UWE Bristol Engineering showcase 2015

Knock Sensor (Bosch)
Vishnu Viswanatha Menon
BEng (Hons) Mechanical Engineering
AUTOMOTIVE ENGINE, PRE-IGNITION SENSING
Pre-ignition is an abnormal combustion occurring in an automotive engine’s combustion chamber when there is an ignition prior
to the spark plug firing. Spark plugs, exhaust valves, metal asperities such as edges of head cavities or piston bowls are parts which
can absorb high temperatures and where deposits can build up lead to pre-ignition. Knock sensors detect vibrations from parts of
the engine block caused by knocking combustion pressure waves. When a knock is detected, signal is sent to the ECU (Engine
Control Unit), where it will respond by changing the spark plug firing by a predetermined number of degrees.
Engine tests were performed on a Rover Engine with a Bosch knock sensor fixed onto the engine.
Figure shows the data received from
the knock sensor on a screen using a
Picoscope.
Fast Fourier Transform (FFT) was
utilised to anlayse the vibration signal
and produce a frequency based signal
Graph generated by MATLAB
using ‘fft’ function depicts
various frequencies present in
the engine vibration
Project Supervisor
NEIL LARSEN
Project summary
An investigation was done on a type of
abnormal combustion called as pre-ignition
occurring in a spark ignited engine. A
detailed study on existing knock sensors and
its functions were done. Mathematical
algorithms using Fourier transforms were
developed in a software called MATLAB to
identify particular frequencies from a
random noise signal. Engine runs were
performed to collect data and these data’s
were fed into MATLAB to validate the
functionality of the algorithm. Further
research was carried out on microprocessors
to implement the algorithm so as to
counteract pre-ignition.
Project Objectives
Understand previous work done on detecting
pre-ignition by major automotive companies
Select a proper method of pre-ignition
detection.
Conduct engine tests using Engine test stand
Analyse Test results using a suitable method
Research on a suitable method to counteract
pre-ignition
Project Conclusion
Pre-ignition is an uncharacteristic
combustion occurring in an engine
combustion chamber and it is vital to provide
measures so as to prevent it from happening.
Engine tests were performed to analyse the
vibrations produced using a knock sensor.
Results from the engine tests provided
enough evidence to validate the use of Fast
Fourier Transform (FFT) to analyse the noise
signals from knock sensor.