Hybrid pneumatic engines, which are designed to follow the downsizing and supercharging paradigm, offer a fuel-saving potential that is almost equal to that of hybrid electric powertrains while inducing much lower additional mass and cost penalties. This paper presents a systematic optimization of the operation of such an engine system. Both two-stroke and four-stroke modes are analysed. The optimized valve and throttle actuation laws for all modes and operating areas lead to generic maps that are independent of the engine size. So far, the pneumatic hybridization of internal combustion engines was thought to require two-stroke operation. This paper presents a novel hybrid pneumatic engine configuration that entails fixed camshafts for both intake and exhaust valves while utilizing variable valve actuation for one charge valve per cylinder only. This configuration is operated entirely in four-stroke modes. Such a configuration requires a careful optimization of its operating strategy to achieve its fuel economy potential. Compared with a full two-stroke operation, only small efficiency losses result from using four-stroke modes with these new operating strategies. Initial measurement results with such an engine system are presented in this paper to confirm the validity of the principles of operation.
Downsizing and turbocharging for retaining the maximal power is a widely used approach to decrease the fuel consumption of spark ignited engines. In general, the trade-off is a substantial driveability loss. In-cylinder boosting has proven to be an effective way to eliminate this problem. Thus far, expensive and complex fully variable valve-trains have been proposed for the air exchange between the air tank and the combustion chamber. This paper is the first of a two-part study that examines the use of a deactivatable camshaft-driven valve with respect to the achievable transient engine performance. The system characteristics and limitations are discussed by using a mean value engine model that is adapted for in-cylinder boosting. A model-based design framework is presented which links the valve system design to a desired engine performance. The companion paper covers control issues and provides experimental verifications.
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