Detecting Start of Combustion using Knock Sensor Signals
Author:
Mats Järgenstedt
Title:
Detecting Start of Combustion using Knock Sensor Signals
Abstract:
The benefits from knowing the start of combustion (SOC) in a direct
injection diesel engine are numerous. Examples are the ability to
optimize the fuel consumption versus the emissions and an increase in
diagnostic features of the injection equipment. By using feedback from
SOC it would also be possible to use less expensive electronics and
mechanics. Engine management systems of today utilize, at very best,
closed loop control of the start of injection with good
precision. However, it is the combustion that produces power and
emissions and since the delay between the start of injection and the
start of combustion varies with several factors, it would be much
better to control SOC.
A new technique for detecting start of combustion by knock signal
evaluation is described. The method is based on measurements from
widely used and inexpensive knock sensors which measure a knock
signal. The signal is thereafter band pass filtered, the envelope of
the resulting signal is calculated and finally compared to a threshold
expressed as a percentage of the maximum value of the envelope. SOC is
said to occur when the envelope exceeds the threshold.
The standard deviation of the delay between the measured start of
injection and the detected start of combustion in all experiments is
less than 0.1 crank angle degree. The method detects SOC in real time
and makes it possible to control SOC with closed loop strategy. The
closed loop control strategy makes it possible for the engine control
system to correct for changes in for example the air temperature,
moisture content, fuel quality and for errors in the accuracy of the
injectors. Thereby the differences between individual cylinders and
different engines can be minimized.
Mats Järgenstedt
2000
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Last updated: 2021-11-10
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