Biodiesel as alternative fuel for marine diesel engine applications: A review
Introduction
Marine transportation activities are mostly driven by marine diesel engines due to their efficiency compared to gasoline engine. Exhaust gases from marine engines can be considered as one of the major causes of air pollution at sea [1], [2]. The most crucial seaborne emission released from the combustion of marine fuels consists of nitrogen oxides (NOX), sulphur oxides (SOX), carbon monoxide (CO), carbon dioxides (CO2), and particulate matter (PM). The presence of these gases will adversely affect the environment and human health with lung cancer, cardiopulmonary deaths, bronchitis, pneumonia and global warming [3]. International Maritime Organization (IMO) reported that the annual shipboard CO2 emissions in 2012 were 938 million tons, which constituted about 2.6% of global human-made emissions of the same substance. This scenario is expected to rise three folds by 2050 if no action is taken. Meanwhile the emissions of NOX and SOX were 15% (19 million tons) and 13% (10.2 million tons) respectively, from their global emissions [4]. In order to cope with this issue, a more stringent regulation is necessary. The latest Marine Pollution (MARPOL) in Annex VI revision recommends limiting the sulphur level from the current 3.50% to 0.50%, effective January 1, 2020. For NOX emissions, it was reduced to Tier II and Tier III for global and North American Emission Control Areas, respectively since January 2016.
On the other hand, the shortage and rising cost of fossil fuels has made renewable energy more popular [5]. In addition, the petroleum-based fuel resources are limited to certain countries [6]. Therefore, there is a need to look for new alternative fuels to cater to the existing market. Based on previous findings, biodiesel was identified as one of the potential resources that fulfil the world's energy demand and can be a prominent candidate as alternative to petroleum-based fuels [7], [8]. Nowadays biodiesel, biofuel and biogas are a form of alternative energy which is rapidly gaining interest among consumers. It is an environmentally friendly energy, non-toxic and has properties similar to diesel fuel [9], [10], [11]. Biodiesel can be applied in diesel engines without requiring any changes to the engine systems as their combustion characteristics are almost similar to the conventional diesel. Biodiesel fuel was discovered by Rudolf Diesel in 1912 and concluded that the use of vegetable oil would be preferred in the future [12]. Biodiesel can be processed from multiple feedstocks. In Europe and the United States, rapeseed and soybean oil are typically used for the production of biodiesel. Tropical countries including Malaysia, Thailand, Indonesia, Nigeria and Colombia extract biodiesel from palm oil. Palm biodiesel that is also referred as Palm Fatty Acid Methyl Ester (PFAME), is produced through the transesterification process. Palm oil has low production cost and is economically viable for biodiesel production [13], [14], [15].
Various engine studies using biodiesel were conducted and the results have shown that the engine performance was on par with conventional diesel. Furthermore, the emissions from biodiesel engine indicate better results compared to fossil fuels [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33]. However, previous results are mostly derived from laboratory experiments conducted on land-based diesel engines. There are very few investigations related to marine engines that were reported so far, especially concerning the practical applications of biodiesel in the marine sector. It is therefore in the great interest of the authors to provide a comprehensive review on biodiesel fuel used for marine diesel engine. This study examines the past findings, history, current issues, challenges and potential solutions of biodiesel used as an alternative fuel in marine diesel engines. The aim of this work is to share useful information with researchers, engineers, ship owners and anyone interested in biodiesel as an alternative to fossil fuels.
Section snippets
Marine diesel engine
Marine diesel engines are nearly identical to land-based automotive engines. Generally, they are larger in size and equipped with fairly complicated systems and operate at a higher efficiency. Marine engine consists of four-stroke and two-stroke diesel engines, which represents 75% and 25% respectively. [34]. Four-stroke engines are primarily used in container ships and bulk carriers, while large two-stroke engines are typically installed for slow speed ships. Generally marine engines can be
Marine fuels
Marine fuels are processed from petroleum crude oil in refineries. Before being used, it is usually stored at bunker stations located in port areas. In today's shipping industry, heavy fuel oil is mostly used to power the main engine during voyage while marine diesel oil and marine gas oil are normally used for auxiliary engines and operation in harbours. There are five types of marine fuels which are categorized based on their blends and viscosity, namely:
- a)
Marine Gas Oil (MGO) – It is identical
Global energy trends
Hydrocarbon or fossil fuels are accounting for more than 80% of today's world total supplied energy. Fossil fuel resources are becoming less day by day and approximately 65.5% of world oil reserves come from Middle East countries [36]. Fig. 1 shows the forecasts of world oil production based on present demand scenario. The maximum production is expected in between 2015 and 2020. After this period, world crude oil would gradually decline in production amount.
The primary energy consumption
Marine emission regulation
Shipping activities have been identified as a significant contributor to global air pollution [9]. Therefore, international emission limitations for ships have been tightened in order to control air pollution. Rules are constantly being altered and improved. They can be divided into state and international regulations. The IMO, is an agency under the United Nations, concerned with improving maritime safety, international shipping security and preventing marine pollution from ships. Air
Biodiesel overview
In short, biodiesel is monoalkyl esters of long chain fatty acids oils derived from renewable lipid sources such as vegetable oil or animal fat [42]. Pure biodiesel that contains 100% biodiesel is commonly referred as B100. Biodiesel blends with petroleum diesel is usually designated as BXX, where XX indicates the biodiesel percentage, for example B80 contains 80% of biodiesel and 20% of petroleum diesel [43].
Engine performance of biodiesel
There are many parameters that can affect the biodiesel performance on marine engines. Among them are the injection pressure, air-fuel mixture quality, injector nozzle design, combustion chamber and ignition delay. Performance may also vary based on quality, biodiesel feedstock and engine operating parameters such as load, speed, torque, etc. The effects of biodiesel fuel on the engine performance features such as brake power, exhaust gas temperature (EGT), brake specific fuel consumption
Exhaust emission of biodiesel
A considerable amount of literature has been published on the effects of biodiesel fuel to the engine exhaust emissions. Many researchers have agreed that the use of biodiesel can reduce engine gas emissions such as hydrocarbon, PM, CO2 and CO, but the NOX may increase. Most studies found that the reduction in exhaust emissions with biodiesel may be due to sufficient oxygen element in the fuel. Based on studies by the US Environmental Protection Agency, the typical relationship between the
Combustion behaviour of biodiesel
Combustion behaviour of biodiesel fuels are an important aspect to consider as it also affects the performance of marine engines. The quality of the biodiesel fuel can be accessed through several combustion parameters including in-cylinder pressure, heat release rate, combustion duration and ignition delay. A discussion on these related parameters is presented in this section.
History of biodiesel application on marine engines
The research of biodiesel fuel in the marine sector has begun since 1998 when a feasibility study initiated the use of soybean biodiesel for recreational boats in the Great Lakes region, North America. The full testing of biodiesel was performed on-board a ship named the NOAA Huron Explorer research vessel by the Great Lakes Environment Research group. It was the first US ship that ran on alternative fuel and operated totally free from petroleum products [12]. Eight years later, the Great Lakes
Recent progress of marine engine manufacturers
Lately, a lot of world's largest marine engine producers began their research and testing with regards to biofuel as well as biodiesel. Wärtsilä, one of the marine engine manufacturers located in Helsinki, Finland, dealt with alternative fuels since 1900s [143]. The efforts began in 2001 with several biodiesel fuels testing such as palm oil, olive oil and other vegetable oils on their engines. These experiments were carried out on a stationary Wärtsilä 6L32 engine in the Vaasa Engine
Marine engine warranties
Most marine engine makers in Europe, United States and Japan have identified the role of biodiesel as an alternative fuel and are growing rapidly. Since then, some manufacturers are assured for their engines to use 100% biodiesel with or without engine modifications. The guarantees issued are based on certain conditions that need to be complied with. In the United States, engine manufacturers will provide their warranty with the use of biodiesel that meets the quality of the ASTM D6751 while in
Issue, challenges and potential solutions
Biodiesel is considered as the most appropriate alternative fuel for replacing existing marine fuels. According to Kołwzan and Narewski, the preferred feedstock is soybean oil, but other sources such as palm oil, sunflower oils and waste oil can be used [12]. Pollutant emissions from marine vessels can be effectively reduced by using neat biodiesel or blends with or without modifications to the engine systems. Most of the major engine makers such as Caterpillar, Wärtsilä, MAN, and Rolls Royce
Conclusions
Outcome of the previous studies have indicated that biodiesel fuel is suitable for use as an alternative fuel for marine engine applications. Many reports have revealed that alternative fuels derived from vegetable oil and animal fats were found to be environmentally friendly, renewable, non-toxic, biodegradable, sulphur free and aromatic. The use of marine fuels blended with these biodiesels can be considered as the proper way to reduce air pollution at sea and simultaneously meet IMO
Acknowledgement
The authors would like to express their deep gratitude to Universiti Malaysia Terengganu (PGRS160359) and Universiti Malaysia Pahang (RDU160152). Thanks to the Ministry of Education, Malaysia for sponsoring the main author with a scholarship under the SLAB scheme (KPT(BS)700113115013).
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