As an alternative to the electric hybrid powertrain, air-hybrid engine concepts have the potential to achieve regenerative braking and air-assisted engine operations for low-carbon vehicle applications. Over the last few years, systematic studies have been carried out by the authors on a number of air-hybrid engine concepts. This paper presents the modelling and experimental results of air-hybrid engine operation enabled by fully variable valve actuation (FVVA). The principle and key operating features of such an air-hybrid engine will be presented first. This is followed by a detailed theoretical analysis of the two-stroke compression and expansion operations enabled by the FVVA system. Finally, experimental results will be presented with regard to the actual performance of a single-cylinder engine operating in the compression mode and expansion mode through the Lotus active valve train system.

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In this paper, an air hybrid engine concept with an one-way intake system will be described and analysed. The investigation started with systematic studies on the effect of various valve opening and closing events on the performance of Compressor Mode (CM) and Expander Mode (EM) operations. After having defined the optimal valve timings for CM and EM operations over a range of engine speeds, the effect of other operating parameters on the performance of the air hybrid engine, such as buffer (or auxiliary) chamber volume, airtank volume and pressure, etc., is examined. It is shown that this concept can be readily implemented in production engines with existing production VVA technologies. The predicted results indicate that it is capable of performing good regenerative braking and large driving torque to start and motor the engines using the stored compressed air.