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Knocking is one of the major issues on modern high compression spark ignition engines, and the actual challenge is how to effectively control its occurrence protecting the engine, without performance impact. Modern cars incorporate knock-sensor systems for engines to minimize knocking, which can maximize engine lifetime, increase power, and improve fuel economy.The choice of the sensor type may depend of a wide number of factors and boundary conditions as the engine size, market segment or fuel. It's very common to use for mass production engines a knock sensor with a wide range bandwidth in detriment of the tuned one.Wide range bandwidth knock sensors are sensible to all engine vibration frequencies, therefore, this knock sensor configuration implies in a more complex signal processing than the necessary for a tuned sensor.

Port fuel injection - PFI - engines are widely available and the calibrations of fuel models are well defined. Modern flex-fuel engines are designed to work with different fuels and a mix of them. However, Brazil’s ethanol is composed of anhydrous Ethanol mixed with 8% distilled water, making it distinct in relation of composition. In a PFI, the fuel mass is mixed to the air mass before entering the combustion chamber in order to keep the mixture most uniform as possible. In this process, heat exchange and partial pressure variation are present and this may lead to volumetric efficiency modification. However, measurement errors may be introduced from the indirect measurement method if it does not considers water content and combustion efficiency to determine volumetric efficiency.