Lean Burn Natural Gas Engine R&D

Oak Ridge National Laboratory

关键词: Natural Gas;    Ornl;    Breakdown;    Cameras;    Magnetic Fields;   

DOI  :  10.2172/940371
RP-ID  :  ORNL96-0260
RP-ID  :  DE-AC05-00OR22725
RP-ID  :  940371

美国|英语

来源: UNT Digital Library

【 摘 要 】

The primary objective of this cooperative research is to develop and verify models of internal combustion engine spark ignition devices in order to improve combustion chamber fuel ignition characteristics and to improve spark plug durability. As a direct result of this joint research, a novel spark plug design was improved. A theory of spark arc motion was developed that explains experimentally observed effects not explained by other published theories. The knowledge developed by this research will be used to further improve spark plugs as well as improve the ignition process in a combustion chamber. The predictive models developed here are compared with experimental measurements, including high-speed photographs, of the spark as it translates across the gap. Two different spark plug configurations were investigated: the conventional or J-gap plug, and a novel spark ignition device (the FANG plug) invented by Cummins, Inc., the CRADA partner. A description of the physics of arc dynamic motion in a spark plug gap, including the effects of an imposed transverse magnetic field, appears here in Appendix A as a result of the analytical effort. The theory proposed here does explain experimentally observed effects not completely explained by other research publications appearing in the scientific literature. These effects are due to pressure and ion, electron, and electrode interactions. A dominant mechanism for electrode erosion is presented for both spark plug configurations. Reversing the polarity of both types of spark plugs has verified this proposed erosion mechanism, according to data collected at Cummins. An extensive series of experiments measured the arc position, voltage, and current as a function of time during the approximately 2 millisecond spark discharge. FANG plug data, obtained with the fast-framing camera experimental apparatus operating at 200,000 frames per second, are presented that show the transverse arc velocity varying directly as the inverse square root of the elapsed time since arc initiation. At the request of Cummins, experiments were performed on three conventional spark plugs identical in design and having the same spark gap, but differing as follows: one was new, another had been used in an engine, and the third was new but had been sandblasted to simulate a used plug. Cummins had observed that only the used plug required a significantly higher breakdown voltage. Experiments at ORNL indicated that the used plug had a significantly higher breakdown voltage confirming the Cummins observations (although the sandblasted plug also exhibited a higher breakdown voltage than the new plug but lower than the used plug), and thus an apparent increase of the arc breakdown voltage results as the plug ages in use. Further analysis of this phenomenon is warranted.