Assessing the Effect of Torque Converter Losses on the NOx Emission and Engine Stability in TGDI AT Vehicle

The emission norms around the world are continuously changing and getting stringent with every revision. India is on its way to make its emission norms at par with that prevailing in the developed nations. The cold-start condition is an important factor affecting vehicle emissions from gasoline direct injection (GDI) and port fuel injection (PFI) vehicles. In this paper, the effects of change in torque converter losses on emissions are experimentally investigated in a TGDI AT vehicle. The instant engagement of the torque converter puts a sudden load on the engine and thus affects its stability. Thus, to overcome the stability issue, Engine Torque has to be simultaneously increased for smooth engagement. As a result, the likelihood of the slightly leaner air-fuel mixture in the cylinder, which results in higher NOx formation, is much greater in an AT vehicle than that of a similar MT vehicle. Additionally, the temporary ineffectiveness of motor vehicle emission controls at startup causes emission to be much higher for a short period after starting than during fully warmed, or stabilized vehicle operation. The experimental result shows that although the decrease in the torque converter losses improves NOx emission, It also affects the engine stability. Thus, To calibrate the Torque converter losses, a tradeoff between engine stability and emission has to be made. Moreover, a comparative analysis between AT and similar variant MT vehicle to understand the sole effect of torque converter on the increased NOx emission suggests that a drop of 6-8% in the NOx margin from the base is due to engagement of the torque converter.