Use of the gas ionization signal for combustion process diagnostics in the cylinder of a spark ignition engine

Abstract

The running diagnostics of the combustion process in an internal combustion engine is essential for increasing its efficiency and to improving its performance indicators. The modern diagnostics of this process no longer concerns only measurements of fast-changing thermodynamic variables, but also measurements of other parameters allowing for its evaluation. The use of electrical or optical methods in diagnostics enables the evaluation of local process parameters, such as occurrence of the flame and its temperature distribution. Actually, there are some new methods under investigation which are proposed for this kind of diagnostic. This article focuses on demonstrating the potential for using an electric signal from the gas ionization to estimate the maximum combustion pressure in a cylinder of an SI engine. This is a comparative analysis of the gas ionization current signal in the cylinder and the fast-changing pressure at fixed operating points of a 4-stroke natural gas powered engine. The study was carried out on a one-cylinder 4-stroke SI engine equipped with a cylinder pressure recording system and monitoring of the cylinder ionization current using appropriate measuring systems. The influence of engine operating conditions on the ability to determine cylinder pressure based on the ionization current signal was analyzed. This impact assessment was analyzed statistically and a strong correlation was found between the analyzed signals. The obtained results point in the potential direction of development of this type of measuring system.

Assessment of possible use of the ionization signal for the combustion process diagnostics in a spark-ignition combustion engine powered by natural gas

“…1. Diagram of the ionization signal measuring circuit [7] Due to the ability of ions and electrons to carry electric charge, a current flow appears (ionization current) proportional to the number of ions located in the vicinity of the electrodes. The measurement resistor, connected in series, has a potential difference proportional to the current of ionization according to the Ohm's law.…”

“…This value was obtained with an ignition advance angle of 19 degrees before TDC. Fuel injection to the inlet channel was carried out at an [7] sciENcE aNd tEchNology angle of 170 degrees before TDC. The fuel dose was kept constant at q o = 16.9 mg/injection.…”

Relations between ion signal and flame propagation in cylinder of a rapid compression machine

“…The current thus obtained is called the ionization current. In the spark-ignition engine, the role of the ionization current sensor can be played by the spark plug conventionally used to ignite the mixture [4,8].…”

Selection of ion sensor operating parameters in quasi-static conditions

“…The ionization signal is used in many engine applications. Popular brands such as Mazda, Saab, BMW and Harley-Davidson [4] successfully use knock detection systems based on the ionization signal. The efficiency and fast response time of such a system has also been successfully used in Formula 1 engines [9].…”

“…The more ions and free electrons are available, the more ionization current could potentially flow in the circuit. The presence of ions in an internal combustion engine results mainly from the phenomenon of chemical and thermal ionization of gas [4]. Both phenomena strongly depend on the process temperature [6,11].…”