###### Abstract  
Vegetable oil as an alternative fuel for diesel engine has attracted much attention all over the world, and it is also expected to achieve the goal of global carbon neutrality in the future. Although the product after transesterification, biodiesel, can greatly reduce the viscosity compared with vegetable oil, the high production cost is one of the reasons for restricting its extensive development. In addition, based on the current research on biodiesel in diesel engines, it has been almost thoroughly investigated. Therefore, in this study, crude palm oil (CPO) was directly used as an alternative fuel to be blended with commercial diesel. The combustion, engine performance and emissions were investigated on a 4-cylinder, turbocharged, common rail direct injection (CRDI) diesel engine fueled with different diesel-CPO blends according to various engine loads. The results show that adding CPO to diesel reduces the maximum in-cylinder pressure and maximum heat release rate to 30 Nm and 60 Nm. The most noteworthy finding is that the blend fuels reduce the emissions of hydrocarbons (HC), nitrogen oxides (NOx) and smoke, simultaneously. On the whole, diesel fuel blended with 30% CPO by volume is the best mixing ratio based on engine performance and emission characteristics. c 2021 11 11502. [[https://doi.org/10.3390/app112311502](https://doi.org/10.3390/app112311502)]([https://doi.org/10.3390/app112311502](https://doi.org/10.3390/app112311502))  
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than that of diesel (about 40-55), which means that diesel engines fueled with biodiesel have better ignition characteristics. Fuel with a high cetane number can shorten the ignition delay, increase the peak combustion pressure and temperature, and promote the formation of NOx. Meanwhile, biodiesel is also a highly oxygenated fuel (about 11-15%). During combustion, it can provide certain oxygen, promote combustion, reduce CO, HC and PM emissions, but slightly increase NOx [6]. In particular, the oxygen content in biodiesel plays an important role in the reduction of CO and PM emissions. Because the diesel engine achieves spontaneous combustion through high pressure and temperature, the mixing degree of fuel and air directly affects the combustion and emission characteristics. Biodiesel has good benefits in improving the local oxygen deficiency area of the mixture. In addition to the above advantages, biodiesel also has some disadvantages compared with diesel fuel, such as high density, high viscosity, high surface tension, and high bulk modulus of elasticity. The higher the kinematic viscosity and surface tension, the larger the diameter of injection droplets, which makes it difficult to vaporize and atomize biodiesel fuel. Therefore, these disadvantages directly affect the fuel injection timing and fuel atomization, resulting in the uneven mixing of fuel and air, thereby increasing the harmful emissions [7; 8]. In order to reduce the impact of the disadvantages of biodiesel on combustion and emission, most researchers choose to use a mixture of biodiesel and diesel. [PERSON] et al. [9] investigated the influence of the use of waste cooking oil biodiesel/blend fuels on performance, combustion and emission characteristics in a Euro IV diesel engine under low engine speed and partial load conditions. They found that engine performance, combustion and emission characteristics were improved with biodiesel addition. [PERSON] et al. [10] studied the performance characteristics of a single cylinder vertical cylinder direct injection diesel engine with rapeseed oil biodiesel blends. It was found that the CO and HC emission of the diesel engine fueled with biodiesel and its blends were lower than diesel fuel. [PERSON] et al. [11] compared the effects of diesel-biodiesel and various metal-oxide based nanoparticles (TiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and SiO\({}_{2}\)) blends on combustion, performance, and exhaust emission characteristics of a single-cylinder diesel engine.