Assessment of the ignition system requirement on diluted mixture spark engines 2020-01-1116
To face the new challenges, spark ignition engines are evolving following some strategies and technologies. Between them, alternative combustion processes based on the dilution of the homogeneous mixture, either with fresh air or with EGR, are being explored. In higher or lower extent, these changes modify in-cylinder thermodynamic conditions during the engine operation (pressure, temperature and gas composition) thus having a direct impact on the spark ignition system requirements that will have to evolve to become more reliable and powerful.
In this framework, an experimental study on the effect of the key in-cylinder conditions on the ignition system performance has been carried in a single-cylinder SI research engine. The study includes EGR, lambda and energizing time sweeps to assess the behavior of the engine in different operating conditions. Furthermore, various IGBT and spark plugs have been tested to check out the influence of these components on the ignition process at high diluted mixtures. Conclusions show that diluted mixtures (with EGR or lambda), even though they require more spark energy to achieve a stable combustion, have a benefit on efficiency providing that the combustion propagates adequately. However, at high diluted conditions the combustion is compromised, so two different approaches were investigated to improve it. Whilst it was checked that increasing the clamping value of an IGBT does not imply necessary a better combustion in all scenarios, the increment of the electrodes gap of the spark plug would require higher clamping voltage at the IGBT, and it had a benefit at very high diluted mixtures providing that the rest of components, in particular the coil, are adequate.
Santiago Molina, Jaime Martin, Ricardo Novella, Josep Gomez-Soriano, Jose Padilla
Universitat Politecnica de Valencia, Littelfuse