Modern Applied Science; Vol. 8, No. 6; 2014 ISSN 1913-1844 E-ISSN 1913-1852 Published by Canadian Center of Science and Education 112 Utilization of Microphone Sensors and an Active Filter for the Detection and Identification of Detonation (Knock) in a Petrol Engine Agus Sujono 1 1 Department of Electrical Engineering, Sebelas Maret University, Republic of Indonesia Correspondence: Agus Sujono, epartment of Electrical Engineering, Sebelas Maret University, Jalan Ir. Sutami no. 36A, Jebres, Surakarta, Republic of Indonesia. E-mail: agus.sujono@ft.uns.ac.id Received: August 15, 2014 Accepted: August 24, 2014 Online Published: September 12, 2014 doi:10.5539/mas.v8n6p112 URL: http://dx.doi.org/10.5539/mas.v8n6p112 Abstract This research proposes a new method for detecting detonation (knock), that is to say the use of microphone sensors and active filters are combined with the identification of the vibration pattern of the engine sound.This is because,in terms of increasingthe fuel efficiency and power of a petrol combustion engine, the problem of detonation is a very serious issue. For this reason, the accurate, rapid and real time detection and identification of detonation also still needs to be developed. Microphone sensorsare inexpensive anddo not need to be mounted on the engine itself, meaning they are not exposed to heat, although the signal processing needs to be conducted carefully. The engine sound is recorded through a microphone and a Sallen-Key active filter is used to filter the detonation signal. Then the signal is processed to obtain the results of the regression of its function envelope. Identification is carried out using the method of calculating of the Euclidean distance of the function envelope regression from the reference signal. This is to make a determination of whether there is a detonation or not. This method is conducted with the help of Matlab. The findingsare that this method is able to detect and identify detonation signals. Keywords: microphone, knock, petrol combustion engines, active filters, Euclidean distance 1. Introduction Microphone sound sensors until now have not been used for the detection of detonation in automobiles. Most of the knock sensors used to detect the engine vibration are piezoelectric accelerometers which detect the occurrence of detonation. The detonation phenomenonis quite complicated to explain, however,in simple terms it is an uncontrolled burning (misfire) that occurs by itself (auto ignition) during the compression stroke, making the machine vibrate hard. There is also decreased power, overheating, a waste of fuel and the engine will be quickly become damaged. Detonation will also occur when the fuel is lower quality and when ignition occurs too early. However, when the timing of the ignition is late, the engine power will decrease drastically. Therefore, the ignition is always arranged so that the timingis as early as possible but not until detonation. Thus, detonation detection is very important in establishing the exact time of ignition (Heywood, 1988). A microphoneused with an activefilter can be used to capture and separate the sounds of engine vibrations when there is detonation given a frequency of detonation vibration of 5-10 kHz. Other sensors used in the detection of detonation include: the most accurate pressure sensor in the cylinder (Galloni, 2012), but these sensors are expensive and not durable; an optical sensor with a quartz window in the combustion chamber which is often constrained by the presence of a crust on the surface of the chamber (Merola et. al., 2007); an ion current sensor in the combustion chamber (Zhang et. al., 2009), which is often constrained by the electrode being burnt. Now, the most widely used is the vibration sensor (knock sensor) in the form of an accelerometer (Vulli et. al., 2008), but because it is installed inside the engine, the heat will affect the sensor’s performance. Acoustic emission (AE) technique has been used in the method of identifying injector faults at diesel engine (Elamin et. al., 2010). Signal filtering is carried out in order to separate the detonation signal from other signals and is done by usinga Sallen-Key active filter,the excellence of which is well known, a type of active high frequency filter (HPF = high pass filter). Other filtration methodsthat have been used include: the band-pass-filter (Galloni, 2012); the Kalman filter method (Ker, et. al., 2006), with, wavelet packet transform (WPT) (Hou et. al., 2009), the time-frequency analysis based on STFT (Vulli et. al., 2008) with real mother wavelet method (Zhang et. al., 2009), the wavelet and fuzzy method (Borg et. al., 2005).