Effects of ambient methanol on pollutants formation in dual-fuel spray combustion at varying ambient temperatures: A large-eddy simulation

In dual-fuel compression ignition engines, a high-reactivity fuel, such as diesel, is directly injected to the engine cylinder to ignite a mixture of low-reactivity fuel and air. This study targets improving the general understanding on the dual-fuel ignition phenomenon using zero-dimensional homogeneous reactor studies and three-dimensional large eddy simulation together with finite-rate chemistry. Using the large eddy simulation framework, n-dodecane liquid spray is injected into the lean ambient methane–air mixture at [Formula: see text]. The injection conditions have a close relevance to the Engine Combustion Network Spray A setup. Here, we assess the effect of two different chemical mechanisms on ignition characteristics: a skeletal mechanism with 54 species and 269 reaction steps (Yao mechanism) and a reduced mechanism with 96 species and 993 reaction steps (Polimi mechanism). Altogether three ambient temperatures are considered: 900, 950, and 1000 K. Longer ignition delay time is observed in three-dimensional large eddy simulation spray cases compared to zero-dimensional homogeneous reactors, due to the time needed for fuel mixing in three-dimensional large eddy simulation sprays. Although ignition is advanced with the higher ambient temperature using both chemical mechanisms, the ignition process is faster with the Polimi mechanism compared to the Yao mechanism. The reasons for differences in ignition timing with the two mechanisms are discussed using the zero-dimensional and three-dimensional large eddy simulation data. Finally, heat release modes are compared in three-dimensional large eddy simulation according to low- and high-temperature chemistry in dual-fuel combustion at different ambient temperatures. It is found that Yao mechanism overpredicts the first-stage ignition compared to Polimi mechanism, which leads to the delayed second-stage ignition in Yao cases compared to Polimi cases. However, the differences in dual-fuel ignition for Polimi and Yao mechanisms are relatively smaller at higher ambient temperatures.

Download Full-text

Large eddy simulation of n-heptane/syngas pilot ignition spray combustion: ignition process, liftoff evolution and pollutant emissions

Energy ◽

10.1016/j.energy.2021.121080 ◽

2021 ◽

pp. 121080

Author(s):

Shenghui Zhong ◽

Shijie Xu ◽

Xue-Song Bai ◽

Zhijun Peng ◽

Fan Zhang

Keyword(s):

Large Eddy Simulation ◽

Pollutant Emissions ◽

Spray Combustion ◽

Ignition Process ◽

Eddy Simulation ◽

Large Eddy

Download Full-text

Hot surface ignition of a wall-impinging fuel spray: Modeling and analysis using large-eddy simulation

Combustion and Flame ◽

10.1016/j.combustflame.2021.02.025 ◽

2021 ◽

Vol 228 ◽

pp. 443-456

Author(s):

Danyal Mohaddes ◽

Philipp Boettcher ◽

Matthias Ihme

Keyword(s):

Large Eddy Simulation ◽

Fuel Spray ◽

Modeling And Analysis ◽

Hot Surface Ignition ◽

Eddy Simulation ◽

Surface Ignition ◽

Large Eddy ◽

Hot Surface

Download Full-text

Simulating Flame Lift-Off Characteristics of Diesel and Biodiesel Fuels Using Detailed Chemical-Kinetic Mechanisms and Large Eddy Simulation Turbulence Model

Journal of Energy Resources Technology ◽

10.1115/1.4007216 ◽

2012 ◽

Vol 134 (3) ◽

Cited By ~ 28

Author(s):

Sibendu Som ◽

Douglas E. Longman ◽

Zhaoyu Luo ◽

Max Plomer ◽

Tianfeng Lu ◽

...

Keyword(s):

Large Eddy Simulation ◽

Turbulence Model ◽

Turbulence Models ◽

Chemical Kinetic ◽

Spray Combustion ◽

Eddy Simulation ◽

Large Eddy ◽

Kinetic Mechanisms ◽

Lift Off ◽

Biodiesel Fuels

Combustion in direct-injection diesel engines occurs in a lifted, turbulent diffusion flame mode. Numerous studies indicate that the combustion and emissions in such engines are strongly influenced by the lifted flame characteristics, which are in turn determined by fuel and air mixing in the upstream region of the lifted flame, and consequently by the liquid breakup and spray development processes. From a numerical standpoint, these spray combustion processes depend heavily on the choice of underlying spray, combustion, and turbulence models. The present numerical study investigates the influence of different chemical kinetic mechanisms for diesel and biodiesel fuels, as well as Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) turbulence models on predicting flame lift-off lengths (LOLs) and ignition delays. Specifically, two chemical kinetic mechanisms for n-heptane (NHPT) and three for biodiesel surrogates are investigated. In addition, the renormalization group (RNG) k-ε (RANS) model is compared to the Smagorinsky based LES turbulence model. Using adaptive grid resolution, minimum grid sizes of 250 μm and 125 μm were obtained for the RANS and LES cases, respectively. Validations of these models were performed against experimental data from Sandia National Laboratories in a constant volume combustion chamber. Ignition delay and flame lift-off validations were performed at different ambient temperature conditions. The LES model predicts lower ignition delays and qualitatively better flame structures compared to the RNG k-ε model. The use of realistic chemistry and a ternary surrogate mixture, which consists of methyl decanoate, methyl nine-decenoate, and NHPT, results in better predicted LOLs and ignition delays. For diesel fuel though, only marginal improvements are observed by using larger size mechanisms. However, these improved predictions come at a significant increase in computational cost.

Download Full-text

Effect of Turbulence-Chemistry Interaction on Spray Combustion: A Large Eddy Simulation Study

10.4271/2019-01-0203 ◽

2019 ◽

Author(s):

Junqian Cai ◽

Tianyou Wang ◽

Ming Jia ◽

Kai Sun ◽

Zhen Lu ◽

...

Keyword(s):

Large Eddy Simulation ◽

Simulation Study ◽

Spray Combustion ◽

Eddy Simulation ◽

Large Eddy

Download Full-text

Large Eddy Simulation of High Reynolds Number Nonreacting and Reacting JP-8 Sprays in a Constant Pressure Flow Vessel With a Detailed Chemistry Approach

Journal of Energy Resources Technology ◽

10.1115/1.4032901 ◽

2016 ◽

Vol 138 (3) ◽

Cited By ~ 9

Author(s):

Luis Bravo ◽

Sameera Wijeyakulasuriya ◽

Eric Pomraning ◽

Peter K. Senecal ◽

Chol-Bum Kweon

Keyword(s):

Large Eddy Simulation ◽

Internal Combustion Engines ◽

Constant Pressure ◽

Engine Performance ◽

Spray Combustion ◽

Pressure Flow ◽

Detailed Chemistry ◽

Eddy Simulation ◽

Large Eddy ◽

Lift Off

In military propulsion applications, the characterization of internal combustion engines operating with jet fuel is vital to understand engine performance, combustion phasing, and emissions when JP-8 is fully substituted for diesel fuel. In this work, high-resolution large eddy simulation (LES) simulations have been performed in-order to provide a comprehensive analysis of the detailed mixture formation process in engine sprays for nozzle configurations of interest to the Army. The first phase examines the behavior of a nonreacting evaporating spray, and demonstrates the accuracy in predicting liquid and vapor transient penetration profiles using a multirealization statistical grid-converged approach. The study was conducted using a suite of single-orifice injectors ranging from 40 to 147 μm at a rail pressure of 1000 bar and chamber conditions at 900 K and 60 bar. The next phase models the nonpremixed combustion behavior of reacting sprays and investigates the submodel ability to predict auto-ignition and lift-off length (LOL) dynamics. The model is constructed using a Kelvin Helmholtz–Rayleigh Taylor (KH–RT) spray atomization framework coupled to an LES approach. The liquid physical properties are defined using a JP-8 mixture containing 80% n-decane and 20% trimethylbenzene (TMB), while the gas phase utilizes the Aachen kinetic mechanism (Hummer, et al., 2007, “Experimental and Kinetic Modeling Study of Combustion of JP-8, Its Surrogates, and Reference Components in Laminar Non Premixed Flows,” Proc. Combust. Inst., 31, pp. 393–400 and Honnet, et al., 2009, “A Surrogate Fuel for Kerosene,” Proc. Combust. Inst., 32, pp. 485–492) and a detailed chemistry combustion approach. The results are in good agreement with the spray combustion measurements from the Army Research Laboratory (ARL), constant pressure flow (CPF) facility, and provide a robust computational framework for further JP-8 studies of spray combustion.

Download Full-text