Numerical Investigation of Injection Strategies for an Air-Fuel Premixed Pre-chamber Engine Concept

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. [GRAPHICS] .