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The increasing interest and requirement for improved electronic engine control during the last few decades, has led to the implementation of several different sensor technologies. The process of utilizing the spark plug as a combustion probe to monitor the different combustion related parameters such as knock, misfire, Ignition timing, and air-fuel ratio have been the subject of research for some time now. The air-fuel ratio is one of the most important engine operating parameters that has an impact on the combustion process, engine-out emissions, fuel economy, indicated mean effective pressure and exhaust gas composition and temperature. Furthermore, air-fuel ratio affects the ion produced during flame kernel initiation and post flame propagation. In this paper, an investigation is made to determine the effect of air-fuel ratio on ion current, using gasoline and methane under different spark plug designs and engine operating conditions.

Most of the previous research on flame ionization in spark ignition engines applied positive polarity on the spark plug center electrode, referred to as positively biased probe. In this paper an investigation is made to determine the characteristics of the ion current signal with negatively biased probe. The factors that contribute to the second ion current peak, reported to be missing with negative polarity, are investigated. Experiments were conducted on a research single-cylinder, spark ignition engine and the negative polarity is applied by a SmartFire Plasma Ignition system. The effect of different spark plug designs and engine operating parameters on the amplitude and timing of each of the two ion current peaks is determined. The results indicated that, with negative polarity, the cathode area is one of the main factors that contribute to the amplitude of the ion current signal, particularly the second peak.

This paper outlines the development of a diesel fuel burner for Diesel Particulate Filter (DPF) regeneration. The burner utilizes the application of a dual featured ignition system that may enable a burner system to be more cost effective, reliable, and efficient than other burners or Diesel Oxidation Catalysts (DOC). The ignition system incorporates high-energy ignition and ion sensing into a single controller. These two features provide many benefits for burner applications. The high-energy ignition provides enhanced light-off characteristics while simultaneously cleaning the electrode surfaces. Ion sensing allows precise flame control through high-speed ignition and flameout feedback. Initial data has already confirmed many of these anticipated benefits.

To test the reliability of the SmartFire® ionization data as a parameter for detecting misfires, we fitted an inline-4 cylinder engine with in-cylinder pressure sensors and compared their data to that provided by ionization current sensing. The ignition circuitry was tested for its ability to recognize misfires, and for its potential to re-strike the ignition early enough in the cycle to provide smooth engine operation. Unique design features of the SmartFire ignition circuit enable the measurement of ion current as early as 300 microseconds after the initiation of the spark discharge, thereby allowing early detection of improper combustion. We compared the indicated mean effective pressure (IMEP) to the integrated ionization signal. When a misfire was measured by the IMEP, the integrated ion signal indicated the misfire as well. The ignition circuitry successfully identified the cycles with improper combustion.