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Autori: CLENCI A., ISPAS N., HARA V., BOBESCU Gh.
Editorial: Proceedings of the World FISITA Automotive Congress, Barcelona, 2004.
The paper outlines the fact that the overall efficiency of a spark ignition engine can only be improved through the maximization of the thermal efficiency on the high frequency working regimes, i.e. the low part loads.
One way of doing this is by getting rid of inefficiencies that for the past hundred years have largely been accepted as inevitable.
Thus, the authors are about to develop a variable volumetric compression ratio engine, in order to overcome the main drawback of the spark ignition engine: the continuous variation of the real rate of compression, caused by the load control method, as it is well-known.
The concept of variable volumetric compression ratio engine is the subject of a patent and it consists in a hinged mechanism.
These being said, the paper will focuse on presenting some experimental results obtained in the following situation: approaching the same working regime (brake force and speed of rotation) with different values of volumetric compression ratio (VCR = 8.5, 10, 11, 12.5). The experiments were conducted on a classical engine equipped successive with cylinder heads corresponding to the presented values of VCR. Actually, from this point of view, it has been tried to outline the parameters (e.g. air-fuel ratio, spark advance etc.), which has to be adjusted in order to have an efficient variable compression ratio engine. Results indicated the evolution of burning process (heat release, rate of heat release etc.) will be presented. Also, during the experiments the authors were able to measure the pollutants level and to make the (VCR – throttle opening – working regime) correlation.
Thus, the paper’s goal is to outline the influence of the volumetric compression ratio (VCR) at very low load on the cycle processes by presenting a comparative analysis.
Cuvinte cheie: spark ignition engine, working regimes, part loads, efficiency, variable compression ratio