Improving Cold Start and Transient Performance of Automotive Diesel Engine at Low Ambient Temperatures 2016-01-0826
Ambient temperature has significant impact on engine start ability and cold start emissions from diesel engines. These cold start emissions are accounted for substantial amount of the overall regulatory driving cycle emissions like NEDC or FTP. It is likely to implement the low temperature emissions tests for diesel vehicles, which is currently applicable only for gasoline vehicles. This paper investigates the potential of the intake heating strategy on reducing the driving cycle emissions from the latest generation of turbocharged common rail direct injection diesel engines at low ambient temperature conditions. For this investigation an air heater was installed upstream of the intake manifold and New European Driving Cycle (NEDC) tests were conducted at -7°C ambient temperature conditions for the different intake air temperatures. Intake air heating reduced the cranking time and improved the fuel economy at low ambient temperatures. Intake air temperatures of 5° and 15°C reduced HC emissions by 40% and 65%, and NOx by 8.5% and 10%, respectively compared to that of at -7°C in the first part of NEDC. The instantaneous emission values were almost close to each other during the later stages of the NEDC cycle and followed the similar trend. Relatively higher intake air temperatures, reduced the diameter and number count of particles and the particulates of 10-23 nm size is accounted for ∼45% for the all intake air temperature conditions. The particle number for the first part of NEDC was ∼25% of the total cycle for the intake air temperatures of -7°C and was reduced to ∼20% with intake air heating. The particulate mass for the first stage of the NEDC cycle was ∼20% of that of NEDC at -7 °C whereas it was reduced to 12-14% of that of NEDC at -7 °C with the intake air heating. The intake heating improved the engine cold start performance as well as reduced the gaseous and particulate emissions significantly over the NEDC at low ambient temperatures.