Abstract
In this study, detailed investigations of scavenged prechamber engine combustion are performed experimentally in a Rapid Com-pression Expansion Machine (RCEM), which allows optical access into the main chamber. OH* chemiluminescence measurements combined with pressure measurements are used to study the effect of varying ignition timing on combustion and cycle-to-cycle varia-tions. The variation of ignition timing (pressure at ignition) showed an optimum ignition point for a given injection duration. Earlier ignition resulted in weaker but more reactive jets, coupled to increased cyclic variations. Later ignition did not significantly affect heat release rate, but increased cyclic variation.
Highlights
Efforts to reduce CO2 emissions from internal combustion engines have led to the use of natural gas as a fuel in lean-burn spark ignition engines [2]
The study undertaken involves the variation of the spark timing with respect to top dead centre (TDC), which was achieved by varying the value of cylinder pressure when the ignition is triggered
Ignition resulted in slower prechamber combustion and the emergence of possibly rich jets early in the cycle, which lead to a delayed and slower main chamber combustion due to the reduced main chamber reactivity at that time, and possibly low turbulence generation from the jets
Summary
Efforts to reduce CO2 emissions from internal combustion engines have led to the use of natural gas as a fuel in lean-burn spark ignition engines [2]. A widely used technology in these engines is prechamber ignition systems, in which the external ignition source is located in a separate small volume, connected to the main chamber via orifices [3, 17]. This setup allows the design for favorable ignition conditions near the ignition source, which result in fast and repeatable early flame propagation. The use of prechamber ignition systems in engines allows the combustion of very lean/diluted mixtures, resulting in higher efficiencies and lower NOx emissions [17]
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