This research investigates two main stages of conversion of port fuel-injected engine to direct-injection. The firs one is the modification of Injection mechanism of CNG direct-injection engine. The second stage is the investigation of Hydrogen effects as an alternative gaseous additive on CNG. The Results were measured at different injection pressures (15, 20, and 25 bar) and various hydrogen enrichment as additive fuel to CNG. At the first stage, results show that compared to the Gasoline port injection system, a CNG direct-injection engine can decrease CO2 emission up to 59.5% and increase NOx emission up to 56.9%. In the second stage, when Hydrogen being used in the fuel mixture, and an increase in the injection pressure (from 15 to 25 bar) in the DI engine along with 30%HCNG applies, the amounts of engine power and torque enhanced about 5.92% and 6.55%, respectively. Also, fuel conversion efficiency increased by up to 6.87% with 25 bar of injection pressure compared to conventional system. Emission reduction up to 32.5% for CO observed in case of using 40%HCNG relative to pure CNG. NOx emission had a reverse correlation with Hydrogen concentration, it increased about 22.5% while using 40% of Hydrogen in volumetric blend HCNG.

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