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CLENCI A., DESCOMBES G., PODEVIN P., HARA V., BOBESCU G. . Considerations on the downsizing technique at the s.i. engine. In Proceedings of the International CONAT Automotive Congress, Brasov, organized under the great patronage of FISITA. 2004.

Abstract: The inefficient running of the spark ignition engine at part loads due to the load control method, but mostly, their major weighting in vehicle’s operation time justifies the interest for the technical solutions, which act in this particular operating range. These drawbacks encountered at low part loads are even more amplified when talking about bigger engines. For instance, it is well known the fact that at the same engine load, a bigger engine is more throttled than a smaller one, so here we can talk about a higher pumping work, a lower real compression ratio and these without mentioning the overall mechanical efficiency, which is also lower. One solution, as mentioned above, is the reduction of the displacement without affecting the power output. Actually, it is what is now commonly known as the downsizing technique.
The combination of downsizing and uploading an engine is known since long time. However, the conversion, in an acceptable way, of this potential to practice is very challenging. On the one hand, the degree of the downsizing is related with the boost pressure. In order to cope with knocking phenomenon, the downsized high-pressure turbocharged gasoline engine requires a lower volumetric compression ratio that limits the efficiency on part loads. Therefore, the degree of the downsizing has been limited and thus, the possible fuel consumption reduction has not yet been fully achieved. On the other hand, other problems are encountered when talking about a downsized turbocharged gasoline engine: insufficient low-end torque, bad starting performance, turbo-lag.
In order to solve these problems an effective combination of the downsized turbocharged gasoline engine with additional technologies is needed.
Thus, the paper will present a so-called adaptive thermal engine, which has in the same time VVA and VCR systems. It will then be demonstrated that it is best suitable for turbocharging, thus being able to talk about a high downsizing factor.

Keywords: efficiency, downsizing, turbocharging, variable compression ratio, variable valve timing

Posted by Adrian CLENCI

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