# Experimental Comparison of Diesel and Crude Rapeseed Oil Combustion in a Swirl Burner
## 1 Introduction  
Renewable liquid fuel utilization has a turbulent history with a general conclusion that our energy demand massively surpasses the potential of arable fields. Fuel crop production, the source of first-generation biofuels, endangers food security [1]. It is predicted by the IEA that oil utilization for power generation will drop in the future [2], however, biofuels for transportation are on a stable incline [3], highlighting aviation [4]. These all can be realized by using waste-to-fuel technologies, like producing biodiesel from waste cooking oil [5], harvesting algae ponds [6], and using peak shaving to convert electricity into fuel when there is excessive power available from principally renewable sources [7]. These three examples are the second, third and fourth generation of biofuels, respectively. The relevance of liquid fuels in the future of energy is secured by their high power-to-weight ratio, i.e., battery development is approaching 1 MJ/kg energy density, while the lower heating value of liquid hydrocarbons is exceeding 40 MJ/kg [8]. Even though the loss during energy conversion is higher for combustion engines, the difference makes it evident that liquid fuels will remain in active use for decades in both transportation and aviation. The few-factor difference in the offered mileage of a vehicle is due to physical limits, since more energy can be stored in hydrocarbon molecules than in ions. Consequently, liquid fuel combustion research is still a critical field, regardless of negative mainstream media communications. To reduce our dependence on fossil fuels, local utilization of alternative energy sources requires a well-established background to help the industry to exploit them. Due to the wide range of physical and chemical properties of alternative fuels, understanding the similarities and differences compared to conventional fuels is essential to safely perform the increase in the renewable content or change to a fully alternative fuel operation. Most renewable fuels are oxygenated by their nature [9], which is favorable from the pollutant emission point of view in internal combustion engines [10]. The renewable fuels can be light (LRF), such as alcohols [11; 12] or heavy (HRF), like animal fat [13], pyrolysis oil and straight vegetable oils [14; 15]. Representatives of the former category are significantly easier to utilize; the currently available technologies are capable of handling them. Nevertheless, chemical compatibility issues might require alternative materials in the fuel system [16]. HRF types require special care. For instance, either the burner [17] or the atomizer [18] may feature depositions over time, which should be addressed to avoid extremely short maintenance intervals. The advantage of liquid fuels is that they can be easily stored and transported. Consequently, they are excellent in increasing the electrical supply safety; hence, thermal power plants running on gaseous fuel can usually seamlessly switch to liquid fuel. The chemical conversion of crude vegetable oils to lighter fuel types [9] solves numerous operational problems, such as poor spray quality, insufficient evaporation and, hence, inadequate fuel-air mixing. These issues all lead to a bad fuel economy combined with increased pollutant emissions. Even though the way forward seems clear, building a biorefinery in less-populated rural areas might lead to an increased carbon footprint overall, and the high investment costs might not be returned at all [19]. Therefore, the direct utilization possibilities of HRF should be addressed. For this purpose, the combustion of standard diesel oil and crude rapeseed oil were compared. The latter fuel is an excellent representative of HRF; not only rapeseed oil combustion can profit from the present study.