The origins of ionization in the exhaust gases of spark ignition engines

✍ Scribed by D. Williams; P.J. Shayler; N. Collings

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 709 KB
• Volume: 81
• Category: Article
• ISSN: 0010-2180
• DOI: 10.1016/0010-2180(90)90034-o

✦ Synopsis

As part of a study of the ion current signals from a Langmuir-type electrostatic probe fitted in the exhaust manifold of a spark ignition engine, the origins of the exhaust gas ionization have been investigated. The ionization is created by chemi-ionization during hydrocarbon oxidation reactions, but the ions rapidly recombine to form neutral species. This work addresses the question of whether the exhaust ionization is predominantly the decayed level from the main combustion reactions, or results from the oxidation of residual fuel components late in the combustion cycle, particularly within the exhaust port. By the application of Langmuir probe theory to the ion current signals from the exhaust, and from a similar probe fitted within the combustion chamber, the exhaust ion concentrations have been calculated to lie in the range 101a-10 Is m -3. These values are consistent with the predictions of a simple model using existing data for ion production and rates of decay. The calculations show that the main combustion reactions can account for the entire ion concentration remaining in the exhaust gases. The nature of the ionization from residual hydrocarbon reactions was studied by both positive and negative probe bias while air and oxygen were injected into the exhaust manifold to promote further reactions. These results showed that the normal exhaust ion concentrations cannot be generated from reactions of this type, confirming the main combustion reactions as the dominant source.