Abstract
Though there are multiple viable powertrain options available for the automotive sector, those that contain internal combustion engines will continue to account for the majority of global sales for the next several decades. It is therefore imperative to continue the pursuit of novel combustion concepts that produce efficiency levels significantly higher than those of current engines. Introducing high levels of dilution in spark ignited (SI) engines has consistently proven to produce an efficiency benefit compared to conventional stoichiometric engine operation. However, this combustion mode can present challenges for the ignition system. Pre-chamber jet ignition enables stable, highly dilute combustion by both increasing the ignition energy present in the system and distributing it throughout the combustion chamber. Previous work by the authors have shown that jet ignition produces 15–25% increases in thermal efficiency over baseline SI engines with only relatively minor changes to engine architecture. Lean combustion in general and jet ignition in particular represent fundamentally different engine operating modes compared to those of conventional stoichiometric SI engines. Therefore, there are some system sensitivities not present in stoichiometric engines that must be investigated in order to fully optimize the jet ignition system. Differing types and magnitudes of charge motion are incorporated in SI engines to aid with mixture preparation but the influence of charge motion over lean combustion performance, particularly in jet ignition engines, is less well understood. This study analyzes the impact that charge motion has on both pre-chamber and main chamber combustion. A 1.5 L 3-cylinder gasoline engine is outfitted with multiple intake port configurations producing varying magnitudes and types of charge motion. Pre-chamber and main chamber combustion stability and other burn parameter responses are analyzed across multiple speeds and loads, including at critical operating points such as a catalyst heating condition. The results show that there is combustion sensitivity to charge motion, resulting in >1 percentage point spread in peak thermal efficiency for the configurations tested, and that this sensitivity manifests most significantly under low ignitability conditions such as heavy dilution. These results provide guidance for future system optimization of jet ignition engines.
Highlights
Stringent global legislation of greenhouse gas emissions from the transportation sector requires a step change in internal combustion engine (ICE) efficiency
Jet ignition engine sensitivity to charge motion is first examined at condition 1, a non-knock limited part load condition (1,500 rpm, 6 bar brake mean effective pressure (BMEP))
An lowest normalized value of IMEPg (LNV) value
Summary
Stringent global legislation of greenhouse gas emissions from the transportation sector requires a step change in internal combustion engine (ICE) efficiency. A method being explored to accomplish this goal is dilute gasoline combustion (Bunce et al, 2014; Bunce and Blaxill, 2016). A major limitation in developing dilute combustion systems is the less favourable ignition quality of the mixture. This has necessitated the development of higher energy ignition sources (Quader, 1974; Yamamoto, 1999). A pre-chamber combustor is one such technology (Germane et al, 1983; Heywood, 1988; Husted et al, 2009). Pre-chamber combustion concepts have demonstrated the potential for stable main chamber combustion at high levels of dilution (Attard et al, 2010)
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