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Natural gas engines are finding wider applications in automobiles due to environmental and operating economics reasons. These applications include add on fitment in gasoline vehicles as well as replacement of diesel engines. In case of replacement of diesel engines, the gas engines are expected to have matching power curve. Typically the performance of an engine is characterized by following three parameters- Max Power, Max Torque, Low end Torque. Through engine design and optimization of engine these parameters can be matched to diesel engine. Then fly-up speed of the engine remains under consideration, which means the second half of engine power curve that is between Max Power speed point and fly-up speed. The present article deals with shaping of the Power-torque curve of an engine beyond Max Power point. The technique used here for Power Curve shaping is controlled leaning operation.

In this paper, the results obtained during the optimization of the dedicated CNG 6-Cylinder naturally aspirated engine are described with the optimization strategy. Most of the diesel engines after conversion to CNG engines are having high valve overlap leading to high HC emission along with less fuel economy and high swirl leads to reduced volumetric efficiency. These issues were examined in detail and experimentation was carried out to assess the effect of low swirl thereby resulting in high flow leading to increase in volumetric efficiency and reduced emissions. The engine variables optimized for CNG operation were the engine compression ratio, ignition timing, spark plug selection, catalytic converter loading, design of first stage regulator with improved heating circuit and second stage pressure regulators, mixer venturi size, power screw setting, and intake/ exhaust system geometry.