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Variable Compression 1


Once the however considerable mechanical problems are solved, large advantages are expected. Engines with smaller cubic capacities or less cylinders could penetrate - especially with part load or low revs - into new ranges of performance. If the engine weight stays low, real consumption savings of up to 10% are possible, especially with lower power output of the engine. The petrol engine might, finally, again approach its lower historical consumption distance to the diesel engine.

How it works

The air-fuel mixture should be compressed maximally before its combustion is initiated shortly before TDC by sparks. During this process, an auto ignition, the fuel reacting too early, must be strictly avoided. Already Nicolaus August Otto realized this fact when he invented the four-stroke engine more than 100 years ago. Up to now engineers get by with changing the ignition time, thus regulating the temperature.

Since it is possible to register the knocking of the engine electronically, a variable compression during the operation of the engine is possible. The magical border of compression of approx. 12,5:1 with optimum combustion-chamber configurations would be outperformed in certain operating conditions and it might perhaps be possible to push forward into the diesel area. Disadvantages due to the charging of petrol engines would likewise be compensated. Unfortunately, here the compression must still be reduced in general, pulling down the engine response time and the part load consumption of the petrol engine.

Both possible solutions introduced on top in the figure make use of an eccentric shaft to control the compression. On the left the cylinder block tips and creates a smaller/bigger compression space. On the right the connecting rod is shortened/lengthened. The left solution is probably more practical, because the shifting mechanics can be realized relatively compact, and there are fewer friction losses. Indeed, this solution is only possible for in-line engines and is quite complicated already. You have to provide for the stability, sealing problems and the difficult form-logical connection of the crankshaft to the camshaft(s).