Energy aspects of the SI engine load adjustment by early closing of inlet or exhaust valve

The theoretical analysis of the SI engine load adjustment has been presented. The load especially in SI engine is highly dependent on the process of charge exchange. This process has significant impact on the effectiveness of an engine work because it is connected with the necessity of overcoming the flow resistance, then with the necessity of doing a work, so-called the charge exchange work. The flow resistance caused by throttling valve is especially high during part load operation. The open theoretical cycle has been assumed as a model of processes proceeding in the engine. Using fully variable inlet and exhaust valves timing the cycle can be realized e.g. according to two systems: system with early inlet valve closing (EIVC) and system with early exhaust valve closing (EEVC). Both systems have been analysed individually and comparatively with the open Seiliger-Sabathe cycle, which is theoretical cycle for the classical throttle governing of an engine load. Benefits resulting from application of the systems with independent inlet and exhaust valves control have been assessed on the basis of the selected parameters: a fuel dose, a cycle work, a charge exchange work and a cycle efficiency. The use of the analysed systems to governing of the SI engine load will enable to eliminate a throttling valve from inlet system and reduce the charge exchange work, especially within the range of part load operation. Decrease of the charge exchange work leads to increase of the internal and effective works, which results in increase of the effective efficiency of the spark ignition engine. Additionally, the EEVC enables realization of the internal EGR.