A Study Of Specificity Mechanism Of HC And CO Emissions In Low And High Temperature Two-stage Combustion

In the early study, reasonably matched injection interval between two injectionstages could realize the new combustion model to simultaneously reduce NOx andsmoke emissions; But the concentration of HC and CO in exhaust exceeded thetraditional combustion pollutants several times.Too much HC and CO would not onlybeyond the harmful emissions standards but also lead thermal efficiency to drop.Therefore, the study of the generation mechanism of HC and CO and the influencingfactors become the research focus.This research is based on experiment on a turbocharged and intercooledcommon rail diesel engine and supplemented by simulation calculation. Reasonablymatched combustion boundary condition, split two-stages combustion into two singlecombustion stages——LTC and high temperature combustion, adjust the injectionparameters, and contrast all these three combustion models. Discuss the formationmechanism of HC and CO in two-stage combustion. Changing the injectionparameters and the intake boundary conditions, discuss the influencing factors of HCand CO.1. Reasonably matched combustion boundary condition, the single LTC andhigh temperature combustion can separately characterize the first stage andthe second stage of two-stage combustion, so it is feasible to use splittingtwo-stage combustion to study specificity mechanism of HC and CO.2. CO emission of two-stage combustion is much lower than the single LTC,soduring two-stage combustion CO emission generated in1st combustionstage oxidized in2nd combustion stage; there’s a great impact on generationof CO emission when main injection parameters and inlet boundaryconditions changed: CO emission was significant deteriorated whileincreasing main injection quantity or being ahead of injection timing, andincreasing inlet temperature or being a flow boundary condition.3. HC emission was derived from fuel hit the wall in1st stage, parts of mixtures unburned and residual unburned fuel mixture in end of2nd combustion stage.HC emission generated in both two combustion stages, and affected mainlyby main injection timing，inlet temperature and mass flow: HC emissiondecreased as injection timing being close to TDC (the timing intervalbetween pilot and main injection was shortened) and raising inlettemperature with high main injection quantity; properly decreasing inlet massflow could effectively reduce HC emission.4. HC emission came into constant in LTC combustion, and there’s little effectby injection timing and quantity.5. NOx emission increased when inlet temperature brought up or inlet massflow decreased. therefore, adjusting inlet boundary conditions to optimize HCand CO emission would be limited by NOx emission.