The objective of this study was to review the previous research in the development of gaseous fuel injector for port injection CNG engine converted from diesel engine. Problem statement: The regular development of internal combustion engines change direction to answer the two most important problems determining the development trends of engines technology and in particular, their combustion systems. They were environmental protection against emission and noise, shortage of hydrocarbon fuels, specific fuel consumption and other technical and economic parameters. Approach: Several alternative fuels has been recognized as having a significant potential for producing lower overall pollutant emissions compared to diesel fuel. Natural gas, which composed predominately by identified as a leading... candidate for transportation applications among these fuels for availability, environmental compatibility and natural gas is that it can be used in conventional diesel engines. Results: Some advantages of CNG as a fuel are octane number is very good for SI engine fuel, engines can be operate with a high compression ratio, less engine emissions and less aldehydes. In the diesel engines converted or designed to run on natural gas with the port injection (sequential) or trans-intake valve-injection system, a high-speed gas jet was pulsed from the intake port through the open intake valve into the combustion chamber, where it caused effects of turbulence and charge stratification particularly at engine parts load operations. The system was able to diminish the cyclic variations and to expand the limit of lean operation of the engine. The flexibility of gas pulse timing offers the potential advantage of lower emissions and fuel consumption. There are several advantages of port injection. The better possibility CNG engine is to equalize the air-fuel ratio of the cylinders, optimization of the gas injection timing and of the gas pressure for different operating conditions. Conclusion: The fuel nozzle injector multi holes geometries development was to produce optimum fuel air mixing and increasing the volumetric efficiency of the engine that will promote a comparable engine performance and efficiency.