Modeling Diesel Spray Flame Lift-Off, Sooting Tendency and NOx Emissions Using Detailed Chemistry With Phenomenological Soot Model

Abstract

A detailed chemistry-based CFD model was developed to simulate the diesel spray combustion and emission process. A reaction mechanism of n-heptane is coupled with a reduced NOx mechanism to simulate diesel fuel oxidation and NOx formation. The soot emission process is simulated by a phenomenological soot model that uses a competing formation and oxidation rate formulation. The model is applied to predict the diesel spray lift-off length and its sooting tendency under high temperature and pressure conditions with good agreement with experiments of Sandia. Various nozzle diameters and chamber conditions were investigated. The model successfully predicts that the sooting tendency is reduced as the nozzle diameter is reduced and/or the initial chamber gas temperature is decreased, as observed by the experiments. The model is also applied to simulate diesel engine combustion under PCCI-like conditions. Trends of heat release rate, NOx and soot emissions with respect to EGR levels and start-of-injection timings are also well predicted. Both experiments and models reveal that soot emissions peak when the start of injection occurs close to TDC. The model indicates that low soot emission at early SOI is due to better oxidation while low soot emission at late SOI is due to less formation. Since NOx emissions decrease monotonically with injection retardation, a late injection scheme can be utilized for simultaneous soot and NOx reduction for the engine conditions investigated in this study.

Numerical study on combustion of diluted methanol-air premixed mixtures

“…It includes the detailed H 2 /O 2 , CO, HCO, CH 2 O, CH 3 , CH 4 , CH 2 OH, CH 3 O and CH 3 OH submechanisms and shows well agreement with the experimental results of laminar flame speeds in the methanol-air flames compared with previous methanol oxidation mechanisms [21]. The applicable conditions of Li mechanism are 300-2200 K in temperature, 0.1-2.0 MPa in pressure and 0.05-6.0 in equivalence ratio.…”

An Eulerian CFD model and X-ray radiography for coupled nozzle flow and spray in internal combustion engines

“…The Lagrangian-Eulerian approach describes the gas-phase in an Eulerian manner while the liquid phase is modeled in a Lagrangian fashion with sub-models for various physical processes (such as breakup, collision, etc.). This approach together with some amount of model calibration has been a great success for modeling the spray, mixture formation, combustion, and engine-out emissions (Amsden et al, 1989;Reitz and Rutland, 1995;Senecal et al, 2003;Torres and Trujillo, 2006;Kong et al, 2007;Lucchini et al, 2009;Som and Aggarwal, 2010) over several decades. The known challenges for this model are the mesh dependency and near-nozzle dense spray assumptions.…”

Optimization study on exhaust emissions and fuel consumption in a dimethyl ether (DME) fueled diesel engine

“…This simplified chemical kinetics model consisted of sub-models, such as a low temperature/negative temperature coefficient region and a pyrolysis/oxidation of high temperature. Furthermore, the NO x formation process during the diesel and DME combustion processes was predicted using a reduced gas research institute (GRI) NO mechanism [32] with the four species (N, NO, N 2 O, NO 2 ) and nine reactions. To predict soot emissions, the two-step phenomenological soot models [33] were applied in this study, including a Hiroyasu soot formation [34] and a Nagle-Strickland-Constable (NSC) oxidation model [35] were applied.…”