# Application Characteristics of Bioethanol as an Oxygened Fuel Additive in Diesel Engines
## 1 Introduction  
As a renewable fuel, biodiesel is widely used in diesel engines. Biodiesel has many advantages, such as a wide source of raw materials, renewable, non-toxic, safe transportation, easy mixing of diesel fuel in any proportion and a high oxygen content can promote combustion [1; 2; 3]. However, at present, most commercial biodiesel is mainly produced by transesterification. Although it is more economical than pyrolysis (thermal cracking) and micro-emulsion, it requires a large amount of strong acid or alkali in the process of transesterification, and also needs a series of water washing and purification, which causes water pollution [4; 5]. In addition, the price of biodiesel is higher than that of diesel fuel due to the cost of raw materials and complex preparation process [6]. For the above reasons, many researchers began to study the application characteristics of ethanol as an additive in diesel engines. As a kind of alcohol, ethanol is mainly used as a gasoline fuel additive in spark ignition engines based on its high octane number [7]. The production of raw materials in the form of major free sugars for large-scale ethanol production worldwide is based on low total fossil consumption. The production process of sugarcane ethanol includes five main units: feed treatment, fermentation, separation, dehydration and stillage evaporation [8]. [PERSON] et al. [9] investigated the influences of four diesel-bioethanol blends (D95E5B0, D90E10B0, D70E15B15 and D60E20B20) on the engine performance and emissions from a diesel engine under various engine loads. They indicated that the BTE slightly decreased and the BSFC increases with increases in ethanol. Moreover, the emissions of nitrogen oxides (NOx), carbon dioxide (CO\({}_{2}\)), hydrocarbon (HC) and carbon monoxide (CO) decreased with the increase in ethanol mixing ratio. [PERSON] et al. [10] investigated diesel-bioethanol binary blends on combustion and emissions from a common rail direct injection (CRDI) diesel engine according to various injection strategies. The results showed that increasing the ethanol mixing ratio had little effect on the peak value of combustion pressure in the cylinder, but increased the heat release rate (HRR) and reduced the emissions of NOx and smoke. [PERSON] et al. [11] studied the engine performance, combustion and emissioncharacteristics in a light-duty diesel engine fueled with higher alcohol-biodiesel-diesel blends. [PERSON] et al. [12] investigated the influence of EGR on the engine performance, emission and combustion characteristics of a CRDI diesel engine fueled with diesel-palm-oil-ethanol ternary blends according to different injection strategies. They found that diesel-palm-oil-ethanol-blended fuels presented a little higher temperature than that of neat diesel fuel in the cylinder. BSFC was increased with a higher content of palm oil and ethanol in the ternary blends. The ternary blends are unfavorable to the reduction in NOx. Only when EGR was operated, NOx can be effectively reduced. [PERSON] et al. [13] studied the effect of bioethanol, diesel and castor oil-blended fuels on the engine performance, emission and combustion of a single-cylinder diesel engine. They reported that the addition of ethanol reduced maximum in-cylinder pressure and HRR and prolonged ignition delay. In addition, the addition of ethanol was only beneficial to the reduction in NO emissions, but did not to the reduction in other exhaust emissions, such as CO, HC and smoke. In summary, most application studies of bioethanol on a diesel engine are based on ternary fuel, that is, diesel-biodiesel-ethanol blends. The results are different for different engines using different ethanol mixtures and operating under different experimental conditions. Therefore, in order to study the effect of directly adding ethanol to a diesel engine on engine performance, combustion and emission characteristics, ethanol was directly blended with diesel fuel according to the volume ratios of 0:100, 5:85, 10:90 and 15:85.