Ignition Improvement for Homogeneous Diluted Gasoline Combustion

Paper #:
  • 2017-01-2244

  • 2017-10-08
The fuel efficiency improvement of gasoline engines can be achieved through lean burn and/or exhaust gas recirculation (EGR). However, the ignition of a diluted cylinder charge tends to be more diverged, owing to the slower ignition and combustion processes. The operable range of diluted combustion in gasoline engines is often limited, e.g. with lambda below 2.0 or EGR rate lower than 30%, owing to the deterioration in mixture ignitability and severe cyclic variations. In addition, the adoption of intensified cylinder charge motion requires further optimizations of ignition system, including the igniter geometric configurations and the temporal modulations over ignition energy delivery and spark discharge pattern. In this work, a variety of spark ignition approaches are investigated to improve the ignition of diluted gasoline engine under homogeneous mixture mode. A spatially distributed spark arcing control is realized based on a three-pole igniter. The spark gaps can be individually energized by the attached ignition coils, in either simultaneous or alternating mode. The sparking current can be modulated to supplement the ignition energy on demand. A pre-chamber spark plug structure is used to generate flame jet for accelerating the early stage combustion. The experimental results on a single-cylinder engine show that on the basis of similar total spark energy levels, the spark distribution can significantly shorten the ignition delay and reduce the cyclic variation. Moreover, the operable limits for lean burn and EGR dilution are extended substantially compared to the conventional spark ignition. The pre-chamber spark plug can shorten the ignition delay and reduce the cyclic variations, but it is less tolerant to dilution because of the less effective scavenging in the vicinity of spark gap. An optimized pre-chamber structure shows improvement of ignitability for the diluted mixtures.
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