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Reducing pollutant emissions of passenger car is one of the main task of manufacturers. One way to reduce emission is to operate SI engine in lean combustion with natural gas. The objectives of this work are, to investigate differences between natural gas and gasoline exhaust emissions and combustion, and then, to show the accuracy of a zero-dimensional two zones thermodynamic model for NOx predictions. Data are acquired in a 4 cylinders bi-fuel engine. With natural gasl, SI engine operates at lower ratio than gasoline leading to a reduce in NOx emission. The thermodynamic model calculates NOx emissions and time burning duration from the cylinder pressure. Typical difference between natural gas and gasoline have been found: With natural gas flame ignition duration decreases and flame propagation duration increases. An improvement of NOx formation model have been developed by locking into account cycle to cycle cylinder pressure in.

The present work is dedicated to the study of air-natural gas mixing in a model intake manifold for Natural Gas Spark ignition engine. A configuration of continuous Natural Gas injection is considered. The fuel injection located upstream the intake valve is submitted to a time varying crossflow with high acceleration and deceleration levels. A physical analysis is developed and presented. Relevant new non-dimensional numbers are established for the engine situation. With this analysis, we compute a critical diameter of injection that characterizes the sensitivity of the jet to the pulsed transverse flow. Experiment is used to check these predictions. Schlieren technique is applied in a test section to obtain instantaneous images of the injection jet phased in the engine cycle. We visualize the global behavior of the jet and consequently the mixing in the intake manifold.