Detailed investigation of pre-ignition in a large spark-ignited hydrogen port fuel injected internal combustion engine by means of optical investigations on a single-cylinder research engine and 3D-CFD simulation

Hydrogen is a promising option to decarbonize energy conversion in internal combustion engines (ICE). A key limiting factor of high-load hydrogen ICE operation is the occurrence of combustion anomalies, including pre-ignition, backfiring into the intake manifold and knocking combustion. The existing literature indicates that there currently exists no generally accepted conceptual model that is able to explain the occurrence of all combustion anomalies for hydrogen-fueled internal combustion engines. This publication is intended to help fill this research gap based on experimental investigations on a single-cylinder research engine (SCE) with hydrogen port fuel injection and spark ignition in the 3 dm 3 displacement per cylinder class and related 3D-CFD simulation work. To enable in-depth combustion analysis and particularly to identify the origin and root cause of pre-ignition, the SCE was instrumented with AVL List GmbH’s “Visiolution” system, an advanced optical instrumentation that relies on fiberoptic sensors in the combustion chamber. Different types of pre-ignition including backfire, early and late pre-ignition could be provoked during engine operation. Backfire and early pre-ignition were found to originate from the piston-liner edge at the “bottom” of the combustion chamber and tend to occur in specific areas at the piston circumference where comparatively rich local mixture prevails. Mixture homogeneity may be key to reduce the risk of backfire and early pre-ignition to occur. The locations of origin suggest that various ignition sources emerging from the piston top land crevice such as hot residual gases or reactive species (e.g. due to reverse blowby) are possible. Late pre-ignition events (i.e. shortly before ignition timing) occurred in large numbers with a random spatial distribution in the combustion chamber and appear to be mostly related to lubricant oil droplet combustion. Future research must study the impact of mixture homogeneity on pre-ignition and strive to better understand the root causes for the underlying processes that provide the required ignition energy.