Measurement of knock and its analysis on turbocharged 600cc formula SAE boost pressure control and sensor signal conditioning

Turbocharging of a FSAE 600cc engine required analysis of knock at high engine speeds. Knock testing on this engine was performed at 8000 and 10000 rpm. The engine was boosted to 150 kPa which was controlled with a Proportional Integral Derivative (PID) controller that actuated an external wastegate. In-cylinder pressure measurements were acquired at 200 kHz. Apart from in-cylinder pressure the other recorded channels were: crank sensor, cam sensor, spark timing and knock sensor. Data Streaming in LabVIEW® was used to acquire the data for the required lengths of time. The streamed data was then post processed also in LabVIEW. The in-cylinder pressure measurement was signal conditioned with the typical charge-amplifier used with piezo sensors. However the other measurements all required some form of in-house signal conditioning which are discussed in this paper. The crank sensor signal was coming from a mechanically modified crank sensor sprocket that did not have any missing teeth. This signal replaced the typical crank-shaft encoder typically used in conjunction with in-cylinder pressure measurements. The cam sensor was an in-house design using an inductive sensor triggered by a magnet inserted in a bolt attached onto the cam drive sprocket. This signal had to be amplified due to the low signal level during cranking. The crank sensor signal together with the cam sensor signal were used as the basis for a software generated crank angle that was required to calculate the instantaneous volume of the engine cylinder. The spark timing signal was a logical AND from all four low voltage (12V) spark plug output commands from the Engine Control Unit (ECU). This signal was required to analyze the effect of spark advance on knock. Finally the knock sensor signal was conditioned to provide a low output impedance to avoid `ghosting' in the National Instruments data acquisition.