2012•Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile EngineeringRequires access
A simple and efficient mild air hybrid engine concept and its performance analysis
Cho-Yu Lee, Hua Zhao, Tom Ma
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Abstract
In this paper, a simplified and more effective approach to achieve mild air hybrid operation in an engine with split intake ports is presented and its performance is analysed. The regenerative engine braking is achieved by operating the engine as a compressor during vehicle deceleration through the application of a cam profile switching device to one of the intake valves. Compared to the previous concepts, the new approach simplifies the control and allows more compressed air to be captured during the compressor mode operation. A four-cylinder 2.0 l diesel engine has been modelled in Ricardo’s WAVE to operate in an air hybrid engine configuration so that the valve timing optimization during the compressor mode and the expander mode operations could be studied. An air hybrid operation map during the compressor mode is then created, in which the amount of air mass charged (g/cycle) during a deceleration is given as a function of engine braking torque and tank pressure. The other air hybrid operation map for the expander mode operation is generated using a program in MATLAB, which allows the compressed air consumption during each cranking to be determined for a given tank pressure and the number of cylinders. In order to evaluate the potential fuel savings of the mild air hybrid engine technology and the availability of the compressed air for additional usages, a driving cycle simulation program has been developed and applied to a light duty vehicle. The vehicle simulation shows that standard vehicle operation during the New European Driving Cycle consumes 677 g of fuel and the mild air hybrid vehicle uses 631.2 g of fuel, which represents a 6.8% reduction in fuel consumption as a result of the regenerative stop–start operations. In addition, the free compressed air is available to provide instant boost so that a highly downsized engine can be used for further improvement in fuel economy without the loss in performance and greater emissions associated with turbo-lag.