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Simultaneous Improvement of Fuel Consumption and Exhaust Emissions on a Multi-Cylinder Camless Engine
Abstract:
Further improvement in fuel consumption is needed for diesel engines to address regulatory requirement particularly for heavy duty diesel in Japan enforced in 2015, in addition to the compliance to the regulatory requirements for exhaust emission, which seems to be more stringent in future. The authors have participated in the project of “Comprehensive Technological Development of Innovative, Next-Generation, Low-Pollution Vehicles” organized by New Energy and Industrial Technology Development Organization (NEDO), and innovative devices such as multi stage boosting system, ultra high-pressure fuel injection system and variable valve actuation (camless) system had been developed in this project from a standpoint of simultaneous improvement of fuel consumption and exhaust emission.
In camless system, intake and exhaust valves are driven by hydraulic pressure. So, fully flexible setting of opening and closure timings and lift of the intake and exhaust valves is possible. In this paper, steady-state operation test was conducted by adopting a combustion chamber with geometric compression ratio of 20.0 and an Electro-Hydraulic Camless System in the multi-cylinder engine with 3 stage turbo charge system. The engine performance and exhaust emissions were compared to same base engine equipped with 3 stage turbo system, piston of geometric compression ratio of 16.2 and cam drive valve train.
As a result of steady-state operation test, potential of improvement of fuel economy was indicated in this engine system. In addition, due to cylinder deactivation operation, further improvement of fuel economy was achieved in extremely low load range by reduction of heat loss. With regard to the BSFC based on JE05 mode -converted value with giving consideration to the result of cylinder deactivation operation, improvement of 8.9% was obtained.
With regard to the early exhaust valve opening (EEVO) for which effect to improve turbo charger response is expected as well as the negative valve overlap (NVO) for which making up for delay of external Exhaust Gas Recirculation (EGR) by internal EGR, the operation for 70 seconds was extracted from JE05 mode operation to implement partially transient operation on trial basis. It was confirmed that both EEVO and NVO were feasible by using this camless system.
Further simultaneous reduction of both fuel consumption and exhaust emission in JE05 mode operation is expected by controlling intake and exhaust valve lift with giving consideration to the effect of external disturbance, improved thermal efficiency by increase of expansion ratio, implementation of each cylinder control for each load range including the switching control to cylinder deactivation operation, and suppression of spike-like NOx and soot emissions by adopting EEVO and NVO.