Internal combustion engines of vehicles which are equipped with classic drivetrains are mostly operating in variable load conditions. This fact especially refers to city driving, where the vehicle speeds are lower than in highway driving, but the accelerations are more frequent and intensive. The efficiency of the engine’s work is among others a load- and crankshaft rotation speed dependent parameter. Generally in low load conditions the efficiency of the engine is low, and in high load the efficiency is high. The authors conducted a series of road tests, searching for ranges of engine power most commonly used in urban traffic, adopting economical, dynamic and balanced driving strategies. In all strategies the passenger vehicle engine was most frequently operating in low power (and low efficiency) conditions. One of the ways to improve the efficiency of an IC engine is to raise its compression ratio (CR). However, high CR in spark ignition engines can be the reason of engine knock in high load and crankshaft rotation speed conditions. Therefore it would be favorable, that high CR would be obtained in low load, and low CR in high load conditions. These results and findings led the authors to build the variable Effective Compression Ratio (eVCR) system. A 4-stroke single cylinder engine was equipped with an electric actuator and its control system, allowing valvetrain-independent intake valve action. This work contains the results of tests of the engines indicated parameters. A dynamometer test bench was used for this purpose. The engine was tested at two operating conditions: firstly with the engines factory compression ratio of 9.2:1, secondly with CR = 11.5. An improvement in engine power and overall efficiency among others was observed in the tested areas of the characteristics. It is worth noting that there was no engine knock observed. This research shall be the introduction for eVCR [5] control system programming.
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