Numerical studies of advanced combustion concepts in hydrogen and methanol compression ignition engines

Research output: ThesisDoctoral Thesis (compilation)

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Abstract

The effects of climate change have led to increasing concern regarding global emissions, especially carbon dioxide (CO2) emissions. A significant
contributor to these emissions is the combustion of fossil fuels in internal combustion engines (ICEs). This combustion process is also responsible for
other harmful emissions such as carbon monoxide (CO), soot, and nitrogen oxides (NOx). Although significant improvements have to be made to
ICEs, making them produce less emissions and high efficiency, it can be very difficult to remove them entirely using fossil fuels. Due to this, interest in
electrification has grown rapidly in recent years. However, electrification of heavy-duty vehicles may not be suitable because of the high energy demand,
which would require a larger amount of batteries and, therefore, less space for payload.
An alternative to electrification is ICEs, which use alternative fuels that can achieve cleaner combustion than fossil fuels. Among the potential
fuels that could replace fossil fuels are methanol, an alcohol-based fuel, and hydrogen, a carbon-free fuel. However, research and development on the
engines operating with these fuels are needed to incorporate them into the engines. In particular, advanced engine concepts, such as low-temperature
combustion (LTC), single-fuel stratification, and dual-fuel stratification have shown great potential for methanol and hydrogen fuel operation. To
this end, an understanding of the combustion behaviour of both of these fuels under these advanced engine concepts is desirable. This thesis used
computational fluid dynamics (CFD) to investigate the combustion and emission process of these fuels in heavy-duty compression ignition engines,
under LTC conditions in single-fuel and dual-fuel engine conditions. For the methanol LTC engine studies, this thesis contributed to the understanding
of the impact of fuel injection timing on engine performance and emissions. The interaction of methanol spray with the engine piston bowl is critical
for the forming of optimal mixture stratification in the engine to achieve simultaneous high efficiency and low emissions of NOx, CO, and unburned
fuels. For the hydrogen single-fuel and dual-fuel engines, this thesis contributed to the development of zero-carbon hydrogen engine operation.
A challenge with hydrogen in CI engines is the controlled combustion. To achieve this, a more reactive fuel such as diesel can be used to ignite the
hydrogen. The first hydrogen work in this thesis investigates this dual-fuel strategy where diesel is injected prior to the hydrogen injection. In this work,
three SOIs are investigated at two different rail pressures. The highest efficiency of 54.9% is achieved at the earliest injection with high rail pressure.
The rail pressure does not significantly impact the efficiency but rather the SOI timing, which results in higher exhaust losses for later injection cases.
A similar trend for NOx and efficiency was observed. In the second hydrogen work, single-fuel stratification is investigated by replacing the diesel
pilot with a hydrogen pilot. The purpose is to create a mixture formation that will provide a sufficient ignition source for the main hydrogen injection.
This was done by a large test matrix where the dwell time and pilot energy share were adjusted. The main injection SOI was set as the SOI for the
highest efficiency case from the dual-fuel simulations. In this study, controlled combustion did not occur without increasing the intake temperature.
This section of the work identified a complex relationship between dwell time, pilot energy share, and intake temperature. For given conditions, an
efficiency of 52% was achieved but with high NOx. To increase the potential time for heating, the main injection SOI was shifted close to TDC. This
allowed for controlled combustion without the need for an increased intake temperature. Larger pilot energy shares resulted in low NOx emissions
since a larger share of the energy was burned under fuel-lean premixed conditions. Finally, LES was carried out on reacting diesel-hydrogen dual-fuel
constant volume case. This study aimed to provide a better understanding of the interaction between diesel and hydrogen by incorporating different
dwell times. The study found that hydrogen ignition occurred after some mixing with the n-heptane. With a longer dwell time, the duration of the
mixing is longer before mixing.
Original languageEnglish
Supervisors/Advisors
  • Bai, Xue-Song, Supervisor
  • Fatehi, Hesameddin, Assistant supervisor
Place of PublicationLund
Publisher
ISBN (Print)978-91-7895-998-3
ISBN (electronic) 978-91-7895-999-0
Publication statusPublished - 2024 Apr 20

Bibliographical note

Defence details
Date: 2024-05-31
Time: 10:15
Place: Lecture Hall M:B, building M, Ole Römers väg 1, Faculty of Engineering LTH, Lund University, Lund. The dissertation will be live streamed, but part of the premises is to be excluded from the live stream.
External reviewer(s)
Name: Xu, Hongming
Title: Prof.
Affiliation: University of Birmingham, United Kingdom.
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Subject classification (UKÄ)

  • Energy Engineering

Free keywords

  • Internal combustion engine
  • methanol
  • hydrogen
  • dual-fuel
  • high-pressure direction injection
  • large eddy simulation
  • Reynolds averaged Navier-Stokes simulation
  • NOx emissions
  • engine efficiency

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