An experimental study on quenching crevice widths in the combustion chamber of a spark-ignition engine

Abstract

Hydrocarbon (HC) emissions from spark-ignition engines are now a major environmental problem in many cities of the world. It is difficult to reduce HC emissions during engine warm-up because the catalysts do not work well at low temperatures. The sources of unburned HCs from spark-ignition engines seem to be crevices in the combustion chamber, oil layer, deposits, and quench layer on the cylinder wall surfaces. Single-surface and two-surface flame quenching (crevice) play a large role in generating unburned HCs. Two-surface flame quenching distances (quenching crevice width) in the combustion chamber of a sparkignition engine were investigated using an ion probe capable of detecting flame arrival at a narrow width. The crevice width could be controlled precisely. Because engine combustion has cycle-by-cycle fluctuations, quenching crevice widths were estimated by the statistical analysis. It was defined as the width when the ion detector could detect flame arrival in 50 of 100 cycles. The effects of the mixture equivalence ratio, exhaust gas recycle (EGR) rate, ignition timing, charging efficiency, and combustion chamber wall temperature on the quenching crevice width were investigated. HC emissions in the exhaust port, cycle-by-cycle combustion fluctuation, and temperature of a quenching plate of the ion probe in the combustion chamber were also estimated in the experiments. The quenching crevice width was relatively uniform at the surface of the combustion chamber except in the area close to the ignition spark plug and end gas. The quenching crevice width increased with leaner mixture ratio, larger EGR rate, lower charging efficiency, greater ignition timing, and lower wall temperature.