# Using Canola Oil Biodiesel as an Alternative Fuel in Diesel Engines: A Review
## 1 Introduction  
Fossil oil resources are being widely exploited, due to the rapid development of the global economy and the ever-growing number of vehicles. Excessive exploitation and utilization of fossil oil can damage the environment [1; 2; 3]. Therefore, although people in modern society live in comfortable environments, they must endure the inconveniences caused by air pollution, including global warming, the greenhouse effect, desertification, acid rain, fog, haze, and volatile organic compounds [4; 5; 6]. In China, fog and haze are particularly important topics. Most of China's cities are shrouded in fog and haze in the winter. For example, in January 2013, there were only five days in Beijing that did not have fog or haze. Environmental pollution can significantly affect people's lives and health [7; 8; 9]. Figure 1 shows foggy and hazy weather in Chongqing, China on 5 January 2017. As shown in Figure 1, people put masks on copper states of children, due to the serious fog and haze. Thus, environmental pollution is a problem that people have been aware of for a long time.  
Biodiesel is an alternative fuel that can solve or reduce the impact of air pollution because of various advantageous characteristics [10; 11; 12; 13; 14; 15]. It has been reported that biodiesel can be used in diesel engines without (or with only minor) engine modifications [16; 17]. Diesel engines are widely used in trucks and commercial vehicles because they have the advantages of large power output and fewer exhaust emissions. Although diesel engines produce lower hydrocarbon (HC) and carbon monoxide (CO) emissions than gasoline engines, their higher nitrogen oxides (NO\({}_{x}\)) and particulate matter (PM) emissions are a problem [18; 19]. However, the biofuel produced from animals and plants can reduce PM emissions due to its inherent characteristics. Biodiesel is a green renewable fuel that produces only carbon dioxide (CO\({}_{2}\)), and can be absorbed by plants as they grow, making biofuels carbon neutral. Thus, using biofuels can significantly reduce global warming and the greenhouse effect [20; 21; 22; 23]. However, pure biofuel cannot be widely used in diesel engines, due to its high viscosity and density. Diesel engines experience many problems when pure biofuels are used, including injector nozzle clogging and plastic tube and pad corrosion [24; 25; 26; 27]. So, biofuels are widely used in the form of a mixed fuel (i.e., biofuel is blended with conventional diesel at a certain ratio) in vehicles in Europe and other developed countries. Figure 2 shows a biofuel station in the United States. There are more than 2700 public E85 stations in the U.S., and high-level ethanol blends are available in more than 40 states. However, in Asia, the blend rate of biodiesel can only reach 5-10% due to technical limitations and other reasons [28; 29; 30; 31].  
Figure 1: Foggy and hazy weather in Chongqing, China (5 January 2017); (a) a tall building that was being built; (b) the corner of the park is shown.  
Figure 2: A biofuel station in the United States (B20: 20% biofuel blended with 80% diesel; E85: 85% ethanol blended with 15% gasoline; E10: 90% ethanol blended with 10% gasoline).  
In this study, we review and summarize the characteristics and applications of canola oil biodiesel (COB) in diesel engines to further the development and application of biodiesel in Asia (especially in China, which has rich biomass resources). This work includes our experimental results that focus on COB, and compares them with others within biodiesel literature. Thus, our work can provide an effective reference for research and application of COB in Asia, especially China.