puristusmäärä

Puristusmäärä, often translated as compression ratio, is a fundamental parameter in internal combustion engines. It represents the ratio of the volume of the combustion chamber when the piston is at the bottom of its stroke (bottom dead center, BDC) to the volume of the combustion chamber when the piston is at the top of its stroke (top dead center, TDC). Mathematically, it is expressed as the total cylinder volume at BDC divided by the clearance volume at TDC. A higher puristusmäärä generally indicates a more efficient engine, as it allows for greater expansion of the burning fuel-air mixture, leading to more power output. However, excessively high puristusmäärä can lead to engine knock or detonation, a phenomenon where the fuel ignites prematurely and uncontrollably, potentially damaging the engine. Engine designers must carefully balance puristusmäärä with other factors like fuel octane rating and ignition timing to achieve optimal performance and reliability. Different engine types, such as gasoline and diesel engines, have significantly different typical puristusmäärä values due to their distinct combustion processes. Diesel engines, for instance, rely on compression ignition and therefore operate with much higher puristusmäärä than gasoline engines, which use spark ignition.