The Novel CNG Direct Injection (CNG-DI) in Spark Ignition Engine: A Technical Review

Compressed Natural Gas (CNG) stands out as one of the most precious alternative fuels well known for its clean-burning attributes and an impressive high-octane number. In contemporary automotive industries, The Port Injection (CNG-PI) system was predominantly served as the basic mechanism for CNG injection in past era. In contemporary automotive industries, the Sequential Injection (CNG-SI) is used in all MPFI engine for its better compatibility which enhances driving comfort. However, this paper pioneers an innovative paradigm by introducing a novel concept called CNG-Direct Injection (CNG-DI), wherein CNG is injected directly into the combustion chamber during compression stroke. In the realm of Spark Ignition (SI) engines, CNG-DI technology yields a substantial enhancement in volumetric efficiency, subsequently bolstering combustion efficiency. The CNG-DI technology particularly remarkable as it enabling of exceptionally lean air-fuel mixtures within the engine operating condition leading to substantial reductions in the fuel consumption. Implementing CNG-DI necessitates specific modifications to the engine, with the cylinder head requiring alteration to accommodate a specialized gas injector which strategically positioned near the spark plug. The coordination between the spark plug, gas injector, and a timer device is pivotal to the success of this system. Furthermore, a well-integrated gas metering system interfaces with the CNG storage tank, ensuring precise control over the injection process. This paper serves as a comprehensive technical introduction to the CNG-DI system, offering an insightful comparison with traditional Port Injection (PI) and sequential injection (SI) methods.