An Ionization Current based Cylinder Gas Pressure Estimation for Knock Detection and Control in a Single Cylinder SI Engine 2009-32-0118
The ionization current across the spark plug gap is obtained by applying a constant voltage using DC power source across the spark gap after the high-voltage discharge. The methodology involves study and comparison of different knock detection methods (cylinder gas pressure, accelerometer and ion current) through literature survey, development of analytical models (ionization current, chemical equilibrium, kinetic Nitric Oxides) to estimate crank angle resolved cylinder gas pressure from the measured values of ionization current. Model refinements and validations, development of Ignition Coil integrated DC power source and ion current measurement circuit, Transistorized Coil Ignition and microcontroller based knock controller have been carried out. Experiments have been conducted to validate the model with the reference method (cylinder gas pressure). The ion current and cylinder gas pressure signals are measured during knocking conditions and it is shown that ion current signals can be used to detect knock.
A circuit to detect ion current by using single spark plug has been developed and applied successfully. The nature of ion currents has been studied and a model has been developed to estimate cylinder gas pressure from this signal. This has been validated and applied to detect presence of knock. A microcontroller-based system with software has been developed to control the spark timing based on knock intensity. The purpose of this work is to implement it in a two wheeler small engine with a long term goal to increase compression ratio in lean burn engines with high likelihood of knock.
Davinder Kumar, A. Ramesh, M.K.Gajendra Babu, P.V. Manivannan
Department of Mechanical Engineering, Indian Institute of Technology Madras
Small Engine Technology Conference & Exposition