The potential of gasoline fueled pre-chamber ignition combined with elevated compression ratio 2020-01-0279
A challenge in today’s automotive combustion research is to increase the thermal efficiency and to meet ever more stringent emission regulations at the same time. In this study, a single cylinder research engine is equipped with a tailored pre-chamber ignition system and operated at two different compression ratios, namely 10.5 and 14.2. Different pre-chamber design variants are evaluated considering both unfueled and gasoline-fueled operation. As for the latter, the influence of the fuel amount supplied to the pre-chamber is discussed.
Due to its principle, the pre-chamber ignition system increases combustion speeds by generating enhanced in cylinder turbulence and multiple ignition sites. This property proves to be an effective measure to mitigate knocking effects. It is shown that less spark retard compared to conventional spark ignition allows to exploit the efficiency benefit of elevated compression ratios also in high load operation for stoichiometric mixtures. Furthermore, auxiliary fueling of the pre-chamber enables ultra-lean combustion (λ=2.0) with very low NOx emission levels. Apart from decreased throttling losses lean burn assists to further suppress knocking in case of elevated compression ratios. Finally it is demonstrated that the combination of ultra-lean combustion and elevated compression ratio leads to a significant improvement of the indicated efficiency with peak values of about 43%. Higher PN emissions in low load and increased heat losses remain challenges of the used pre-chamber ignition system.
Andreas Stadler, Henning Sauerland, Martin Härtl, Georg Wachtmeister
Technische Universitat Munchen, Hitachi Europe GmbH