Experimental Investigation of Transient Emissions (HC and NOx) in a High Speed Direct Injection (HSDI) Diesel Engine

The experiments were conducted by increasing torque at constant speed and by increasing speed at constant torque, in conventional diesel combustion regions. The emissions from the two locations are compared. The transient effects of Exhaust Gas Recirculation (EGR) rates and injection timing on HC and NOx are described and the effects of linear and step load change on emissions are compared. Base EGR was set with an EGR valve on the engine; the position of the valve was then held constant throughout the transient. The pressure history in one of the cylinders was measured as well.

The results show that peak emissions of NOx occurred when a step load change was applied for constant speed and constant torque cases at low EGR levels, but there were no evident step load change effects on NOx when higher EGR levels were used. NOx emissions were very sensitive to transient operation of changing injection timing and EGR rates for constant speed and constant torque cases. The HC measurement showed little sensitivity to transients when the EGR valve was closed. The HC emission sensitivity to transients increased dramatically when EGR rate was increased. It should be noted that injection timing and EGR rate affected engine torque and speed for a constant quantity of fuel injected.