Significant improvements in the power density and efficiency of lean-burn large gas-engines with a prechamber and their high flexibility in meeting fluctuating power requirements illustrate the potential for using these engines in stationary power generation and in the transportation sector. Since these engines have comparatively low CO2 and NOx-emissions, they are seen as a promising solution to meet stricter emission standards. However, current combustion concepts for these engines must be enhanced to improve their performance and emission behavior; simulation methods play a major role in this process. It is critical to know and understand the fundamental processes and their relationships in the prechamber and main combustion chamber; conducting detailed analyses makes this possible. Zero-dimensional methods are suitable for these analyses. Due to their shorter calculation times, they allow extensive parameter variations to be investigated. Common methods in this area are limited to calculating performance and emission related values only in the main combustion chamber. Since a considerable share of NOx-emissions from high-performance lean-burn gas-engines arise in the prechamber, it is imperative to conduct a separate thermodynamic analysis of the prechamber and its interaction with the main combustion chamber. This paper presents a zero-dimensional method with which NOx-emissions from the prechamber can be calculated separately from the emissions of the main combustion chamber. To this end, it is necessary to conduct thermodynamic analyses of both the chambers and to consider their interaction. The measurement data for development and validation of this method is provided by tests on a single-cylinder engine with separate cylinder-pressure indication for both the chambers. Based on the results of the analyses, it can be determined to what extent each of the two systems is involved in the formation of nitrogen-oxides. With knowledge of the origin of NOx-emissions, measures may be enacted that reduce total NOx-emissions.

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<div class="section abstract"><div class="htmlview paragraph">To achieve global climate goals, greenhouse gas emissions must be drastically reduced. The energy and transportation sectors are responsible for about one third of the greenhouse gases emitted worldwide, and they often use internal combustion engines (ICE). One effective way to decarbonize ICEs may be to replace carbon-containing fossil fuels such as natural gas entirely, or at least partially, with hydrogen. Cost-effective development of sustainable combustion concepts for hydrogen and natural gas/hydrogen mixtures in ICEs requires the intensive use of fast and robust simulation tools for prediction. The key challenge is appropriate modeling of flame front propagation.</div><div class="htmlview paragraph">This paper evaluates and applies different approaches to modeling laminar flame speeds from the literature. Both appropriate models and reaction kinetic calculations are considered. The most promising approaches are then combined with various approaches for turbulent combustion as the basis for determining zero-dimensional burn rates. In developing these approaches, one particular challenge is to make the models able to correctly represent flame front propagation with a 0-100% share of hydrogen in the mixture as well as consider the resulting effects. In particular, the destabilizing effects of an increasing share of hydrogen, which can be described by the Lewis number not equal to one, are examined.</div><div class="htmlview paragraph">Finally, validation of the model results involved not only classic comparison of analyzed cylinder pressure curves and other engine performance parameters but also direct comparison of measured and modeled flame front propagation based on experimental measurement data from ion current probes. The measurements were made on a single-cylinder research engine with a cylinder head equipped with ion current probes attached to the spark plug sleeve around the spark plug.</div></div>