Intake air heating strategy to reduce cold-start emissions from diesel engines

Diesel engine cold-start performance is influenced by the ambient temperature conditions, engine design, fuel, lubricant and engine operating conditions. This paper investigates the potential of air heating strategy in reducing the particulate emissions from the latest generation of turbocharged direct-injection diesel engines at very cold ambient temperature conditions. New European Driving Cycle (NEDC) tests were conducted at -7 degrees C ambient temperature conditions for the different intake air temperatures. Intake air heating reduced hydrocarbon emissions by 35 and 55% and nitrogen oxides emissions by 8 and 10% for intake air temperatures of 5 and 15 degrees C, respectively, during the cold-start phase of the emission driving cycle. The cold-start phase of the NEDC cycle accounted for 1/4 of the total particulates, and the use of intake air heating reduced its proportion to 1/5. More than 50% of the particulates are less than 23 nm in diameter for all the intake air temperature conditions, and the intake air heating reduced the particulate number concentration significantly. The surface area of accumulation mode particles was higher than that of the nucleation mode, and the total particle surface area decreased with the intake air heating.