Pre-Chamber Ignition as a Key Technology for Highly Efficient SI Engines – New Approaches and Operation Strategies

Authors

Dipl.-Ing. M. Sens, Dr.-Ing. E. Binder, Dipl.-Ing. A. Benz, Dr. rer. nat. L. Krämer, Dipl.-Ing. K. Blumenröder, Dipl.-Ing. M. Schultalbers, IAV GmbH, Berlin / Gifhorn

Year

2018

Print Info

Fortschritt-Berichte VDI, Series 12, No 807

Summary

This paper describes the potential of using a passive and active pre-chamber system in a conventional spark-ignition (SI) engine.
Preliminary investigations involved 3D CFD simulation to analyze the influence of relevant design parameters on the fluid mechanics and thermodynamic properties of the pre-chamber. Simulation provided the basis for deriving promising layouts. The pre-chamber insert designed deliberately departs from existing designs to provide a high level of flexibility in varying different geometric parameters. New operating strategies have also been introduced and examined, such as active thermal pre-chamber conditioning which helps to improve low-load and cold-starting capability. Instead of using all-liquid fuel, an active pre-chamber concept with low-pressure injection of a fuel/air mixture was also capable of achieving a significant reduction in chemical losses inside the pre-chamber.
Optimizing the layout of a passive pre-chamber significantly reduces the knock tendency during high-load operation and makes it possible to increase the compression ratio by approximately two units. Fuel consumption in the relevant map range is reduced by 2-4%. In the WTLP cycle, fuel consumption is improved by approximately 3%. Pressure pulsations accompanying pre-chamber application make it harder to identify knock which is why it was necessary to define a new knock criterion developed in the course of the project.
Analyzing the loss chain of the passive pre-chamber reveals two influencing factors that are shown to be particularly relevant. At low load additional wall heat losses caused by the additional pre-chamber wall surface prevail. At higher load instead, additional wall heat losses result from greater turbulence in combustion chamber wall proximity caused by jets deeply penetrating the chamber.
The new approach by IAV involving low-pressure air/fuelmixture injection into the pre-chamber shows significant potential for increasing the air/fuel ratio in homogeneous-lean operation at air/fuel ratios of 2.2 and beyond, this being accompanied by relatively low chemical losses. During homogeneous-lean operation with ultra-low specific NOx emissions of approx. 0.3 g/kWh, this was able to improve fuel consumption by approx. 10% over stoichiometric operation.