<p>Lean burn natural gas engines offers low particulate emissions than diesel counterparts and provides higher efficiency when compared to stoichiometric operation. However with lean burn strategy, three way catalysts (TWC) compatibility is lost due to oxidized exhaust stream. In comparison, EGR dilution strategy can maintain compatibility with emission after treatment systems. The maximum tolerated EGR levels are limited by the combustion stability degradation resulting from poor flame speed at higher EGR fractions. Pre-chamber spark ignition (PCSI) systems, known to increase dilution tolerance in SI engines under lean conditions, was evaluated as a means to improve EGR dilution tolerance. Scavenging of residuals within the pre-chamber is typically a concern with these systems and as such studies on these systems working with various levels of EGR ratios are rare. In this work an unscavenged <i>(or unfueled, or passive) </i>PCSI system installed in a medium-duty natural gas engine is modeled using CONVERGE CFD code. Simulation results are compared against the experimental data in terms of in-cylinder pressure and heat release rates from low to high (10% to 22%)&nbsp; EGR levels. Prediction capability of two combustion models, multi-zone well-stirred reactor and a flamelet based combustion modeling approach i.e. G-equation, are compared and evaluated under these conditions within the RANS framework. It was found that the residual stratification, caused by mixing of trapped residuals with EGR constituents, coupled with turbulence levels within the prechamber affected the overall combustion behavior and induced cyclic variability.</p>

A Numerical Study on the Effects of Egr Dilution in a Pre-Chamber Ignited Natural Gas Engine

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2021/volume/85512

ASME 2021 Internal Combustion Engine Division Fall Technical Conference (ICEF2021)

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