Abstract
In order to clarify the reason why the NOx emissions factor becomes higher with vehicle acceleration at intersections etc., two freight vehicles of different emission model years, equipped with EGR systems for reduction of NOx, were tested by an on-board NOx measurement system. Higher NOx emissions factors were observed at vehicle starts in lower-gear operations for each vehicle though the total NOx mass emissions of the later model vehicle were less. Larger NOx mass emissions were clearly observed in the engine operation area of lower engine speed and load in real traffic conditions though the NOx mass emissions in steady state conditions was less. NOx emissions characteristics were analyzed in view of engine torque, NOx mass emissions, and the EGR rate, and considering the rate of engine speed change. It was found that lower-gear operations made the rate of engine speed change higher and also the EGR rate lower resulting in higher NOx emissions. This seems to be one of the factors to engender the intensive NOx pollution at roadsides.
