Abstract Fuel injection pressures in diesel engines play an important role in engine performance and emissions obtaining treatment of combustion. In the present diesel engines such as common rail diesel engine, the injection pressures can be increased about 1500–2000 bars. In this study, the effects of injection pressure on bsfc and exhaust emissions have been investigated. Experiments have been performed on a direct-injection turbocharged diesel engine. Emissions and engine bsfc values have been measured in 13 speed and load conditions based on ECE-R49 test by changing injection pressure from 200 to 300 bars. Results show that higher injection pressure reduces HC and bsfc, due to better mixing, causes faster combustion. Also it is found that NOx and CO2 are not substantially changed by injection pressure. Smoke behaves differently due to injection pressure. This is because of injection pressure effect on ignition delay and exhaust temperature. These parameters affect re-burning soot at the late combustion phase. In term of emissions control in turbocharged diesel engine, this research work proposes variable injection pressure in stead of constant injection pressure.

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