Relations among NOx, Pressure Rise Rate, HC and CO in LTC Operation of a Diesel Engine

This study aims to determine strategies for improving the relations between the pressure rise rate and emissions of nitrogen oxide (NOx), hydrocarbons (HC), and carbon monoxide (CO) in low temperature combustion (LTC) operation of a diesel engine. For this purpose, an analysis was conducted on data from experiments carried out using a single-cylinder direct-injection diesel engine with variation in the injection quantity, injection timing, exhaust-gas recirculation (EGR) rate, injection pressure, injection nozzle specification and combustion chamber geometry. The results reveal that the pressure rise rate and NOx exhibit similar tendencies when varying injection timing and EGR rate, which is opposite to CO and total HC (THC) emissions, regardless of injection quantity. When the injection quantity is increased, smoke emission becomes problematic in the selection of the injection timing. Change in the injection pressure and nozzle orifice size resulted in no significant improvement of NOx-pressure rise rate-CO-THC relation. The proper combination of combustion chamber and spray direction offers an improvement; however, different combinations are required for different injection quantity. Two-stage injection is advantageous, because it provides a significant reduction in the pressure rise rate and additional combustion control factors such as injection quantity ratio, and first- and second-injection timings contribute to maintaining low level emissions.