High demands are placed on large gas engines in the areas of performance, fuel consumption and emissions. In order to meet all these demands, it is necessary to operate the engine in its optimal range. At high engine loads the optimal operation range becomes narrower as the engine comes closer to the knocking or to the misfire limit. The ambient conditions are of increasing importance in this range of operation. Variations in humidity influence the engine’s burn rate characteristics. An increase in humidity reduces the burn rate and increases the combustion duration. This increase in combustion duration has the same effect as retarding the time of ignition. Thus the thermal efficiency is reduced. Additionally, the engine is more likely to misfire as humidity increases. The cylinder temperature affects the engine fuel efficiency, knocking, exhaust gas temperature and particularly NOx emission. An increase in manifold air temperature results in higher NOx emission, heat transfer and knocking tendency. To avoid knocking, the time of ignition must be retarded resulting in lower engine efficiency. In this paper the effects of changes in humidity and temperature of the intake air on engine performance were examined in a lean burn pre-chamber natural gas engine. Tests on a single cylinder research engine were carried out. Effects on knocking and misfire limit, NOx emissions and fuel consumption were investigated depending on engine load. The interpretation of the results was supported by an extended analysis of losses.
LDM COMPACT is a methodology, which permits the development of highly efficient combustion concepts for non-natural gas (NNG) engines without extensive testing on a multi-cylinder engine as well as tailor-made engine solutions for the special characteristics of NNG (LDM stands for LEC Development Methodology). Starting with a description of the baseline LDM, which incorporates the general approach for efficient engine development, this paper introduces the improved approach of LDM COMPACT and outlines each of the required steps, i.e., the preselection and basic design of essential engine parameters based on simulation, fundamental experiments on special test rigs, and experimental optimization of the concept on a single cylinder research engine. The fundamentals and main innovative features of the methodology are discussed. Two recent development projects (combustion of blast furnace gas and combustion of flare gases) are provided as examples of its application. In these examples, extensive use of simulation to evaluate different engine configurations permitted a significant share of optimization work to be completed in advance. The pre-optimized concepts were tested and validated on a single cylinder research engine. By applying LDM COMPACT, it was possible to develop the combustion concepts in a short amount of time and implement them into the multi-cylinder engine directly on-site.
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