Search Results

Two main properties distinguish the structure of a turbulent flame from that of a laminar flame: ionization current of high intensity and high burning velocity. The first of these two quantities was directly measured in the combustion chamber of a typical European spark ignition engine by means of a Langmuir's probe, while the second was calculated starting from the pressure-time history measured with a piezoelectric transducer. The experimental results show the strong influence of the initial flame propagation on the type of the subsequent combustion during the rest of the cycle. The mathematical elaboration of the experimental data showed that the flame propagation mechanism is consistent with the hypothesis that turbulent combustion is caused by successive self-ignitions, as suggested by Russian authors.

The detection of cyclic dispersion, knocking, preignition, misfiring and other phenomena related with abnormal combustion in spark ignition engines has been extensively studied in the past. The transducers most commonly used detect pressure and/or ionization in the combustion chamber. By employing transducers that detect engine head movement it has been possible to examine these phenomena without particular engine modifications, thus enabling measurements to be made in commercial cars. These transducers are used in conjunction with electronic apparatus that gives quantitative measurements of the extent of the abnormal combustion. Results obtained by these means are reported with particular emphasis on high speed knock (a problem presently encountered with European cars), preignition and misfiring. On the basis of the test results a technique is developed utilizing the electron scanning microscope to recognize a posteriori if the piston failure is due to knock or preignition.

Carbonaceous material associated with potent carcinogens such as 3-4 benz(a)pyrene (BaP) and other polynuclear aromatic (PNA) hydrocarbons constitutes by far the greatest part of the particulate found in the exhaust gases of an internal combustion engine. The probable precursors of carbon particles are radicals formed in the incomplete combustion zone while their nucleation is made possible by ions originating in the flame. Ion current instantaneous values were measured by means of a modified Langmuir's probe, thus calculating thickness and speed of the flame in an engine cylinder. Relations between ion current and collected soot weight were examined. Fuel quality and additive influences over carbon and PNA formation were obtained.