Title: A numerical investigation on methane combustion and emissions from a natural gas-diesel dual fuel engine using CFD model

Abstract

Natural gas (NG)-diesel dual fuel engines have been criticized for their high emissions of unburned methane. The past research on methane emissions from dual fuel engines has focused on the measurement of methane concentration in exhaust gases. The development of approaches capable of minimizing methane emissions requests the detailed spatial distribution of methane in-cylinder during the combustion and post combustion processes. However, it is difficult to experimentally measure the spatial distribution of methane in-cylinder. Here this research presents a numerical study on the combustion process of a NG-diesel dual fuel engine using the computational fluids dynamics (CFD) model CONVERGE coupled with a reduced primary reference fuel (PRF) mechanism. The model was validated against the heat release process and the emissions of nitrogen oxide, methane and carbon monoxide measured in a single cylinder dual fuel engine. The validated CFD model was applied to investigate the combustion of methane and n-heptane and the spatial distribution of methane in the dual fuel engine. This is most likely the first attempt to visualize the spatial distribution of methane in dual fuel engines using CFD. The objective of this study is to numerically simulate the methane combustion process, especially the methane present outside the pilotmore » spray, quantify the methane combustion in each combustion stage, and visualize the spatial methane distribution in cylinder. The results showed that the momentum produced by the pilot fuel injection and combustion pushed the combustion products of pilot fuel and methane within the pilot spray plume toward the unburned methane-air mixture. Such a movement enhanced the mixing of the hot combustion products and the relatively cold unburned methane-air mixture during the main combustion process and dominated the combustion of methane presented outside the pilot fuel spray plume. Based on the simulation results at a low load condition (4.05 bar), the main combustion process consumed 43–53% of the methane fumigated into the intake mixture. The post-combustion oxidation process consumed 17–29% of the intake methane, which was 36.2–51.8% methane that survived the main combustion process. In comparison, 27–35% methane emitted the engine without participating the combustion process. The unburned methane at exhaust valve opening was mainly observed at the center of the cylinder. In comparison, the contribution of the crevice and boundary layer around the cylinder liner to methane emissions was relatively small. The slip of methane through the dual fuel engines was due to the fact that the premixed mixture was too lean to support the propagation of the turbulent flame initiated by the pilot fuel and the lack of pilot fuel vapor reaching the center of the combustion chamber because of the geometric limitations of the fuel injection system and the reduced mass of pilot fuel injected into the cylinder. The approaches aiming to enhance the combustion of methane and minimize methane emissions from dual fuel engines should focus on those capable of increasing the volume of pilot fuel vapor formed after injected into the cylinder.« less

Authors:

Li, Yu ^[1]; Li, Hailin ^[1]; Guo, Hongsheng ^[2]; Li, Yongzhi ^[3]; Yao, Mingfa ^[3]

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+ Show Author Affiliations

1. West Virginia University, Morgantown, WV (United States)
2. National Research Council Canada, Ottawa (Canada)
3. Tianjin University (China)

Publication Date:

Wed Aug 02 00:00:00 EDT 2017

Research Org.:

West Virginia Univ., Morgantown, WV (United States)

Sponsoring Org.:

USDOE Office of Fossil Energy (FE); Natural Resources Canada; National Research Council Canada

OSTI Identifier:

1537982

Alternate Identifier(s):

OSTI ID: 1549619

Grant/Contract Number:  

FE0013689

Resource Type:

Accepted Manuscript

Journal Name:

Applied Energy

Additional Journal Information:

Journal Volume: 205; Journal Issue: C; Journal ID: ISSN 0306-2619

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

42 ENGINEERING; CFD model; dual fuel engine; methane emissions; post-combustion oxidation