NumericalanalysisofAddedSyntheticGasEffectsonNaturalGasCombustioninaHomogeneousChargeCompressionIgnition (HCCI) Engine

Homogeneous Charge Compression Ignition (HCCI) engines due to reduction of NOx and soot emission and also their high flexibility in using different fuel blends, are suitable substitute for conventional diesel engines. Control of combustion initiation is the main challenge in using these engines. However, the use of natural gas as a clean fuel has always been an attractive choice for many numerical and experimental researchers. Due to high octane number of natural gas, this fuel is resistant to auto-ignition; so in order to improve ignition timing, some additives should be supplied. In this study, the effects of added reformer gas on natural gas combustion have been investigated using a multi zone thermodynamic model. Studies have been performed on the CFR engine. Also, probability distribution function for initial temperature stratificationand the effects of residual gas in the engine is considered. Some important parameters such as factors affecting start of combustion, output power, efficiency, and engine emissions have been investigated. The results show that the added synthetic gases can be an appropriate candidate for ignition timing control. Added inlet synthetic gas has a negligible effect on power and IMEP, but causes advanced ignition and increases heat release rate. With increasing heat release rate and maximum temperature, the thermal efficiency will be decreased and NOx production will be increased.