Characteristics of Transient NO Emissions Based on the First Firing Cycle Analysis of Cold-Start 2006-01-1050
The First Firing Cycle (FFC) is very important at cold-start. Misfiring of the first firing cycle can lead to significant HC emissions and affect the subsequent cycles. This paper presents an investigation of characteristics of transient NO emissions in a small LPG SI engine with electronic gaseous injection system. To determine the optimal excess air coefficient ( λ=[A/F]/[A/F]stoic) of the first firing cycle, the emission of instantaneous NO was proposed as a useful criterion to judge if the combustion is occurred or not.
A fast response NO detector- Cambustion fNOx400, based on the chemiluminescence's (CLD) method, has been employed to measure continuous, transient emissions of NO during the first firing cycle in the exhaust port of the engine. At the same time, the transient cylinder pressure, instantaneous crankshaft speed of the engine and engine-out HC emissions were measured and recorded.
Test results show that the excess air coefficient directly influences the FFC's cylinder pressure, engine speed, HC and transient NO emissions. As the excess air coefficient is reduced from the lean misfiring limit, NO emissions increase quickly, then reduce quickly and then reduce slowly. The relationship between peak cylinder pressure and real time NO emissions can be split into 3 ranges: lean-combustion, transition and rich-combustion. Transient NO emissions can be used to identify the first occurrence of combustion (FFC) - even at the dilute combustion limit. This is because the engine emission of NO indicates the combustion occurrence in cylinder.