In this study, a numerical investigation of different premixed gaseous injection
strategies was performed to understand their impact on the scavenging and
mixture formation of an air-fuel premixed pre-chamber with high exhaust gas
recirculation (EGR) operations. EGR dilution is effective for reducing coolant
heat loss, pumping work at throttled conditions, and mitigates knock at
high-load conditions, thus increasing engine efficiency. To further extend the
EGR limit of an air-fuel premixed pre-chamber engine, the effects of different
injection strategies (including timing, duration, pressure, pre-chamber volume,
and hardware) on the EGR level, trap efficiency, and parasitic loss were
determined. Regardless of injection duration and upstream pressure, injecting
too early not only increased the amount of the injected premixed gas leaking
into the main chamber but also was inefficient in reducing the EGR level in the
pre-chamber. To reduce the EGR level in the pre-chamber to a level where
successful ignition and combustion of the pre-chamber mixture is possible, the
injection timing should be delayed to be close to the ignition timing. A
premixed air-fuel injection is thus proposed to reduce the time required for
air-fuel mixing in the pre-chamber. With a delayed end of injection (EOI), both
leakage amount and EGR level were reduced compared to the cases with earlier
injection timings. The results show that an injection with 15 bar upstream
pressure, 20 CA duration, EOI of −20 CAD aTDC (ignition timing), and with guided
injection hardware for the base pre-chamber volume resulted in about 0.17% air
compression parasitic loss, over a 94% trap efficiency, at the same time
maintaining the mean EGR level in the pre-chamber below 20%, ensuring good
pre-chamber combustion. With a 50% increase in pre-chamber volume from the base
case, the parasitic loss increased by 65% (from 0.17% to 0.28% loss), indicating
a problem with a larger pre-chamber with a separate air valve and injector.
