Abstract
Variable valve mechanisms are usually applied to a gasoline combustion engine to improve its power performance by controlling the amount of intake air according to the operating load. These mechanisms offer one possibility of resolving the conflict of objectives between a further reduction of raw emissions and an improvement in fuel efficiency. In recent years, variable valve control systems have become extremely important in the diesel combustion engine. Importantly, it has been shown that there are several potential benefits of applying variable valve timing (VVT) to a compression ignition engine. Valve train variability could offer one option to achieve the reduction goals of engine-out emissions and fuel consumption. The aim of this study was to investigate the effects on part load combustion and emission performance of internal exhaust gas recirculation (EGR) by variable exhaust valve lift actuation using a cam-in-cam system, which is an electronically variable valve device with a variable inside cam retarded to about 30 degrees. Numerical simulation based on GT-POWER has been performed to predict the NOx reduction strategy at the part load operating point of 1200 rpm in a four-valve diesel engine. A GT-POWER model of a common-rail direct injection engine with internal EGR was built and verified with experimental data. As a result, large potential for reducing NOx emissions through the use of exhaust valve control has been identified. Namely, it is possible to utilize heat efficiently as recompression of retarded post injection with downscaled specification of the exhaust valve rather than the intake valve, even if the CIC V1 condition with a reduction of the exhaust valve has a higher internal EGR rate of about 2% compared to that of the CIC V2 condition.
Highlights
In diesel engines, a robust compression-ignited combustion strongly depends on the cylinder charge temperature, composition, and cylinder pressure during valve train events [1]
The effect of internal exhaust gas recirculation (EGR) by variable valve actuation with post injection using a full-circuit GT-POWER model verified by experimental data was investigated to predict auto-ignited combustion performance that includes in-cylinder pressure and temperature, heat release, indicated specific fuel consumption (ISFC), indicated mean effective pressure (IMEP), and NOx emission
Recompression internal EGR leads to negative valve overlap effects and a higher temperature in engine operation, due to its trapping of burnt gas and limited air flow, creating a high temperature inside the cylinder
Summary
A robust compression-ignited combustion strongly depends on the cylinder charge temperature, composition, and cylinder pressure during valve train events [1]. Variable valve actuation (VVA) technology refers to a technique or combination of technologies that changes valve timing, valve duration, and valve lift, etc., depending on operating conditions and operating strategies, instead of opening and closing intake and exhaust valves with a single, fixed-cam profile. The compression ignition engine shows the required characteristics of the variable valve system which. Sci. 2018, 8, 597 can control the opening period of the valve. These VVA mechanisms have limited valve lift and timing control, depending on the shape of the mechanism and method in which it is operated
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