to the reduction in the effective compression ratio followed by the reduction in the thermal efficiency in terms of the thermodynamics. The volumetric efficiency decreased owing to the backflow of the in-cylinder charge into the intake manifold. This implied that intake boosting was necessary not only to recover the efficiency to the original level but also to extend the engine load with a sufficient amount of air. The manipulation of cam profiles yielded further improvement in the trade-off relationship between the nitrogen oxide emissions and the smoke emissions. The flow field measurements obtained using particle image velocimetry and direct imaging of the combustion of the fuel spray demonstrated that the asymmetric cam profile effectively increased the swirl ratio inside the cylinder. Further improvement in the trade-off relationship between the nitrogen oxide emissions and the smoke emissions was realized because of this increased swirl intensity, which provided a better environment for air utilization. The smoke emissions were suppressed without a significant increase in the nitrogen oxide emissions.

Emission Reduction Strategies for Small Single Cylinder Diesel Engine Using Valve Timing and Swirl Ratio

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Segment a cam contour with generalized cross product

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Influence of gas distribution port parameters on in-cylinder working pressure of Annular Connecting Straight Cylinder Engine

“…The gas distribution systems of different engine configurations are quite different. The traditional reciprocating piston engine generally uses the cooperation of the valve and the valve seat to seal the working chamber, and controls the movement of the valve by designing the cam profile to realize the opening and closing of the valve 5 . The overhead camshaft type is to place the camshaft directly above the valve, eliminating the need for tappets and push rods, which has been selected by more engine manufacturers for smaller inertial force and the stable working state at high speed.…”