Transferability of Insights from Fundamental Investigations into Practical Applications of Prechamber Combustion Systems

Efforts to reduce CO2 emissions from spark ignition engines have driven engine development
to lean-burn or high-dilution operation, which results in high combustion variability
as well as increased unburned hydrocarbon emissions. A widely used technology
to reduce these issues are prechamber ignition systems, in which the external ignition
source is located in a separate small volume, connected to the main chamber via small
orifices. This setup allows for design of favourable ignition conditions near the ignition
source, which results in fast and repeatable early flame propagation. The pressure
increase resulting from combustion taking place inside the prechamber leads to the
ejection of jets containing hot combustion products and possibly active radicals into
the main chamber, which ignite the lean or diluted mixture; this process is often dubbed
turbulent jet ignition or TJI. The use of TJI systems in engines allows the combustion
of very lean/diluted mixtures, resulting in higher efficiencies and lower NOx emissions.
In this work we shed light into the importance of quenching for practical applications
involving turbulent jet ignition. ... mehrThis is achieved through optical investigations in a generic,
constant volume test-rig, combined with zero-dimensional (0-D) model calculations.
The 0-D model is applied to the generic setup and in real engine applications
under varying operating conditions, in order to highlight the relative importance of
quenching under the various thermochemical conditions encountered. The results indicate
that thermal quenching in the nozzle should not be expected due to the small
flame thickness under high pressure encountered in internal combustion engines. Nevertheless,
under the jet mixing conditions expected in engines, hydrodynamic quenching
due to mixing of burned products with unburned (cold) main chamber mixture can
be expected. In most engine conditions, the re-ignition process of the initially quenched
jet after their exit from the prechamber is expected to be so fast, that quenching will
not be apparent in most measurements.