Mixing and Autoignition of Underexpanded Methane Jets at High Pressure Conditions
OPEN ACCESS
Loading...
Author / Producer
Date
2020
Publication Type
Doctoral Thesis
ETH Bibliography
yes
Citations
Altmetric
OPEN ACCESS
Data
Rights / License
Abstract
Dual-fuel internal combustion engines with high-pressure direct injection of natural gas
into the cylinder and ignition assist via a diesel pilot offer reduced emissions of carbon
dioxide, particulate matter and nitrogen oxides compared to standard diesel engines, while
achieving higher thermal efficiency and power output than natural gas engines operating
in other modes, while additionally eliminating problems of incomplete combustion at part
load, including substantial methane slip. The fundamentals of high pressure gaseous jets,
however, are relatively poorly understood. The objective of this thesis to obtain insight
into the development, mixture formation and autoignition of underexpanded methane jets
at high pressure conditions. To this end, a multi-dimensional computational framework
for consistent treatment of single-phase flow with real-gas thermodynamics is established
and verified against high fidelity simulation results from extensively validated solvers.
The significance of real-gas corrections is also assessed. Subsequently, Reynolds-Averaged
Navier-Stokes simulations with the newly established framework are validated against
Schlieren and Tracer Laser Induced Fluorescence measurements in an optically accessible
constant volume chamber, equipped with a prototype gas injector. For injection
pressures up to 300bar and for supercritical pressure ratios up to 10, non-reactive jet
development is examined in terms of global jet characteristics, such as mass flow rates,
jet tip penetration and jet volume, and compared to scaling laws from literature. The
influence of parametric variations in injection pressure, chamber pressure and pressure
ratio on both macroscopic and local mixture formation is investigated and interpreted
qualitatively with the aid of those laws. In a third step, the autoignition of underexpanded
methane jet at injection pressures between 200 and 500bar and at back pressures
between 40 to 125bar is investigated numerically. Particular care is taken through a
two-stage workflow to simultaneously ensure accurate chemical kinetics, inclusion of real-gas
effects, sufficient resolution for the complex shock structures and reliable description
of turbulence-chemistry interaction with the Conditional Moment Closure combustion
model. The predicted ignition delays are conceptually interpreted and quantified as an
interplay of jet reactivity and of jet aerodynamics, whereas ignition locations show much
lower variability. A semi-empirical correlation for autoignition delay as a function of
chamber temperature, chamber pressure, injection pressure and injection temperature
is ultimately constructed, which compares favourably to independent experimental measurements
from literature and shows modest improvements over the simpler Arrhenius
model.
Permanent link
Publication status
published
External links
Editor
Contributors
Book title
Journal / series
Volume
Pages / Article No.
Publisher
ETH Zurich
Event
Edition / version
Methods
Software
Geographic location
Date collected
Date created
Subject
CFD simulations; real gas thermodynamics; internal combustion engines; Conditional moment closure; methane jets
Organisational unit
03611 - Boulouchos, Konstantinos (emeritus) / Boulouchos, Konstantinos (emeritus)