Emissions from auxilliary engines on ships
Table of Contents
summary
Types of Auxiliary Engines
Diesel Engines
Gas Turbines
Steam Turbines
Diesel-Electric Engines
Battery Energy Storage Systems
Emissions Overview
Types of Emissions
Trends and Impacts
Environmental Impact
Overview
Air Quality
Marine Ecosystems
Climate Change
Mitigation Strategies
Regulatory Framework
International Regulations
National Implementation
Future Goals and Reviews
Regulatory Measures
Overview of Emission Regulations
Compliance Strategies
Impact Assessment and Adaptation
Local and National Considerations
Environmental Strategies
Technologies for Emission Reduction
Selective Catalytic Reduction (SCR)
Dual Fuel (DF) Engines
Liquefied Natural Gas (LNG)
Emission Control Areas (ECAs) and Regulatory Compliance
Scrubber Systems
Case Studies
Overview of Studies on Auxiliary Engine Emissions
Case Study Methodology
Technical and Economic Analysis
Infrastructure and Stakeholder Collaboration
Current Initiatives and Support for Developing Countries
Future Trends
Decarbonization Initiatives
Public-Private Collaboration
Operational Efficiency Improvements
Challenges and Future Prospects
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summary
are a significant contributor to maritime air pollution, impacting both environmental
and public health. Auxiliary engines, which include diesel, gas turbines, steam turbines, and emerging technologies like battery energy storage systems, are essential
for powering various onboard systems but are responsible for emitting harmful
pollutants such as carbon dioxide (CO2), nitrogen oxides (NOx), sulfur oxides (SOx),
and particulate matter (PM). CO2 emissions, which account for approximately 98%
of total emissions from these engines, are particularly concerning due to their role in
climate change.[1][2] The rise in emissions has raised alarms, especially in heavily
trafficked port areas, where spikes in pollution levels have been documented, leading
to urgent calls for regulatory action and technological advancements.[3]
Notable controversies surrounding emissions from auxiliary engines focus on their
substantial contribution to both local and global air quality degradation, with studies
linking increased shipping activity to heightened respiratory health issues in nearby
populations.[4][5] As international trade continues to grow, the International Maritime
Organization (IMO) has implemented measures like MARPOL Annex VI, which sets
strict limits on SOx and NOx emissions and establishes Emission Control Areas
(ECAs) to enforce compliance. However, the effectiveness of these regulations is
debated, given the challenges of monitoring and enforcement in the vast maritime
environment.[6][7]
The transition to greener alternatives, such as liquefied natural gas (LNG), dual
fuel engines, and innovative technologies like selective catalytic reduction (SCR),
presents opportunities to mitigate emissions and enhance energy efficiency. Despite
these advancements, significant barriers remain, including the need for comprehensive infrastructure, investment, and collaboration among stakeholders to facilitate
widespread adoption of cleaner technologies in the shipping industry.[8][9] The future
trajectory of emissions from auxiliary engines hinges on the successful integration of
environmental regulations, technological innovations, and a commitment to sustainable practices, with a focus on addressing the socioeconomic challenges posed by
this transition.[9]
Types of Auxiliary Engines
Auxiliary engines on ships play a critical role in ensuring the operational efficiency of
various onboard systems. These engines, distinct from the main propulsion engine,
come in several forms, each designed to meet specific requirements regarding power
generation and operational efficiency.
Diesel Engines
Diesel engines are the most prevalent type of auxiliary engine found on ships.
They are valued for their efficiency and reliability, providing power for essential
systems such as air conditioning, lighting, and various machinery.[10] Diesel engines
typically represent a significant portion of the total fuel consumption onboard, often
accounting for up to 15% in diesel-mechanical vessels.[11] Their design allows for
effective energy production, particularly at higher loads, which enhances overall
engine performance and efficiency.
Gas Turbines
Gas turbines are primarily utilized in larger vessels that require high-speed propulsion
or rapid response times for emergency power. Known for their fast acceleration and
high power output, gas turbines serve as both propulsion sources and auxiliary
power generators, particularly in dynamic maritime operations.[12] Their lightweight
construction and ability to operate efficiently under varying loads make them suitable
for advanced naval applications.
Steam Turbines
Though less common in modern vessels, steam turbines remain in operation on
some older ships. These engines generate electricity or drive auxiliary systems by
converting steam produced in a boiler into mechanical energy. The use of steam
turbines reflects an earlier era of maritime engineering, and while they are not as
prevalent today, they still play a role in certain ship designs.[12]
Diesel-Electric Engines
Diesel-electric engines represent a flexible solution for auxiliary power generation
by converting diesel fuel into electrical energy. This adaptability allows ships to
manage varying power demands effectively and provides a more efficient alternative
to traditional mechanical systems.[10] Diesel-electric setups can optimize fuel usage
and minimize emissions, making them increasingly popular in modern maritime
engineering.
Battery Energy Storage Systems
Emerging technologies such as battery energy storage systems are gaining traction
as sustainable alternatives for auxiliary power. These systems store electrical energy
generated from various sources, including auxiliary diesel engines, and can be
deployed when needed. This approach not only reduces emissions but also enhances
energy efficiency on ships, contributing to greener maritime operations.[10]
The evolution of auxiliary engines reflects ongoing advancements in maritime technology, aiming to improve efficiency, reliability, and environmental sustainability
across the industry. As regulations regarding emissions become stricter, the adoption
of hybrid and alternative energy solutions is likely to expand further.[13]
Emissions Overview
Emissions from auxiliary engines (AEs) and boilers on ships significantly contribute
to maritime air pollution, primarily releasing various harmful pollutants. The primary
pollutants emitted from these engines include carbon dioxide (CO2), nitrogen oxides
(NOx), sulfur oxides (SOx), and particulate matter (PM). CO2, resulting from fuel
combustion, constitutes the largest share of total emissions, particularly from AEs,
where it accounts for approximately 98% of total emissions[1]. In contrast, NOx and
CO emissions, while much lower in percentage, represent significant environmental
concerns due to their contribution to secondary pollutants such as ozone and
particulate matter[1][2].
Types of Emissions
[3]
[2]
[2]
[14]
Trends and Impacts
The analysis of emissions data from 2019 to 2021 indicates an exponential increase
in all examined pollutants, particularly during periods of port congestion. For instance,
the total emissions from the LA and LB ports spiked dramatically, with November
2021 recording between 502.5 to 538.8 tons of emissions during 22 days of waiting
time, illustrating the cumulative impact of shipping activities on air quality[3].
Moreover, the reduction of SOx and NOx emissions has had a notable effect on
lowering the concentrations of particulate matter, particularly secondary particulate
sulfate and nitrate, enhancing overall air quality in affected regions[2]. However, the
complex interactions among various pollutants necessitate ongoing monitoring and
regulation to mitigate their environmental and health impacts effectively.
Environmental Impact
Overview
The environmental impact of emissions from auxiliary engines on ships is significant,
particularly concerning air quality and marine ecosystems. These engines contribute
to the release of various pollutants, including sulfur oxides (SOx), nitrogen oxides
(NOx), particulate matter (PM), and greenhouse gases (GHGs), which can have
detrimental effects on both human health and the environment[4][3].
Air Quality
Shipping activities are a substantial source of air pollution, especially in coastal areas
and harbor cities. Emissions from ships can significantly degrade air quality, threatening the health of populations living nearby. For example, studies have shown a strong
correlation between ship traffic and increased respiratory-related hospitalizations in
areas close to ports[4][3]. Pollutants like carbon monoxide (CO) and volatile organic
compounds (VOCs) emitted by ships not only pose health risks but also contribute to
the overall burden of air pollution globally. In 2014, it was estimated that international
shipping accounted for approximately 2.2% of global annual CO2 emissions, with
projections indicating a potential increase of 50% to 250% by 2050 due to growth in
world trade[5].
Marine Ecosystems
The effects of emissions extend beyond air quality, impacting marine environments
as well. The rise in CO2 levels can lead to ocean acidification, adversely affecting
marine biodiversity and the health of ecosystems. According to the Intergovernmental
Panel on Climate Change (IPCC), if global warming exceeds 1.5–2.5°C, there is a
heightened risk of extinction for 20–30% of assessed marine species[4]. Additionally,
the transportation of polluted air from land to sea can exacerbate the contamination
of marine environments[4][15].
Climate Change
The shipping industry significantly influences the climate carbon cycle. The release of
air pollutants can disrupt the natural balance, leading to an increase in anthropogenic
emissions that remain in the atmosphere[4]. This cycle contributes to global warming,
which in turn poses irreversible impacts on climate systems[4][15].
Mitigation Strategies
To mitigate these adverse effects, various strategies are being proposed and implemented. These include enhancing pollutant treatment methods, reducing energy
consumption, and adhering to stricter emissions regulations. The European Union's
directive on sulfur content in marine fuels is an example of such regulatory measures
aimed at decreasing emissions from shipping activities[5]. However, the effectiveness
of these regulations may be delayed, necessitating ongoing research to assess their
combined impact on air quality and public health[3][5].
Regulatory Framework
The regulation of emissions from auxiliary engines on ships is primarily governed by
the International Maritime Organization (IMO) through the International Convention
for the Prevention of Pollution by Ships (MARPOL), specifically Annex VI, which
addresses air pollution from ships. Adopted in 1997, Annex VI has undergone several
amendments via a "tacit acceptance" process, allowing it to maintain relevance in
light of evolving environmental standards. As of November 2022, it has 105 Parties,
representing approximately 96.81% of the world's merchant shipping by tonnage[6].
International Regulations
MARPOL Annex VI sets stringent limits on sulfur oxides (SOx) and nitrogen oxides
(NOx) emissions. These limits are enforced through the establishment of Emission
Control Areas (ECAs) where more stringent standards apply. For instance, the sulfur
content in marine fuels is progressively reduced to achieve a target of 0.5% by weight
by 2020, with stricter limits of 0.1% for ships at berth in certain EU ports[5][7]. The
regulation also mandates the introduction of an Energy Efficiency Existing Ship Index
(EEXI) to improve the energy efficiency of existing vessels and reduce their carbon
intensity[6].
National Implementation
The effective implementation of these international regulations at the national level
requires coordination among various ministries and institutions within individual
countries. This involves integrating international obligations into national laws while
also considering local regulations[16]. Countries with significant interests in international shipping must ensure that their national frameworks align with MARPOL
provisions to effectively control emissions from auxiliary engines[16].
Future Goals and Reviews
The 2023 IMO Greenhouse Gas (GHG) Strategy emphasizes further reductions in
carbon intensity across international shipping, targeting at least a 40% reduction in
CO2 emissions per transport work by 2030 compared to 2008 levels, with an ambition
for net-zero GHG emissions around 2050[6]. To facilitate this, a review of current
regulations is set to be completed by January 2026, which may lead to additional
amendments aimed at enhancing the enforcement mechanisms and data collection
systems related to emissions[6].
Through these frameworks, the IMO aims to address the environmental impact
of maritime operations effectively, ensuring compliance and promoting sustainable
practices within the industry.
Regulatory Measures
Overview of Emission Regulations
The regulatory framework for controlling emissions from auxiliary engines on ships
primarily revolves around the International Maritime Organization's (IMO) MARPOL
Annex VI, which sets limits on sulfur oxides (SOx) and particulate matter emissions.
Regulation 14 establishes specific limit values and outlines means for compliance,
allowing for both primary methods, which prevent pollutant formation, and secondary
methods, which involve post-formation removal techniques[17]. The implementation
of these regulations is crucial in reducing the carbon intensity of international shipping
while maintaining a balance between environmental sustainability and economic
viability[6].
Compliance Strategies
Regulations provide a structured approach for achieving compliance, including the
Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Indicator
(CII). These regulations incentivize vessels to improve their energy efficiency and
reduce carbon emissions by focusing on their operational practices and technical
designs[18]. Alternative compliance options, such as Vessel Incident Events (VIEs)
and Terminal Incident Events (TIEs), offer pathways for regulated entities when
standard emissions reductions are not feasible due to specific circumstances[19].
Impact Assessment and Adaptation
In adopting these measures, the Marine Environment Protection Committee (MEPC)
of the IMO conducted a comprehensive impact assessment to evaluate potential
negative impacts on states, particularly small island developing states (SIDS) and
least developed countries (LDCs)[6]. This assessment emphasized the necessity of
ongoing reviews to adapt regulations as needed, ensuring that disproportionately
negative impacts are addressed adequately. Amendments to the regulations can be
proposed and adopted based on these evaluations, as stipulated under Article 16 of
the convention[6].
Local and National Considerations
Effective implementation at the national level necessitates a comprehensive understanding of the interlinkages among various ministries and institutions. National regulations must consider international obligations, existing laws, and local regulations
to identify regulatory gaps and deficiencies in global agreements concerning air
pollution and greenhouse gas emissions[16]. This holistic approach is essential to
facilitating a successful transition toward lower emissions in the shipping industry.
Environmental Strategies
Proactive environmental strategies that exceed regulatory requirements are believed
to yield benefits, including enhanced recognition from communities and institutions.
Such strategies encourage shipping companies to adopt greener practices based
on moral commitments rather than merely complying with regulations[5]. However,
it is also acknowledged that the implementation of certain measures, like low-sulfur
fuels, may inadvertently lead to increased CO2 emissions and shifts toward more
carbon-intensive transport modes[18].
Thus, while the regulations provide a framework for emissions control, ongoing
research and adaptability are essential to address the complexities and unintended
consequences associated with the transition to more sustainable shipping practices.
Technologies for Emission Reduction
Selective Catalytic Reduction (SCR)
Selective catalytic reduction (SCR) is recognized as one of the most effective technologies for reducing nitrogen oxides (NOx) emissions from marine engines. It operates by injecting urea into the exhaust stream, where it vaporizes and decomposes
to form ammonia (NH3). This ammonia then reacts with NOx on a catalytic substrate,
effectively converting it to nitrogen (N2) with a reduction efficiency of up to 95%
under optimal conditions.[8] However, practical implementations typically achieve
a reduction of around 80-85% due to various operational constraints. A significant
challenge associated with SCR technology is maintaining exhaust gas temperatures
between 330-350 °C, particularly when using residual fuels that contain high sulfur
content, as excessive temperatures can lead to the formation of ammonium sulfate,
causing clogging issues.[8]
Dual Fuel (DF) Engines
Dual fuel (DF) engines represent another promising technology for emission reduction in marine applications. These engines can operate on both natural gas
and heavy fuel oil (HFO), providing flexibility in compliance with varying emission
regulations. When functioning as lean-burn gas engines, DF engines can achieve
NOx emissions that are approximately 85% lower than in HFO mode. Additionally,
sulfur oxide emissions are virtually zero when using natural gas, and CO2 emissions
can be reduced by around 30% due to the low carbon-to-hydrogen ratio of methane.
Consequently, DF engines can achieve IMO Tier II compliance in HFO mode and
Tier III compliance in gas mode.[8]
Liquefied Natural Gas (LNG)
The adoption of liquefied natural gas (LNG) as a marine fuel is gaining momentum,
particularly in eco-zones such as Northern Europe and the United States. The
significant reduction in NOx and sulfur oxides associated with LNG usage has led
to its increasing acceptance as a viable alternative to traditional fuels. In Norway,
the implementation of the Norwegian NOx fund has catalyzed a shift toward natural
gas engines, with many vessels in the offshore and ferry sectors now operating on
LNG. Despite the promise of LNG, challenges remain, such as the need for extensive bunkering infrastructure and international standards to facilitate its widespread
adoption across different shipping sectors.[8]
Emission Control Areas (ECAs) and Regulatory Compliance
The introduction of stricter regulations, such as those outlined in the IMO Tier III
standards, has heightened the need for innovative emission reduction technologies.
Engine manufacturers are exploring a variety of solutions, including after-treatment
technologies and alternative fuel options, to meet these evolving requirements. These
measures aim to not only reduce NOx and sulfur oxides but also address particulate
matter and total hydrocarbon emissions effectively.[8]
Scrubber Systems
Marine scrubbers, particularly open-loop systems, have been employed to comply
with sulfur emission limits by washing out sulfur oxides from exhaust gases. However,
there is ongoing debate about their environmental impact, with some studies indicating that while scrubbers reduce gaseous sulfur emissions, they may not significantly
mitigate particulate matter effects and could have harmful side effects on water
quality. Regulatory bodies, such as the EU and the IMO, continue to assess scrubber
usage and seek harmonization in guidelines to address these concerns.[5]
Case Studies
Overview of Studies on Auxiliary Engine Emissions
A comprehensive literature review has identified 118 studies addressing emissions
from auxiliary engines on ships, which provide a foundation for analyzing contemporary factors influencing decarbonization efforts in the maritime sector.[3][5] This
section explores case studies focusing on various propulsion systems, specifically
comparing traditional diesel engines with hybrid alternatives, to evaluate their environmental impacts and economic viability.
Case Study Methodology
The methodology of the case studies involves analyzing two ships with similar
technical specifications but differing propulsion systems—one utilizing a conventional
diesel engine and the other equipped with hybrid technology. The analysis emphasizes key performance indicators, including CO2 emissions and fuel consumption,
over daily, monthly, and annual periods. To ensure the accuracy of the findings,
several influencing factors such as engine type, fuel type, and operational hours were
meticulously accounted for in the comparisons.[15]
Technical and Economic Analysis
In assessing the technical aspects of various technologies compliant with the International Maritime Organization (IMO) Tier III standards, case studies demonstrate
the advantages of switching to hybrid systems. For example, the examination of
a Panamax tanker revealed that it spends approximately 17% of its operational
time in Emission Control Areas (ECAs), where stricter emissions regulations are
enforced. This necessitated the exploration of effective technologies that align with
these regulations while considering lifecycle costs and operational efficiency.[8]
Moreover, the economic analysis included sensitivity assessments due to fluctuations in fuel prices, which have a significant impact on operational expenses (OPEX)
and capital expenses (CAPEX) associated with adopting new technologies.[8] The
findings indicated that operating on gas represents a robust alternative, satisfying
future legislative requirements while maintaining lower lifecycle costs.
Infrastructure and Stakeholder Collaboration
The transition to low-carbon fuels and technologies necessitates substantial investment in scalable infrastructure at ports and bunkering facilities. Shipowners require
assurance that adequate support systems will be in place for the fuels being adopted
in their vessels, emphasizing the importance of collaboration among stakeholders,
including ports, energy suppliers, and governments. Regulatory frameworks like
FuelEU Maritime play a pivotal role in promoting investments in low-carbon shipping
initiatives.[20]
Current Initiatives and Support for Developing Countries
Several initiatives are underway to assist developing nations, particularly Least Developed Countries (LDCs) and Small Island Developing States (SIDS), in addressing
challenges related to emissions from auxiliary engines. The GHG SMART project,
among others, offers capacity-building training to enhance the implementation of
environmental regulations and technologies in these regions.[21]
Through case studies, ongoing research, and collaborative efforts, the maritime
industry is advancing towards more sustainable practices, showcasing the viability
of innovative solutions in reducing auxiliary engine emissions while addressing
economic considerations.
Future Trends
Decarbonization Initiatives
As the maritime industry moves towards decarbonization, the adoption of low-carbon
and zero-carbon fuels is becoming increasingly critical. Various production pathways
for these fuels, such as biofuels and hydrogen-based options, are being explored,
although they exhibit significant differences in their environmental footprints.[22] The
"Future Fuels and Technology for Low-and Zero-Carbon Shipping" project led by
the Government of the Republic of Korea and the IMO aims to identify incentives
and regulatory mechanisms to promote the uptake of these cleaner alternatives,
highlighting the urgent need for investment in technologies that will be relevant by
2040 and beyond.[9]
Public-Private Collaboration
To facilitate the transition, effective collaboration between public authorities and
industry stakeholders is essential. This includes pilot projects and initiatives aimed
at enhancing operational efficiency through green shipping corridors, which can expedite the energy transition in shipping.[9] Public-private partnerships are expected
to create opportunities for knowledge sharing and innovation, helping stakeholders
capitalize on early adoption advantages while driving steep greenhouse gas (GHG)
reductions in the sector.[9]
Operational Efficiency Improvements
Improving the efficiency of auxiliary engines plays a pivotal role in reducing fuel consumption and emissions. Techniques such as optimizing engine loads and minimizing
the number of auxiliary engines in operation can significantly decrease overall fuel
use.[12][10] Emerging technologies, including the use of renewable energy systems
and hybrid solutions like wind-solar systems, show potential for reducing GHG
emissions, although they are not yet considered viable alternatives for widespread
commercial shipping.[5]
Challenges and Future Prospects
Despite progress, significant challenges remain. The integration of environmental
sustainability with economic viability is critical for the successful adoption of cleaner
technologies in maritime operations.[5] The focus will need to shift towards ensuring a
just and equitable transition that addresses the needs of diverse stakeholders, especially in the Global South, while also considering the social and environmental costs
associated with current practices.[9] Overall, the future of emissions from auxiliary
engines on ships hinges on technological innovations, collaborative frameworks, and
a commitment to sustainable practices within the industry.
References
[1]: What are auxiliary engines on ship? - Cosmic Marine Services
[2]: Improved auxiliary engine load - International Maritime Organization
[3]: The Importance of Ship’s Auxiliary Engines: Keeping Vessels Running ...
[4]: Marine Ancillary Diesel Engine Emissions Reduction Using ... - MDPI
[5]: Insights into the Global Characteristics of Shipping Exhaust Emissions ...
[6]: The impact of ship emissions on air quality and human health in the ...
[7]: Acute port congestion and emissions exceedances as an impact of COVID ...
[8]: Understanding Various Components of Exhaust Gas Emissions from Ships
[9]: Research on the carbon emissions traceability inventory and multi ...
[10]: Towards the IMO’s GHG Goals: A Critical Overview of the ... - MDPI
[11]: Comparative Analysis of CO2 Emissions, Fuel Consumption, and Fuel Costs ...
[12]: EEXI and CII - ship carbon intensity and rating system - IMO
[13]: Emission Standards: IMO Marine Engine Regulations - DieselNet
[14]: National Action Plan to address GHG emissions from ships
[15]: Sulphur oxides (SOx) and Particulate Matter (PM) – Regulation 14 | IMO
[16]: Reducing international shipping’s carbon intensity through the IMO’s ...
[17]: Ocean-Going Vessels At Berth Regulation - California Air Resources Board
[18]: Low emission engine technologies for future tier 3 legislations ...
[19]: Challenging road ahead for retrofitting to dual-fuel engines - DNV
[20]: Cutting GHG Emission From Shipping – 10 Years Of Mandatory Rules
[21]: IMO’s work to cut GHG emissions from ships
[22]: The implications of the IMO Revised GHG Strategy for shipping


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