# Comparative Analysis of Partially Renewable Composite Fuels Based on Peat, Lignite and Plant Oil
## 3 Results and Discussion
### Composite Fuel Gasification Products  
The optimal composition of peat or lignite with rapeseed oil can be determined by considering the variations in the gasification products versus the component ratio of the fuel. Gasification (see Figure 1) proceeded with external heating (the intensity of the light flow to the fuel surface was about 880 W/cm\({}^{2}\)), and the fuel temperature typically reached maximum values within a couple of seconds. Such external heating allowed for fuel temperatures as high as 500-600 \({}^{\circ}\)C without the contribution of the heat of the reaction (e.g., in a nitrogen atmosphere). It is clear in Figure 5 that the overall gas production goes down with an increase in the fraction of RO. The concentrations of the gases under study were obtained here by using integral averaging throughout the process. The production of almost all the considered gases was maximum in the conversion of the P + RO mixture (35 wt% and 65 wt%). A similar extremum was recorded in the conversion of the L + RO mixture with 40 wt% RO. Thus, these particular compositions look optimal in terms of combustible gas production. The production of combustible gases exceeded that of non-combustible ones by 10-15% in the case of the optimal fuel composition. The gas production intensity was higher in the conversion of the L + RO mixture because of much higher temperatures of this process (see Section 3.2). However, when the oil fraction was increased above the optimal level, the process quickly decayed. It occurred due to the enhanced evaporation of the volatile components of oil, as well as due to the heat-consuming oil pyrolysis. Lower heat production due to the oxidation of a smaller amount of the fossil fuel component goes in parallel with an increase in the RO fraction. The analysis of the chemical composition of producer gas obtained for fuel compositions with different oil fractions showed the presence of an evident peak of combustible gas production (red curves in Figure 5a,c) when the peat-oil ratio was about 1:2. This fuel contained about 67 wt.% renewable component. The optimal lignite-based composition contains 40 wt% renewables. Thus, the proposed approach paves the way for fuels with a rather low content of fossil fuels and a lower price compared to fuels involving only renewable resources or pure plant oils. In contrast to the traditional gasification techniques, the proposed approach allows the fuel conversion at normal pressure when most of the energy is obtained from the external source through the high-power radiation flow. These differences of process conditions determine the specific aspects of the presented conversion regime, such as an absence of a great amount of hydrogen typical of high-pressure conversion [33] or different biomass conversion methods [14; 34]. Looking at the production of sulfur and nitrogen oxides, one can see that the concentrations of SO\({}_{2}\) in the conversion of the optimal P + RO composition are twice as low as in the conversion of pure peat. It occurs because the composition contains a considerable amount of oil that does not have sulfur. An increase in the production of NOx occurs due to the process temperature increase. The chosen conditions of the conversion (excess air ratio of about 0.9) are close to the conditions described in [35] that potentially allowed decreased NOx production during the conversion of the biomass. The conversion of the optimal L + RO composition produced 1.5 times more oxides of sulfur and nitrogen relative to the conversion of pure lignite. The reason for that is due to a higher conversion temperature due to a much more effective contribution of oxidation heat in the fuel heating. In general, some properties of composite fuels (density, heat conductivity, etc.) can be estimated using additive relations, based on the fraction of their components. However, high-temperature processes usually imply the chemical interaction between the composite fuel components [33]. This typically leads to a significant deviation from the predicted trends.