Development of BS-III CNG Engine for Heavy Commercial Vehicle

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. It was observed that intake system plays an important role for homogenous mixing, thereby lambda becomes close to unity. Two type of mixer designs viz. variable venturi and fixed venturi were tried out and their effect on emission was assessed.