## 1 Introduction  
Diesel engines are robust, powerful and efficient enough, therefore they are widely used in trucks, off-road vehicles, farming machineries, electricity generation plants and so on. More and more diesel engines are put into use which consumed a great quantity of diesel fuel. For example, as showed in Figure 1, in 2017 in China, about 180 million tons of diesel fuel had been consumed [1]. As it is known, diesel engine heterogeneous combustion occurred within its cylinders results in higher NOx and PM emissions [2; 3]. The statistic data of the regulated pollutants of CO, HC, NOx and PM of vehicles are showed in Figure 2, which is cited from China Vehicle Environmental Management Annual Report (2018) [4]. It can be seen that diesel vehicles contribute almost 100% PM and 68.3% NOx emissions of vehicles. To give a direct impression about the share rate, for example in Beijing, the vehicles contribute about 45% of total air PM 2.5 pollution. Biodiesel was thought to be CO\({}_{2}\) neutral and sustainable. With attention to the reduction of PM 2.5 and the greenhouse effect gas CO\({}_{2}\), it drew great research interests and efforts in the past decade and got a rising market world widely. Therefore, China is so confident to carry out biodiesel application programs to control the emission from diesel vehicles following the world trend and to cease the pressure of petroleum importation as well. The biodiesel market entered a booming period since 2006 and reached a key milestone in 2011 to follow the United Nations Framework Convention on Climate Change in the world, which is showed in Figure 3. Figure 3 also shows a similar development trend of biodiesel in the US, EU and China [5; 6; 7]. In the US, 2016 market was a record high of 2.8 billion gallons according to EPA figures showed in Figure 4. In Europe Union, driven by the Renewable Energy Directive, biodiesel should be 10% till 2020. The produced and imported quantity of biodiesel in 2017 was 14 million tons according to Figure 5. It was about 10% of biodiesel in transport diesel approximately. In China, promoted by China the 12 th and 13 th Five-Year Plan for Renewable Energy Development [8; 9]. Biodiesel Industry Development Policy [10], it can be seen from Figure 6 that the development of the domestic biodiesel market has truly entered a booming period after 2013. In 2017, China biodiesel production is about 1.1 million tons. Even if 5% biodiesel is added to the petro diesel, the market will be at least 9 million tons accordingly. There is a vast market space for the development of biodiesel. So, it is important to carry out studies of biodiesel for its application in engines, especially in China. Figure 1: The statistic gasoline and diesel consumption from 2010 to 2017 [1]. Figure 2: Vehicle emission share rate according to fuels [4]. A number of studies have examined the emission impacts of biodiesel [5; 11; 12; 13; 14; 15; 16; 17]. The commonly accepted results are showed in Figure 4 from a US DOE report [18]. It can be seen that more biodiesel means better reduction of CO, HC and PM of the engine, however, biodiesel was mostly used with petrodiesel in a lower proportion due to the fuel properties of density, viscosity, oxidation stability, et al., and their complex effects on the fuel spray atomization, evaporation and combustion. In practice, most countries allow 5% or less than 10% blending with petrodiesel. For example in the quality of European diesel fuels, it is specified by the EN 590 standard, FAME content is 7% as regulated by Directive 2009/30/EC [19]. There are several advantages and disadvantages for the application of biodiesel as engine fuel [5; 11; 12; 13; 14; 15; 16; 17; 20]. They are summarized as below. Figure 4: Trends in percentage change of pollutant emissions with biodiesel content [18]. Figure 3: (**a**) Worldwide biodiesel productions; (**b**) US biodiesel market; (**c**) Biodiesel consumption in EU; (**d**) China biodiesel production from 2013 to 2017 [5; 6; 7]. It is renewable, safe and biodegradable.